Journal of Memory and Language 64 (2011) 211–232
Contents lists available at ScienceDirect
Journal of Memory and Language
journal homepage: www.elsevier.com/locate/jml
Why brother and sister are not just siblings: Repair processes
in agreement computation
Nicola Molinaro a,⇑, Francesco Vespignani b, Roberto Zamparelli b, Remo Job b
a
b
BCBL, Basque Center on Cognition, Brain and Language, Donostia, Spain
Dipartimento di Scienze della Cognizione e della Formazione, University of Trento, Rovereto (TN), Italy
a r t i c l e
i n f o
Article history:
Received 3 March 2010
revision received 30 November 2010
Available online 8 January 2011
Keywords:
Agreement
Repair
Reanalysis
ERPs
LAN
P600
a b s t r a c t
In the present study we analyze how the cognitive system deals on-line with number
agreement mismatches and whether this on-line process influences the off-line interpretation of the sentence. In two ERP experiments we monitored the on-line processing consequences of subject-verb agreement mismatches, focusing on the integration of a following
number- marked related constituent. In Experiment 1, after initial detection of a mismatch
between a plural noun phrase (The siblings) and its singular verb, indexed by LAN + P600,
ERP correlates of agreement processing difficulties were recorded on a following modifier
when it was plural. In Experiment 2, after detection of the mismatch between two conjoined singular noun phrases in subject position (The brother and the sister) and the verb,
indexed by a short-lived P600, only the singular modifier showed indexes of agreement
processing difficulties. These findings support the hypothesis that when processing a morphosyntactic mismatch, the cognitive system constructs on-line a well-formed internal
representation of the sentence fragment. This on-line regularization allows comprehenders
to easily integrate additional incoming constituents and also influences off-line interpretation of the message (Experiment 3).
Ó 2010 Elsevier Inc. All rights reserved.
Introduction
The phenomenon of agreement, together with fixed
word order and case marking, is one of the three main
ways in which languages signal grammatical relations
(Nichols, 1986). Many researchers have stressed the ability
and automaticity with which speakers tacitly respect and
use agreement rules in the sentences they produce (for
example, Berent, Pinker, Tzelgov, Bibi, & Goldfarb, 2005;
Bock, Nicol, & Cutting, 1999). Many behavioral (De
Vincenzi, 1991; Pearlmutter, Garnsey, & Bock, 1999;
Wagers, Lau, & Phillips, 2009) and neurophysiological
(Coulson, King, & Kutas, 1998; Osterhout & Mobley,
1995) studies on language comprehension have shown
⇑ Corresponding author. Address: BCBL, Basque Center on Cognition,
Brain and Language, Paseo Mikeletegi, 69, 20009 Donostia, Spain. Fax: +34
943 309 052.
E-mail address: [email protected] (N. Molinaro).
0749-596X/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jml.2010.12.002
that agreement information has a rapid and measurable
impact on cognition. An agreement mismatch such as The
boys runs. . . leads to an immediate reaction by the comprehender within a few hundred milliseconds of the detection
of the incongruence. Interestingly, such an error, while
temporarily disrupting sentence comprehension, does not
necessarily affect the ability to construct a coherent interpretation of the sentence meaning. Comprehenders are in
fact able to understand nearly every utterance, not only
ambiguous sentences, but also truly ungrammatical ones.
As indicated by Hoftadter (1979, p. 26), one of the
‘‘essential abilities for intelligence [is] certainly [. . .] to make
sense out of ambiguous or contradictory messages’’.
This plasticity in dealing with syntactic incongruities
and recovering from erroneous analyses is an essential skill
of the parser that is useful not only for communicating
with non-proficient speakers (e.g. children and second language speakers) but also for language learning (Osterhout,
McLaughlin, Pitkanen, Frenck-Mestre, & Molinaro, 2006).
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
In addition, native speakers can easily handle environmental noise, ambiguities, speech errors, hesitation and repetitions, which are typical of every-day language; this
confirms the cognitive ability to mentally restructure a disrupted incoming input into a well-formed message.
To explain the robustness of the cognitive system in
dealing with ‘formal’ inconsistencies during comprehension, some researchers have proposed that language processing
relies
on
highly
economical
strategies
(heuristics): critical semantic information would be extracted to achieve sentence interpretation (Bever, 1970;
Ferreira & Patson, 2007), without necessarily performing
a detailed syntactic analysis of the sentence.
However, grammatical cues constrain the semantic
interpretation of most utterances and could play a critical
role during the on-line comprehension of a sentence. For
example, when processing an decontextualized string like
The boys runs. . . (an incongruence apparently resolved in
less than a second, see Osterhout and Mobley (1995); but
also De Vincenzi et al. (2003), for a direct comparison between behavioral and neurophysiological correlates of
number agreement mismatches), the parser has no semantic or discourse level information available to interpret the
mismatch.
In these cases, two things could happen when the disagreeing constituent is detected: either (i) the ‘opposing’
values of the two mismatching constituents are kept in
memory until further disambiguating information arrives,
or (ii) the internal mental representation of one constituent (i.e. the number of either the subject noun phrase or
verb) is coerced in order to fit with the other. Both hypotheses are plausible, given the architectural properties of the
cognitive system.
The first hypothesis would imply that the cognitive system can process multiple alternative parses of a sentence
structure at a time. Thus, in a sentence like The boys
runs. . ., there would be no need to select either the noun
or the verb number to be assigned to the incongruent sentence. The ungrammatical fragment presenting the two
alternative values (plural and singular respectively) would
be available to the parser until further ‘disambiguating’
information arrives; at which point the different alternatives could be weighted differently, depending on the support for one interpretation or the other. For example, when
all the relevant semantic and discourse level information is
controlled for within the sentence, the choice of selecting
singular or plural would depend on perception of another
number-marked word during the unfolding sentence. A
series of models of sentence comprehension (multiple constraint models: MacDonald, Pearlmutter, & Seidenberg,
1994; Trueswell, Tanenhouse, & Kello, 1993) have pointed
to the ability of the cognitive system to keep in memory
multiple alternatives during the processing of an ambiguous sentence structure. In this view, the short-lived processing cost elicited by a mismatching word (the verb in
The boys runs. . .) would be due to the increased memory
load of keeping the alternative representations active.
The coercion hypothesis, on the other hand, is reminiscent of what in the psycholinguistic literature is termed
on-line repair, i.e. the ability of the cognitive system to
immediately modify the internal representation of an
ungrammatical sentence fragment to build an internal
well-formed syntactic representation of the sentence. The
need to build such well-formed syntactic sentence representations would be for reasons of economy: it would require less cognitive resources to keep in mind an
unambiguous and well structured message than a noisy
one. In addition, immediate on-line repair of the number
mismatch would allow easier (and faster) integration of
the incoming material. A similar approach has been pursued by classical serial models of sentence processing (De
Vincenzi, 1996; Frazier, 1990; Frazier & Fodor, 1978) to explain reanalysis effects in garden-path constructions. The
fact that these models are implemented serially means
that only a single structural interpretation can be pursed
at one time, requiring a distinct monitoring system to revise and repair the initial interpretation, if need arises. In
this framework, reanalysis and repair mechanisms are considered as independent and essential elements of the
whole cognitive architecture, given that in the first stage
the parser pursues the simplest structural choice – due to
economy of time and resources – which sometimes turns
out to be the wrong one. The parser is thus assumed to
be prone to error. This implies that upon encountering
inconsistent linguistic material, the first possibility to explore is that a comprehension error has occurred.
If serial models assume that a choice between alternative analyses has necessarily to be performed immediately,
multiple constraint models do not exclude that one interpretation could be preferred, having a higher level of activation than a competing one: repair and reanalysis can
thus be described in terms of changes to the differential
activation level or ranking of different alternatives operated by the same mechanism that performs the initial
structuring of the incoming words, without assuming a
specialized mechanism based on independent parsing
principles (Grodner, Gibson, Argaman, & Babyonyshev,
2003).
The aim of the present study is to analyze the processing routines by which the human parser deals on-line with
an agreement mismatch: the findings will help to clarify
the processes involved in the revision of ungrammaticalities and their influence on the overall interpretation of
the sentence. We will also evaluate the impact that these
on-line processing routines have on the off-line interpretation of the sentence.
ERP evidence on syntactic resolution
In a series of previous experiments (Molinaro, Kim,
Vespignani & Job, 2008; Vespignani, Molinaro & Job, in
press) we tried to demonstrate that after an agreement
mismatch where two alternative interpretations are available for the mismatching feature, only one of them is pursued on-line and incrementally projected on for further
sentence processing. We studied the electrophysiological
correlates (Event Related Potentials, ERPs) of the comprehension of grammatically anomalous sentences which contained two anomalies, one early and one late. The main aim
was to verify how the processing of the later anomaly was
affected by the processing of the early anomaly. We developed this paradigm to evaluate the possible on-line
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
resolution of the disagreement between two constituents
at the beginning of the sentence. Subject-verb (Molinaro,
Kim, et al., 2008) and determiner-noun (Vespignani et al.,
in press) morphosyntactic number mismatches were presented at the beginning of the sentence; in a subsequent
position, a constituent – marked 3rd person – was manipulated so that it could agree either with the first or with
the second mismatching element. The rationale behind
this manipulation was to contrast the ERP correlates of
the third constituent in the two conditions (and with the
fully grammatical one) in order to verify if only one of
them, or both, showed signs of agreement processing
difficulties.
We focused on the ERP correlates as a dependent measure, given their extremely high temporal resolution. Number agreement violations have been extensively studied
with this technique and show a biphasic electrophysiological pattern starting around 250–300 ms and returning to
the baseline around 1 s after the detection of the mismatch
(Osterhout, McLaughlin, Kim, Greenwald, & Inoue, 2004).
The two main components of this pattern are the Left Anterior Negativity (LAN), a left-frontal increased negativity between 300 and 450 ms, and the P600, a long-lasting
positive shift between 500 and 1000 ms.
The LAN has been reported in languages with both relative word order freedom and full paradigms of agreement
(Italian: Angrilli et al., 2002; Finnish: Leinonen, Brattico,
Jarvenpaa, & Krause, 2008; Spanish: Silva-Pereyra &
Carreiras, 2007) and in more fixed word order languages
with residual agreement (Dutch: Hagoort & Brown, 2000;
English: Osterhout & Mobley, 1995; German: Roehm,
Bornkessel, Haider, & Schlesewsky, 2005). For example,
Leinonen et al. (2008) directly compared violations of
inflectional and derivational morphology in Finnish: in
the former violation LAN was elicited, while the latter
elicited an N400 in the same time window, a component
classically related to semantic processing difficulties
(Kutas, Van Petten, & Kluender, 2006). The LAN is thus considered to reflect a stage of processing related to the early
detection of a morphosyntactic violation (Bornkessel &
Schlesewsky, 2006; Friederici, 2002; Munte, Matzke, &
Johannes, 1997). LANs are also elicited by determiner-noun
agreement violations at the sentence level: Barber and
Carreiras (2005) reported LAN for both number (Los chico;
The (+P) kid (+S)) and gender violations (La chico; The (+F)
kid (+M)) in Spanish. Also, Molinaro, Vespignani, and Job
(2008) reported the same effect for both gender and phonotactic (Il scoiattolo; The (+IL) squirrel (+LO)) violations
in Italian. The LAN component thus shows sensitivity to
the target element form when it is involved in core agreement relations.
