The role of temporal segmentation markers
in discourse processing 1
Yves Bestgen° and Wietske Vonk*
°Fonds national de la recherche scientifique
Université catholique de Louvain
Place du Cardinal Mercier, 10 B1347 Louvain-la-Neuve Belgique
[email protected]
* Max Planck Institute for Psycholinguistics and University of Nijmegen
ABSTRACT.
Recent studies have shown that temporal expressions like around two o'clock and
then are used by speakers and writers to signal thematic shift, and that and is used to signal
continuity in narratives. The present paper focuses on the comprehension function of these
markers. The role of the markers was investigated by measuring the availability of words
from the preceding text. Results from three experiments suggest that temporal markers modify
the availability of preceding words. Segmentation markers like around two o'clock and then
reduce this availability while continuity markers like and improve this availability. These
results are compatible with the hypothesis that segmentation markers lead readers to not
integrate new information with preceding information, but to put the new information into a
separate structure.
.
In the last ten years, corpus analysis and experimental research showed that
speakers and writers exploit devices like punctuation, referential expressions, and
temporal expressions to highlight theme shifts in discourse (Bestgen, 1992; Bestgen
& Costermans, 1994; Costermans & Bestgen, 1991; Fayol & Abdi, 1988; Peterson
& McCabe, 1991; Segal, Duchan, & Scott, 1991; Vonk, Hustinx, & Simons, 1992).
It is generally postulated that these segmentation markers should keep listeners and
readers from trying to relate the new incoming information to the preceding
information. Do they really help readers and how? After describing some temporal
expressions used by speakers and writers to signal the segmentation of their
discourse, the present report will focus on the role of these temporal segmentation
markers during the comprehension of text.
1
Yves Bestgen is supported by the Belgian Fund for Scientific Research.
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Temporal markers of segmentation
The linguistic devices used by speakers and writers to express temporal relation
between successive actions or events have been the subject of a large number of
linguistic and psycholinguistic studies. These studies have shown that the simplest
way for the speaker or the writer to accomplish this task is to express two
subsequent actions in two juxtaposed sentences: "I woke up. I had breakfast." Since
Reichenbach's (1947) seminal work, a number of writers have quoted this strategy as
the default process. This simple strategy implicitly indicates that the second event
follows the first (Dowty, 1986; Hinrichs, 1986; Partee, 1984). The strategy can be
modulated to highlight the continuity or the discontinuity of actions or events by
introducing a connective between the two sentences (Fayol, 1986; Segal et al.,
1991). For continuity, the preferred connective is the asymmetrical and (Lakoff,
1971). For discontinuity, people prefer to use then, next, or afterwards. These
devices place the second (new) event in relation to the preceding one by using an
intrinsic time scale that is internal to the narrative. However, they give only partial
information about the temporal organization of the narrative since the amount of
time spent in each action must be determined by context (Moens & Steedman,
1988). Speakers and writers can improve on this by using an absolute reference
framework, indicating explicitly the time of the day when an action started (e.g.,
around 10 o'clock). Following Ehrich and Koster's analysis of spatial marker in
description (1983), Costermans and Bestgen (1991) called this kind of temporal
indication an anchorage marker because it anchors the starting time of an action in
an absolute time scale external to the narrative. In some sense, it gives a
synchronization signal to the addressee.
Concentrating on simple narratives about daily events, Costermans and Bestgen
(1991) have argued in favor of the discourse structuring function of these temporal
expressions. In a corpus analysis of forty daily events, they observed that speakers
introduced anchorage markers and temporal adverbs when there was a theme shift in
the activities, but that speakers in cases of high continuity either did not use any
specific device or used and. These observations were extended and confirmed in
experimental studies in which subjects were given the gist of narratives that they had
to communicate either orally or in writing (Bestgen, 1992; Bestgen & Costermans,
1994; Costermans & Bestgen, 1991). For instance, Bestgen (1992) analyzed the
development of the child's capacity to organize discourse both cognitively and
linguistically. Children of six, eight, and eleven years old, as well as adults, had to
transform a series of pictures into a story. Later in a metacognitive task, these
subjects were asked to describe the structure perceived in the content of the
narrative. Results indicated that children as young as eight express the hierarchical
structure of a narrative by means of the different classes of temporal markers
presented above.
The functional organization of these four temporal devices (i.e., the anchorage
marker, then and other temporal adverbs, no temporal expression, and and) is
Temporal markers of discourse structure 3
summarized in Figure 1. The vertical dimension displays the strength with which
they highlight the (dis)continuity in narratives. And marks high continuity between
the actions or events described in two sentences. Then marks discontinuity. The
anchorage marker signals high discontinuity.
