Evidence against competition
during syntactic ambiguity resolution
Roger P.G. van Gompel
University of Dundee
Martin J. Pickering
University of Edinburgh
Jamie Pearson
University of Edinburgh
Simon P. Liversedge
University of Durham
Short title: Syntactic ambiguity resolution
Journal of Memory and Language (2005), 52, 284-307.
This is the pre-publication manuscript.
The published version may slightly differ.
Address correspondence to:
Roger P. G. van Gompel
School of Psychology
University of Dundee
Dundee DD1 4HN
Scotland, United Kingdom
Tel: +44 1382 388117
Fax: +44 1382 229993
Email: [email protected]
Abstract
We report three eye-movement experiments that investigated whether alternative syntactic
analyses compete during syntactic ambiguity resolution. Previous research (Traxler, Pickering,
& Clifton, 1998; Van Gompel, Pickering, & Traxler, 2001) has shown that globally ambiguous
sentences are easier to process than disambiguated sentences, suggesting that competition does
not explain processing difficulty. However, the disambiguation in these studies was delayed
relative to the initial point of ambiguity, so they do not rule out models which claim that
competition is very short-lasting. The current experiments show that globally ambiguous
sentences are easier to process than disambiguated sentences even when the disambiguation is
immediate. Furthermore, globally ambiguous sentences are no harder to process than
syntactically unambiguous sentences. We argue that the results are inconsistent with currently
implemented constraint-based competition models, and support variable-choice reanalysis
models such as the unrestricted race model.
Keywords:
sentence processing, syntactic ambiguity resolution, reanalysis, competition
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As the existence of “garden-path” sentences demonstrates, people sometimes experience
processing difficulty when they have to resolve syntactic ambiguities. There has been a lot of
research into what kinds of sentences cause disruption and what strategies people use when
faced with syntactic ambiguity, but there has been much less investigation of the processes that
cause processing difficulty during syntactic ambiguity resolution. Current proposals are
generally compatible with one of two alternatives: Processing disruption is caused by the
detection of a misanalysis and/or subsequent reanalysis (e.g., Frazier, 1987; Pritchett, 1992), or
it is caused by competition between multiple analyses (e.g., MacDonald, Pearlmutter, &
Seidenberg, 1994; McRae, Spivey-Knowlton, & Tanenhaus, 1998).
Researchers have often used experimental results to argue that processing difficulty
reflects reanalysis (e.g., Frazier & Rayner, 1982; Rayner, Carlson, & Frazier, 1983) or
competition (e.g., MacDonald, Just, & Carpenter, 1992; MacDonald, 1994; McRae et al., 1998;
Spivey & Tanenhaus, 1998). However, Van Gompel, Pickering, and Traxler (2000, 2001)
argued that most results are in fact compatible with either account. More specifically, they
argued that results by MacDonald et al. (1992), MacDonald (1994), and McRae et al. (1998),
which are often taken to provide evidence for competition models, are also consistent with
reanalysis models. For example, McRae et al. found that sentences like The burglar arrested by
the cop was ... were harder to process at arrested by than sentences like The cop arrested by the
burglar was .... In both sentences, frequency constraints support the (incorrect) main clause
analysis (as in The cop arrested someone.). In the former sentence, plausibility supports the
(correct) reduced relative analysis, and so the two analyses receive approximately equal support
and compete; but in the latter sentence, plausibility supports the main clause analysis, so there
is no appreciable competition. However, these results are equally compatible with a reanalysis
account in which the processor initially adopts the main clause analysis (for whatever reason),
and reanalyzes when it discovers that this analysis is implausible (see Van Gompel et al.,
2001).
Reanalysis and competition models
According to reanalysis models, processing difficulty during syntactic ambiguity resolution
occurs when the processor discovers a misanalysis in the syntactic structure it has built up to
that point and has to revise its initial structure. Most reanalysis models are serial models (e.g.,
Frazier, 1987, Pritchett, 1992), that is, they claim that the processor adopts only a single
analysis at a time, both during its initial analysis and during subsequent reanalysis. However,
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parallel models which claim that syntactic analyses are abandoned if they are very disfavored
(e.g., Gibson, 1991, Jurafsky, 1996) can also be considered reanalysis models. Similarly,
reanalysis-like effects may occur in ranked parallel models which assume that the reranking of
syntactic alternatives results in processing difficulty.
We distinguish between two types of reanalysis models. Deterministic or fixed-choice
reanalysis models claim that the processor always uses the same processing strategy during its
initial analysis. Only when the processor’s initial analysis is incorrect or unlikely does the
processor have to reanalyze and difficulty occurs. To clarify this, let us consider example
sentences (1) from Traxler, Pickering, and Clifton (1998):
1a. The son of the driver that had the moustache was pretty cool. (globally ambiguous)
1b. The driver of the car that had the moustache was pretty cool. (high attachment)
1c. The car of the driver that had the moustache was pretty cool. (low attachment)
The relative clause that had the moustache can be attached either to the first noun phrase (high
attachment to NP1, the son in [1a]) or to the second noun phrase (low attachment to NP2, the
driver in [1a]) (Cuetos & Mitchell, 1988). In (1a), both analyses are equally plausible; but in
(1b) only high attachment is plausible, and in (1c) only low attachment is plausible.
According to fixed-choice models, the processor always adopts the same analysis during
initial processing (or if it is a ranked parallel model, it always ranks the same analysis highest).
For example, the garden-path model (Frazier, 1987) predicts that for the sentences in (1) the
processor always adopts the analysis that is favored by the late closure strategy, that is, low
attachment of the relative clause. Because low attachment is implausible in (1b), fixed-choice
models predict that the processor will have to reanalyze and that this sentence should be
particularly hard to process. In contrast, both (1a) and (1c) should be easy, because the initial
low analysis is plausible and no reanalysis should be necessary. It does not matter whether the
high attachment analysis is also plausible (as in [1a]), because fixed-choice reanalysis models
claim that this analysis is never considered.
Non-deterministic or variable-choice reanalysis models make different predictions. They
claim that during its initial analysis, the processor may sometimes adopt (or rank highest) the
high attachment analysis and sometimes the low attachment analysis. An example of a
variable-choice model is the unrestricted race model (Traxler et al., 1998; Van Gompel et al.,
2001). It claims that at each word, the different analyses of a syntactic ambiguity are engaged
in a race and that the syntactic structure that is completed fastest is adopted. During the race,
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the processor attempts to construct the syntactic analyses in parallel. Importantly, the
construction of multiple analyses does not increase processing difficulty, because the processes
that lead to construction of the different analyses draw upon independent processing resources.
The processor only completes one analysis, with alternative analyses being abandoned before
they are completed. If information prior to the ambiguity provides strong support for a
particular analysis (i.e., the ambiguity is biased), the construction of this analysis is facilitated,
so the analysis nearly always wins the race and is adopted. But when prior information
provides roughly equal support for the two analyses (i.e., the ambiguity is balanced), then each
analysis is adopted approximately half the time (presumably because people favor different
analyses for different sentences, and because there is some random noise in the construction
process). As in most other sentence processing models, syntactic processing works on a wordby-word basis: The processor adopts a single syntactic analysis before it incorporates the next
word into the syntactic structure. If information provided by the next word is inconsistent with
the structure built so far (e.g., the word renders the structure implausible or sufficiently
unlikely), the processor is forced to reanalyze. The detection of the misanalysis and the
subsequent reanalysis cause processing disruption.
The unrestricted race model claims that both syntactic and non-syntactic information that
occurs before the ambiguity begins (e.g., at that in [1]) can determine the speed with which a
particular analysis is constructed and hence the likelihood with which a particular analysis is
adopted. The model focuses on the mechanisms that cause disruption during syntactic
ambiguity resolution, and does not specify the relative importance of the factors that affect
initial analysis. The model also constrains the use of information that becomes available to the
processor at the initial point of ambiguity (e.g., that in [1]). When a syntactic ambiguity occurs
at a particular word, the processor constructs an initial syntactic analysis using only major
category information of this word (e.g., whether a word is a noun or verb) and any information
that occurred prior to it. Other linguistic information (e.g., semantic plausibility) provided by
the word at which the ambiguity begins cannot be used until after the processor has constructed
its initial syntactic analysis.
Assuming that there is no strong preference for either high or low attachment in sentences
such as (1) (see evidence from Traxler et al., 1998 discussed below), the unrestricted race
model (and other variable-choice models) predict that the processor should initially adopt the
high and low attachment analysis approximately half the time each. Therefore, the initial
analysis is implausible half the time in both the high and low attachment condition, and
reanalysis is predicted to occur in both conditions. In contrast, reanalysis should never occur in
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the globally ambiguous condition, because the initial analysis is plausible regardless of whether
high or low attachment was initially adopted. Hence, the unrestricted race model predicts that
the high and low attachment conditions should both be harder to process than the globally
ambiguous condition.
In contrast to reanalysis models, competition-based models claim that during syntactic
ambiguity resolution, two (or more) analyses are activated at the same time, and they compete.
If the analyses are activated to approximately the same extent because they receive similar
support, competition is particularly strong. This results in processing disruption. The bestknown competition models are constraint-based theories (MacDonald, 1994; MacDonald et al.,
1994; McRae et al., 1998; Spivey-Knowlton & Sedivy, 1995; Tabor & Tanenhaus, 1999;
Trueswell, Tanenhaus, & Garnsey, 1994), which claim that all syntactic analyses of an
ambiguous structure are activated in parallel and that all sources of linguistic and probabilistic
information are used immediately during syntactic ambiguity resolution (but cf. Boland, 1997;
Boland & Blodgett, 2001; Boland & Boehm-Jernigan, 1998, for a different type of constraintbased account). However, other models also employ competition as a mechanism of ambiguity
resolution (e.g., Stevenson, 1994; Vosse & Kempen, 2000).
It is impossible to test all possible versions of competition models in a single set of
experiments, so the current experiments test the predictions of currently implemented
constraint-based competition theories (e.g., MacDonald et al., 1994; McRae et al., 1998; Spivey
& Tanenhaus, 1998; Tabor & Tanenhaus, 1999) which claim that all sources of linguistic and
probabilistic information simultaneously affect syntactic ambiguity resolution and importantly,
that they should have an immediate effect on competition between syntactic analyses. When
linguistic and probabilistic constraints provide approximately equal support for two analyses,
strong competition should occur, rendering the sentence hard to process. But when the
constraints clearly favor one of the analyses, little competition should occur, and processing
should be easy.
Examples of constraint-based competition models that have been worked out in detail are
the competition-integration model (McRae et al., 1998; Spivey & Tanenhaus, 1998) and the
visitation set gravitation model (Tabor, Juliano, & Tanenhaus, 1997; Tabor & Tanenhaus,
1999). The competition-integration model assumes that all possible analyses of a syntactic
ambiguity are activated in parallel. The activation levels are determined by multiple sources of
linguistic and probabilistic constraints. At each word of the syntactic ambiguity, the analysis
that is supported most by the various constraints receives the highest initial activation. As a
result of cycles of forward and backward activation between the analyses and the constraints,
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this analysis gradually becomes more strongly activated, until it reaches a threshold level and
the processor moves on to the next word. Processing time is modeled as the number of cycles
it takes to reach this threshold. The competition-integration model predicts that reaching the
threshold takes longer when the initial activation levels of the analyses are close than when
they are very different. When the constraints support syntactic analyses to a similar extent,
strong competition occurs, and this causes processing difficulty.
The visitation set gravitation model makes similar predictions. It assumes that sentence
fragments can be mapped in a multidimensional space, with fragments that tend to have similar
continuations in the language being close to each other in space, and fragments that tend to be
followed by different continuations having distant positions in space. Clusters of sentence
fragments that tend to be followed by continuations that are similar in syntax and semantics
form attractors, which represent possible continuations of sentence fragments. Hence both
syntax and semantics affect syntactic processing.