Some authors have reported LAN effects during the
reading of grammatical sentences that required working
memory resources to be comprehended (Kluender & Kutas,
1993; Streb, Rosler, & Hennighausen, 1999). An interesting
distinction has been made between the morphosyntactic
LAN and the working memory LAN (Fiebach, Schlesewsky,
& Friederici, 2002): the former has been termed focal LAN
since its onset is around 300 ms and it returns to baseline
around 450 ms; the latter is the sustained LAN, a component with similar latency that does not come back to the
213
baseline. In the present study we focus on the focal LAN
that has been consistently reported for morphosyntactic
processing difficulties.
The LAN is consistently reported in association with a
later positive shift starting around 500 and lasting until
1000 ms. This so-called P600 has received less attention
in the ERP studies on agreement processing, despite the
fact that it has provided very interesting insights into the
brain mechanisms involved in feature checking (Barber &
Carreiras, 2005; Molinaro, Vespignani, et al., 2008; Nevins,
Dillon, Malhotra, & Phillips, 2007). Initially, the P600 was
generically considered a marker for syntactic processing
difficulties (Osterhout & Mobley, 1995); however, a significant body of research has demonstrated that the P600 is
sensitive to violations of structural-based expectancy in
both linguistic (Coulson et al., 1998; Hsu, 2009; Kim &
Osterhout, 2005; Osterhout, Holcomb, & Swinney, 1994)
and non-linguistic materials (Patel, 2003; for reviews
Kuperberg, 2007; Osterhout, Kim, & Kuperberg, in press).
For the purposes of the present study, we mainly consider
the literature on syntactic violations, in which the finding
of earlier negative components in response to syntactic
violations (as discussed by Friederici, 2002) has led to a
general consensus in associating the P600 following the
LAN to late reanalysis and repair processes elicited by syntactically anomalous sentences.
We, among others, have proposed a particular hypothesis
of the P600 to agreement violations as reflecting two processing stages (Barber & Carreiras, 2005; Carreiras, Salillas,
& Barber, 2004; Hagoort & Brown, 2000; Kaan & Swaab,
2003a; Molinaro, Vespignani, et al., 2008). In the following
is some of the evidence that has motivated this view.
The earlier stage of the P600 would correspond to the
increased positivity starting at 500 until about 700 ms.
During agreement computation, this stage would be involved in building structural dependencies of the sentence,
while interfacing with the available non-syntactic information (as suggested by Bornkessel & Schlesewsky, 2006;
Kuperberg, 2007). Recent findings of larger ‘early P600s’
for agreement violations involving person feature manipulations (assumed to involve discourse level representations, Sigurdsson, 2004; see Mancini, Vespignani,
Molinaro, Laudanna, & Rizzi, 2009; Nevins et al., 2007),
support the idea of a stage at which the cognitive system
is accessing higher discourse level information to detect
the source of the error. Interestingly, in these studies the
early P600 effect is salient also in the frontal portion of
the scalp (as suggested by Kaan and Swaab, 2003a, 2003b).
In a later stage (after 700 ms), the P600 has a more posterior distribution and would reflect the repair of illformed sentence constructions. The finding of larger ‘late
P600s’ for costlier feature repair processes supports the
dissociation of this subcomponent (Barber & Carreiras,
2005; Molinaro, Vespignani, et al., 2008; Silva-Pereyra &
Carreiras, 2007). Interestingly, when contextual semantic
information strongly biases a specific suffix for the target
verb (-ed), a late P600 effect (700–900 ms) has been reported for an unexpected suffix (-ing; Kim & Osterhout,
2005). This is possibly due to the repair process operating
on the target verb inflectional morphology: as discussed
above, the system would accumulate evidence in order to
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
map all the available information concerning the source of
an error during the first P600 stage. If the ill-formedness of
the sentence representation is affected by a morphological
property of the target word, a repair could then be made
on-line, but only at this later stage. In other words, a prolonged P600 would represent the additional effort spent
in regularizing an incongruent utterance with a prominent
error.
Long-lasting P600s elicited by the detection of a number agreement mismatch in initial sentence positions have
also been reported in previous studies of on-line resolution
of number agreement violations (Molinaro, Kim, et al.,
2008; Vespignani et al., in press). In both of these studies
the number of a disagreeing constituent (verb in the former and noun in the latter study) influenced agreement
processing on a third, number-marked, related constituent
(a reflexive pronoun in the former and a verb in the latter
study): we found evidence of agreement processing difficulties when the third constituent mismatched in number
with the second element (while it agreed with the first),
but no effect when the third constituent mismatched in
number with the first element (while it agreed with the
second). For example, when processing ungrammatical
sentences like those in (1)
(1)
a. The famous dancers was nervously preparing
herself. . .
b. The famous dancers was nervously preparing
themselves. . .
We reported ERP correlates of agreement processing
difficulties both at the verb and at the following plural
reflexive pronoun in 1b. The singular reflexive pronouns
(in 1a), on the other hand, did not differ from the grammatical control sentence.
These findings are suggestive of a general, process-oriented explanation based on, for example, linear order of
processing. In this framework, when encountering the
number mismatch at the verb, the need for continuous
processing of further incoming material would compel
the comprehender to resolve the ungrammaticality online: if this is indeed the case, incoming items (following
the ungrammaticality) could be integrated in a wellformed partial sentence structure, allowing an easier interpretation of the message intended by the speaker/writer.
This on-line regularization would not necessarily reflect
the off-line meta-linguistic analysis of the error (in which
rumination and off-line conscious reprocessing could be
critical), but would represent a fast and easy solution to
provide the cognitive system with a well-formed internal
representation of the sentence fragment (that would be
stored in working memory) during the on-going processing
of the sentence. The fact that an error was encountered and
the nature of this error could be recorded in episodic memory, i.e. in a different storage from the one holding the sofar-parsed structure.
Assuming this natural tendency towards regularization
of noisy linguistic input during comprehension, once an
agreement mismatch has been detected (for example, after
reading the verb in 1), we assumed that the system should
either modulate the internal representation of the currently-processed item (critical word) or revise the internal
representation of the previous (mismatching) constituent
in working memory. In other words, the cognitive system
could either ‘ignore’ the information provided by the currently-processed item (the verb in 1), considering it a
speaker/writer misspelling/mispronunciation, or ‘manipulate’ the information provided in the previous sentence
fragment (the subject in 1), that is supposed to be still active in working memory. According to this hypothesis (that
we termed Repair), when the mismatch at the second constituent is detected, the ungrammaticality is immediately
resolved by assigning a coherent number value to the
whole sentence fragment.1 For example, in a word by word
presentation of a sentence like (1a) (Molinaro, Kim, et al.,
2008), the initial mismatch between the subject noun
phrase and the verb would be revised on-line based on the
number of the verb, i.e. singular. When processing the following reflexive pronoun, a number mismatch with its antecedent (the noun phrase in subject position) would no
longer be detectable, since the internal representation of
the subject has been revised to singular after detecting the
mismatch with its verb.
According to this account, a number mismatch is immediately re-interpreted coercing the number of the first mismatching constituent (stored in working memory) to the
number of the (more recent) second constituent, rather
than the opposite. This strategy would thus consist in
immediately adapting the number value of the constituents that are stored in working memory when detecting
a mismatch on a following constituent that is under consideration: in the example above (1), the number of the
subject noun phrase would be adapted to singular because
of the verb number. Interestingly, the fact that the information that is within the focus of attention (i.e. the constituent where the mismatch is detected) drives this on-line
mismatch resolution by imposing its value is supported
by studies on sequentially presented information (Cowan,
2001; McElree, 2001, 2006; Meng & Bader, 2000).2
However, an alternative explanation is possible that
does not exclude that multiple alternative representations
are kept in memory until relevant disambiguation, a
1
With the term Repair we do not assume any theoretical approach to the
type of model that our findings could explain (either serial or multiple
constraints). As previously indicated, both models could support the idea
that a single interpretation is pursued (or more active) after an incongruent
sentence structure.
2
Using this type of paradigm, we were concerned about the possibility
that in earlier experiments our participants could develop ad-hoc processing strategies due to high number of agreement violations presented both
within a sentence and across the whole experiment. These strategies could
have caused the pattern of results reported here. Thus, we ran a control
experiment in which we presented the critical conditions of Vespignani
et al. (in press) to two different groups of subjects (for example, if we
consider the conditions presented in Table 1, Group 1 saw only the PluralSingular-Plural condition, while Group 2 saw only the Plural-SingularSingular condition of Experiment 1). Since participants of each Group saw
always the same type of mismatch combination, the ad-hoc strategy
hypothesis predicted no differences at the third critical constituent.
However, we replicated Vespignani et al.’s (in press) findings, thus
supporting the idea that repair is performed on-line through a mandatory
process.
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
strategy that we term Recency. We could hypothesize, for
instance, that number agreement processing is not so critical for sentence comprehension and is checked only to
evaluate local consistency between structurally related
elements. What we would measure when presenting a
number mismatch (i.e. LAN + P600) would not correlate
with any repair process. In this proposal, linear recency is
critical (for similar proposals see Tabor, Galantucci, & Richardson, 2004): the inconsistency detected at the second
constituent (in 1) is left in stand-by, but the system goes
on checking the agreement between the second and the
third constituent. In this case there would be no need to
presuppose a repair of the ungrammaticality, but the processes underlying the P600 would be sensitive only to local
agreement consistency between parts of the same phrase.
The value of the subject noun in initial position would
not affect the processing correlates of the reflexive pronoun, and the processing of multiple alternatives would
be performed and dynamically weighted based on the
amount of evidence incrementally processed. In example
(1) ERP correlates of processing difficulties between subject and verb emerge because of local incoherence; without considering this mismatch, similar ERP correlates
would emerge at the reflexive pronoun only in 1b, because
of local mismatch with the previous verb, irrespective of
the subject value.
The present study
In the present study we aim to contrast the Repair and
the Recency hypotheses by ‘blocking’ the hypothesized repair strategy at work for mismatches as in (1), in which
the number of the subject is revised to agree with the verb.
To do this, we tested our paradigm with a structure in the
first position that could not be coerced to acquire the number of the following mismatching constituent. If the plurality of the noun phrase in subject position is not expressed
through morphophonological information (as in The boy-s)
but through the use of multiple independent discourse
entities, as in a conjoined noun phrase, it should not be
possible to mentally manipulate the numerosity of the
subject referents. Thus, when detecting a mismatch between a conjoined-plural subject (such as The boy and the
girl) and its verb (a singular one), it should not be possible
to reduce the two subject entities to singular.
As in previous studies on Italian sentences, we adapt
the paradigm exemplified in Table 1.
We designed three experiments; the first two experiments focused on the ERP correlates of the on-line interpretation of different types of agreement mismatches.
These first two experiments are aimed at disentangling
the Repair and the Recency hypotheses and provide evidence of the on-line processing routines employed by the
cognitive system to interpret an agreement mismatch.
The third (behavioral) experiment is focused on evaluating
the consequences of these on-line processes on the off-line
aware interpretation of this type of ungrammatical
sentences.
Experiment 1: Inflectionally plural subject
Experiment 1 focuses on the on-line interpretation of a
mismatch between an inflectionally plural noun phrase in
subject position and its verb, and the mapping of the processing consequences onto the agreement computation
with a subsequent modifier. This experiment is aimed at
replicating previous findings (Molinaro, Kim, et al., 2008;
Vespignani et al., in press): while in previous experiments
the subject number was balanced (merging plural and
Table 1
Examples of the experimental sentences used in Experiments 1–3.