Continuity
And
I woke up
and I had breakfast
(nothing)
I woke up
I had breakfast
Sequencer
I woke up
then I had breakfast
Anchor
I woke up
around eight o'clock I had breakfast
Discontinuity
Figure 1. Functional organization of the four temporal devices.
Segmentation markers and comprehension.
The temporal markers outlined above belong to the general class of discourse
markers (Redeker, 1991; Schiffrin, 1987), that also includes cue phrases like now or
first (Grosz, Pollack and Sidner, 1989) and text-signaling devices like headings,
pointer words or typographical cues (Lorch, 1989). In general terms, these devices
point out specific aspects of the content of a text or express the semantic and
pragmatic connections between discourse segments. We use the term "segmentation
markers" to refer more specifically to the second function: signaling topic continuity
and discontinuity.
This paper addresses whether segmentation markers modify the processing of
text. A few previous studies have tried to show an effect of various segmentation
markers on comprehension, but the results were largely negative. Stark (1988) found
no effect for the presence and the position of paragraph marks on a number of
relevant variables (e.g., total reading time and ratings of text coherence, text quality
and reading ease). Similarly, Peterson and McCabe (1991) found that connectives
4 Version finale dans Discourse Processes, 19 , 385-406..
did not improve narrative comprehensibility. Fayol (1989) was able to show an
effect of the misuse of punctuation marks on total reading time and question
answering, but these results were inconsistent across age groups.
These studies do not support a general effect of segmentation markers on
comprehension. Vonk et al. (1992) were able to draw a different conclusion,
however, by testing a specific hypothesis about the effects of segmentation markers
in on-line processing of texts. They investigated the discourse function of referential
expressions that give more information than needed to identify the referent (i.e., a
noun phrase when a pronominal anaphor is sufficient). Having shown that these
overspecified expressions can act as segmentation markers, they next studied the
impact of these expressions on discourse processing. Using a probe recognition task
that directly tapped the accessibility of words encountered in the preceding part of a
text, these authors found that preceding words are less available to the reader after
an overspecified expression. Readers took more time to say that they had seen a
given word after such an overspecified expression.
This observation can be interpreted in line with current conceptions of discourse
comprehension. Understanding a text is generally seen as an incremental process in
which new sentences are integrated, by default, with the preceding ones. This
mechanism has sometimes been called the nextness principle (Ochs, 1979). Ohtsuka
and Brewer (1992) propose two principles that are very similar to the nextness
principle: The Immediate Integration Principle (Discourse comprehension is
facilitated when new information is introduced into the discourse in such a way that
it can be integrated immediately into an already constructed model of underlying
event structure), and the Consistency principle that adds that the new information
should be attached to the preceding, just comprehended information. In
Gernsbacher's structure building framework (1990), the mechanism is a mapping
process that allows increasing the size of a substructure by integrating the incoming
information. The integration process is facilitated when writers linguistically express
the relations that link two contiguous statements (Halliday & Hasan,1976; Myers,
1991; van Dijk & Kintsch, 1983). However, when new information is less coherent
or not coherent, for instance when there is a theme shift (Vonk et al., 1992), the
integration process does not succeed, and readers are led to construct a new partition
in their discourse representation. Consequently, previous information is no longer in
the ongoing substructure, and readers have difficulties accessing this information
(Anderson, Garrod & Sanford, 1983; Gernsbacher, 1990; Vonk et al., 1992). In this
framework, the role of a segmentation marker is to signal the presence of a theme
shift, and thus to prompt the readers to start the construction of a new substructure.
This line of reasoning predicts that readers should encounter difficulties accessing
old information after reading a segmentation marker, even when there is no theme
shift, and this is the result observed by Vonk et al. (1992).
The first goal of the present paper is to expand and generalize Vonk et al.'s study
using another kind of text and marker. While that study investigated the role of
overspecified referential expressions in expository texts, this paper analyzes the role
Temporal markers of discourse structure 5
of temporal markers in narratives. Being able to generalize the results of Vonk et al.
across a new type of text and a new type of marker would bring strong support to the
claim that segmentation markers modify the availability of old information.
However, there are at least two possible reasons why this generalization will be
difficult to make. First, expository texts are usually more difficult to understand than
narrative ones. If readers rely more on segmentation markers when the text is more
complicated, it is possible that segmentation markers are less effective with
narratives. Second, concerning Vonk et al.'s markers, one can argue that an
overspecified referential expression, which is the subject of a sentence, is
particularly central to the construction of the mental representation of a discourse
while temporal markers are less central, and thus can be disregarded by readers.
Experiment 1 attempted to generalize Vonk et al.'s results by showing that the
strongest temporal marker (i.e., the anchorage marker) reduces the availability of
words from the preceding text.