During sentence processing, at each word the sentence fragment read so far is mapped in
the multidimensional space and the mapping subsequently gravitates to an attractor. Processing
time is modeled as the time to reach an attractor. This time is directly influenced by the
strengths of the constraints favoring that attractor. Thus, when the sentence fragment can take
continuations similar to the fragments in just one cluster, it will start off at a position very close
to this single attractor, and the mapping corresponding to the sentence fragment will quickly
gravitate towards it. In contrast, when the sentence fragment can take continuations that are
similar to two or more attractors, and these attractors exert a similar force on its mapping, the
word string takes relatively longer to gravitate towards one of them. In such a case, the
attractors, which represent the alternative structures of a syntactic ambiguity, compete, and
processing difficulty ensues.
Currently implemented constraint-based competition models such as the competitionintegration model and the visitation set gravitation model predict that processing time is longer
when the constraints support two syntactic analyses to an approximately equal extent than
when the constraints strongly favor a single analysis. Thus, the most straightforward
constraint-based prediction for sentences such as (1) seems to be that the globally ambiguous
sentence (1a) should be harder to process than the disambiguated sentences (1b) and (1c). In
the globally ambiguous sentence, the constraints favor both analyses to an approximately equal
extent (assuming that there is no strong preference for one of the analyses, see below). As a
result, competition between the analyses should be severe, and processing difficulty is
predicted to occur. In contrast, because semantic plausibility immediately affects syntactic
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ambiguity resolution, the plausible analysis in the disambiguated sentences should receive more
support than the implausible analysis, and therefore processing should be relatively easy. 1
In order to test the predictions of competition and reanalysis models, Traxler et al.
(1998) tested relative clause attachment ambiguities such as (1). First, they observed no
differences between the high and low attachment conditions, indicating that there was no strong
preference for either analysis. Second, and most crucially, they observed that globally
ambiguous relative clauses (1a) were easier to read than disambiguated relative clauses (1b)
and (1c). This pattern was confirmed in a second experiment that used reflexive pronouns
(himself/herself) to disambiguate. Furthermore, Van Gompel et al. (2001) showed that verb
phrase/noun phrase attachment ambiguities such as the hunter killed only the poacher with the
rifle were easier to read when they were globally ambiguous than when they were
disambiguated by plausibility towards either the verb phrase attachment analysis (i.e., killed
using the rifle) or noun phrase attachment analysis (i.e., the poacher who had the rifle). These
findings support variable-choice reanalysis models but appear inconsistent with fixed-choice
reanalysis models and constraint-based competition models.
Long- versus short-lasting competition
However, there is an important caveat to the conclusions from Traxler et al.'s (1998) and Van
Gompel et al.'s (2001) results. It is possible, in principle, to distinguish between two types of
constraint-based competition models. Long-lasting competition models claim that syntactic
analyses remain activated in parallel throughout the ambiguous region until disambiguating
information is encountered, at least in cases where two analyses are approximately equally
supported. Competition is not resolved until the disambiguation is reached. Examples of longlasting competition models are MacDonald et al. (1992) and the visitation set gravitation model
(Tabor et al., 1997; Tabor & Tanenhaus, 1999). The visitation set gravitation model predicts
that at that in (1) the mapping of the sentence fragment (e.g., the son of the driver that ...) starts
off between two attractors, because the sentence does not provide information that strongly
biases towards one of the analyses. Competition occurs at that, because it takes a long time
before the mapping of the sentence fragment reaches one of the attractors. Competition
continues at the words had and the, because the mapping of the sentence fragment again starts
off between two attractors and again has to gravitate to one of them. However, at moustache,
competition should be weaker in the disambiguated conditions (1b) and (1c) than in the globally
ambiguous condition, because plausibility information supports only a single analysis in the
8
disambiguated conditions whereas both analyses are approximately equally supported in the
globally ambiguous condition (1a). Therefore, (1a) should be harder to read than (1b) and (1c)
after readers have reached moustache in (1). Other long-lasting competition models such as
MacDonald et al. (1992) make the same predictions. Clearly, these models fail to account for
Traxler et al.'s and Van Gompel et al.'s results, because they showed that the globally ambiguous
sentences were easier to read than the disambiguated sentences.
However, the results from Traxler et al. (1998) and Van Gompel et al. (2001) may be
compatible with short-lasting competition models. Such models assume that syntactic analyses
are initially activated in parallel and compete, but that a single analysis rapidly wins out and
receives much more activation than its alternative(s). As a result, competition occurs at the
initial point of ambiguity (e.g., that in [1]), but not on the words following it, even when these
words provide no disambiguating information. The competition-integration model (McRae et
al., 1998; Spivey & Tanenhaus, 1998) can be considered as an example of a short-lasting
competition model. Competition should occur at the initial point of ambiguity (that in [1])
because it takes many processing cycles before the activation of one of the analyses is much
higher than its alternative and the processor can move on to the next word. However, at the
next word (had) competition between the analyses should be weaker (even in the absence of
biasing information), because it is assumed that the final activation levels of the preceding
word function as one of the constraints determining the activation of the analyses. Because the
final activation levels of the preceding word always strongly favor one of the analyses,
competition decreases from one word to the next (with the rate determined by a free parameter)
and one may assume that a single analysis is selected once the activation of its alternatives is
sufficiently low.
In Traxler et al.'s (1998) and Van Gompel et al.'s (2001) experiments, the disambiguation
(e.g., at moustache in [1]) followed the initial point of disambiguation (at that). Short-lasting
competition models predict that high and low attachment should compete for selection at that in
both the ambiguous and the disambiguated sentences. However, if one of the analyses rapidly
receives more activation than the alternative and is quickly selected (say, at had the), only a
single analysis would be available at moustache. As a result, short-lasting competition models
make the same predictions as the unrestricted race model. When only a single analysis is
selected, either as the result of competition or a race between the analyses, the two models act
in the same way. Given that there is no strong preference for either analysis, the processor will
select each analysis approximately half the time. When the semantics of the disambiguating
word moustache is inconsistent with this analysis, the processor has to reanalyze. Hence,
9
processing difficulty occurs on approximately half the trials in the disambiguated conditions,
whereas no difficulty occurs in the globally ambiguous condition. In sum, the results from
Traxler et al. and Van Gompel et al. may be compatible with the unrestricted race model, but
also with constraint-based competition models if one assumes that competition is short-lasting.
Overview of the experiments
The aim of the experiments in this article is to provide evidence that not only long-lasting, but
also short-lasting constraint-based competition models can be ruled out as general models of
syntactic ambiguity resolution. We conducted three eye-movement reading experiments. We
first investigated whether the results from Traxler et al. (1998) would replicate by testing
relative clause ambiguities such as (2) in Experiment 1.
2a. The bodyguard of the governor that will be retiring after the troubles is very rich. (globally
ambiguous)
2b. The governor of the province that will be retiring after the troubles is very rich. (high
attachment)
2c. The province of the governor that will be retiring after the troubles is very rich. (low
attachment)
They are similar to the materials in Traxler et al. (1998), in that the disambiguation (at retiring)
follows the initial point of ambiguity (at that). As discussed above, results from such
ambiguities discriminate between the unrestricted race model and long-lasting competition
models, but they do not necessarily discriminate between the unrestricted race model and shortlasting competition models. Therefore, in Experiment 2, we used relative clause ambiguities
such as (3).
3a. I read that the bodyguard of the governor retiring after the troubles is very rich. (globally
ambiguous)
3b. I read that the governor of the province retiring after the troubles is very rich. (high
attachment)
3c. I read that the province of the governor retiring after the troubles is very rich. (low
attachment)
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The materials were based on those used in Experiment 1, but in contrast to (2), the
disambiguation in (3b) and (3c) is immediate, that is, the semantic disambiguation at retiring
coincides with the initial point of syntactic ambiguity. (Another difference is that they are
embedded in an additional clause in order to control for length differences between [3a-c] and
[3d] below.) In contrast to sentences such as (2), the processor cannot select a single analysis
before retiring in (3), so constraint-based competition models predict that strong competition
should occur at or shortly following retiring in the ambiguous condition even if competition is
short-lasting. Given that plausibility information should have an immediate effect, competition
should be much weaker in the disambiguated conditions. Hence, both long- and short-lasting
constraint-based competition models predict that the globally ambiguous condition (3a) should
be harder to read than the disambiguated conditions (3b) and (3c).
In contrast, the unrestricted race model predicts that globally ambiguous sentences should
be easier to process than disambiguated sentences, even when the disambiguation is immediate.
It assumes that the processor first has to construct a syntactic analysis before it can evaluate its
plausibility. Thus, in all conditions in (3), the processor initially adopts each analysis
approximately half the time at retiring. In the disambiguated conditions the processor is forced
to reanalyze approximately half the time, whereas in the globally ambiguous condition,
reanalysis does not occur.
To provide a further test of the models, we also tested syntactically unambiguous
sentences such as (3d) in Experiment 2.
3d. I read quite recently that the governor retiring after the troubles is very rich. (syntactically
unambiguous)
Constraint-based competition models predict that no competition should occur in unambiguous
sentences, because only a single analysis is syntactically possible. Hence, they should be much
easier to process than the globally ambiguous sentences. In contrast, the unrestricted race
model predicts that both sentences should be equally easy to process, because in both cases, the
processor adopts a single analysis without considering possible alternatives.
Finally, Experiment 3 used a different ambiguity to test the predictions of the models.
This ambiguity, exemplified in (4), involves attachment of an adverbial phrase (yesterday
morning) to verb phrases rather than noun phrases. Furthermore, the disambiguation is
performed by an adverbial whose temporal features are incompatible with the tense of the verb
phrase.
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4a. The carpenter sanded the shelves he attached onto the kitchen wall yesterday morning,
according to the foreman. (globally ambiguous)
4b. The carpenter sanded the shelves he will attach onto the kitchen wall yesterday morning,
according to the foreman. (high attachment)
4c. The carpenter will sand the shelves he attached onto the kitchen wall yesterday morning,
according to the foreman. (low attachment)
As in Experiment 2, the disambiguation is immediate (at yesterday), so the predictions of the
models are the same: Constraint-based competition models predict that the ambiguous
condition should be harder to read than the disambiguated conditions, whereas the unrestricted
race model predicts the reverse pattern.
Experiment 1
In this experiment, we investigated whether Traxler et al.'s (1998) results would replicate by
using relative clause attachment ambiguities with a disambiguation that followed the initial
point of ambiguity, as illustrated in (2) above. Assuming that there is no strong preference for
either high or low attachment (as in Traxler et al., 1998), the unrestricted race model predicts
that the ambiguous condition should be easier to read than both disambiguated conditions.
Long-lasting competition models, which claim that competition in (2a) lasts until the
disambiguation at retiring (e.g., MacDonald et al., 1992; Tabor & Tanenhaus, 1999), predict
that the ambiguous condition should be harder to process than the disambiguated conditions.
However, if competition is short lasting and competition is resolved before retiring in (2a), the
predictions are the same as those of the unrestricted race model.
Method
The experiment consisted of two plausibility pretests and an eye-movement reading
experiment.
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Participants
All participants in all parts of the experiments reported here were native speakers of English.
No one participated in more than one experiment or pretest reported in this article. Participants
in the eye-tracking experiments had normal vision.
In Experiment 1, 36 participants, all students from the University of Glasgow, were paid
to take part in the eye-tracking experiment. Four further participants were excluded from the
analyses of the eye-movement experiment, three because they had a very high percentage of
tracker losses, and one because she answered more than 25% of the questions incorrectly.
Items
We constructed 50 items similar to (2) above from which we selected thirty items on the basis
of our plausibility norms (see plausibility pretests below). See the Appendix for the complete
list of materials. All items consisted of a complex noun phrase (the + noun + of the + noun),
which was the subject of the main clause, followed by a relative clause and the rest of the main
clause. The relative clause consisted of that + has been/had been/used to + verb + noun phrase
or prepositional phrase.
We constructed the relative clause so that in the ambiguous condition (2a) high and low
attachment were equally plausible. In the high attachment condition (2b), attachment to the
first noun phrase was plausible but the verb in the relative clause (e.g., retiring) made
attachment to the second noun phrase implausible. In the low attachment condition (2c), the
verb made attachment to the first noun phrase implausible but attachment to the second noun
phrase was plausible. The words preceding the disambiguating verb (that + has been/had
been/used to) were always consistent with either analysis.