Experiment 1: Inflectionally plural subject
Condition
Subject
PPP
I fratelli
The siblings
PSP
I fratelli
The siblings
PSS
I fratelli
The siblings
Verb phrase
giunsero a casa
arrived [+P] at home
giunse a casa
arrived [+S] at home
giunse a casa
arrived [+S] at home
Modifier
stanchi della giornata.
tired [+P] by the day.
stanchi della giornata.
tired [+P] by the day.
stanco della giornata.
tired [+S] by the day.
Experiment 2: Conjoined noun phrase subject
Condition
Subject
CPP
Il fratello e la sorella
The brother and the sister
CSP
Il fratello e la sorella
The brother and the sister
CSS
Il fratello e la sorella
The brother and the sister
Verb phrase
giunsero a casa
arrived [+P] at home
giunse a casa
arrived [+S] at home
giunse a casa
arrived [+S] at home
Modifier
stanchi della giornata.
tired [+P] by the day.
stanchi della giornata.
tired [+P] by the day.
stanco della giornata.
tired [+S] by the day.
Experiment 3: Grammatical judgement and repetition
Condition
Initial segment
PP
Dopo una dura giornata di lavoro
After a day of hard work
PS
Dopo una dura giornata di lavoro
After a day of hard work
CP
Dopo una dura giornata di lavoro
After a day of hard work
CS
Dopo una dura giornata di lavoro
After a day of hard work
Subject
i fratelli
the siblings
i fratelli
the siblings
il fratello e la sorella
the brother and the sister
il fratello e la sorella
the brother and the sister
Verb phrase
giunsero a casa.
arrived [+P] at home.
giunse a casa.
arrived [+S] at home.
giunsero a casa.
arrived [+P] at home.
giunse a casa.
arrived [+S] at home.
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singular stimuli), the present study only focuses on plural
subjects (with the mismatching verb always singular). First
of all, we expect ERP correlates of agreement processing difficulties at the verb (a LAN followed by a P600 in line with
previous studies). Crucially, differential effects are expected
at the modifier position when comparing conditions PSP and
PSS: the two main hypotheses under consideration, Repair
and Recency, predict that the number marked modifier –
which refers to the subject – should elicit a P600 only when
it mismatches with the verb (in Table 1, the Modifier position in the PSP condition in Experiment 1):
a. The Repair hypothesis states that the mismatch
between the subject noun phrase and the verb is
immediately interpreted according to the verb number (in line with previous findings); if the following
modifier mismatches with the number of the subject
noun (now revised to singular), an ERP index
of agreement processing difficulties should be
recorded at the plural modifier (considering the
P600 amplitude on the modifier: PSP > PSS).
b. In the Recency hypothesis, since the system is sensitive to the relation between constituents that are in
linear proximity, the P600 would be mainly sensitive
to linear local mismatches between structurally
related constituents. Since in the PSP condition there
is no consistency between the singular verb and the
plural modifier (part of the same verb phrase), processing difficulties should be evident at the modifier
position for PSP but not for PSS (considering the P600
amplitude on the modifier: PSP > PSS).
Although the two hypotheses are different in nature,
implying a qualitatively different model at work during
the processing of syntactic incongruencies, it is interesting
to note that they make the same predictions in Experiment
1. Experiment 2 is designed to contrast these alternative
models.
Experiment 2: Conjoined noun phrase subject
In Experiment 2, we use the same design, studying the
processing consequences of the on-line computation of a
number mismatch between two coordinate singular noun
phrases in subject position and their verb. ERP correlates
of agreement mismatch are expected at the verb position.
Critically, different predictions can be made for the processing of the modifier based on the alternative hypotheses
we presented above:
a. Following the Repair proposal, a mismatch between
a coordinated subject and its verb should not be
resolved on the basis of the verb number, since the
plurality of the subject (extracted by the coordination of two distinct entities) cannot be reduced to
singular. We thus expect the subject plurality to
drive disagreement resolution and the following
modifier to elicit a P600 only when it disagrees with
the subject referents, despite the fact that it agrees
(locally) with the verb (Table 1, the Modifier position
in the CSS condition in Experiment 2, considering the
P600 amplitude on the modifier: CSS > CSP).
b. Following the Recency hypothesis, however, the
expected outcome is the opposite. Suppose that the
parser has suspended its judgment on the subjectverb mismatch and is checking the local consistency
of the following number-marked elements. At the
modifier, the system should be more sensitive to
the local coherence between the verb and the modifier, part of the same verb phrase; so we should
expect a P600 when the verb and the following modifier mismatch locally, irrespective of the type of the
number feature expressed by the previous subject.
Interestingly, no plural marker is expressed in the
CSS condition, since all the sentence elements are
singular (considering the P600 amplitude on the
modifier: CSP > CSS).
A summary of the predictions of these first two experiments is reported in Table 2.
Experiment 3: Grammatical judgment and repetition
Experiment 3 is designed to study the off-line interpretation of an ungrammatical sentence. As previously mentioned, we assume that comprehenders are aware of the
ungrammaticality, but, given the need to proceed with
the on-going sentence parsing when an error is encountered, a temporary repair is automatically pursued on-line
(to integrate the following incoming constituents in a wellstructured partial phrase marker). We are thus interested
in two types of evidence: (i) evaluating the end-ofsentence grammaticality judgment for the different conditions and (ii) determining how the on-line resolution of the
ungrammaticality affects the off-line interpretation of the
whole ungrammatical sentence.
For this reason we asked to a group of Italian speakers
for an end-of-sentence speeded grammaticality judgment
on a set of items presenting the subject-verb constructions
investigated in the first two experiments. These items presented the subject-verb structures studied in Experiment 1
(inflectionally plural subject-verb) and in Experiment 2
(conjoined subject-verb), that could be grammatical or
not; sentences did not contain any further mismatching
constituents (see Experiment 3 in Table 1). We expected
high levels of accuracy in the grammaticality judgment of
these items.
In addition, we asked our participants to repeat the
sentence after the grammaticality judgment and, in case of
error detection, to correct it; this task was adapted from
Meng and Bader (2000). We were interested in determining
Table 2
Predictions concerning the ERPs elicited by the number marked modifier in
Experiments 1 and 2.
Experiment 1: Inflectionally plural subject
Repair hypothesis
PSP
P600
PSS
No effect
Recency hypothesis
P600
No effect
Experiment 2: Conjoined noun phrase subject
Repair hypothesis
CSP
No effect
CSS
P600
Recency hypothesis
P600
No effect
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
the number value of the to-be-corrected sentences: this
procedure permits an evaluation of the final (off-line) interpretation of the agreement mismatches. This experiment
was in fact designed to verify a possible parallelism between
the on-line and the off-line interpretation of subject-verb
mismatches.
Experiment 1: Inflectionally plural subject
Method
Participants
Twenty-four Italian native speakers participated in the
experiment. Mean age of the participants was 24.77 years
(SD = 4.17). All participants were right-handed and had
normal or corrected to normal vision.
Materials
A set of 120 Italian experimental sentences was composed. All of the sentences consisted of a plural noun
phrase in subject position and a verb at the beginning of
the sentence. We did not use either collective nouns or
very infrequent nouns in subject position. In contrast to
previous experiments, the verb was not an auxiliary (see
Molinaro, Kim, et al., 2008), but a lexical verb. The verb
was always intransitive and was followed by a singular
prepositional phrase and then a third critical constituent,
which was a number marked modifier of the noun in subject position. The noun within the intervening prepositional phrase had feminine grammatical gender to avoid
agreement attraction phenomena with the following critical adjective that was always masculine. In this design, the
modifier could always easily refer to the noun in subject
position. The prepositional phrase was used to introduce
a temporal lag between the presentation of the second
and third critical elements: this time lag was designed to
allow the possible P600 effect – elicited by the subjectverb mismatch at the verb – to come back to the baseline
before the presentation of the third constituent. The critical modifier was never at the end of the sentence to avoid
wrap-up effects (Osterhout & Holcomb, 1995) overlapping
with the critical effects of interest. From the 120 sentences
plural sentences (constituting the PPP condition) we derived, as shown in Table 1 (upper section), 120 sentences
belonging to the PSP condition (where both the subject
noun and the modifier were plural: I fratelli [+P] giunse
[+S] a casa stanchi [+P] della giornata.) and 120 sentences
belonging to the PSS condition (where both the verb and
the modifier were singular: I fratelli [+P] giunse [+S] a casa
stanco [+S] della giornata.). Despite number incongruities
(i.e. one or more participants in the message), the agreement manipulation never affected the thematic roles overall, so that the first noun phrase could always be
interpreted as the subject of the sentence.
The resulting 360 sentences were combined in three
lists of 120 sentences with 40 sentences per condition
(PPP, i.e. the control condition, PSP and PSS), so that each
sentence was presented in one different condition across
lists. Two hundred fillers with different syntactic structures were added in the experiment. None contained
217
topicalized constituents. Eighty of these fillers presented
agreement violations so that each participant saw an equal
number of correct and incorrect sentences in the whole
experiment.
Procedure
Each participant was seated in a dimly illuminated silent room. Words were displayed on a monitor in white
letters on a dark-grey background. Each word was presented for 300 ms, followed by a 300 ms blank screen. Sentence order was randomized and every five sentences on
average participants were asked to answer a YES/NO comprehension question using keyboard buttons. Comprehension questions never referred to the number of referents in
the sentence, for example: ‘Did somebody arrive home
tired?’ The number of questions was balanced across
conditions.
Participants were instructed not to blink or move their
eyes during sentence presentation and they were told that
in some sentences there could be syntactic errors. However, they were encouraged to focus on the whole message
of the sentence. To familiarize them with the procedure a
practice block of 20 items was presented before the experiment, some of which had the structure used in the experiment. On average, the experiment took about 2 h per
participant, including electrode montage and debriefing.
Data acquisition and analysis
EEG was recorded from 17 tin electrodes placed on the
scalp with the aid of an elastic cap at standard positions
(10–20 system): Fp1, Fp2, Fz, F3, F4, Cz, C3, C4, Pz, P3,
P4, O1, O2, T7, T8, P7, and P8. Additional external electrodes were placed on mastoids and around eyes (Veog ,
Veog+, Heog , Heog+). All sites were referenced to the left
mastoid (A1). Impedance was kept below 5 kX for mastoid
and scalp electrodes, and below 10 kX for EOG electrodes.
Data were acquired at a sampling rate of 250 Hz with a
low-pass filter with 100 Hz cutoff frequency and a 10s time
constant.
EEG recordings were off-line filtered with a 30 Hz lowpass filter and re-referenced to the average activity of the
two mastoids. Raw data inspection was performed independently for each subject in order to mark the artifacts
(ocular activity, muscular activity and heartbeat) in the
EEG recording during the whole experimental session:
recordings were highly affected in five participants by
heartbeat. Since this rhythmic activity would influence
the final ERP results, we performed an ICA based artifact
correction procedure. Following an Independent Component Analysis (ICA) on each participant recording, the independent components that explained artifactual activity
were identified by visual inspection and subtracted. After
the ICA correction we segmented the whole EEG recording
in epochs ( 300 to 1300 ms) based on the trigger positions
corresponding to the critical target word onsets. We then
rejected the epochs that were marked as containing artifacts in the pre-ICA raw data inspection: this resulted in
the exclusion of two participants from the following analyses and 5.7% of rejections on average in the remaining 22
participants (no differences across conditions in the
number of rejections F < 1). Artifact-clean shorter epochs
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
( 200 to 1000 ms) were then baseline-corrected to the
average activity in the 200 ms interval before target word
presentation. Epochs were then averaged separately for
each participant and condition: we thus extracted ERPs
at the Verb and at the following Modifier for each condition (PPP, PSP, PSS). Despite the fact that the two ungrammatical conditions were identical up to the Verb position,
we analyzed them separately at the Verb, in order to evaluate that in both cases ERP indexes of agreement detection
were elicited and came back to the baseline before the processing of the following critical position.