In the two subsequent experiments, we took a closer look at the impact of
segmentation markers on the availability of previous information. In the second
experiment, we compared the four levels of temporal markers presented in Figure 1.
As indicated above, production studies have shown that temporal markers can be
located on a continuity/discontinuity dimension. We tested the comprehension
corollary of this dimension by comparing the effect of these four levels on the
availability of old information. Specifically, a marker used to highlight the most
important breaks should reduce the availability of old information the most. The
third experiment further considered the function of and in signaling a high level of
continuity.
EXPERIMENT I
Subjects read simple narratives, presented in short segments of two to five
words, at a self-paced rate. At some points in each text, they had to indicate whether
a word was or was not present in the preceding part of the text (probe recognition
task). In the experimental trials, the content of the segment just before the probe was
manipulated: in one version of the text, this segment contained an anchorage
marker, while, in the other version, it contained a number of words of the same
length that expressed a normal continuation for the narrative. We hypothesized that
subjects should be slower in indicating that a word was present in the text after an
anchorage marker than after no temporal marker.
Method
Subjects
Twenty subjects, all students at the Catholic University of Louvain and native
speakers of French, took part in the experiment.
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Materials
The materials consisted of 12 experimental, 20 filler and three practice texts.
They were all simple narratives about the actions undertaken by one or more
characters. These texts were divided in short segments of two to five words. The
texts were 5 to 8 sentences long (13 to 24 segments). Table 1 shows the original
French version of one of the experimental texts and its English translation.
Two versions of each experimental text were constructed. They were identical up
to a critical sentence. In the marked condition, the first segment of this critical
sentence contained only an anchorage marker (mean length: 3.25 words, 17.08
characters). In the unmarked condition, this first segment was just a simple
continuation and contained approximately the same number of words and characters
(mean length: 3.17 words, 16.50 characters). From the critical segment on, the two
versions differed in their contents, with the marked version expressing a
discontinuous content.
For each experimental text, we chose a probe word in the sentence immediately
preceding the critical sentence. Probe words were always singular nouns. There
were one or two segments between the probe word and the critical segment.
Because half of the experimental probes were presented immediately after a
temporal phrase, non-experimental probes were presented to obscure the purpose of
the study. Each text contained one to three probes. Subjects were informed that if a
second or third probe was contained in the text, the word had always appeared after
the last preceding probe presentation. Sixty-five probes were presented; 33 of them
were positive trials. The experimental probe was the first probe in seven texts, and
the second probe in the five other texts. In these five texts, there were at least nine
textual segments between the first filler probe and the experimental probe. The
words that did not appear in the text were related to the content of the text, e.g., the
word drink for a text that describes a man who is eating in a restaurant and has
ordered a beer and a coffee.
Design
Two counterbalanced sets of materials were constructed. In each set, six texts
were in marked condition, and the other six in the unmarked condition. Across the
two sets, each text appeared once in each experimental condition. These two sets of
materials were given to two randomly selected groups of subjects. Ten different
random text orders were created and each one was used for only one subject in each
group.
Procedure
The experiment was run on an Apple Macintosh Computer (SE30). Segments
were presented left justified in the vertical middle of the screen with a nonproportional font (Courier 14). Probe words were centered on the horizontal and
vertical dimension and presented in the same font as the text.
Temporal markers of discourse structure 7
Ce samedi
This Saturday
Pierre est allé
Peter went
au zoo
to the zoo
avec son papa.
with his father.
Ils ont pris
They went
XXXXX
samedi
Saturday
le train.
by train.
Ils ont commencé
They began
par visiter
by visiting
le bâtiment
the building
des reptiles.
of reptiles.
Ils se sont arrêtés
They stopped
devant chaque cage
in front of each cage
pour lire
to read
les notices explicatives.
the explanatory notes.
Unmarked version
ils ont regardé
They were looking at
XXXXX
cage
cage
un énorme cobra
a big cobra
en train de dîner
eating its diner.
Marked version
Vers midi trente
Around twelve thirty
XXXXX
cage
cage
ils ont été dîner
they went to eat
au self-service.
at the cafeteria.
Note: "samedi" (Saturday) was a non-experimental probe. "cage" (cage) was the
experimental probe.
Table1 : Example of the materials used in Experiment 1.
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The presentation of each new text was preceded by a sentence that prompted the
subject to press the space bar. The key press caused the first segment to appear on
the screen, followed by the other segments as soon as the subject pressed the key.