--------------------------------------------------------INSERT TABLE 1 ABOUT HERE
---------------------------------------------------------
Attachment plausibility pretest. To ensure that our plausibility manipulation was
working as intended, we tested the plausibility of the relative clause as a modifier of either NP1
or NP2. Eighteen participants took part. For each of the 50 items, we constructed a question
set such as (5), which asked participants to rate the plausibility of the events described by the
relative clauses.
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5a.
Can a bodyguard of a governor retire?
5b.
Can a governor of a province retire?
5c.
Can a province of a governor retire?
5d.
Can a governor retire?
5e.
Can a province retire?
5f.
Can a governor retire?
We used questions that unambiguously questioned the events in the relative clauses. They
always had the form Can + subject NP + verb (+ something/someone). The questions did not
include the phrase that followed the verb in the experimental items, as it was crucial for the
purposes of the eye-movement experiment to test that the verb disambiguated the sentences.
For the high attachment questions (5a-c), the whole noun phrase complex was taken as the
subject NP because it was thought that the plausibility of attachment to NP1 might be affected
by the fact that is was modified by NP2. For the low attachment questions (5d-f), NP2 was
taken as the subject. The verb was always the infinitive form of the main verb in the relative
clauses of the experimental item sets. If the verb required a direct object noun phrase, it was
followed by something or someone, as appropriate. Conditions (5c) and (5e) were derived
from analyses that were constructed to have implausible interpretations. All other conditions
were derived from analyses that were constructed to be plausible. Conditions (5d) and (5f) are
identical for the item in (2) because NP2 was the same in the globally ambiguous and low
attachment conditions, but this was not always the case (see Appendix).
Participants rated all 50 items such as (5) in all six versions on a 7-point scale, with 7
indicating very plausible and 1 very implausible. At least 20 items appeared between two
conditions of the same item.
From our original 50 items, we selected 30 that met our criteria. ANOVAs treating
question type (high attachment question [5a-c] vs. low attachment question [5d-f]) and
experimental condition (ambiguous [5a, d] vs. high attachment [5b, e] vs. low attachment [5c,
f]) as within-participants and –items variables revealed an interaction: F1 (2, 34) = 1009.46, p <
.01; F2 (2, 58) = 302.00, p < .01. As Table 1 shows, the events described by (5c) and (5e) were
rated as implausible, and the events in the other conditions were rated as plausible. Planned
comparisons showed that the plausibility of the two attachment sites for the high and low
attachment experimental conditions differed significantly (all ps < .01), but not for the
ambiguous experimental condition (F1 (1, 34) = 2.29; p = .14; F2 < 1). Thus, our plausibility
manipulations worked as intended.
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Main clause plausibility pretest. This test examined the plausibility of the complex noun
phrase as the subject of the main clause. Eighteen participants rated the plausibility of 50 sets
of sentences such as (6) on a 7-point scale.
6a.
The bodyguard of the governor is very rich.
6b.
The governor of the province is very rich.
6c.
The province of the governor is very rich.
The sentences were identical to the ambiguous, high attachment and low attachment condition
respectively, except that the relative clause was omitted. Participants rated all 50 items in all
three conditions. At least 20 sentences appeared between two versions of one item.
Table 1 shows the mean rating for each condition for the 30 items that were selected.
ANOVAs treating condition as a within-participants and -items variable revealed no effect: F1
(2, 34) = 1.31, p = .28; F2 < 1. Thus, any differences in reading difficulty between the
experimental sentences are not due to differences in plausibility in the main clause.
Frequency and length of the noun phrases. The log lemma frequency of the nouns in the
noun phrase complex was controlled between the conditions for the 30 items that we selected
for the eye-tracking experiment (see Table 1) using the CELEX data base (Baayen,
Piepenbrock, & Van Rijn, 1993). An ANOVA treating noun (noun 1 vs. noun 2) and condition
(ambiguous vs. high attachment vs. low attachment) as between items variables revealed no
main effects or interaction (Fs < 1.1). We also controlled the length of the noun phrase
complex (see Table 1). An ANOVA with the variable condition as a between items variable
revealed no differences (F < 1).
Fillers. The experiment included 68 fillers. Nine fillers contained a relative clause. Five
relative clauses modified a subject, two an indirect object, and two a prepositional phrase.
None of the relative clauses contained an attachment ambiguity that was similar to the
experimental items.
Comprehension questions. Forty-eight sentences were followed by a question, with half
of them requiring a “yes” response and half a “no” response. Fifteen of the experimental
sentences were followed by a question (see Appendix). These questions focused on different
aspects of the sentences, but participants did not have to resolve the ambiguity to answer the
question.
Design
15
We used 30 items such as (2), each having three conditions. We constructed three lists
comprising 10 items from each condition, with exactly one version of each item appearing in
each list, together with the fillers and comprehension questions. The items were placed in a
single random order, with six fillers preceding the first experimental sentence and three fillers
following a break half way through the experiment. Twelve participants were randomly
assigned to each list.
Procedure
Participants' eye movements were recorded with a Fourward Technologies Dual Purkinje
Generation 5.5 eye tracker which monitored the right eye (though viewing was binocular). The
tracker had an angular resolution of 10' arc. A computer displayed the items on a screen 77 cm
from the participants' eyes. The screen displayed 3.8 characters per degree of visual angle.
The tracker monitored participants' gaze location every millisecond and the software sampled
the tracker's output to establish the sequence of eye fixations and their start and finish times. A
bite bar and head restraint were used to minimize head movements.
Each participant was run individually. The experimenter told the participant to read the
sentences carefully in order to understand them, but to read at his or her normal rate. Next, the
participant completed a calibration procedure. Before each item or filler a calibration check
was performed, and the calibration was repeated if necessary. Each item was presented on two
lines, with the line break always in the final region (see definition below). In the experimental
items, the line break was always just before or after the penultimate word. After reading the
sentence, the participant pressed a button which led to the presentation of the comprehension
question or the next trial. Participants received immediate feedback when they answered a
question incorrectly. The experiment took about forty minutes.
Analyses
Prior to all analyses, trials with major tracker losses were excluded. If a fixation was shorter
than 80 ms and within one character space of the previous or next fixation, it was assimilated to
this fixation. All remaining fixations shorter than 80 ms were excluded. Following Rayner and
Pollatsek (1989), we assume that readers do not extract much information during such short
fixations. We also excluded fixations longer than 800 ms.
16
We analyzed three regions, indicated by brackets below:
7. The bodyguard of the governor that will be[ retiring][ after the troubles][ is very rich.]
These regions corresponded to (1) the disambiguating verb in the relative clause (the
disambiguating region, 5-15 characters), (2) the rest of the relative clause (the postdisambiguation region, 12-28 characters), and (3) the final region (13-27 characters). Spaces
between regions were included in the following region. The regions are indicated in the
Appendix.
For each region, four eye-tracking measures were calculated. First-pass time is the sum
of all fixation times starting with the first fixation inside a region until the first fixation outside
the region (either to the left or right) provided that the reader has not fixated subsequent text.
For regions consisting of a single word, first-pass time corresponds to gaze duration (Rayner &
Duffy, 1986). First-pass regressions are the percentage of leftward eye movements that cross
the region's left boundary initiated immediately after a first-pass fixation in the region.
Regression-path time (Brysbaert & Mitchell, 1996; Konieczny, Hemforth, Scheepers, & Strube,
1997; Liversedge, Paterson, & Pickering, 1998; Traxler, Bybee, & Pickering, 1997; cf. Duffy,
Morris, & Rayner, 1988) is the sum of all fixation times starting with the first fixation inside
the region until the first fixation to the right of the region, again provided that the reader has not
fixated subsequent text. Finally, total time is the sum of all fixations in a region.
For all reading time measures, the data for a particular region were excluded if the
reading time measure for that region was zero. The first-pass regression datum for a region
was excluded if first-pass time was excluded. Additionally, if reading times for two or more
consecutive regions were zero in a measure, reading times for the regions following them were
excluded from that measure. We assumed that participants could not have processed the
sentence completely if this was the case.
Eye-movement studies have shown that a variety of different measures can provide the
earliest indication of syntactic processing difficulty (Liversedge & Findlay, 2000; Rayner,
1998). Although initial effects of syntactic ambiguity resolution in first-pass times have
frequently been reported (e.g., Ferreira & Clifton, 1986; Rayner et al., 1983; Trueswell,
Tanenhaus, & Kello, 1993; Trueswell et al., 1994), the earliest effects can also occur in
measures such as first-pass regressions (Liversedge, Pickering, Clayes, & Branigan, 2003;
Meseguer, Carreiras, & Clifton, 2002; Traxler et al., 1998; Van Gompel et al., 2001),
regression-path times (Brysbaert & Mitchell, 1996; Konieczny et al., 1997; Meseguer et al.,
17
2002; Van Gompel & Pickering, 2001) and total times (Carreiras & Clifton, 1999; Traxler et
al., 1998). Furthermore, while some studies have shown the earliest effects in the critical,
disambiguating region (e.g., Ferreira & Clifton, 1986; Rayner et al., 1983; Trueswell et al.,
1993, 1994), other studies have found the earliest effects in the region following
disambiguation (Meseguer et al., 2002; Pickering & Traxler, 1998; Traxler et al., 1998; Van
Gompel et al., 2001). Using very similar relative clause attachment ambiguities, Traxler et al.
(1998) observed their earliest effects in first-pass regressions from words immediately
following the disambiguating word (Experiments 2 and 3) and in total times for the
disambiguating region (Experiment 1). Therefore, given the similarity of our materials to those
of Traxler et al., we might expect our earliest effects to occur in similar measures and regions.
Results
Participants made 10% errors on the comprehension questions. The mean error rates for the
globally ambiguous, high and low attachment conditions were 15%, 9%, and 7% respectively
and the response times were 2349 ms, 2311 ms, and 2384 ms. Analyses with condition
(ambiguous vs. high attachment vs. low attachment) as a within-participants and -items variable
and participant/item group (I-III) as a between-participants and -items variable showed no
differences between conditions for the response times (Fs < 1), although there was a significant
effect for the error rates (F1 (2, 66) = 4.26, p = .02; F2 (2, 24) = 6.63, p < .01). Participants
made more errors in the ambiguous condition than in the high attachment (F1 (1, 66) = 3.65, p
= .06; F2 (1, 24) = 5.68, p = .02) and low attachment condition (F1 (1, 66) = 8.21, p < .01; F2
(1, 24) = 12.79, p < .01), but given that the questions did not require participants to resolve the
ambiguity, it is unlikely that these results are very informative of syntactic ambiguity
resolution. We return to this in the General Discussion.
The analyses of the eye-movement measures included incorrect trials. We excluded 0.4%
of trials because of major tracker losses, 4.2% of fixations because they were shorter than 80
ms and 1.1% of fixations because they were longer than 800 ms. No more than 0.8% of the
data was excluded from any of the measures in a particular region because reading times for
two or more consecutive regions were zero.
Table 2 presents the mean reading times and percentage of first-pass regressions by
condition. For each eye-tracking measure and each region, we conducted two ANOVAs, one
with participants and one with items as the random variable (F1 and F2 respectively). We first
conducted ANOVAs with condition as a within-participants and -items variable and animacy
18
(attachment to animate vs. inanimate NP) as a within-participants and between-items variable.
We also included participant/item group as a between-participants and -items variable in order
to eliminate the variance caused by random differences between groups (Pollatsek & Well,
1995). However, there were no interactions between condition and animacy in any of the
measures, so we report ANOVAs collapsed over animacy. Planned comparisons between the
ambiguous condition and the disambiguated conditions are reported below. We present the
results of all analyses for which the effect of condition reached significance by participants or
items (p < .05).