Single channel ERP data were averaged in different spatially homogeneous groups in order to reduce global variance and the number of levels to be interpreted in
repeated measure ANOVAs (Greenhouse–Geisser corrected). We planned two different clusters of electrodes.
The first one was aimed at evaluating the LAN component,
which is usually maximal at the left-fontal electrodes. We
define this as the Quadrant analysis in which we calculated
the average activity of the following clusters: left anterior
(LA: F3, C3, T7), right anterior (RA: F4, C4, T8), left posterior
(LP: P3, P7, O1) and right posterior (RP: P4, P8, O2). In the
relative two-way ANOVA we contrasted the three conditions in a pairwise manner. Factors were Condition (two
levels corresponding to the each contrast: PPP vs. PSP,
PPP vs. PSS, PSP vs. PSS) and Cluster (four levels corresponding to the four quadrants). The second analysis was designed to better evaluate the P600 component, which is
usually maximal along the midline electrodes with
possible topographical differences in the anterior-posterior
dimension. The Longitude analysis was run on three clusters: frontal (F: F3, Fz, F4), central (C: C3, Cz, C4) and parietal (P: P3, Pz, P4). In the relative two-way ANOVA we
contrasted Condition (two levels for each pairwise contrast) and Cluster (three levels: F, C and P). Each analysis
was performed on specific time windows of interest corresponding to the expected modulations in amplitude for
each component: LAN (350–450 ms), early P600 (500–
800 ms) and late P600 (800–1000 ms). For both analyses,
in the ‘Results’ section we report significant values for
the Cluster factors only when they interact with the Condition. If this was the case, post-hoc analyses were performed on each Cluster; False Discovery Rate correction
(Benjamini & Hochberg, 1995) was applied to the resulting
p-values.
Results
Behavioral data
Participant accuracy in the comprehension questions
was 91%. This indicates that the participants were able to
extract the meaning of the whole sentence even in the
ungrammatical conditions. Indeed, no differences were
found in the accuracy across conditions (F(2, 42) < 1).
ERPs elicited at the Verb position
Grand-averages elicited in the Verb position (reported in
Fig. 1, negative values are plotted up) showed a left-frontal
Fig. 1. Event-related potentials elicited by the Verb for the inflectionally plural subject manipulation (Experiment 1). Solid thin line represents the PPP
condition; dashed line represents the PSP condition; solid thick line represents the PSS condition. Vertical bars delimit the time windows of interest in the
statistical analysis. Negative values are plotted up.
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
increased negativity around 400 ms for both the PSP and the
PSS conditions compared to the Control. We identified this as
a focal LAN. This component was followed in both cases by a
long-lasting positive effect. In the early phase (500–800 ms),
this component is evident in both the anterior and the posterior electrodes, while in the latter phase (800–1000 ms)
it is mainly evident in the posterior electrodes.
In the 350–450 ms time window (LAN interval), the
comparison between PSP and PPP condition showed an
interaction between Cluster and Condition in the Quadrant
analysis (F(3, 63) = 3.568, p < 0.05; 95% Confidence Interval = ±3.448). Post-hoc contrasts for each cluster of the
Quadrant analysis revealed a main effect in the LeftAnterior cluster (t(21) = 2.638, p < 0.05) where the PSP
condition (M = 0.402 lV) was more negative than the
PPP condition (M = 0.576 lV).
In the same time window the Quadrant ANOVA comparing the PSS with the PPP condition revealed both a main
effect of Condition (F(1, 21) = 4.379, p < 0.05; 95%
CI = ±1.988) and the interaction between Cluster and Condition (F(3, 63) = 4.479, p < 0.05; 95% CI = ±3.691). Post-hoc
analysis showed again significant effect in the Left-anterior
cluster (t(21) = 3.896, p < 0.05): compared to the PPP condition (M = 0.576 lV), the PSS condition showed a more
negative effect (M = 0.597 lV).
Finally, the comparison between PSP and PSS conditions
did not reveal any significant effects at this stage.
In the following time window (500–800 ms; early P600
interval), the PSP–PPP comparison showed a main effect of
Condition in the Longitude analysis (F(1, 21) = 5.398,
219
p < 0.05; 95% CI = ±2.45) thus confirming the widely distributed early P600 effect in this time window. The PSP
condition was in fact more positive (M = 2.274 lV) than
the PPP condition (M = 1.457 lV) across midline clusters.
Similarly, the PSS–PPP comparison showed a main effect
of Condition both in the Quadrant analysis (F(1, 21) =
6.377, p < 0.05; 95% CI = ±2.002; PSS M = 0.895 lV; PPP
M = 1.684) and in the Longitude analysis (F(1, 21) = 8.606,
p < 0.01; 95% CI = ±2.172; PSS M = 2.385 lV; PPP M =
1.457).
Again, no effect emerged in the PSP–PSS comparison (no
F > 2).
In the late P600 interval (800–1000 ms) the PSP–PPP
comparison revealed an interaction between Condition
and Cluster in the Quadrant analysis (F(3, 63) = 7.242,
p < 0.01; 95% CI = ±4.715). Post-hoc comparisons showed
significant differences both in the Left-Posterior cluster
(t(21) = 2.081, p < 0.05; PSP M = 1.9726 lV; PPP M =
2.9773 lV) and in the Right-Posterior cluster (t(21) =
3.343, p < 0.05; PSP M = 1.9903 lV; PPP M = 3.5726 lV)
confirming the posterior distribution of the effect. In the
Longitude analysis the interaction between Condition and
Cluster also emerged (F(2, 42) = 7.602, p < 0.01; 95%
CI = ±5.3655). Following planned contrasts showed that
the effect was significant in the Parietal cluster (t(21) =
2.838, p < 0.05) where the PSP conditions (M = 2.434 lV)
was more positive than the PPP (M = 4.067 lV).
The PSS–PPP comparison showed an interaction between
Condition and Cluster both in the Quadrant (F(3, 63) =
12.813, p < 0.001; 95% CI = ±7.725) and in the Longitude
Fig. 2. Event-related potentials elicited by the modifier for the inflectionally plural subject manipulation (Experiment 1). Solid thin line represents the PPP
condition; dashed line represents the PSP condition; solid thick line represents the PSS condition. Vertical bars delimit the time windows of interest in the
statistical analysis. Negative values are plotted up.
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
(F(2, 42) = 6.674, p < 0.01; 95% CI = ±6.958) analysis. In the
former analysis the interaction is due to the effect in the
Left-Posterior cluster (t(21) = 2.462, p < 0.05; PSS M =
1.99 lV; PPP M = 3.157 lV), while in the latter analysis only
a marginal effect emerged in the Parietal cluster
(t(21) = 1.834, p < 0.08) where the PSS condition (M =
3.213 lV) was more positive than the PPP (M = 2.434 lV).
No significant effects emerged in the PSP–PSS comparison (all Fs < 1).
ERPs elicited at the Modifier position
Grand-average waveforms (Fig. 2, negative values are
plotted up) showed a larger positive effect starting around
500 ms for the PSP condition compared to the other two
conditions. The PSS condition in fact does not seem to reliably dissociate from the PPP condition. No clear sign of a
LAN is visually detectable in the waveforms.
Statistics in the 350–450 ms LAN interval did not reveal
any reliable differences (all Fs < 1.5).
In the early P600 time window (500–800 ms) the comparison between PSP and PPP showed a main effect of Condition in the Quadrant analysis (F(1, 21) = 4.602, p < 0.05;
95% CI = ±1.38): the effect is due to a more positive amplitude for the PSP condition (M = 1.488 lV) compared to the
PPP (M = 0.931 lV). A main effect of condition emerged for
this comparison also in the Longitude analysis
(F(1, 21) = 5.993, p < 0.05; 95% CI = ±1.439) as evidenced
by the mean values across midline clusters (PSP
M = 1.813 lV; PPP M = 1.063 lV).
While the PSS–PPP comparison did not show any significant effects, the PSP–PSS analysis showed a main effect of
Condition in the Longitude analysis (F(1, 21) = 4.369,
p < 0.05; 95% CI = ±1.08) as the PSP condition
(M = 1.813 lV) was more positive than the PSS one
(M = 1.258 lV) across midline clusters.
In the following time window (800–1000 ms; late P600
interval), the pattern was similar to the previous time window. The PSP–PPP comparison showed main effect of Condition both the Quadrant (F(1, 21) = 6.664, p < 0.05; 95%
CI = ±2.62; PSP M = 2.264 lV; PPP M = 1.341 lV) and in
the Longitude analyses (F(1, 21) = 7.527, p < 0.05; 95%
CI = ±3.22; PSP M = 2.433 lV; PPP M = 1.177 lV).
In the same time window the PSS and the PPP did not
differ. However, the PSP–PSS contrast showed main effects
of condition in both types of analysis (Quadrant: F(1, 21) =
4.971, p < 0.05; 95% CI = ±1.91; PSP M = 2.264 lV; PSS
M = 1.583 lV; Longitude: F(1, 21) = 5.504, p < 0.05; 95%
CI = ±3.04; PSP M = 2.433 lV; PSS M = 1.389 lV).
Summary of results
In this first experiment we replicated previous findings
on subject-verb agreement violations. As consistently reported by previous studies, the morphosyntactic mismatch
between the probable subject noun and the verb elicited a
LAN component followed by a long-lasting P600. The P600
in the earlier time window shows a wide topographical
distribution, while in the latter time window it is mainly
posterior.
In line with previous data (Molinaro, Kim, et al., 2008)
on mismatch resolution, only when the modifier disagrees
with the verb (and agrees with the subject noun phrase,
PSP) do ERPs show a clear P600 effect compared to the
grammatical condition (PPP). On the other hand, the condition in which the modifier disagrees with the subject noun
phrase (and agrees with the verb, PSS) behaved similarly to
the control condition (PPP). These findings are in line with
the two main hypotheses considered in the Introduction,
Repair and Recency.
The fact that we did not find any LAN on the modifier
could be due to the type of agreement feature processed
in this position: the across-phrase relation between the
subject antecedent noun and the modifier in the present
experiment is not a structural agreement relation, unlike
verb-subject agreement, which is triggered in a Spec-Head
configuration. In terms of processing, after reading a noun
phrase in initial position an active expectation would be
triggered for the verb, but not for an adjunct.
Experiment 2 is designed to contrast the two hypotheses: according to the Repair hypothesis, a different ERP pattern at the modifier is expected with respect to Experiment
1 (see predictions in Table 2). Since the subject is composed by two conjoined noun phrases, it cannot be reduced
to singular, and the repair cannot be performed at the following mismatching verb adapting the internal representation of the subject. However, replicating the findings of
Experiment 1 would support the Recency (in terms of local
feature consistency) hypothesis.
Experiment 2: Conjoined noun phrase subject
Method
Participants
Twenty-two Italian native speakers (mean age
22.81 years; SD = 3.69) took part in Experiment 2. All of
them were right-handed and had normal or corrected to
normal vision.