After the critical segment the key press produced a row of five X's in the middle of
the screen. After 500 msec, the X's were replaced by the probe word. Subjects had to
indicate whether the word had occurred or had not occurred in the text by pressing
one of two keys on the keyboard, labelled "yes" and "no". The screen was then
cleared, and 500 msec later the following segment of the text was presented. Finally,
each text presentation ended with an obligatory three-second pause. Subjects were
allowed to rest between the texts. Subjects were instructed to use their left hand to
press the space bar and their right hand to press the "yes" and "no" keys, the index
finger for yes and the middle finger for no.
The task was explained to the subjects with the help of an example printed on
paper. After reading the written example, subjects processed this example on the
computer and completed two other practice texts before beginning the experiment.
Subjects completed the experiment alone in the room.
To insure that subjects tried to understand the content of the texts, and not only
read to perform the probe recognition task, subjects were informed that after the
reading task they had to discriminate summaries of texts presented to them from
summaries of other texts. After the reading task, subjects were debriefed, and no
discrimination task was administered.
Results
Probe recognition time was measured as the time between the onset of the probe
word on the screen and the press of one of the answer keys by the subject. Nine
reaction times (3.75%) were discarded because subjects answered incorrectly to the
probe. In addition five reaction times that were 3 or more standard deviations from
the mean were discarded, leaving a total of 226 reaction times (94%) out of the
original 240 to be analyzed .
For each subject and for each text, a mean response time to the probe word was
calculated for both conditions. The mean reaction time across subjects was 1200
msec in the marked condition and 1102 msec in the unmarked condition. A t-test for
repeated measures revealed this difference was significant, in both the subject
analysis (t1(19)= 2.17; p<0.05), and the item analysis (t2(11)= 3.51; p<0.01).
Subsequent analyses showed no statistically significant differences for the reading
time of the critical segments.
Discussion
This experiment confirmed our hypothesis: the presence of a temporal
segmentation marker reduces the accessibility of preceding information. Still, some
Temporal markers of discourse structure 9
methodological questions about this experiment must be raised.
First, subjects were asked to answer more than one probe word in each text. The
aim of this procedure, as advocated by Kintsch and Mross (1985) in the case of a
lexical decision task, was to prevent subjects from noticing the factor manipulated in
the study. The drawback of this procedure is that it probably increased the salience
of the probe recognition task for the subjects. It seems difficult however to see how
this can be used against the conclusion of the study because if the subjects directed
their attention toward the words, for instance by trying to memorize them, this could
only reduce the effect of a discourse factor like the presence or absence of a
segmentation marker.
A more problematic methodological factor in this experiment is that the critical
sentences were not the same with respect to their semantic content: that is the
marked sentence expressed a theme shift while the unmarked sentence contained no
such shift. At first glance, this may not be an important problem because subjects
read the content of the thematic shift only after answering the probe. However, they
saw the first segment of the critical sentence with its continuous content in the
unmarked condition before they answered the probe. One can wonder whether the
effect observed is due to the segmentation marker, which impairs the access of the
preceding information, or to the continuous content of the very first segment in the
unmarked condition, which possibly could improve the access of the preceding
information. The second experiment controls for this factor by using critical
sentences of the same meaning and in most conditions exactly the same words.
A limitation of Experiment 1 is that it opposed only two of the four temporal
marking cues as presented in Figure 1. Earlier studies (Bestgen, 1992; Costermans
& Bestgen, 1991; Bestgen & Costermans, 1994) concluded that two kinds of
segmentation marker are produced (anchorage marker and then) if discontinuity is
expressed, and that no marker is used or and is produced to express continuity.
Anchorage markers are used for the most important theme shifts while and is used
in case of very high continuity. One aim of the second experiment was to determine
if the same gradient could be observed in comprehension.
EXPERIMENT II
In Experiment 2, four devices that express the temporal relation between
successive actions were compared for their strength in reducing the availability of
preceding information. These devices, in order from signaling the most important
discontinuity to the most important continuity, were: anchorage marker, then, no
marker, and. Subjects were presented texts, sentence by sentence in a self-paced
paradigm. Once in each text, they were asked to decide whether a word was present
or not in the preceding sentences. The sentence just preceding the probe was varied.
At the beginning of the sentence, one of the three temporal markers was presented or
no marker introduced the sentence. We predicted that reaction time to the probe
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should be linearly related to the segmentation strength of these four devices, i.e., the
reaction time should increase in the order: and, no marker, then, and anchorage
marker.
Method
Subjects
Twenty subjects, all students at the University of Louvain, took part in the
experiment. All subjects were native speakers of French.
Materials
The materials consisted of 16 experimental, 16 filler and three practice texts.
Four of the experimental texts were modified versions of filler texts from
Experiment 1. All other experimental texts were the slightly modified experimental
texts of Experiment 1. The texts were 5 to 10 sentences long. Table 2 shows the
original French version of one of the experimental texts and its English translation.