--------------------------------------------------------INSERT TABLE 2 ABOUT HERE
---------------------------------------------------------
Disambiguating region. Regression-path times for this region showed an effect that was
significant by items (F2 (2, 54) = 3.86, p = .03), but not by participants (F1 (2, 66) = 2.36, p =
.10). Assuming that this effect is real, planned comparisons suggested that the ambiguous
condition was easier to read than the low attachment condition (F1 (1, 66) = 4.72, p = .03; F2
(1, 54) = 7.71, p < .01) but not than the high attachment condition (F1 (1, 66) = 1.02, p = .32;
F2 (1, 54) = 2.04, p = .16). Total reading times showed a clearer effect of condition (F1 (2, 66)
= 5.77, p < .01; F2 (2, 54) = 5.59, p < .01). Total times for the ambiguous condition were
shorter than for both the high attachment condition (F1 (1, 66) = 9.96, p < .01; F2 (1, 54) =
9.27, p < .01) and low attachment condition (F1 (1, 66) = 7.12, p = .01; F2 (1, 54) = 7.40, p <
.01).
Post-disambiguation region. There was an effect of condition in first-pass regressions
(F1 (2, 66) = 4.88, p = .01; F2 (2, 54) = 5.48, p < .01), regression-path times (F1 (2, 66) = 6.58,
p < .01; F2 (2, 54) = 6.45, p < .01) and total times (F1 (2, 66) = 5.58, p < .01; F2 (2, 54) = 5.61,
p < .01). Planned comparisons showed that the ambiguous condition was easier to read than
both the high attachment condition (first-pass regressions: F1 (1, 66) = 6.59, p = .01; F2 (1, 54)
= 7.10, p = .01; regression path: F1 (1, 66) = 10.99, p < .01; F2 (1, 54) = 10.90, p < .01; total
times: F1 (1, 66) = 7.83, p < .01; F2 (1, 54) = 7.96, p < .01) and low attachment condition (firstpass regressions: F1 (1, 66) = 7.97, p < .01; F2 (1, 54) = 9.22, p < .01; regression path: F1 (1,
66) = 8.61, p < .01; F2 (1, 54) = 8.28, p < .01; total times: F1 (1, 66) = 8.88, p < .01; F2 (1, 54)
= 8.85, p < .01).
19
Final region. In regression-path times, we observed an effect of condition that was
significant by participants (F1 (2, 66) = 3.28, p = .04) but marginal by items (F2 (2, 54) = 2.99,
p = .06). The ambiguous condition appeared to be easier to read than the high attachment
condition (F1 (1, 66) = 4.25, p = .04; F2 (1, 54) = 3.94, p = .05) and the low attachment
condition (F1 (1, 66) = 5.50, p = .02; F2 (1, 54) = 4.98, p = .03).
Discussion
Experiment 1 showed that when the disambiguation is delayed relative to the initial point of
ambiguity, relative clauses that are semantically disambiguated toward high or low attachment
are harder to read than globally ambiguous relative clauses. The earliest fully significant
effects occurred in first-pass regressions and regression-path times for the post-disambiguation
region, although the marginal effect in regression-path times for the disambiguating region
provides some indication that the difficulty with the low attachment condition occurred slightly
earlier. These results replicate the findings of Traxler et al. (1998). They support variablechoice reanalysis models such as the unrestricted race model, which claims that reanalysis
should occur on some trials for disambiguated sentences but never for globally ambiguous
sentences. They are inconsistent with long-lasting competition accounts, in which competition
between syntactic analyses lingers until the reader encounters a disambiguation (e.g.,
MacDonald et al., 1992; Tabor & Tanenhaus, 1999). However, constraint-based competition
models which claim that competition is resolved very rapidly are consistent with the pattern of
results that we observed in Experiment 1. We conducted Experiment 2 to contrast this type of
model with the unrestricted race model.
Experiment 2
In Experiment 2, we investigated relative clause attachment ambiguities such as in (3), repeated
here as (8):
8a. I read that the bodyguard of the governor retiring after the troubles is very rich. (globally
ambiguous)
8b. I read that the governor of the province retiring after the troubles is very rich. (high
attachment)
20
8c. I read that the province of the governor retiring after the troubles is very rich. (low
attachment)
8d. I read quite recently that the governor retiring after the troubles is very rich. (syntactically
unambiguous)
Because the disambiguation in the disambiguated conditions (8b) and (8c) is immediate,
constraint-based competition models predict that the processor cannot select a single analysis
before it reaches the point of semantic disambiguation, even if competition is short-lasting.
Therefore, they predict that strong competition should occur in the ambiguous condition at or
shortly following the critical word retiring in the globally ambiguous condition, whereas
competition should be much weaker in the disambiguated conditions. In contrast, the
unrestricted race model predicts that the globally ambiguous condition should be easier than the
disambiguated conditions.
In order to provide a further test of the models, we also investigated a syntactically
unambiguous condition, exemplified in (8d). We controlled for length with (8a-c) by including
additional words that introduced no further ambiguity. Because this was done by including an
additional clause at the beginning of the sentence, we also included an extra clause to the other
conditions in Experiment 2. Constraint-based competition models predict that (8d) should be
easy to process, because there is only one analysis, so no competition can occur. The
syntactically unambiguous condition should therefore be much easier than the globally
ambiguous condition. In contrast, according to the unrestricted race model (and most other
reanalysis models), the syntactically unambiguous condition (8d) should be no easier or harder
than the globally ambiguous condition (8a). In both conditions, the processor adopts a single
analysis, and in neither condition is the processor forced to reanalyze.
Method
Participants
Thirty-two participants were paid to take part in the eye-tracking experiment. Three additional
participants were excluded because they had a very high percentage of tracker losses.
Items
There were 28 sets of items similar to (8); see Appendix. The items were the same as in
Experiment 1, but differed in the following ways: (1) the ambiguous region between the noun
21
phrase complex and the disambiguating verb in the relative clause was removed so that the
disambiguation was immediate, at the verb in the relative clause; (2) if the verb form was an
infinitive in Experiment 1, it was replaced by a present or past participle form in Experiment 2;
(3) a clause was added to the beginning of all conditions (e.g., I read quite recently that); (4) the
unambiguous condition was constructed by removing NP1 and of from the ambiguous
condition, and by adding additional words to the beginning of the sentence so that it had a
similar length as the other conditions; (5) the end of a few items was slightly changed so that at
least two words following the relative clause could appear on the first line; (6) two items were
discarded to make the number of items divisible by 4. Analyses of the plausibility pretest
results, and the frequency and length of the nouns for the 28 selected materials were
statistically very similar to the results reported in Experiment 1. See Table 1 for all item
characteristics.
The experiment included 71 fillers. Three fillers contained a relative clause, one
modifying a subject, one an indirect object, and one a prepositional phrase. None of the fillers
contained a relative clause that had a similar attachment ambiguity as the experimental items.
Fourteen experimental items were followed by a comprehension question.
Design, procedure, and analyses
These were the same as in Experiment 1, except as follows. There were 28 items, each having
four conditions. We constructed four lists of items, consisting of 7 items from each condition.
Eight participants were randomly assigned to each list. We analyzed three regions, indicated
by brackets below:
9. I read quite recently that the governor[ retiring][ after the troubles][ is very rich.]
These regions corresponded to: (1) the disambiguating verb in the relative clause (the
disambiguating region), (2) the rest of the relative clause (the post-disambiguation region), and
(3) the final region.
Results
Participants made 8% errors to the comprehension questions. The mean error rates for the
globally ambiguous, high attachment, low attachment, and syntactically unambiguous
conditions were 9%, 10%, 18%, and 7% respectively and the response times were 2775 ms,
22
2765 ms, 3125 ms, and 2682 ms. ANOVAs with condition (ambiguous vs. high attachment vs.
low attachment vs. unambiguous) and participant/item group (I-IV) as variables showed no
significant differences in errors rates (F1 (3, 84) = 2.23, p = .09; F2 (3, 30) = 2.06, p = .13)
although there was a difference in response times (F1 (3, 84) = 3.73, p = .01; F2 (3, 30) = 2.65,
p = .07). However, there was no indication that response times for the ambiguous condition
were slower than for any of the other conditions (Fs < 1).
The analyses of the eye-movement measures included incorrect trials. We excluded 1.7%
of trials because of tracker losses, 3.7% of fixations because they were shorter than 80 ms, and
0.7% of fixations because they were longer than 800 ms. No more than 0.5% of the data was
excluded from any of the measures in a particular region as a result of reading times for two or
more consecutive regions being zero.
Table 3 presents the mean reading times and percentage of first-pass regressions by
condition. We first conducted ANOVAs with condition as a within-participants and -items
variable, animacy (attachment to animate vs. inanimate NP) as a within-participants and
between items variable, and participant/item group. However, there were no interactions
between condition and animacy in any of the measures, so we report ANOVAs collapsed over
animacy. Planned comparisons between the ambiguous condition and all other conditions are
reported below. We present the results of all analyses for which the effect of condition reached
significance by participants or items.
--------------------------------------------------------INSERT TABLE 3 ABOUT HERE
---------------------------------------------------------
Disambiguating region. No significant differences occurred in any of the measures.
Post-disambiguation region. A significant effect of condition occurred in first-pass
regressions (F1 (2, 84) = 3.27, p = .03, F2 (2, 72) = 2.81, p = .05) and total times (F1 (2, 84) =
5.38, p < .01, F2 (2, 72) = 4.09, p < .01). Planned comparisons for first-pass regressions
showed that the ambiguous condition produced fewer first-pass regressions than the low
attachment condition (F1 (1, 84) = 8.77, p < .01, F2 (1, 72) = 7.53, p < .01), but that it did not
differ from either the high attachment or unambiguous condition (Fs < 1). Most important for
our investigation of competition and reanalysis as mechanisms of syntactic ambiguity
resolution, total times showed that the ambiguous condition was read faster than both the high
attachment condition (F1 (1, 84) = 6.41, p = .01, F2 (1, 72) = 4.61, p = .04) and low attachment
23
condition (F1 (1, 84) = 8.96, p < .01, F2 (1, 72) = 7.05, p = .01), suggesting that processing
difficulty was due to reanalysis rather than competition. The ambiguous condition did not
differ from the unambiguous condition (Fs < 1).
Final region. There was an overall effect of condition in first-pass regressions (F1 (2, 84)
= 3.62, p = .02, F2 (2, 72) = 2.93, p = .04), but planned comparisons showed that the
ambiguous condition did not significantly differ from any of the other conditions (Fs < 2.88, p
> .09). We also observed an effect of condition in regression-path times (F1 (2, 84) = 4.32, p <
.01, F2 (2, 72) = 3.29, p = .03). The ambiguous condition was read faster than the low
attachment condition (F1 (1, 84) = 6.04, p = .02, F2 (1, 72) = 5.07, p = .03), but did not differ
from the unambiguous condition (Fs < 1), nor from the high attachment condition (F1 (1, 84) =
1.32, p = .25, F2 (1, 72) = 1.10, p = .30). 2
Discussion
Experiment 2 yielded two new findings. First, it showed that when the disambiguation is
immediate, relative clauses that are semantically disambiguated towards high or low attachment
are harder to read than globally ambiguous relative clauses. This result provides evidence
against constraint-based competition models, both models that claim that competition is longlasting and models that claim that competition is resolved very rapidly. Rather, the results
support the unrestricted race model, because it predicts that reanalysis should occur in both
disambiguated conditions, but not in the ambiguous condition.
Second, none of the eye-movement measures showed any evidence that globally
ambiguous relative clauses were harder to read than syntactically unambiguous relative clauses.
This finding is also contrary to the predictions of competition models, because they predict
strong competition in the ambiguous condition, but no competition in the unambiguous
condition. 3 Again, this pattern of results supports the unrestricted race model, which claims
that reanalysis does not occur in either condition.
The difficulty with the low attachment condition occurred slightly earlier, in first-pass
regressions from the post-disambiguation region, than the difficulty with high attachment,
which first appeared in total times in the same region. A similar pattern was observed in
Experiment 1, which showed that the low attachment condition was harder than the ambiguous
condition in regression-path times for the disambiguating region, whereas the earliest
difference between the high attachment and ambiguous condition occurred in the following
region. In both experiments, readers seemed to experience difficulty earlier when they adopted
24
a high attachment analysis that turned out to be implausible than when they adopted an
implausible low attachment analysis. One possible explanation for this is that there was a slight
bias towards high attachment in our materials and that this resulted in a stronger and therefore
perhaps earlier effect in the low attachment condition. However, this explanation seems
somewhat unlikely, given that most studies show that similar relative clause attachment
ambiguities are balanced (Carreiras & Clifton, 1993; Traxler et al., 1998) or have a bias
towards low attachment (Carreiras & Clifton, 1999). Instead, it may be that semantic
evaluation is faster for high attachment than for low attachment, perhaps because NP1 is part of
the main assertion of the clause, whereas NP2 is not (Frazier, 1990). Readers may detect an
implausibility in the main assertion more rapidly than an implausibility in a more subordinate
assertion.