Material
We adapted the stimuli used in the previous experiment,
introducing two coordinated singular noun phrases in subject position. Thus, after two coordinate noun phrases a plural verb followed in the CPP control condition and a singular
verb followed in the two critical experimental conditions
(see examples in Table 1). After two coordinate singular
noun phrases, the following verb is a grammatical continuation only when it is plural. The choice of two singular nouns
in the mismatch conditions was aimed at under-specifying
the inflectional morphology that marks for plural. We tried
to reduce possible local attraction effects between the conjoined noun phrase and the verb. During sentence comprehension, number attraction effects are stronger when the
sentence is ungrammatical (Wagers et al., 2009). However,
these effects are stronger in singular subject-plural verb
configurations, while the structure we used is constituted
by a plural subject-singular verb. We thus exclude possible
attraction effects influencing the interpretation of the number mismatch.
In addition to these experimental sentences we added
200 filler sentences with a different syntactic structure:
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
80 sentences contained grammatical violations not involving number agreement mismatches. Again, no filler contained a topic structure.
Procedure
The same as in Experiment 1.
Data acquisition and analysis
We used the same strategy of acquisition and analysis
as in Experiment 1. The manual rejection in this second
experiment resulted in the exclusion of 6.2% of epochs on
average (no differences across conditions in the number
of rejections F < 1).
Results
Behavioral data
Participants answered the comprehension questions
with an overall accuracy of 93%. No accuracy difference
was found across conditions (F(2, 42) < 1).
ERPs elicited at the Verb position
In this position, the mismatch between the plural coordinate Subject and the Verb elicited a more positive effect
between 500 and 800 ms evident at frontal and parietal
electrodes for both the CSP and the CSS condition. Neither
a LAN nor a late P600 was evident for these two conditions
compared to the CPP condition (Fig. 3, negative values are
plotted up).
221
In the 350–450 ms time window (LAN interval) the
analysis did not reveal any significant effects related to
Condition (no F-value was associated to a probability lower
than p = 0.5). In the later time interval (500–800 ms; early
P600) the CSP–CPP comparison revealed a main effect of
Condition in the Longitude analysis (F(1, 21) = 4.703,
p < 0.05; 95% CI = ±2.23) due to the larger positivity in this
time window for the CSP condition (M = 0.475 lV) compared to the CPP (M = 0.312 lV).
Also the CSS–CPP comparison revealed a main effect of
Condition in the Longitude analysis (F(1, 21) = 4.982,
p < 0.05; 95% CI = ±1.91), due to the positive effect for the
CSS condition (M = 0.514 lV).
In the 800–1000 ms interval (late P600) no effect related to the Condition factor emerged (only in the CSP–
CPP comparison was the effect of Condition lower than
p = 0.2 in the Longitude analysis; F(1, 21) = 3.065, p = 0.19).
ERPs elicited at the Modifier position
As evident in Fig. 4, ERPs in this position showed a positive shift for the CSS condition compared to the other two
conditions (CPP and CSP) that did not differ between each
other. Again, there is no sign of a LAN in the early time
window.
The statistics in the 350–450 ms time interval did not
show any significant effects related to Condition in the
pairwise comparisons (all p-values > 0.5).
In the early P600 time window (500–800 ms) the CSS–
CPP comparison showed an interaction between Condition
and Cluster in the Quadrant analysis (F(3, 63) = 3.773,
Fig. 3. Event-related potentials elicited by the Verb for the conjoined noun phrase subject manipulation (Experiment 2). Solid thin line represents the CPP
condition; dashed line represents the CSP condition; solid thick line represents the CSS condition. Vertical bars delimit the time windows of interest in the
statistical analysis. Negative values are plotted up.
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
Fig. 4. Event-related potentials elicited by the modifier for the conjoined noun phrase subject manipulation (Experiment 2). Solid thin line represents the
CPP condition; dashed line represents the CSP condition; solid thick line represents the CSS condition. Vertical bars delimit the time windows of interest in
the statistical analysis. Negative values are plotted up.
p < 0.05; 95% CI = ±4.63) due to the larger positive effect in
the Left-Posterior cluster (t(21) = 2.471, p < 0.05) for the
CSS (M = 0.386 lV) compared to the CPP (M = 0.562 lV).
The same comparison revealed an interaction between
Condition and Cluster also in the Longitude analysis
(F(2, 42) = 8.39, p < 0.01; 95% CI = ±2.93): in the Parietal
cluster the CSS condition (M = 0.782 lV) was more positive
(t(21) = 2.125, p < 0.05) than the CPP condition
(M = 0.145 lV).
In the same time window the CSS–CSP comparison also
showed an interaction between Cluster and Condition in
the Longitude analysis (F(2, 42) = 7.402, p < 0.01; 95%
CI = ±2.21). This last interaction reflects the larger positivity for the CSS condition (M = 0.782 lV) compared to the
CSP condition (M = 0.017 lV) in the Parietal cluster
(t(21) = 2.174, p < 0.05).
In this time interval CPP and CSP did not differ
statistically.
In the following time interval (800–1000 ms; late P600),
the CSS–CPP comparison showed an interaction between
Condition and Cluster in the Longitude analysis
(F(2, 42) = 5.503, p < 0.05; 95% CI = ±3.76). This interaction
reflects the larger positive effect (t(21) = 2.588, p < 0.05)
for the CSS condition (M = 1.887 lV) compared to the CPP
(M = 0.848 lV).
The CSS–CSP comparison showed an effect of condition
both in both analyses (Quadrant: F(1, 21) = 4.731, p < 0.05;
95% CI = ±1.98; CSS M = 0.995 lV; CSP M = 0.517 lV; Longitude: F(1, 21) = 4.701, p < 0.05; 95% CI = ±3.042.23; CSS
M = 0.811 lV; CSP M = 0.227 lV).
Finally, the CSP–CPP comparison did not reveal any significant effects related to Condition (all p-values higher
that p = 0.5).
Summary of results
Two main findings emerged in Experiment 2. First, in
the verb position, no LAN effect was observed, and the
P600 elicited by the agreement mismatch emerged only
in the early (500–800 ms) time window; this last effect
was topographically distributed across the scalp (Fig. 5
shows the difference waves between the average ERPs elicited by the violation conditions and the control in both
Experiments 1 and 2), as also confirmed by the lack of
interaction between the Condition and the Cluster factors.
Second, in the following modifier position, a P600 effect
emerged only for the CSS condition, compared to both the
CPP and the CSP condition that did not differ from each
other. These results contrast with the findings of Experiment 1, in which we recorded the opposite pattern: the
PSS condition did not differ from the PPP, while the PSP
condition elicited a P600. In addition, in line with the findings of Experiment 1, in Experiment 2 we did not find any
LAN at the modifier position, thus suggesting that a qualitatively similar processing mechanism (in different conditions) was elicited at the modifier position in the two
experiments (see Fig. 6 where we report the difference
waves between the conditions that elicited the P600 on
the modifier position, PSP in Experiment 1 and CSS in
Experiment 2, minus the Control condition).
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
F3
Fz
F4
Experiment 1:
Verb
Position
*I fratelli (+P) giunse
(+S)...1
Experiment
Experiment 2
Experiment 2:
*Il fratello e la sorella giunse (+S)...
LAN
T7
C3
Cz
P7
P3
Pz
C4
T8
P4
P8
early & late P600
−4
µV
O1
O2
Experiment 1
Experiment 2
−2
ms
−200
200
1000
2
N Exp1
p1
L AN
early P600
Exp2
Exp1
late P600
Exp2
Exp1
Exp2
Fig. 5. Difference waveforms between the average of the two mismatching conditions (mean of PSP and PSS for Experiment 1 and CSP and CSS for
Experiment 2) and the grammatical condition (PPP in Experiment 1 and CPP in Experiment 2) at the Verb in Experiment 1 (inflectionally plural subject
manipulation) and Experiment 2 (conjoined noun phrase subject manipulation). The maps referring to the critical ERP components are calculated between
350 and 450 ms for the LANs, between 500 and 800 ms for the early P600s and between 800 and 1000 ms for the late P600s.
Across-experiment comparison
We also compared the findings across the first two
experiments. Given the high number of violations required
by the experimental design and the high number of items
per condition used in an ERP experiment we decided to
manipulate the type of noun phrase (inflectionally plural
or conjoined) in subject position as a between experiment
factor. In order to avoid the development of particular
strategies for processing the experimental sentences, we
used a large number of fillers (200 further sentences). This
technical constraint did not make it possible to play the
subject type as a within subject factor.
Thus, we ran further statistical analyses to evaluate the
effects across the between subject manipulation of subject
type. We ran the statistics used in both experiments, adding a further factor, Experiment, implemented in the ANOVAs as a between subject factor. For each sentence position
and each time window of interest we ran both the Quadrant and the Longitude analysis. In the Quadrant analysis
we ran a three way ANOVA with the following factors:
Condition (pairwise comparisons, where X could be both
P and C: XPP–XSP, XPP–XSS, XSP–XSS), Cluster (four levels:
LA, RA, LP, RP) and Experiment (two levels: Experiment 1
and Experiment 2). In the Longitude ANOVA the same factors were used: Condition, Cluster (three levels: Frontal,
Central and Parietal) and Experiment. The main effects of
interest in this last analysis comprise the interaction with
the Experiment factor.
ERPs elicited at the Verb position
In the LAN time window (350–450 ms) the Quadrant analysis revealed the critical interactions between Condition,
Cluster and Experiment for both the XPP–XSP (F(3, 126) =
2.667, p < 0.05) and the XPP–XSS comparison (F(3, 126) =
2.817, p < 0.05). This interaction with the Experiment factor
confirms the reliability of the LAN in Experiment 1 compared
to Experiment 2. In Fig. 5 we plotted the difference waves between the average ERPs elicited by the violation conditions
and the correct condition on the verb in the two experiments.
It is evident that the LAN emerged only in Experiment 1.
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Fig. 6. Difference waveforms at the modifier position between the condition eliciting the P600 effect and the control condition: in Experiment 1 the
difference is calculated from the PSP–PPP subtraction, i.e. the comparison showing the P600 effect in Experiment 1; in Experiment 2 the difference is
calculated from the CSS–CPP subtraction, i.e. the comparison showing the P600 effect in Experiment 2. The maps of the P600s are extracted from average
activity in the whole P600 time window (i.e. both the early and the late window: 500–1000 ms).
In the early P600 time window (500–800 ms) no interaction with the Experiment factor emerged (all Fs < 1.5). In
the following time window (800–1000 ms), statistics
showed interactions between Condition, Cluster and
Experiment
both
in
the
XPP–XSP
(Quadrant:
F(3, 126) = 5.691, p < 0.01; Longitude: F(3, 126) = 6.669,
p < 0.01) and the XPP–XSS (Quadrant: F(3, 126) = 7.426,
p < 0.01; Longitude: F(3, 126) = 4.353, p < 0.05) comparison. This means that the late stage of the P600 is different
between the two experiments, larger in Experiment 1 compared to Experiment 2 in the posterior electrodes of the
scalp (see late P600 effects in Fig. 5).
(Longitude analysis: F(3, 126) = 4.491, p < 0.05); finally,
also the XSP–XSS comparison showed the triple interaction
between Condition, Cluster and Experiment (Longitude
analysis: F(3, 126) = 3.171, p < 0.07).
The similar pattern of effects emerging in the two time
windows (Fig. 6) robustly confirms that very similar effects
are elicited in the two experiments, even if in opposite
directions. In Fig. 6 we plotted the difference waves between the condition that elicited the P600 on the modifier
position (PSP in Experiment 1 and CSS in Experiment 2) and
the control. Since the effect was similar across time windows we plotted the maps for the whole P600 time
window.