For each of the experimental texts, one sentence between the fourth and seventh
sentence served as the critical sentence. Four versions of the critical sentence were
constructed: an anchorage version, an unmarked version, an and version, and a then
version. The anchorage version was constructed by introducing a temporal anchor in
the beginning of the original sentence (mean length of the sentences in the anchor
condition: 9.44 words, 48.75 characters). For the unmarked version the original
sentence was modified by adding approximately the same number of words and
characters as the temporal anchor contained (mean length of the sentences in the
unmarked condition: 9.44 words, 47.88 characters). The and and the then critical
sentences were constructed by adding these connectors to the unmarked sentence.
So, the critical sentence in the two last conditions was always one word (two or four
characters) longer than the unmarked critical sentence. In contrast to the first
experiment, the texts did not have punctuation marks, because the insertion of a fullstop before and is not very common in French.
For each experimental text, the probe word was chosen from the sentence
preceding the critical sentence.The filler texts were identical to the ones used in the
first experiment except that only one probe word was selected for each text. These
probe words did not appear in the texts and were presented to the subject after an
arbitrarily chosen sentence between the third and the seventh sentence of the filler
texts.
Temporal markers of discourse structure 11
après son travail Monique entra dans une librairie
after her work Monique went into a bookshop
elle prit un journal
she took a newspaper
elle chercha un livre pour sa mère
she looked for a book for her mother
and
Unmarked
Sequence marker
Anchorage marker
et elle se rendit compte que le magasin allait être fermé
and she realized that the bookshop was closing
elle se rendit compte que le magasin allait être fermé
she realized that the bookshop was closing
puis elle se rendit compte que le magasin allait être fermé
then she realized that the bookshop was closing
vers six heures elle vit que le magasin allait fermer
around six o'clock she saw that the bookshop was
closing
Probe recognition word
XXXXX
mère
mother
elle prit un roman sur la table
she took a novel from the table
elle se dirigea vers la caisse
she made her way to the cashier
Tanle 2 : Example of the materials used in Experiment 2.
Procedure
The procedure was similar to the one used in the first experiment except for the
following modifications. First, as indicated above, the texts were presented sentence
by sentence and not segment by segment. Consequently, the probe was presented
not immediately after the marker, but after the complete sentence. Second, only one
probe was used in each text to prevent subjects from paying too much attention to
the probe recognition task. Finally, to insure that subjects tried to understand the
content of the texts, and not only read for solving the probe recognition task,
subjects were prompted, after the last sentence of ten texts, to write a one sentence
continuation to the narrative.
Results
The answers to the 320 experimental probes were analyzed. Thirty-six reaction
times (11.25%) were discarded because the subject answered the probe incorrectly.
An analysis of the distribution of these errors by texts showed that the probe word of
one text was correctly answered by only 9 (including one outlier) of the 20 subjects,
while the other texts were correctly answered by at least 14 subjects. Moreover, in
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the anchorage marked condition, this text was correctly answered by only one
subject. Various hypotheses can be proposed to explain the high difficulty of the
probe in this text2. We chose to disregard this text in all the analyses. Four reaction
times that were at least 3 standard deviations from the mean were also discarded.
The four means, ordered as predicted, are presented in Figure 2. Two analyses
were performed on the data: one treating subjects as a random factor (F1) and one
treating items as a random factor (F2). The predicted monotonic trend, tested by an
F test for linear trend (Braver & Sheets, 1993), was significant (F1(1,19)= 7.47;
p<0.025 and F2(1,14)= 6.56; p<0.025).
Although there was no significant difference between the and and the unmarked
conditions (F1 and F2 <1), nor between the then and the anchor conditions (F1 and
F2 <1), the one degree of freedom contrast between the two continuity markers
(and, unmarked) and the two discontinuity markers (then, anchor) was significant
(F1(1,19)= 6.90, p<0.025; F2(1,14)= 6.87, p<0.025).
1300
Reaction Time
1280
1260
1240
1220
1200
And
No marker
Then
Anchor
Marker Condition
Figure 2. Reaction time (in msec) to the probe recognition word as a function of
the marker condition (Experiment 2).
Discussion
These results support those of Experiment 1 by indicating that temporal markers
2
This text was one of the four filler texts from the first experiment that were adapted to fill
the role of experimental text in the second experiment. The test sentence was avec l'aide des
autres animateurs il forma des groupes ("with the help of the other youth leaders, he formed
the groups") and the probe word was aide ("help"). At least two reasons can justify the greater
difficulty of the probe word. First, it is introduced in an adverbial phrase which is very
secondary to the theme of the text. Second, at a morphological level, subjects had seen the
lexical string l'aide in which l' is the reduced form of la while the probe word was aide.