Regardless of the pattern of differences between the high- and low-attachment conditions,
both disambiguated conditions were harder to read than the globally ambiguous condition. It is
this pattern of results that provides evidence against constraint-based competition models.
Experiment 3
The critical finding of Experiment 2 was that the globally ambiguous condition was easier than
either of the disambiguated conditions, even though disambiguation occurred on the first word
of the ambiguity. In Experiment 3, we investigated whether this effect held for a different type
of ambiguity, involving attachment to verb phrases rather than noun phrases, and for a different
type of disambiguation, disambiguation by an adverbial whose temporal features are
incompatible with a verb's tense rather than disambiguation by semantic plausibility. If the
pattern is similar to previous experiments, it would provide further evidence that competition is
not the mechanism underlying syntactic ambiguity resolution and would lend further support to
a variable-choice reanalysis account like the unrestricted race model.
We employed sentences such as (4), repeated below as (10).
10a. The carpenter sanded the shelves he attached onto the kitchen wall yesterday morning,
according to the foreman. (globally ambiguous)
10b. The carpenter sanded the shelves he will attach onto the kitchen wall yesterday morning,
according to the foreman. (high attachment)
25
10c. The carpenter will sand the shelves he attached onto the kitchen wall yesterday morning,
according to the foreman. (low attachment)
In (10a), the adverbial phrase yesterday morning can be attached either to the verb phrase in the
first clause (high attachment to sanded the shelves) or the second clause (low attachment to
attached [the shelves] to the kitchen wall), because the adverbial phrase is consistent with the
tense of either verb. In the high attachment condition (10b), the adverbial phrase is
disambiguated towards attachment to the verb phrase in the first clause, because the tense of the
first clause is consistent with the adverbial phrase, whereas the tense of the second clause is
not. In the low attachment condition (10c), the adverbial phrase is disambiguated towards
attachment to the verb phrase in the second clause, because only the tense of the second clause
is congruent with the adverbial phrase. Importantly, the disambiguation is immediate because
the disambiguation occurs at the initial point of syntactic ambiguity (at yesterday).
Constraint-based competition models predict that the adverbial's temporal information
should affect the initial activation of the analyses, so it should have an immediate effect on
competition between the high- and low-attachment analyses. Strong competition should occur
in the ambiguous condition, because the adverbial phrase is consistent with both analyses,
whereas only a single analysis is supported in the disambiguated conditions. Altmann, van
Nice, Garnham, and Henstra (1998) showed a bias for the low attachment analysis in very
similar structures. If the bias for low attachment is so strong that very little competition occurs
in the ambiguous condition, this condition may be no harder to read than the low attachment
condition. Note, however, that competition in the globally ambiguous condition can never be
weaker than in the low attachment condition. Hence, constraint-based competition models
cannot account for results that show that the globally ambiguous condition is easier than the
low attachment condition.
The unrestricted race model predicts that if there is no strong bias towards either
analysis, reanalysis is predicted to occur on some proportion of trials in both disambiguated
conditions, so both should be harder than the globally ambiguous condition. If, on the other
hand, there is a strong bias towards the low attachment analysis, the unrestricted race model
predicts that this analysis is adopted on nearly all trials. As a result, the low attachment
condition may be no harder to read than the globally ambiguous condition. However, the
model could not explain results that show that the low attachment condition is easier than the
ambiguous condition.
26
Method
The experiment consisted of a plausibility pretest and an eye-movement reading experiment.
Participants
Fifty-four participants, 42 from the University of Dundee and 12 from the University of
Edinburgh, were paid to take part in the eye-tracking experiment. Six further participants were
excluded from the analyses, four because they had a high percentage of tracker losses, and two
because they answered 25% or more of the questions incorrectly.
Items
We constructed 52 items in six conditions similar to (10) from which we selected 36 materials
that satisfied our plausibility criteria (see Appendix). The first clause always consisted of a
subject, a verb, and a direct object. The second clause was always a (reduced) relative clause
that modified the direct object in the first clause. It consisted of a pronoun (referring to the
subject of the first clause), a verb, and a prepositional phrase. The prepositional phrase was
included because there is some evidence (Altmann et al., 1998) that increasing the distance
between the verb in the second clause and the adverbial phrase makes adverbial phrase
attachment to the second clause less strongly preferred (i.e., the ambiguity is more balanced).
The prepositional phrase was followed by an adverbial phrase that could be attached either to
the first or the second clause. The adverbial phrase consisted of either yesterday or tomorrow,
followed by a specific time of the day (e.g., morning, afternoon, evening). Importantly, in the
high and low attachment conditions, the temporal features of yesterday/tomorrow resulted in an
immediate disambiguation. In these conditions, there was no point in the sentence where both
high and low attachment were possible. Finally, the second clause was followed by a
prepositional phrase or a third clause, which enabled us to detect reading time differences that
occurred after the disambiguating adverbial phrase was read.
We counterbalanced for length and lexical differences between past and future tense
verbs: In addition to conditions (10a-c), each item contained three further parallel conditions in
which the past tense verbs in (10a-c) were replaced by future tense verbs and vice versa, and in
which the adverbial phrase was congruent with a future tense (e.g., tomorrow morning). From
our initial 52 items, we selected 36 materials on the basis of our plausibility norms (see
plausibility pretest).
27
Plausibility pretest. It is possible that sentences which have two clauses in the same
tense are more plausible than sentences which have two clauses with a different tense. In order
to ensure that all conditions were equally plausible, we conducted a plausibility pretest for all
52 materials that we constructed. Twelve participants rated the plausibility of sentences such
as (11) on a 7-point scale. The sentences in (11) correspond to the different combinations of
tenses used in the experimental sentences.
11a. The carpenter sanded the shelves he attached onto the kitchen wall. (past tense + past
tense)
11b. The carpenter will sand the shelves he will attach onto the kitchen wall. (future tense +
future tense)
11c. The carpenter sanded the shelves he will attach onto the kitchen wall. (past tense + future
tense)
11d. The carpenter will sand the shelves he attached onto the kitchen wall. (future tense + past
tense)
Both (11a) and (11b) were included, because in the eye-movement experiment, the ambiguous
condition occurred in two versions, one with two past-tense verbs and one with two futuretense verbs. We selected 36 items for which the plausibility ratings did not differ between
conditions, with the mean for condition (11a) being 5.5 and the mean for each of the conditions
(11b-d) being 5.6. ANOVAs treating condition (11a-d) as a within-participants and -items
variable showed no differences (Fs < 1.2).
The experiment included 86 fillers. Forty items were followed by a comprehension
question. Twelve questions followed an experimental item. The questions focused on different
aspects of the sentences, but did not require participants to resolve the ambiguity.
Design, procedure, and analyses
These were the same as in Experiments 1 and 2, except for the following. We used 36 items,
each having six conditions (including the three conditions that counterbalanced for tense). We
constructed six lists comprising six items from each condition, with exactly one version of each
item appearing in each list, together with 86 fillers. Nine participants were randomly assigned
to each list. The sentences were divided into regions as follows:
28
12. The carpenter sanded the shelves he attached onto the kitchen wall[ yesterday morning,][
according to][ the foreman.]
The regions corresponded to (1) the adverbial phrase (the disambiguating region, 16-21
characters), (2) the word(s) immediately following the adverbial phrase (9-18 characters; the
post-disambiguation region) (3) the rest of the sentence (9-17 characters). Each item was
presented on two lines, with the line break in the experimental items immediately following the
preposition in the main clause (e.g., onto in [11]).
Results
Participants made 10% errors to the comprehension questions. The error rates for the globally
ambiguous, high attachment, and low attachment conditions were 8%, 4%, and 10%
respectively, and the response times were 2274 ms, 2279 ms, and 2232 ms. ANOVAs on the
error rates with condition (ambiguous vs. high attachment vs. low attachment) and
participant/item group (I-VI) as variables were significant by participants, but not by items (F1
= 3.81, p = .03; F2 = 1.50, p = .26). Analyses of the response times did not show an effect (Fs
< 1).
The analyses of the eye-movement measures included incorrect trials. We excluded 2.6%
of trials because of tracker losses, 3.3% of fixations because they were shorter than 80 ms, and
0.3% of fixations because they were longer than 800 ms. No more than 1.6% of the data was
excluded from any of the measures in a particular region because reading times for two or more
consecutive regions were zero.
Table 4 presents the mean reading times and percentage of first-pass regressions by
condition. ANOVAs treated condition (ambiguous vs. high attachment vs. low attachment) as
within-participants and -items variable, and participant/item group (I-VI) as a betweenparticipants and -items variable. We collapsed across the variable tense, because it was
included as a counterbalancing variable to control for length and lexical differences between
the verb tenses. Planned comparisons between the ambiguous condition and the disambiguated
conditions are reported below. We present the results of all analyses for which the effect of
condition reached significance by participants or items.
29
--------------------------------------------------------INSERT TABLE 4 ABOUT HERE
---------------------------------------------------------
Disambiguating region. First-pass times (F1 (2, 96) = 8.18, p < .01; F2 (2, 60) = 10.34, p
< .01), regression-path times (F1 (2, 96) = 3.74, p = .03; F2 (2, 60) = 6.39, p < .01), and total
times (F1 (2, 96) = 6.10, p < .01; F2 (2, 60) = 9.46, p < .01) for this region showed a significant
effect of condition. Planned comparisons showed that first-pass times were longer in the high
attachment condition than in the ambiguous condition (F1 (1, 96) = 10.99, p < .01; F2 (1, 60) =
15.54, p < .01), whereas there was no difference between the ambiguous and low attachment
condition (Fs < 1). A similar pattern occurred in regression-path and total times: Longer
reading times in the high attachment condition than in the ambiguous condition (regressionpath times: F1 (1, 96) = 7.38, p < .01; F2 (1, 60) = 12.67, p < .01; total times: F1 (1, 96) = 6.01,
p = .02; F2 (1, 60) = 10.48, p < .01), but no difference between the low attachment and
ambiguous conditions (regression-path times: F1 (1, 96) = 1.65, p = .28; F2 (1, 60) = 2.26, p =
.14; total times: Fs < 1).
Post-disambiguation region. The most crucial result occurred in first-pass times for the
post-disambiguating region (F1 (2, 96) = 3.93, p = .02; F2 (2, 60) = 4.29, p = .02). Planned
comparisons showed that the ambiguous condition took less time to read than both the high
attachment condition (F1 (1, 96) = 4.75, p = .03; F2 (1, 60) = 6.17, p = .02) and low attachment
condition (F1 (1, 96) = 6.84, p = .01; F2 (1, 60) = 6.69, p = .01), suggesting that processing
difficulty was due to reanalysis rather than competition.
Final region. No significant differences were observed in this region. 4
Discussion
Experiment 3 showed, once more, that globally ambiguous sentences are easier to process than
disambiguated sentences. As in Experiment 2, this pattern occurred even though the
disambiguation was immediate. However, Experiment 3 extends the findings of Experiment 2
in that it showed that the pattern of results is not confined to a particular type of ambiguity or
disambiguation.
Processing difficulty in the high attachment conditions occurred somewhat earlier, in
first-pass and regression-path times for the disambiguating region, than the difficulty in the low
attachment conditions, which occurred in first-pass times for the post-disambiguation region.
30
The results from Experiment 3 indicate that difficulty occurred earlier when the disambiguation
was inconsistent with low attachment (in the high attachment conditions) than when it was
inconsistent with high attachment (in the low attachment conditions). One possibility is that
readers discovered the incongruency between the adverbial phrase and the verb's tense faster
when the adverbial phrase was close to the incongruent verb than when it was distant.