ERPs elicited at the Modifier position
Experiment 3: Grammatical judgement and repetition
As for this latter position, the pairwise comparisons in
the P600 time windows confirm the differential effects
across the two experiments. In fact in the 500–800 ms time
window the Longitude analysis showed an interaction between Condition and Experiment for the XPP–XSP comparison (F(1, 42) = 4.358, p < 0.05); the same interaction
emerged also for the XSP–XSS (F(1, 42) = 9.797, p < 0.01)
and, marginally significant, for the XPP–XSS comparison
(F(1, 42) = 3.36, p < 0.074).
The following time window (800–1000 ms) showed a
similar trend. The XPP–XSP comparison showed interaction
between Condition and Experiment (Longitude analysis:
F(1, 42) = 7.951, p < 0.01); the XPP–XSS comparison showed
interaction between Condition, Cluster and Experiment
In the third experiment we evaluated the off-line interpretation of a number mismatch between subject and verb.
We used a paradigm developed by Meng and Bader (2000)
in their Experiment 4. They required participants to judge
the grammaticality of German sentences and then to repeat them; in case of ungrammaticality they were required
to provide a corrected version of the stimulus. These
authors used sentences where wh-phrases and their finite
verb disagreed in number. When required to repeat and
correct those sentences, participants tended to alter the
morphosyntactic case feature on the initial wh-phrase, instead of changing the morphosyntactic number feature of
the following finite verb. These findings suggest that a
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
morphosyntactic mismatch is interpreted off-line based on
the properties of the more recent constituent. If this is true,
a mismatch between an inflectionally plural subject and a
singular verb (condition PS, Experiment 3, in Table 1)
should be corrected based on the verb number (singular);
we however expect the opposite correction when two conjoined nouns are presented in subject position (condition
CS, Experiment 3, in Table 1).
This experiment is aimed at verifying three main aspects
of the off-line processing of number agreement mismatches. Through this paradigm we can first evaluate the
accuracy with which participants detect the subject-verb
ungrammaticalities off-line, to make sure they are aware
of the errors. Second, we can determine if the on-line effects
we recorded on the modifier position reflect the off-line
meta-linguistic interpretation of the mismatch. Experiment
1 showed that an inflectionally plural subject-singular verb
mismatch is interpreted on-line as singular, while Experiment 2 showed a conjoined subject-singular verb to be
interpreted as plural. It is interesting to see how participant
correct off-line these number mismatches. Third, it is possible to verify if a conjoined subject is more resistant to the repair strategy, as assumed throughout the whole paper: in
fact we proposed that a conjoined noun phrase cannot be
revised to singular since this would imply deleting one referent, thus altering the nature of the message.
Method
Participants
Twenty-two Italian students (12 females, mean age:
21.35 years; age range: 19–24 years) taking part in the
Erasmus program of the University of the Basque country
participated in Experiment 3 in exchange for 10€. All of
them were native Italian speakers visiting Spain for less
than 1 month.
Materials
We selected a subset of 48 sentences from the dataset
used in the previous two Experiments. Twenty-four sentences from Experiment 1 and 24 sentences from Experiment 2 were adapted for the purposes of the present
experiment. In Experiment 3 the set adapted from Experiment 1 had the following structure: a plural noun phrase
was immediately followed by the verb that was never in
sentence final position; the position of the critical words
varied across items. The subject and the verb were the only
two number-marked elements in the sentence ‘‘Dopo una
dura giornata di lavoro i fratelli giunsero a casa.’’ – After a
day of hard work the siblings arrived home; see PP, Plural
subject – Plural verb, condition in Table 1, lower panel).
The set extracted from Experiment 2 had the same structure, but the subject was constituted by two conjoined singular NPs (‘‘Dopo una dura giornata di lavoro il fratello e la
sorella giunsero a casa.’’ – After a day of hard work the brother and the sister arrived home; see CP, Conjoined subject Plural verb, condition in Table 1). We balanced the number
of words per sentence in the different conditions (the average number of words was 12.5).
From these 48 sentences we composed the number
agreement violations modifying the number of the verb
225
to singular (. . .giunsero. . . ? . . .giunse. . .; see PS and CS
conditions in Table 1, lower panel). We then created two
lists with 12 sentences per condition (PP, PS, CP and CS)
so that each participant did not see the same sentence in
two different conditions.
In order to avoid any bias toward singular or plural responses, 52 additional fillers were used. Since the experimental material was mainly constituted by plural
sentences, the fillers mainly contained grammatical singular sentences and singular sentences containing gender
violations in which we expected the repetition to be singular, plus some sentences with a singular subject following a
plural constituent (never its verb). Each participant was
presented with 100 sentences, half of them grammatically
correct and half not.
Procedure
Participants were seated in a quiet room. The experimental sentences were presented on a notebook screen
word by word at the center of the screen, similarly to the
previous ERP experiments (white letters on a dark-grey
background). However, rate of presentation was not fixed.
In the previous experiments, the long SOA (600 ms) between subsequent words was driven by the need of avoiding overlap of the ERP components elicited by each word
with the ones elicited by the following one. Since we did
not record EEG in this experiment, we used a rate of presentation that better simulated speech or reading rate,
with shorter words presented for a shorter interval compared to longer words.
Thus, a fixation cross at the center of the screen warned
the participant that a sentence was going to start. After participant’s button press, each word of the sentence was presented for 187 ms plus 27 ms for each letter of that word
(see Nieuwland & Kuperberg, 2008). No blanks were presented between words and the last word of the sentence
was followed by a period. Immediately after sentence presentation a prompt appeared on the screen asking for a
speeded grammaticality judgment of the sentence (Was
the sentence grammatically correct?). Participants were required to answer as fast and as accurately as possible by
pressing the corresponding YES/NO buttons on a joypad.
After the participant’s answer an additional prompt appeared on the screen asking the participant to repeat the
sentence (Now repeat). Participants were required to repeat
the sentence verbatim as accurately as possible if the sentence was grammatically correct. In case of grammatical
errors participants were required to provide a corrected
version of the sentence. There was no specific requirement
on the type of correction to be made, participants had just
to produce a grammatical version of the sentence. Participants were required to respond immediately, even if there
was no explicit time limit. For each trial we reported the
number assigned to the whole repeated sentence (either
Singular (S) or Plural (P)), considering the repetition correct
when both the subject and the verb were reported in the
correct order.
Five practice sentences preceded the experimental
items; the whole experiment, that was divided in two
blocks with a 5 min pause in the middle, lasted approximately 45 min.
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
Data analysis
Participants whose accuracy across the whole experiment was lower than 80% in the grammatical conditions
(PP and CP in Table 1) were excluded from analyses.
Response time and accuracy of the speeded grammaticality judgment were analyzed grouping by both subjects
(F1) and items (F2). Response times that were more than
three standard deviations longer than the average response
of that subject were considered outliers. Two-way analysis
of variance on these data considered the following factors:
Grammaticality (Correct vs. Violation) and Type of plurality (Inflectionally plural subject vs. Conjoined subject).
The main analysis focused on the number of Singular
and Plural repetitions for each condition that were compared through a Chi-Squared test. In this analysis we only
considered the items whose grammaticality was correctly
judged. Direct comparison between the proportion of corrections in different conditions was pursued using the 2sample test for equality of proportions (Wilson, 1927); a
correction of continuity was applied. We mainly compared
the corrections between the two correct conditions (PP and
CP) and the two ungrammatical ones (PS and CS).
Results
Response times
Three participants were excluded from further analyses
since their performance in the whole experiment was lower than the accuracy threshold in the grammatical conditions. Average RTs for each condition are reported in
Table 3. Statistics did not show any significant effect; there
was only a marginal effect of Type of plurality in the bysubject statistics (F1(1, 18) = 3.769, p = 0.068), suggesting
a slightly more difficult judgment for the Conjoined subject
conditions (M = 1772 ms, SD = 603 ms) compared to the
Inflectionally plural subject conditions (M = 1669 ms,
SD = 472 ms). It is possible that the higher number of
words involved in the grammaticality judgment of the conjoined conditions affected reading times.
Table 4
Accuracy of the speeded grammaticality judgments in the four critical
conditions of Experiment 3. The lower panel show the statistics calculated
in the ANOVA.
Condition
Average accuracy levels (SD)
PP (plural–plural)
CP (conjoined–plural)
PS (plural–singular)
CS (conjoined–singular)
95.1%
90.9%
91.6%
86.2%
ANOVA (2 2: Grammaticality Type of Plurality)
Grammaticality
F1(1, 18) = 0.05,
n.s.
F1(1, 18) = 5.09,
p < 0.05
F1(1, 18) = 4.73,
p < 0.05
Type of plurality
Grammaticality Type of Plurality
Repetitions
When correctly judged, in 10.6% of the cases either the
repetition did not correspond to the stimulus or was forgotten by the participant (defined as Other in Table 5). In
the former case, participants forgot either subject or verb
information; in many cases the thematic roles were not reported correctly.
Number of Repetitions and relative percentage across
all the participants is reported in Table 5.
The Correct conditions were repeated correctly in the
majority of cases (PP: 178 (P) vs. 13 (S), Chisquared = 142.53, df = 1, p < 0.001; CP: 152 (P) vs. 29 (S),
Chi-squared = 83.58, df = 1, p < 0.001). The effect was more
stable for the Inflectionally plural condition than the Conjoined subject condition (Chi-squared = 6.98, df = 1,
p < 0.01).
(449)
(636)
(500)
(584)
Grammaticality
F1(1, 18) = 0.32, n.s.
Type of plurality
F1(1, 18) = 3.76,
p = 0.068
F1(1, 18) = 2.86,
p = 0.108
Grammaticality Type of Plurality
100
90
CP
CS
PP
PS
60
ANOVA (2 2: Grammaticality Type of Plurality)
80
1618 ms
1790 ms
1719 ms
1754 ms
70
Average RT (SD)
PP (plural–plural)
CP (conjoined–plural)
PS (plural–singular)
CS (conjoined–singular)
Accuracy
Type fo plurality, p<0.05
% of correct judgements
Condition
F2(1, 92) = 0.01,
n.s.
F2(1, 92) = 3.73,
p = 0.054
F2(1, 92) = 2.52,
n.s.
higher accuracy for the Inflectionally plural subject conditions (M = 93.3%, SD = 7.8%) compared to the Conjoined
subject conditions (M = 88.5%, SD = 11.7%). Planned comparisons however did not show any significant difference
in those contrasts (see barplots in Fig. 7).
Accuracy
Average accuracies for each condition are reported in
Table 4. A main effect of Type of plurality reflects the
Table 3
Response times (RT) of the speeded grammaticality judgments in the four
critical conditions of Experiment 3. The lower panel show the statistics
calculated in the ANOVA.
(6.6)
(7.2)
(8.8)
(16.3)
F2(1, 92) = 0.41,
n.s.
F2(1, 92) = 1.27,
n.s.
F2(1, 92) = 2.86,
n.s.
Conjoined subject
Inflectionally plural subject
Fig. 7. Accuracy levels in the four critical conditions of Experiment 3.
Dark grey bars indicate the Correct conditions (CP, conjoined subjectplural verb and PP, inflectionally plural subject-plural verb), while the
light grey bars indicate the Violation conditions (CS, conjoined subjectsingular verb and PS, inflectionally plural subject-singular verb).
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N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
Table 5
Number (and percentage) of Singular and Plural repetitions calculated over the whole set of responses given by participants in the
four critical conditions of Experiment 3.