Temporal markers of discourse structure 13
of segmentation reduce the accessibility of old information. Markers that are used by
speakers and writers to indicate a high degree of discontinuity result in the most
reduction in accessibility, while markers that are used to signal a high degree of
continuity result in the most accessibility. The results in Figure 2 indicate also that
the four conditions may be divided into two categories: and and unmarked versus
then and the anchorage marker. Compared to the unmarked condition, then and the
anchor act as markers of segmentation, but the case of and is less clear-cut. Our
results do not indicate that and acts as a marker of high continuity: The difference
between the and condition and the unmarked condition was not significant.
This lack of effect could be due to the fact that and fulfills various discourse
functions in texts. Although and can act as a marker of high continuity, it can also be
introduced between two sentences which are semantically not very related, but
which belong to the same discourse (Bestgen, 1992; Costermans & Bestgen, 1991;
Peterson & McCabe, 1987; Schneuwly, 1988). Furthermore, it can be used to signal
the end of a narrative (Bestgen, 1992; Fayol, 1986; Mouchon, Fayol, & Gombert,
1989). In this case, and does not express local continuity, but closes the list of
sentences that form the text. This interpretation is possible in the present experiment
because the experimental procedure didn't allow subjects to predict the length of the
texts as the sentences appeared one at a time in the middle of the screen and the texts
varied greatly in length (between 5 and 10 sentences). Inspection of the materials
suggests that the target sentence was indeed the final sentence in two texts, and that,
in another text, the first word of the last sentence was and. These other discourse
functions of and could explain that in relatively long texts this connective is not very
different from the unmarked condition. Could we conclude from this discussion that
the picture would be different when and is used to connect the only two sentences of
a very simple paragraph? In this case, and should act specifically as a marker of
high continuity.
Data collected by Caron, Micko, and Thüring (1988) support instead the
hypothesis that and has no effect on the integrating process in two-sentence
paragraph. They asked German and French subjects to learn pairs of one-clause
sentences that were either connected by because or and or that were simply
juxtaposed. They found that because improves the recall of the second sentence
when cued by the first sentence as compared with the no connective condition, but
also as compared with the and condition. In two of their three studies, and produced
a lower recall than the no connective condition. These observations, which are
interpreted by Caron et al. in terms of "more or less successful construction of an
integrated representation" (p.322), seem to call into question the continuity function
of and even in two-sentence paragraphs. Still, the results of Caron et al. (1988)
could be due to some characteristics of their materials. In order to study the
construction of inferences, they used semantically unrelated pairs of sentences like
"The priest was able to build the new church. The computer had made a serious
error." By doing this, they violated the constraint of common topic (Fillenbaum,
1977). In Caron et al.'s experiments, and is used as a logical operator that can
14 Version finale dans Discourse Processes, 19 , 385-406..
connect any proposition with any other proposition. One can wonder about the
possible generalization of such kind of studies to the everyday use of connectives
(Fillenbaum, 1977). Furthermore, the tense of the verbs in Caron et al.'s sentences
(past for the first verb and pluperfect for the second) allowed "subjects to consider
the first sentence as describing a state, and the second one as describing an event
antecedent to that state" (p.321), an interpretation that contradicts the temporal
orientation of and.
In summary, the absence of a significant difference between the and condition
and the unmarked condition in Experiment 2 can be explained by the various
discourse functions that this connective can play in relatively long texts, functions in
which and is not a marker of continuity. Another possibility is that and has no effect
on the processing of continuity and discontinuity in long texts nor in short texts,
because this connective is simply disregarded by readers. A third experiment was
conducted to test the integration function of and in two-sentence paragraphs. We
presented subjects with pairs of sentences connected by and, no connective or then.
We addressed also the semantic relatedness question, raised above, by manipulating
the thematic continuity between the two sentences of each pair.
EXPERIMENT III
Subjects read two-sentence paragraphs, presented one word at a time by means
of a Rapid Serial Visual Presentation. After reading the two sentences, subjects had
to decide whether a sequence of letters was a French word or not (lexical decision
task3). In the experimental trials, the target sequence of letters was always a word,
which had appeared in the first sentence of the corresponding pair. Two factors were
manipulated.
First, the two sentences were connected by then or and or were not explicitly
connected. Our prediction was that the availability of words from the first sentence
should be affected by the type of connective used. And should instruct the subject to
integrate the two sentences into one structure. Then should force subjects to not
integrate the two sentences, but to put each one in its own structure. When there is
no marker between the two sentences, subjects would be free to construct a new
structure or to map the second sentence into the ongoing one depending on the
continuity between the information expressed by the two sentences. Reaction times
in this unmarked condition should thus fall between the and and the then conditions.