Alternatively, the ambiguity in Experiment 3 may be somewhat biased towards low attachment
(see Altmann et al., 1998, for evidence). If this is the case, the unrestricted race model predicts
that readers should adopt low attachment on a larger percentage of trials than high attachment,
so disambiguation towards high attachment should involve reanalysis on a larger proportion of
trials. Across all trials, this would result in more processing difficulty for the high attachment
conditions and as a result, processing difficulty in these conditions may be detected in earlier
eye-movement measures than difficulty in the low attachment conditions.
However, the crucial result is that, similar to Experiments 1 and 2, the disambiguated
conditions were harder to read than the ambiguous sentences. Regardless of the exact measures
and regions in which the difficulty in the disambiguated conditions occurred, constraint-based
competition models cannot account for the fact that there is a reading time advantage for the
globally ambiguous condition.
General Discussion
All three experiments reported in this paper showed that globally ambiguous sentences are
easier to read than disambiguated sentences. This pattern of results occurred for ambiguities
that involved attachment of a relative clause to a noun phrase (Experiments 1 and 2) and
ambiguities involving attachment of an adverbial phrase to a verb phrase (Experiment 3).
Furthermore, it occurred regardless of whether the disambiguation was delayed until a few
words after the disambiguation (Experiment 1) or whether it occurred at the initial point of
syntactic ambiguity (Experiments 2 and 3). Finally, globally ambiguous sentences were no
harder to read than syntactically unambiguous sentences (Experiment 2).
The results are very hard for constraint-based competition models to explain (e.g., McRae
et al., 1998; Spivey & Tanenhaus, 1998; Tabor et al., 1997; Tabor & Tanenhaus, 1999). These
models predict that when two analyses receive approximately equal support from the various
constraints, severe competition should occur, resulting in processing difficulty. In contrast,
when one analysis receives much more support than its alternative, there should be little
31
competition and processing should be easy. Crucially, because all sources of information are
assumed to have an immediate effect on the activation of the analyses, all sources of
information, including semantic plausibility and a word's temporal features, should influence
the extent to which the analyses compete. Thus, constraint-based competition models predict
that globally ambiguous sentences should be harder to process than disambiguated sentences,
but clearly, this prediction was not supported by the results from our experiments.
As mentioned in the Introduction, in theory it is possible that competition is very shortlasting, because one analysis may quickly receive more activation than its alternative(s) and
may therefore be selected very rapidly. This assumption would account for the results from
Experiment 1, where the semantic disambiguation occurred a few words after the initial point
of syntactic ambiguity. It is possible that in this experiment, the processor had selected a single
analysis before the disambiguation, and that as a result, we did not observe any evidence for
competition. However, Experiments 2 and 3 ruled out this account. Short-lasting competition
models predict that when the disambiguation (by semantic information or a word's temporal
features) occurs at the initial point of syntactic ambiguity, the processor cannot select a single
analysis before the disambiguation. Because constraint-based theories assume that semantic
information and a word's temporal features have an immediate effect on syntactic ambiguity
resolution, competition should be stronger in globally ambiguous sentences than in
disambiguated sentences. However, Experiment 2 showed that when the semantic
disambiguation was immediate, globally ambiguous sentences were still easier to read than
disambiguated sentences. Experiment 3 used a different type of ambiguity and showed that the
same pattern of results occurs when the sentences are disambiguated by temporal features of a
phrase rather than by plausibility information. Finally, constraint-based competition models
predict that no competition should occur in the syntactically unambiguous condition in
Experiment 2, so it should be much easier to process than the globally ambiguous condition.
However, no differences between these conditions were observed. In the context of the reliable
differences that were observed between the globally ambiguous and disambiguated conditions,
this is particularly striking. In the syntactically unambiguous condition, only a single analysis
can receive activation, so no competition can occur. It should therefore have been much easier
to process than the globally ambiguous condition.
Fixed-choice reanalysis models (e.g., the garden-path model, Frazier, 1987) also cannot
account for our data, because they claim that the processor is deterministic and should adopt the
same syntactic analysis on all trials. Assuming that the processor adheres to a late closure or
recency strategy, it should always adopt low attachment. Therefore, the processor never has to
32
reanalyze in the low attachment sentences, and these sentences should be no harder than the
globally ambiguous sentences. However, all three experiments showed that both the high and
low attachment sentences were harder to process than the globally ambiguous sentences, ruling
out a deterministic processor.
Our results are straightforwardly accounted by variable-choice reanalysis models (e.g.,
the unrestricted race model, Van Gompel et al., 2001). Such models assume that the processor
adopts a single analysis of a syntactic ambiguity on a probabilistic basis. If information prior to
the ambiguity provides strong support for a particular analysis, the likelihood of it being
adopted is very high, whereas the likelihood that the alternative analysis is adopted is very low.
In contrast, when two analyses are about equally supported by prior information, each analysis
is adopted approximately half the time. Processing difficulty is assumed to occur when the
initial analysis turns out to be ungrammatical or implausible and the processor has to reanalyze.
Variable-choice reanalysis models explain why difficulty occurred in both disambiguated
conditions in our experiments. Because information prior to the ambiguity did not result in a
strong bias for either analysis, the processor adopted each analysis on some proportion of trials.
When this initial analysis was subsequently evaluated for plausibility (Experiment 1 and 2) or
congruency of tense information (Experiment 3) and turned out to be implausible or
incongruent, the processor had to reanalyze. In contrast, the initial analysis was always
plausible and congruent in the globally ambiguous conditions, so no reanalysis occurred.
Furthermore, because the processor only constructs a single analysis in globally ambiguous
sentences, they should be no harder to process than syntactically unambiguous sentences.
Indeed, Experiment 2 showed no reliable difference between the globally ambiguous and
syntactically unambiguous condition, even though there were reliable differences between the
globally ambiguous and disambiguated conditions.
The aim of the experiments was to contrast the predictions of the unrestricted race model
with currently implemented constraint-based models that claim that competition between
syntactic analyses causes processing difficulty. Our results provide evidence against this type
of constraint-based theory and lend support to the unrestricted race model. Here, we consider
two alternative explanations of our results. First, we consider constraint-based theories which
assume that syntactic structures do not compete in the particular ambiguities that we
investigated. Second, we discuss the hypothesis that no difficulty occurs in globally ambiguous
sentences because readers fail to resolve the ambiguity.
First, some constraint-based theories may assume that competition between syntactic
analyses occurs for some ambiguities, but not for the ones we have studied. One modification
33
of constraint-based theories would be to assume that competition occurs between arguments,
but not between adjuncts. Most constraint-based theories are lexicalist theories, in that they
assume that syntactic ambiguity resolution is a form of lexical ambiguity resolution (e.g.,
Boland & Blodgett, 2001; MacDonald et al., 1994; Trueswell et al., 1994). One possibility is
that competition only arises when a syntactic ambiguity is the result of an indeterminacy related
to a lexical entry (e.g., an ambiguity related to the lexical entry's morphological form, word
category or argument structure). Because adjuncts are not part of a lexical entry, competition
does not occur for ambiguous adjuncts. In contrast, arguments are often considered to be part
of a word's lexical representation, and therefore competition may occur for ambiguous
arguments. The results from the experiments reported here and in Traxler et al. (1998) and Van
Gompel et al. (2001) do not rule out this type of account, because all experiments arguably
tested adjunct attachment ambiguities.
Another possibility, proposed by Pearlmutter and Mendelsohn (2000), is that the extent to
which syntactic analyses compete depends on the degree to which the analyses are compatible
in terms of their syntactic, lexical, and semantic properties. When their properties are highly
incompatible, syntactic alternatives compete, but when they share many properties, the
activation of one syntactic alternative reinforces the activation of the other. In the latter case,
both analyses are retained in parallel, and processing difficulty occurs when one of the analyses
is implausible. Assuming that the structures in our experiments were highly compatible, this
would account for the absence of competition. However, it is unclear how the processor
ultimately selects the most plausible analysis in the disambiguated sentences.
In sum, because the current experiments and those reported in Traxler et al. (1998) and
Van Gompel et al. (2001) investigated a limited set of ambiguities, they cannot rule out the
possibility that competition occurs for other types of syntactic ambiguities. However, what the
results do make clear is that competition is not a mechanism that applies to syntactic ambiguity
resolution in general.
Second, we consider the possibility that no difficulty occurs in globally ambiguous
sentences, because they are not fully resolved. Globally ambiguous sentences may be easier to
process than disambiguated sentences because failing to resolve an ambiguity may be less
costly than adopting a single analysis. This prediction contrasts with that of the unrestricted
race model, which claims that for balanced ambiguities, the processor adopts each attachment
half the time. Note that the results from the comprehension questions did not indicate whether
participants resolved the ambiguities, because they did not show any clear pattern. Although
Experiment 1 suggested that participants made more errors after globally ambiguous sentences,
34
this pattern was not replicated in Experiments 2 and 3. Furthermore, it is unlikely that the
questions are very informative about online ambiguity resolution, because they constitute an
offline measure of sentence processing and did not require participants to resolve the
ambiguity.
We discuss two versions of models which claim that globally ambiguous sentences
remain unresolved. According to the first type of model, the processor simultaneously
activates multiple analyses of a syntactic ambiguity in parallel without there being competition
between them. The previously discussed Pearlmutter and Mendelsohn (2000) model is an
example of such a model. Tabor and Hutchins (2004) provide a more detailed implementation
of a model in which ambiguous phrase structures can simultaneously be attached to more than
one node. In the syntactic ambiguities that they consider, simultaneous attachments of a single
phrase are unstable, so one attachment rapidly wins out. However, one might assume that if
two attachment sites are approximately equally preferred, as in our globally ambiguous
sentences, the system stabilizes in a state of two attachment sites for the ambiguous phrase.
Whether such stabilization is faster than the stabilization that occurs when the processor adopts
a single analysis in the disambiguated sentences is currently unclear and needs further
modeling. However, probably more problematic for Tabor and Hutchins’s model is to account
for our finding that globally ambiguous sentences are as easy to process as syntactically
unambiguous sentences, because it is unclear why the system would stabilize equally fast in a
configuration with two possible structures as in a configuration with only one.
A second version of a non-resolving model assumes that, rather than making both
attachments, the processor does not attach the globally ambiguous phrases either high or low in
our experiments. Ferreira, Bailey, and Ferraro (2002) argued that the processor may not attach
these phrases because it does not have enough information to resolve the ambiguity. On this
account, globally ambiguous sentences are easy to read because they are not fully processed,
whereas disambiguated sentences are hard because the processor has to select a single analysis.
A model which may be revised in such a way that it is compatible with this hypothesis is Tabor
and Tanenhaus's (1999) visitation set gravitation model. In the current model, it is assumed
that processing times are slow when the constraints in favor of different attractors are evenly
balanced, because it takes a long time for the mapping of a sentence fragment to reach an
attractor. However, it may be possible to modify the model so that such slow movement to an
attractor is interpreted as high stability by the language processor and that, as a result, it quickly
proceeds to the next word. In such a situation, the mapping of the sentence fragment would
never reach an attractor, that is, no single analysis would be accessed and the ambiguity would
35
never be resolved. Most crucially, however, equal support for two analyses would result in fast
rather than slow processing.
Note, however, that this would result in a change to how the model explains syntactic
ambiguity resolution, because the current implementation assumes that the mapping of the
sentence fragment always needs to reach an attractor before the processor can move on to the
next word. That is, the processor always immediately resolves the ambiguity. If this
assumption is given up, it is unclear whether the model still makes the correct predictions for
ambiguities such as those considered in Tabor and Tanenhaus (1999) and Tabor et al. (1997).
It is also unclear whether the revised model would account for our finding that globally
ambiguous sentences are as easy to process as syntactically unambiguous sentences. One
would have to assume that reaching a stable state when the evidence for the two parses is
evenly balanced is as fast as reaching a stable state due to gravitation to an attractor. Explicit
modeling is needed to determine whether this type of model makes the right predictions in such
cases.
In conclusion, our experiments provide evidence against competition as a general
mechanism of syntactic ambiguity resolution and as an explanation of why difficulty occurs
during the processing of syntactically ambiguous sentences. Rather, our experiments suggest
that the detection of an initial syntactic misanalysis and its subsequent reanalysis are a more
plausible way of accounting for processing difficulty during syntactic ambiguity resolution.