Condition
Singular repetitions
Plural repetitions
Other
Total
PP (plural–plural)
CP (conjoined–plural)
PS (plural–singular)
CS (conjoined–singular)
13 (6.2%)
29 (14.1%)
124 (57.2%)
34 (17.2%)
178 (85.2%)
152 (73.4%)
66 (30.4%)
145 (73.6%)
18
26
27
18
209
207
217
197
The main interest of the experiment was, however, in
the repetitions involving corrections of the sentence grammaticality. The CS condition was robustly corrected to plural (CS: 145 (P) vs. 34 (S), Chi-squared = 68.83, df = 1,
p < 0.001); on the other hand, PS was corrected to singular
the majority of the times (PS: 66 (P) vs. 124 (S), Chisquared = 17.7, df = 1, p < 0.01).
The selection of the singular in the PS condition (PS:
124–66 = 58) appears less robust compared to the selection of the plural in the CS condition (CS: 145–34 = 111).
We thus compared the proportion of Singular repetitions
for the PS condition to the proportion of Plural repetitions
for the CS condition. The 2-sample test for equality of proportions showed a significant difference in this dimension
(Chi-squared = 10.78, df = 1, p < 0.01). Given that the analysis was run on proportions, we exclude a possible influence of repetitions classified as Other.
(8.6%)
(12.5%)
(12.4%)
(9.1%)
effect at the verb is more prominent for violations
involving an inflectionally plural subject, while the effect
observed off-line for this condition is weaker compared
to the conjoined subject condition.
Nonetheless, the available findings strongly support the
hypothesis that a Repair process is performed on-line, and
has an effect on the off-line interpretation of the ungrammatical input. An inflectionally plural subject-singular verb
construction tends to be revised to singular, while a conjoined subject-singular verb tends to be corrected to plural.
General discussion
In the present study we analyzed the on-line resolution
of subject-verb number agreement mismatch and its impact on the off-line interpretation of the sentence
ungrammaticality.
Summary of results
The Repair hypothesis
While the contrast between Experiments 1 and 2 supported the Repair hypothesis, Experiment 3 showed that
the hypothesized repair process has an effect also on the
off-line interpretation of an ungrammatical sentence. We
thus first showed that Italian speakers had high levels of
accuracy in the detection of the number mismatches (higher than 80%). Second, we showed that when the cognitive
system detects a number mismatch between a conjoined
noun phrase and a singular verb, the number of the subject
drives the resolution of the mismatch. This effect is very
strong, as evident in the amount of plural repetitions for
the CS conditions (see Table 5). On the other hand, the mismatch between an inflectionally plural subject and a singular verb is corrected to singular, in line with previous
findings that highlight the pivotal role of the second element in the resolution of a morphosyntactic incongruence
(Meng & Bader, 2000; Molinaro, Kim, et al., 2008;
Vespignani et al., in press). This is a surprising result, since
it is widely assumed that number values are interpreted in
the noun position and for this reason supposed to drive
mismatch resolution in a subject-verb mismatch. Third,
we confirmed the hypothesis that a conjoined noun phrase
is more resistant to the repair strategy compared to the
inflectionally plural subject.
As evident in Table 5, the percentage of singular repetitions for PS is lower than the percentage of plural repetitions for CS. As previously noted, off-line meta-linguistic
judgments on number mismatches should not necessarily
be similar to the on-line immediate resolution of the
ungrammaticality, since further variables could influence
this off-line evaluation. It is worth noting that the ERP
An interesting dissociation was recorded at the modifier
position in the first two experiments. In Experiment 1, a
P600 was elicited by the PSP condition, while in Experiment 2 the same effect was elicited by the CSS condition.
This ERP similarity (a P600 with a central-posterior distribution, especially in its later time window, without any
LAN) indicates that a similar computation is elicited in
the two cases. This mechanism is consequential to the
on-line processing of the mismatch between subject and
verb. Indeed, the ERP effects at the modifier position in
the two experiments suggest insights into the on-line
interpretation of the number mismatch at the verb
position.
In Experiment 1 (I fratelli giunse – The siblings arrived
[+S]) we proposed that the system has to immediately select one number value to solve the incongruence (Repair
hypothesis: see also Molinaro, Kim, et al., 2008; Vespignani
et al., in press): as shown by some authors, the last presented element has a pivotal role in the comprehension
of sequentially presented information (Cowan, 2001;
McElree, 2001, 2006; Meng & Bader, 2000). In order to
build a well-formed sentence fragment (thus allowing an
easier integration of further incoming constituents), the
internal representation of the ungrammatical sentence is
repaired to be grammatical: in Experiment 1 the number
of the verb is maintained as anchoring value and the internal representation of the inflectionally plural subject noun
is revised to singular. This is possible since the number of
the subject referent has been extracted by the inflectional
morphology of the head noun (see also Meng & Bader,
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2000). Reanalyzing the subject numerosity to singular
makes the following modifier ungrammatical when it is
plural (and grammatical when it is singular). The P600 effect recorded only on the plural modifier (PSP condition)
confirms our analysis. Thus, our interpretation of the phenomenon is that the sentence processor needs to operate
an immediate Repair of the ungrammaticality (number disagreement) to integrate new incoming constituents with a
temporarily well formed phrase marker incrementally
stored in working memory.
However, as we stated previously (Molinaro, Kim, et al.,
2008), alternative explanations are possible for the P600
pattern at the modifier position in Experiment 1. According
to the Recency analysis, agreement features could be handled by the processing routines mirrored in the P600 just
as surface cues for dealing with local (short-distance) relations. This would explain the P600 at the modifier when it
mismatches with the surface properties of the local verb
(but not with those of the subject noun phrase). A repair
mechanism would not then be needed to explain the findings in Experiment 1.
Experiment 2 (Il fratello e la sorella giunse – The brother
and the sister arrived [+S]) permits contrasting these alternative explanations. The Recency hypothesis predicts a
P600 on the plural modifier, i.e., when it mismatches locally with the verb. This was not the case, since we recorded a P600 on the modifier when it was singular:
given the P600 in this condition (CSS condition), the Recency hypothesis cannot hold, since the whole sentence
does not have any constituent morphophonologically
marked to plural.
These findings strongly support the Repair hypothesis.
The manipulation we performed in Experiment 2 was designed to ‘block’ the repair strategy we observed in Experiment 1 (see also Experiment 3 repetitions for the CS
condition): in fact, manipulating the representation of the
coordinate subject would imply removing one of the two
referent noun phrases, thus altering the nature of the
whole message. In this frame, the number of the subject
cannot be revised without affecting the nature of the
whole message. Here, the parser selects the plurality of
the coordinate subject as a referent value for interpreting
the number agreement mismatch. A possible interpretation is that in Experiment 2, since the subject representation cannot be altered, it is the number of the verb which
should be re-interpreted to plural. This would cause a mismatch with the following singular modifier, eliciting the
P600 observed in the CSS condition. In this view, the plurality of the subject referents in a conjoined noun phrase is
semantically more stable (being not re-interpretable) compared to the plurality extracted by the morphophonological properties of the subject noun phrase used in
Experiment 1.
This hypothesis fits well with the shorter P600 effect recorded on the verb in Experiment 2. The more ‘prominent’
violation on the verb in Experiment 1 thus elicits a more
complex electrophysiological pattern (LAN followed by a
long-lasting P600) compared to Experiment 2. In our opinion, the additional processing in Experiment 1 reflects the
additional work operated by the parser to revise the subject representation (stored in working memory) to singular
(for similar explanation of the late phase of the P600 see
Barber & Carreiras, 2005, and Molinaro, Vespignani, et al.,
2008, who propose a reanalysis process based on Faussart,
Jakubowicz, & Costes, 1999). On the other hand, in Experiment 2 the impossibility of coercing a coordinate subject to
singular renders the number of the verb misleading. Consequently, the cognitive system invests less resources in
the processing of the mismatching verb, without altering
the information stored in working memory; this is reflected in the less prominent ERP responses recorded at
the verb in Experiment 2 (lack of late P600, see Fig. 5).
Experiment 3 showed that this on-line repair process
has an influence also on the off-line interpretation of the
sentence. When processing a subject-verb number agreement mismatch, participants are aware of the ungrammaticality of the sentence, as evidenced by the high levels of
accuracy in all conditions. This good performance reflects
the fact that our participants did not ignore the morphosyntactic properties of our sentences. The only significant
difference we obtained was between the inflectionally plural subject conditions and the conjoined subject conditions, accuracy being slightly lower and response times
longer in the latter. This difference is possibly due to the
greater difficulty in processing subject-verb agreement
with conjoined subject phrases that are inherently more
complex.
More critical for our study, the off-line correction of the
number mismatch (as evidenced by the number of repetitions in the violation conditions, see Table 5) was identical
to the on-line resolution, as evidenced by the P600 effects
on the modifier position (see Fig. 6). This additional evidence provides further support for the reliability of the Repair hypothesis as a critical processing routine by means
of which the cognitive system processes agreement irregularities. However, we are not claiming that the on-line repair
directly determines the off-line interpretation of the sentence, but that it has an influence on it. If the on-line repair
determined the off-line sentence interpretation, we would
have expected no difference in the proportion of inflectional
subject correction to singular compared to conjoined phrase
subject corrections to plural. In contrast, however, the P600
recorded on the modifier in the two cases is very similar (see
‘Across-experiment comparison’). Thus, additional factors
can influence the off-line interpretation of the sentence
and the on-line repair is just one relevant factor.
Given the present data, it is possible to speculate about
the nature of the representation on which the repair is carried out. The fact that repair could be performed only when
the subject number value is morphological could mean
that what is mentally modified is the feature [Number] of
the initial nominal. However, according to some authors
(Bornkessel & Schlesewsky, 2006; Friederici, 2002), repair
should be seen as a very late stage of processing. This
would support the idea that this process should target a
more abstract and less linguistic-specific internal representation, one connected to semantic and discourse level
information.
This proposal would be supported by off-line linguistic
evidence. In Italian or French, the courtesy form for a 2nd
person singular subject pronoun can use a 2nd person plural form (voi/vous, respectively). The main verb agrees in
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
the plural with this pronominal subject, but any subsequent participle or adjective appears in the singular, agreeing in gender and number with the logical subject (i.e. the
singular addressee), not with the verb (see (2) for Italian):
Similarly, a sentence that begins with I ragazzi pensa. . .
‘the boys thinks[+S] . . .’ could continue with a perfectly
grammatical post-verbal subject, as in (4)3:
(4)
(2)
Voi
siete
stato
felice
you[+P] have[+P] been[+S] happy[+S]
‘‘yousing-formal have been happy’’
This strongly suggests that the number of the first nominal does not directly interact with the modifier, which
would be mainly sensitive to the logical number of the
subject.
In sum, the findings on the modifier in Experiments 1 and
2 confirm the strategy of the cognitive system to immediately repair an incongruent sentence on-line: an agreement
mismatch triggers an immediate repair through which the
system, after integrating all the available information, selects a unique number value for the grammatical disagreement. If the mismatch is based on the pluralization of a
discourse entity based on morphophonological information
extracted from the noun’s inflection, the value of the last
processed constituent coerces the internal representation
of the subject; otherwise, when relevant information dominates the value of the processed mismatching constituent,
this regularization strategy (mirrored in the prolonged
P600 effect recorded in Experiment 1) is blocked and the system relies on the number of the sentence fragment already
stored in memory, somehow ‘ignoring’ following number
values. This on-line process influences the interpretation
of the whole message, in that it constrains the build-up of
the internal restructured representation of the message intended by the source.