Second, we constructed for each first sentence two possible second sentences
that varied in how much they related to the first sentence. The related sentence
expressed an action related to the action described in the first sentence and
performed by the same actor. The less related sentence expressed a different action,
3
We introduced this procedural modification because in a self-paced paradigm using only
two sentence texts, subjects could adopt a specific memory strategy to recognize the probe.
Temporal markers of discourse structure 15
but performed by the same individual. This factor was introduced in the design
because we wanted to address the semantic relatedness question as raised in the
discussion of Caron et al.'s study (1988). It is quite possible that a less related
second sentence reduces the availability of the words of the first sentence by leading
readers to construct two discontinuous structures. Apart from this main effect of
relatedness, an interaction between the topic relatedness factor and the marker factor
may be observed if one of these two factors limits or cancels the effect of the other.
For instance, the marker manipulation could be so strong that the topic relatedness
effect could only be observed in the unmarked condition. Finally, it is possible that
our semantic manipulation would produce no effect at all because the grammatical
subject of both second sentences was always a pronoun that referred to the subject
of the first sentence. This referential continuity could overcome the semantic
relatedness.
Method
Subject
Thirty-six subjects, all students at the Catholic University of Louvain and native
speakers of French, took part in the experiment.
Materials
The experimental items consisted of 36 items about two actions performed by
the same agent. The first sentence contained a word with a length of five to seven
characters that was used for the lexical decision task. This word occurred in half of
the cases at the end of the sentence and in half of the cases just after the main verb.
For each first sentence, two second sentences, of exactly the same length in number
of words, were written: one for the related condition and one for the less related
condition. The former consisted of a sentence that expressed an action very closely
related to the action described in the first sentence; the latter consisted of a sentence
that expressed a different action performed by the same individual. The subject of
the second sentence was always expressed as a personal pronoun which referred to
the subject of the first sentence. In this way, the common topic constraint was
guaranteed. Each item contained 15 words, 7 or 8 in the first sentence and,
respectively, 8 or 7 in the second one. Table 3 shows the original French version of
one of the experimental items and its English translation.
Three versions of the second sentences were constructed: a then version, an and
version, and an unmarked version. The length of the second sentence in each of the
three versions was equalized by adding one word to the unmarked version. This was
done by changing the tense of the second sentence from the "passé simple" (e.g., Il
visita , meaning He visited), which is constructed as the English simple past (He
visited), into the "passé composé" (e.g., Il a visité, meaning He visited), which is
constructed as the English present perfect (He has visited). We chose this
modification because the two tenses are more or less interchangeable in French.
16 Version finale dans Discourse Processes, 19 , 385-406..
More precisely, the "passé-simple" and the "passé-composé" have a very similar
meaning in a narrative. In oral discourse, the "passé-composé" is almost the only
one used, while in writing it is currently more and more used instead of the "passésimple" (Grevisse, 1986). The tense of the first sentence was modified as well in the
Unmarked
Related
Unmarked
Less related
Then
Related
Then
Less related
And
Related
And
Less related
Lexical decision
item
Question
le touriste a fait une photo du monument
the tourist has taken a photo of the monument
il a visité le musée des sciences naturelles
he has visited the museum of natural sciences
le touriste a fait une photo du monument
the tourist has taken a photo of the monument
il a pris un bain plein de mouse
he has had a bath full of bubbles
le touriste fit une photo du monument
the tourist took a photo of the monument
puis il visita le musée des sciences naturelles
then he visited the museum of natural sciences
le touriste fit une photo du monument
the tourist took a photo of the monument
puis il prit un bain plein de mouse
then he had a bath full of bubbles
le touriste fit une photo du monument
the tourist took a photo of the monument
et il visita le musée des sciences naturelles
and he visited the museum of natural sciences
le touriste fit une photo du monument
the tourist took a photo of the monument
et il prit un bain plein de mouse
and he had a bath full of bubbles
photo
photo
le touriste était
the tourist was
en ville
en avion
in town
on a plane
Note: The semantically more correct translation of the French tense passé simple is the
English tense simple past (e.g., il a fait is more correctly translated by he took than by he has
taken).
Table 3 : Example of the materials used in Experiment 3
Temporal markers of discourse structure 17
unmarked condition. Because this supplementary functional word always appeared
before the target word in the first sentence, the number of words between the
presentation of the target word in the text and the presentation of the target word for
the lexical decision was the same in all conditions.
There were 45 filler items, which were similar to the experimental items. In 33
of these items, a pseudo-word was used as target string for the lexical decision task.
In the remaining 12 filler items, a real word, which did not appear in the sentence
was used. The sentences of one third of the filler items were connected by then,
another third by and, and the remaining third were in the "passé composé" without a
temporal connective. Finally, there were eight practice items.