We have argued that the results are inconsistent with current constraint-based competition
models, and that the results are straightforwardly explained by the unrestricted race model, a
variable-choice reanalysis model.
36
APPENDIX
The brackets indicate analysis regions.
Items from Experiment 1
The phrases used in the three conditions are given within the braces in the order {ambiguous,
high attachment, low attachment}.
1.
The {altar of the temple, temple of the priest, priest of the temple} that has been[
disintegrating][ over the years][ was very important.]
2.
The {rudder of the boat, boat of the native, rower of the boat} that had been[ sawn][ from
the wood][ looked very impressive.]
3.
The {section of the field, land of the farmer, farmer of the land} that had been[ sown][
early this spring][ pleased the lord.]
Was the lord delighted?
4.
The {basement of the tenement, tenement of the landlord, landlord of the tenement} that
used to[ contain][ lots of junk][ is very gloomy.]
Did the {tenement have a basement, landlord have a tenement, tenement have a landlord}?
5.
The {tower of the castle, castle of the lord, lord of the castle} that has been[ decaying][ due
to acid rain][ is very old.]
6.
The {stopper of the decanter, collector of the porcelain, porcelain of the collector} that had
been[ broken][ in the accident][ was very old.]
7.
The {collar of the jacket, shirt of the tailor, designer of the jacket} that has been[ sewn][ in
a very skilful way][ looks quite stylish.]
8.
The {rudder of the vessel, yacht of the playboy, builder of the yacht} that had been[
corroding][ under the paint][ troubled the sailor.]
Was the sailor relaxed?
37
9.
The {jacket of the suit, suit of the judge, maker of the suit} that had been[ worn][ during
the meeting][ looked very unfashionable.]
10. The {region of the country, country of the tyrant, tyrant of the country} that used to[
neighbour][ the poor nation][ is quite wealthy.]
Is the {region of the country, country of the tyrant, tyrant of the country} rich?
11. The {diamond of the collection, diamond of the millionaire, owner of the diamond} that
had been[ stolen][ in the raid][ is very beautiful.]
Did anything disappear during the raid?
12. The {base of the statue, statue of the queen, sculptor of the statue} that had been[ hewn][
from the granite][ was very strong.]
Had marble been used?
13. The {tunic of the costume, costume of the actor, wearer of the costume} that had been[
woven][ in the mill looked][ very beautiful.]
Was the mill very beautiful?
14. The {garage of the cottage, cottage of the farmer, owner of the cottage} that used to be[
teeming][ with hundreds of mice][ was very ugly.]
Were there hundreds of rats?
15. The {brother of the reviewer, reviewer of the article, article of the scientist} that used to[
phone][ from the United States][ is very weird.]
16. The {client of the lawyer, lawyer of the company, mansion of the lawyer} that had been
[laughing][ at the joke][ looked very smart.]
17. The {bodyguard of the governor, governor of the province, province of the governor} that
will be[ retiring][ after the troubles][ is very rich.]
Will someone quit after a great success?
38
18. The {assistant of the professor, professor of the department, department of the professor}
that was[ smiling][ at the student][ is quite excellent.]
Did someone look angrily at the student?
19. The {accomplice of the burglar, burglar of the bungalow, revolver of the burglar} that had
been [forgiven][ by the victims][ was soon discovered.]
Were the victims vengeful?
20. The {servant of the prince, servant of the palace, palace of the prince} that has been[
strolling][ through the gardens][ is very old.]
21. The {colleague of the admiral, captain of the battleship, battleship of the admiral} that will
be [talking][ to the woman][ is leaving soon.]
Will someone speak to a woman?
22. The {companion of the courier, rider of the motorbike, motorbike of the courier} that has
been [waving][ to the pedestrian][ is very reliable.]
Did someone greet the pedestrian?
23. The {patient of the surgeon, surgeon of the hospital, limousine of the surgeon} that had
been [walking][ down the corridor][ is quite old.]
24. The {colleague of the rector, rector of the university, office of the rector} that has been
[drinking][ the pleasant wine][ is well-known.]
Was the wine good?
25. The {apprentice of the joiner, repairman of the agency, equipment of the joiner} that used
to [smoke][ in the canteen][ looked quite strange.]
Did someone use to smoke in the entrance?
26. The {sister of the survivor, survivor of the disaster, lifebelt of the survivor} that had been
[woken][ by the turmoil][ was in a bad state.]
27. The {advisor of the mayor, mayor of the village, village of the mayor} that had been[
driven][ to the meeting][ had a lot of problems.]
39
28. The {admirer of the painter, painter of the picture, picture of the painter} that has been
[humming][ the familiar tune][ is very nice.]
29. The {shrubbery of the park, garden of the duke, gardener of the park} that used to[
contain][ many beautiful plants][ had been really pleasant.]
30. The {guard of the prisoner, guard of the prison, cell of the prisoner} that had been[
beaten][ up during the interrogation][ is in a state.]
Items from Experiment 2
The phrases used in the three conditions are given within the braces in the order {ambiguous,
high attachment, low attachment, unambiguous}.
1.
{Ed assumed that the altar of the temple, Ed assumed that the temple of the priest, Ed
assumed that the priest of the temple, Almost everybody assumed that the temple}[
disintegrating][ over the years][ was very important.]
2.
{The man gathered that the rudder of the boat, The man gathered that the boat of the
native, The man gathered that the rower of the boat, The man and his friends gathered that
the boat}[ sawn][ from the wood][ looked very impressive.]
Had wood been used?
3.
{The man said that the section of the field, The man said that the land of the farmer, The
man said that the farmer of the land, The man from the village said that the field}[ sown][
early this spring][ pleased the lord.]
4.
{Colin noted that the basement of the tenement, Colin noted that the tenement of the
landlord, Colin noted that the landlord of the tenement, Almost at once Colin noted that the
tenement}[ containing][ lots of junk][ was very gloomy.]
Did Colin fail to note that the {basement, tenement, landlord, tenement} was gloomy?
40
5.
{The guide said that the tower of the castle, The guide said that the castle of the lord, The
guide said that the lord of the castle, The other day the guide said that the castle}[
decaying][ due to acid rain][ was very old.]
6.
{Sue thought that the stopper of the decanter, Sue thought that the porcelain of the
collector, Sue thought that the collector of the porcelain, Margaret apparently thought that
the decanter}[ broken][ in the accident][ was very old.]
Had a vase been broken in the accident?
7.
{Pam thought that the collar of the jacket, Pam thought that the shirt of the tailor, Pam
thought that the designer of the jacket, Kate certainly thought that the jacket}[ sewn][ in a
very skilful way][ looked quite stylish.]
8.
{Eric saw that the rudder of the vessel, Eric saw that the yacht of the playboy, Eric saw
that the builder of the yacht, Eric could clearly see that the vessel}[ corroding][ under the
paint][ troubled the sailor.]
9.
{Simon admitted that the jacket of the suit, Simon admitted that the suit of the judge,
Simon admitted that the maker of the suit, My friend Alisdair admitted that the suit}[
worn][ during the meeting looked][ very unfashionable.]
Did Simon think the {jacket, suit, maker, suit} looked fashionable?
10. {Neil read that the region of the country, Neil read that the country of the tyrant, Neil read
that the tyrant of the country, Some time ago Neil read that the country}[ neighbouring][
the poor nation][ was quite wealthy.]
Did Neil read about the {region, country, tyrant, country}?
11. {Harry mentioned that the diamond of the collection, Harry mentioned that the diamond of
the millionaire, Harry mentioned that the owner of the diamond, The other day Patrick
mentioned that the collection}[ stolen][ in the raid][ was very beautiful.]
12. {The boy reckoned that the base of the statue, The boy reckoned that the statue of the
queen, The boy reckoned that the sculptor of the statue, The nice little boy reckoned that
the statue}[ hewn][ from the granite][ was very strong.]
41
13. {The tailor thought that the tunic of the costume, The tailor thought that the costume of the
actor, The tailor thought that the wearer of the costume, The tailor definitely thought that
the costume}[ woven][ in the mill][ looked very beautiful.]
14. {Joe noted that the garage of the cottage, Joe noted that the cottage of the farmer, Joe noted
that the owner of the cottage, Some time ago Joe noted that the cottage}[ teeming][ with
hundreds of mice][ was very ugly.]
Were there hundreds of rats?
15. {Max said the brother of the reviewer, Max said the reviewer of the article, Max said the
article of the scientist, Matthew and Richard said the reviewer}[ phoning][ from the United
States][ was a bit weird.]
16. {The clerk heard that the client of the lawyer, The clerk heard that the lawyer of the
company, The clerk heard that the mansion of the lawyer, The other day the clerk heard
that the lawyer}[ laughing][ at the joke][ looked very smart.]
Did anyone think the joke was funny?
17. {I read that the bodyguard of the governor, I read that the governor of the province, I read
that the province of the governor, I read quite recently that the governor}[ retiring][ after
the troubles][ is very rich.]
18. {Ben agrees that the assistant of the professor, Ben agrees that the professor of the
department, Ben agrees that the department of the professor, Sebastien certainly agrees that
the professor}[ smiling][ at the student][ is quite good.]
19. {The police said the accomplice of the burglar, The police said the burglar of the
bungalow, The police said the revolver of the burglar, The new police officer said that the
burglar}[ forgiven][ by the victims][ was soon discovered.]
Were the victims vengeful?
20. {Mike asked if the servant of the prince, Mike asked if the servant of the palace, Mike
asked if the palace of the prince, Michael asked a few times if the prince}[ strolling][
through the gardens][ was very old.]
Did Mike ask a question?
42
21. {John wonders why the colleague of the admiral, John wonders why the captain of the
battleship, John wonders why the battleship of the admiral, The captain of the ship
wonders why the admiral}[ talking][ to the woman][ is leaving so soon.]
22. {Peter asked if the companion of the courier, Peter asked if the rider of the motorbike,
Peter asked if the motorbike of the courier, Peter asked a number of times if the courier}[
waving][ to the pedestrian][ was very reliable.]
Did Peter say that the {companion, rider, motorbike, courier} was reliable?
23. {Liz thinks that the patient of the surgeon, Liz thinks that the surgeon of the hospital, Liz
thinks that the limousine of the surgeon, Katherine seems to think that the surgeon}[
walking][ down the corridor][ is quite old.]
Has anyone been in the corridor?
24. {Zoe heard that the colleague of the rector, Zoe heard that the rector of the university, Zoe
heard that the office of the rector, Zoe heard several days ago that the rector}[ drinking][
the pleasant wine][ is well-known.]
Was the wine good?
25. {Jody thought the apprentice of the joiner, Jody thought the repairman of the agency, Jody
thought the equipment of the joiner, Jennifer and her friend thought the joiner}[ smoking][
in the canteen][ looked quite strange.]
26. {It was reported that the sister of the survivor, It was reported that the survivor of the
disaster, It was reported that the lifebelt of the survivor, It was reported without delay that
the survivor}[ woken][ by the turmoil][ was in a bad state.]
Had the turmoil woken up anyone?
27. {It was rumoured that the advisor of the mayor, It was rumoured that the mayor of the
village, It was rumoured that the village of the mayor, It was rumoured for a long time that
the mayor}[ driven][ to the meeting][ had a lot of problems.]
28. {Jane thought that the admirer of the painter, Jane thought that the painter of the picture,
Jane thought that the picture of the painter, Jessica immediately thought that the painter}[
humming][ the familiar tune][ was very nice.]
Was the tune little known?
43
Items from Experiment 3
Only the globally ambiguous past tense condition is given. The other conditions can be derived
from it by replacing the past tense verbs with future tense verbs and replacing yesterday by
tomorrow.
1.
The farmer milked the cattle he led through the steep mountains[ yesterday morning,][
Susan seems][ to think.]
2.
The florist watered the plants she put into the small greenhouse[ yesterday morning,][
Simon seems][ to think.]
3.
The zookeeper tranquillised the lion he moved into a larger enclosure[ yesterday
afternoon,][ the visitors][ are informed.]
4.