Repair vs. Reanalysis
One important aspect of the present study is that it was
carried out in Italian, a language with greater word order
freedom than English (the language investigated in Molinaro, Kim, et al., 2008). Working on the agreement between subject and main verb in a null-subject language
like Italian leaves open the theoretical possibility of a local
structural ambiguity. The problem is that in the presence
of a number mismatch between the sentence-initial nominal and the main verb, the parser might no longer interpret this nominal as the subject, but as a topicalized
element whose gap is expected to appear later in the sentence. The ill-formed English sentences in (1) begin just
like the perfectly well-formed Italian (3) (where pro indicates the presence of an unpronounced singular subject,
and i famosi danzatori is a left topic, picked up by the -li
pronoun, object of aspettando).
(3)
I famosi danzatori stava nervosamente
aspettandoli dalle 9
the famous dancers[3p+P] pro was[3p+S]
nervously waiting-for-them since 9
‘‘as for the famous dancers, he was nervously
waiting for them since 9 o’clock’’
229
I ragazzi pensa Carlo a prenderli
the boys thinks Carlo to collect them
‘‘as for the boys, Carlo intends to collect them’’
Structures of this sort, though very common in spoken
language, are not present in the experimental stimuli of
our experiment, but the word by word presentation modality gives the participants ample time to consider them. Thus,
the existence of such structures might support the development of an alternative (topic) interpretation of the sentence
to the initially preferred first-nominal-as-subject. In other
words, after encountering a mismatching verb after an initial nominal, the system could revise its initial preference
to a topic one (either a pro or a post-verbal construction).
This additional strategy (at work in null-subject languages),
that we can call Reanalysis, predicts that the system either
re-interprets completely the sentence structure or activates
parses additional to the first-nominal-as-subject one. The
discovery of a gap and/or a sentential subject in the continuation of the sentence would constrain the type of structure
to be assigned to the sentence. We think this is an important
aspect of the present study, since many sentence processing
models state that when faced with a syntactic irregularity,
the system exploits all the possible grammatical alternatives before considering the sentence as ungrammatical
(Garden-Path model, Frazier, 1987; but also MacDonald
et al., 1994; Tabor et al., 2004).
For example, when reading the verb in Experiment 1
the parser could postulate the existence of a null singular
subject that agrees with the verb. Here, the ERP effects recorded on the verb could represent the additional activation of a topic construction. Whether the topic is
coordinated or not should make no difference at all, so
we can hypothesize that a similar reanalysis is operated
after reading the verb also in Experiment 2. However, the
findings on the modifier are critical, since we would have
expected the same results in both Experiments 1 and 2:
in fact, if the following modifier is singular, it would simply
agree with this subject, while if it is plural we would expect processing difficulties due to the fact that the system
realizes that the topic interpretation is not the correct
parse (considering the P600 amplitude on the modifier
we would have expected the following ERP pattern: Experiment 1: PSP > PSS, Experiment 2: CSP > CSS). Critically, this
was not the case, indicating that the Repair explanation is
the only possible interpretation of the findings emerging
in the present study.
These findings have interesting implication for the type
of parsing involved in Italian subject-verb mismatches. In
3
Note that by marking pro in (3) in the canonical position for overt
subjects we are not committing ourselves to a specific linguistic structure
for null or post-verbal subjects, nor to a particular mental realization of
these constructions. Evidently, the parser must be able to handle these
cases without hesitations. The way this is performed is an interesting
research topic, but one which is orthogonal to our present argument.
230
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
fact, when faced with a mismatch between the number of
the initial nominal and a following verb, the system could
possibly reanalyze the sentence as a topic structure
(Reanalysis hypothesis, see examples 3 and 4). This type
of structure is less frequent in Italian than that in which
the first nominal is the subject; however, it is syntactically
acceptable and it could be a viable alternative interpretation (for an Italian speaker). Many theoretical proposals
(Frazier, 1987; MacDonald et al., 1994; but see also Fodor
& Ferreira, 1998) have stressed the ability of the parser
to pursue any alternative grammatical parse (that is faithful to the input), once it is compelled to perform reanalysis
of an ongoing interpretation. Our findings seem to be at
odds with this, since we find evidence that the system continues with its initial choice (first-nominal-as-subject)
even if it is not faithful to the input, instead of assuming
a less preferred (but more faithful to the input) interpretation of the sentence, at least in the experimental setting of
our study. This would confirm the ability of the processing
system to easily deal with local mismatches and repair
them on-line, before accessing further possible disambiguating information.
ERPs effects at the Verb position
Distinct ERP effects emerged at the mismatching verb in
the first two experiments (see Fig. 5 for a direct comparison of the difference waves). Even if this distinction was
not the main focus of our study, we think that this dissociation is worthy of comment, since it could stimulate further research on the processing of subject-verb
agreement. While the mismatch in Experiment 1 is detected after processing the inflectional morphology of the
noun phrase in subject position (I fratelli giunse – The
[+P] siblings arrived [+S]), in Experiment 2 the mismatching verb follows a coordinate noun phrase (Il fratello e la
sorella giunse – The [+S] brother and the [+S] sister arrived
[+S]). The main finding is that a LAN emerges in this position in the former case but not in the latter. We are not
committed to how the initial computation happens here,
but the qualitative difference observed at the verb position
across experiments suggests that somehow the mismatch
between the coordinated subject and its verb is recognized
more slowly than the more prominent inflectional mismatch in Experiment 1.
From a linguistic point of view, this is not surprising.
There is considerable evidence that the coordination morpheme and (and its equivalent in other languages), unlike
number inflection, does not insert a plural feature value.
(5), for instance, shows that conjunction of singular quantificational nominals only marginally triggers plural agreement, in Italian as in English; (6) shows that the
conjunction of certain mass nouns inside a noun phrase
does not license a plural determiner in Italian, though it
can trigger plural verb agreement (Heycock & Zamparelli,
2005; the phenomenon is even more visible in English in
the contrast between the acceptable this boy and girl are
dancing together and these (two) boy and girl are dancing
together); finally (7) shows that the conjunction of sentential subjects, which arguably carry no number feature, triggers singular verb agreement (Zamparelli, 2008).
(5a)
(5b)
(6)
(7)
Nessun linguista e nessun filosofo pensa/pensano
che il linguaggio sia facile
No linguist and no philosopher thinks [+S]/think
[+P] that the language is easy
Ogni genitore ed ogni insegnante voleva/volevano
parlare
Every parent and every teacher wanted [+S]/
wanted [+P] speak [+INF]
La/Le tua pazienza e determinazione sono ben
note a tutti
The [+S]/the [+P] your patience and
determination are well-known [+P] to
everybody
[Che Marco sia qui] e [che Maria sia partita]
sembra strano/sembrano strani
[that Marco is here] and [that Maria has left]
seems strange [+S]/seem strange [+P]
Some authors (Osterhout et al., 2004) have questioned
the reliability of the LAN effect as an index of morphosyntactic processing. This is due to the fact that while some
agreement relations elicit a LAN (subject-verb agreement),
others do not (e.g. anaphoric agreement, for a comparison
see Osterhout & Mobley, 1995). In our opinion, this dissociation is not accidental but could reflect distinct processing difficulties related to the structural properties involved
in the resolution of the agreement relation in most cases.
Unfortunately, the agreement structures implemented in
our two experiments vary on a number of dimensions. First
of all, the inflectional mismatch in Experiment 1 is less
complex and easier to detect compared to that of Experiment 2. Syntactic complexity has been shown to elicit only
a P600 component more evident in its earlier stage (Kaan,
Harris, Gibson, & Holcomb, 2000; Osterhout & Holcomb,
1992); this component is morphologically very similar to
the one reported for the mismatch between a conjoined
noun phrase and its verb in Experiment 2. Secondly, while
the subject-verb mismatch in Experiment 1 is determined
only by the inflectional morphology of the noun phrase in
subject position, this type of morphological information is
underspecified on the subject in Experiment 2 (see examples 5–7): it could be that the operation that controls for
the consistency between subject and verb features does
not have as a target inflectional information, but information that directly maps onto the referent information. Consequently, the plurality of a conjoined noun phrase would
be notionally more complex (Heycock & Zamparelli, 2005),
since the number value has to be computed from the
semantics of the two singular referents (much as in Marci
told Annaj that theyi+j should leave). The processing stage indexed by the LAN could then be sensitive to the formal vs.
notional nature of the agreement relation. Thirdly, the local
relation between the verb and the preceding noun in our
structures is different: while the noun preceding the singular verb in Experiment 1 is plural (. . .fratelli giunse. . . – siblings arrived [+S]), in Experiment 2 it is singular (. . .sorella
giunse. . . – sister arrived [+S]). It should be noted that
attraction phenomena are stronger with singular subjectplural verb configurations (see Pearlmutter et al., 1999;
N. Molinaro et al. / Journal of Memory and Language 64 (2011) 211–232
Wagers et al., 2009), while the configuration we studied in
this paper was plural subject-singular verb. Nevertheless,
we cannot exclude that this difference affected the processes correlating to the LAN (a component shown to be
sensitive to the inflectional morphology of two structurally
related constituents in a sentence context, Barber &
Carreiras, 2005; Friederici, 2002; Molinaro, Vespignani,
et al., 2008). Fourthly, the verb position in the linear order
of the sentence is different across experiments (in third position for Experiment 1, and in sixth position in Experiment
2). Given that some components (such as for example the
N400, Kutas et al., 2006) vary systematically with word position, waveform comparison across word positions is
inherently problematic. However, Barber and Carreiras
(2005, see also Molinaro, Kim, et al., 2008) directly compared the detection of a syntactic violation in different sentence positions, reporting a smaller P600 at the beginning
of the sentence compared to a later position; this difference goes in the opposite direction compared to our study,
where a mismatch in an earlier position elicited a larger
P600 compared to a later position. Thus, in our opinion,
the different agreement relation implemented across
experiments is crucial in explaining the different electrophysiological patterns observed.
In order to better detail the factors that elicit the LAN
component, further studies on the processing of different
types of conjoined noun phrases are needed. Nonetheless,
the present findings are suggestive of different processing
routines that could be involved in agreement computation.
Conclusions
Coherently with previous studies (see also Molinaro,
Kim, et al., 2008; Vespignani et al., in press) we have shown
that when a morphosyntactic mismatch is detected, the system performs an immediate interpretation of the ungrammaticality, selecting a single value that makes the whole
sentence representation steadier, otherwise the processing
of an ungrammatical phrase marker cannot proceed (Frazier
& Clifton, 1996). These findings do not provide evidence for
any specific model of sentence comprehension. For example,
our main finding is that subject number (when inflectionally
derived) is revised when a mismatch is detected at the verb;
this could result in a single parse in working memory or multiple parses where the revised parse is simply the most active. However, it is important to note that when
encountering a number mismatch, an immediate regularization of the ungrammatical input is pursued in order to create an internal well-formed representation of the sentence.
We have provided evidence for number agreement mismatches, but the same principles could potentially be extended to all types of morphosyntactic mismatch (see also
Meng & Bader, 2000). Critically, on-line repair is not only
sensitive to the formal properties of the input sentence,
but evaluates every type of relevant information (as for conjoined phrases, see Heycock & Zamparelli, 2005).
Acknowledgments
We are grateful to Arthur Samuel, Itziar Laka, Horacio
Barber, Margaret Gillon-Dowens, Andrea Martin and
231
Simona Mancini for useful comments on the present paper.
Part of the research funds were provided by a PRIN 2005
Grant to R.J. N.M. is partially supported by the ‘‘Juan de
la Cierva’’ program from the Spanish Ministry of Education
and Science. Special thanks to Lyn Frazier.
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