The gardener examined the seedlings he planted into the fertile soil[ yesterday afternoon,][
the groundskeeper][ is certain.]
Was the groundskeeper unsure?
5.
The cyclist oiled the bicycle he raced around the famous track[ yesterday afternoon,][ the
commentator][ is certain.]
Was the track well-known?
6.
The mountaineer trained the crew he guided through the dangerous valley[ yesterday
evening,][ a local man][ is positive.]
7.
The accountant calculated the wages he inserted into an existing spreadsheet[ yesterday
afternoon,][ according to][ Catherine.]
8.
The expert valued the ancient parchment he submitted into the special archives[ yesterday
afternoon,][ Karen seems][ to believe.]
9.
The knight sharpened the sword he took onto the nearby battlefield[ yesterday morning,][
the princess][ commented.]
44
10. The carpenter sanded the shelves he attached onto the kitchen wall[ yesterday morning,][
according to][ the foreman.]
Were the shelves for the living room?
11. The shepherd sheared the sheep he herded into a large paddock[ yesterday night,][ some
friends][ tell me.]
12. The secretary photocopied the document she distributed around the relevant offices[
yesterday lunchtime,][ a colleague][ remembered.]
13. The handyman serviced the dishwasher he fitted into the refurbished kitchen[ yesterday
afternoon,][ the landlady][ was told.]
14. The electrician checked the security cameras he fixed onto the outside wall[ yesterday
afternoon,][ a neighbour][ seems to assume.]
Were the cameras for inside the building?
15. The seamstress altered the ball gown she fitted onto a special mannequin[ yesterday night,][
the tailor][ is fairly sure.]
Did the gown require some alterations?
16. The soldier infiltrated the enemy troops he followed through the nearby forest[ yesterday
night,][ an officer][ reported.]
17. The dictator tortured the revolutionary he threw into the notorious prison[ yesterday night,][
the villagers][ found out.]
18. The dancer practiced the steps she incorporated into her favourite routine[ yesterday night,][
Benjamin is][ fairly sure.]
Did the dancer like the dance routine?
19. The secretary revised the timetable she posted onto the new noticeboard[ yesterday
lunchtime,][ a co-worker][ told the boss.]
Was the boss informed?
45
20. The manageress interviewed the applicant she showed around the main building[ yesterday
afternoon,][ according to a salesman.
21. The manager spoke to the employee he invited onto the advisory team yesterday lunchtime,
the chairman][ was told.]
22. The fisherman repaired the lobster pots he threw into the secluded water[ yesterday
morning,][ Monica seems][ to think.]
Was the fisherman fishing for shrimp?
23. The mechanic cleaned the headlamps he installed onto the reconditioned car[ yesterday
afternoon,][ the co-driver][ informs us.]
24. The prison officer handcuffed the convict he sent into solitary confinement[ yesterday
evening,][ the governor][ can reveal.]
25. The travel rep entertained the tourists she accompanied onto the visitors’ coach[ yesterday
lunchtime,][ the driver][ said to us.]
Were the tourists travelling by car?
26. The animal trainer groomed the horse he rode around the enormous stables[ yesterday
lunchtime,][ my neighbour][ tells me.]
27. The businesswoman discussed the proposals she added onto the company’s website[
yesterday afternoon,][ Adam explained][ at once.]
Did the company have an Internet site?
28. The presenter telephoned the celebrity he invited into the backstage area[ yesterday
evening,][ the newspapers][ found out.]
29. The childminder looked after the toddler she walked around the botanic gardens[ yesterday
evening,][ according to][ Victoria.]
30. The dealer weighed the drugs he smuggled through the secluded checkpoint[ yesterday
night,][ an informer][ can confirm.]
46
31. The chairman evaluated the businessman he invited onto the important committee[
yesterday morning,][ the management][ believes.]
32. The lawyer questioned the woman he called onto the witness stand[ yesterday morning,][
Keith is][ quite convinced.]
33. The actress telephoned the journalist she invited onto the spectacular set[ yesterday
evening,][ a friend][ recently leaked.]
34. The corporal punished the recruits he sent into the derelict barracks[ yesterday night,][ the
lieutenant][ told everyone.]
Were the barracks still occupied?
35. The frogman tagged the shark he followed through the dangerous reef[ yesterday morning,][
Emma realised][ at once.]
Did Emma realise straight away?
36. The inventor checked the components he fitted into the latest machine[ yesterday
lunchtime,][ an assistant][ explained.]
47
Author notes
This research was supported by ESRC grant no. R000223521, awarded to Roger van Gompel
and Martin Pickering, and by an Edinburgh University Development Trust Award, awarded to
Martin Pickering. We would like to thank Matt Traxler for valuable discussions about the
research reported in this article, Helen East, Leila Kalliokoski, Whitney Tabor, and an
anonymous reviewer for comments on an earlier version of this article, and Jacqueline
Thomson for her help in collecting the data.
48
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52
Table 1
Experiment 1 and 2: Item characteristics
______________________________________________________________________________________________________________
Experiment 1
______________________________________
Experiment 2
_____________________________________
ambiguous NP1 attachment NP2 attachment ambiguous NP1 attachment NP2 attachment
___________________________________________________________________________________________________________________
Attachment plausibility pre-test:
Plausibility NP1 attachment paraphrase
Plausibility NP2 attachment paraphrase
6.3 (.06)
6.5 (.06)
6.4 (.06)
1.9 (.07)
1.8 (.07)
6.5 (.06)
6.4 (.06)
6.5 (.06)
6.4 (.06)
1.8 (.07)
1.7 (.07)
6.4 (.06)
Main clause plausibility
5.0 (.08)
5.0 (.09)
4.8 (.09)
5.0 (.08)
5.0 (.09)
4.8 (.09)
Log lemma frequency of nouns:
noun1
noun2
2.3 (.11)
2.3 (.13)
2.4 (.14)
2.5 (.12)
2.2 (.15)
2.4 (.12)
2.3 (.12)
2.3 (.13)
2.4 (.14)
2.5 (.13)
2.2 (.16)
2.4 (.13)
Length of NP complex in characters:
13.6 (.42)
13.4 (.50)
13.5 (.46)
13.7 (.45)
13.6 (.51)
13.6 (.49)
___________________________________________________________________________________________________________________
Notes. Log frequency is based on the number of occurrences in the Celex database (17.9 million words). Standard errors are in parentheses.
53
Table 2
Experiment 1: Means
_____________________________________________________________________________
disambiguating
post-disambiguation
final
region
region
region
_____________________________________________________________________________
First-pass reading times (ms):
ambiguous
high attachment
low attachment
312 (8)
314 (8)
315 (8)
574 (14)
586 (16)
566 (13)
861 (24)
917 (26)
874 (26)
First-pass regressions (%):
ambiguous
high attachment
low attachment
17.7 (2.1)
19.1 (2.2)
20.9 (2.3)
8.5 (1.5)
15.3 (1.9)
16.3 (2.0)
58.3 (2.8)
61.3 (2.8)
64.2 (2.7)
Regression-path times (ms):
ambiguous
high attachment
low attachment
384 (12)
410 (15)
439 (21)
660 (20)
757 (27)
746 (22)
1853 (63)
2022 (69)
2051 (69)
Total times (ms):
ambiguous
high attachment
low attachment
403 (12)
458 (15)
453 (16)
738 (20)
817 (26)
824 (21)
1070 (27)
1132 (30)
1133 (29)
_____________________________________________________________________________
Notes. The regions were as follows (delimited by brackets):
The bodyguard of the governor that will be[ retiring][ the after the troubles][ is very rich.]
Standard errors are in parentheses.
Table 3
Experiment 2: Means
_____________________________________________________________________________
disambiguating
post-disambiguation
final
region
region
region
_____________________________________________________________________________
First-pass reading times (ms):
ambiguous
high attachment
low attachment
unambiguous
378 (10)
354 (11)
356 (9)
364 (11)
552 (16)
574 (19)
570 (17)
555 (17)
851 (22)
840 (25)
842 (23)
841 (26)
First-pass regressions (%):
ambiguous
high attachment
low attachment
unambiguous
12.1 (2.3)
9.5 (2.1)
8.4 (2.0)
9.5 (2.1)
13.6 (2.3)
16.0 (2.5)
23.6 (2.9)
16.7 (2.6)
63.4 (3.4)
64.4 (3.4)
69.1 (3.2)
56.1 (3.6)
Regression-path times (ms):
ambiguous
high attachment
low attachment
unambiguous
441 (16)
420 (18)
423 (19)
436 (20)
723 (35)
754 (33)
801 (34)
708 (25)
2046 (116)
2166 (122)
2330 (137)
1945 (108)
Total times (ms):
ambiguous
high attachment
low attachment
unambiguous
542 (21)
578 (25)
601 (27)
550 (25)
797 (31)
880 (37)
899 (33)
789 (27)
1065 (35)
1103 (34)
1073 (36)
1019 (33)
_____________________________________________________________________________
Notes. The regions were as follows (delimited by brackets):
I read that the bodyguard of the governor[ retiring][ after the troubles][ is very rich.]
Standard errors are in parentheses.
55
Table 4
Experiment 3: Means
_____________________________________________________________________________
disambiguating
post-disambiguation
final
region
region
region
_____________________________________________________________________________
First-pass reading times (ms):
ambiguous
high attachment
low attachment
514 (8)
556 (10)
515 (9)
334 (6)
349 (7)
351 (7)
436 (11)
439 (11)
447 (11)
First-pass regressions (%):
ambiguous
high attachment
low attachment
9.7 (1.2)
12.9 (1.4)
11.3 (1.3)
3.2 (0.7)
3.4 (0.7)
5.4 (0.9)
40.9 (2.0)
40.4 (2.0)
36.9 (2.0)
Regression-path times (ms):
ambiguous
high attachment
low attachment
614 (16)
703 (22)
651 (20)
390 (17)
419 (21)
421 (15)
1224 (67)
1204 (63)
1174 (64)
Total times (ms):
ambiguous
high attachment
low attachment
665 (16)
716 (15)
652 (14)
433 (10)
455 (11)
451 (11)
498 (12)
513 (13)
513 (13)
_____________________________________________________________________________
Notes. The regions were as follows (delimited by brackets):
The carpenter sanded the shelves he attached onto the kitchen wall[ yesterday morning,]
[ according to][ the foreman.]
Standard errors are in parentheses.
56
1
If there were a strong bias for one analysis in the globally ambiguous sentences, then there
would be relatively little competition. It might then be impossible to detect any difference
between the globally ambiguous sentences and sentences that are disambiguated towards the
preferred analysis. However, it is important to note that competition in the globally ambiguous
sentences can never be weaker than in the disambiguated sentences, so the globally ambiguous
sentences can never be easier to process.
2
Because the syntactically unambiguous and globally ambiguous conditions differed both in
content and syntax before the disambiguating region, processing differences may have occurred
before this region. In order to check this, we analyzed the region consisting of I read that the
bodyguard of/I read quite recently that and the region the governor (which was identical in the
ambiguous and unambiguous conditions). None of the eye-movement measures showed any
differences in these regions.
3
Constraint-based models assume that all sources of information, including plausibility, affect
competition. However, one could consider an alternative account, according to which the use of
plausibility information is delayed and syntactic competition takes place before plausibility
information forces reanalysis. Such an account predicts that the globally ambiguous condition
should be easier to read than the disambiguated conditions (due to reanalysis), but syntactic
competition in the globally ambiguous condition should make it harder to read than the
unambiguous condition. The results did not provide evidence for the latter prediction.
Although some of the measures showed that the ambiguous condition was perhaps numerically
slightly harder than the unambiguous condition, in none of the measures this difference came
close to significance. If there is syntactic competition in the ambiguous condition, its effect on
processing difficulty is clearly much weaker than the effect of reanalysis, indicating that
syntactic competition is not as central to explanations of processing difficulty as reanalysis.
4
We also analyzed eye-movement measures for the first line of the materials (e.g., The carpenter
sanded the shelves he attached onto) and the region on the second line just preceding the
disambiguating region (e.g., the kitchen wall). No effect of condition was observed, indicating
that there were no plausibility differences before the disambiguating region.
57