For each item, a question was constructed containing a statement followed by
two possible continuations. The subjects' task was to choose the most probable
continuation. These questions were sometimes related to a word present in the items,
but they could also refer to a possible inference that readers can draw from the
content of one of the sentences or of the sentences in combination. For most of the
experimental items, two different questions were written, one for each level of the
relatedness factor.
Design
Six counterbalanced sets of materials were constructed. Each set contained the
same number of items in each of the six experimental conditions. Across the six
sets, each item appeared once in each experimental condition. The six sets were
given to six randomly selected groups of subjects. Six different random orders were
generated and each one was used for only one subject in each group.
Procedure
The experiment was conducted on an Apple Macintosh computer (SE30). Each
item was presented word by word in the middle of the screen, centered on the
horizontal dimension. A non-proportional font (Courier 14) was used. At the start of
each trial, a fixation pattern (7 asterisks) appeared on the screen. After 500 msec,
this pattern was replaced by the first word that remained on the screen during 300
msec. The next word appeared 16.7 msec later in the same position and for the same
time. After each of the sentences, the screen remained blank for a time period
equivalent to the presentation of two words (634 msec).
After the interval following the second sentence, the lexical decision trial started.
First, two lines appeared, drawn in such a way that one was just above the usual
position of a word and the other just below. After 300 msec, a sequence of letters
was inserted between the two lines. The subjects' task was to indicate whether these
letters formed a French word or not by pressing one of two keys on the keyboard,
labeled "yes" or "no". Index fingers were kept on these keys during the trial.
After subjects pressed one of the keys, the comprehension question appeared on
the screen. The first part of the statement was centered in the middle of the screen.
18 Version finale dans Discourse Processes, 19 , 385-406..
The two plausible continuations appeared below it, one on the left side of the screen
and the other on the right side. The subjects' task was to press the key that was on
the same side as the most plausible alternative. After each trial, subjects were
allowed to rest before they started the next trial.
Subjects were told that they were participating in a study about "delayed
memory" and that they must read two-sentence paragraphs, answering a
comprehension question as fast and as correctly as possible. Subjects were also
informed that between these two tasks, they would have to indicate whether a
sequence of letters was a French word. Although this task was presented as a
distractor task (delayed memory), it was stressed that they had to give their answers
quickly and correctly because otherwise their answer to the comprehension question
could not be considered. These tasks were explained to the subjects in concrete
terms with the aid of an example printed on paper.
Subjects completed eight practice items, followed by the 81 other items. These
81 items were subdivided into nine blocks of nine items. A message printed on the
screen indicated to the subjects the end of each block.
After the experiment, subjects were thanked for their participation and the
experimenter explained the objective of the experiment. In the debriefing, subjects
told that they were unaware of the tense manipulation in the material, and that they
focused on the question answering task as stressed in the instructions.
Results
1020
Related
Less Related
Reaction Time
1000
980
960
940
920
900
And
No marker
Then
Marker Condition
Figure 3. Reaction time (in msec) to the lexical decision word as a function of
the marker condition and the relatedness condition (Experiment 3).
Temporal markers of discourse structure 19
Fifteen reaction times were discarded because subjects made an incorrect lexical
decision. Fourteen reaction times that were at least 3 standard deviations from the
mean were also discarded. In all, less than 2.5% of the data was discarded. Two
analyses of variance were performed: one treating subjects as a random factor (F1)
and one treating items as a random factor (F2). These analyses, both treating the
relatedness condition and the marker condition as within subjects factors, revealed a
main effect of the marker condition (F1(2,70)=5.32, p<0.01; F2(2,70)=5.34,
p<0.01), but neither a main effect for the relatedness condition (F1 and F2 < 1) nor
an interaction between the relatedness condition and the marker condition
(F1(2,70)=1.08, p>0.30; F2 < 1). Although there was neither a global interaction nor
a main effect for the relationship, subsequent analyses were conducted to compare
the two relatedness conditions separately for each marker condition. None of these
analyses reached an acceptable level of significance (the minimum probability value
was greater than 0.15).
The mean reaction times are presented in Figure 3. The three levels of the
marker condition follow a highly significant monotonic trend (F1(1,35)= 9.02,
p<0.01; F2(1,35)= 11.25, p<0.01) that confirms our prediction. Contrary to the
results of the second experiment, the difference between the and condition and the
unmarked condition is statistically significant (F1(1,35)=4.93, p<0.05;
F2(1,35)=5.06, p<0.05). However the difference between the unmarked condition
and the then condition is not significant (F1(1,35)=1.45; F2<1).
Discussion
Results of this third experiment confirm the results of the two preceding
experiments: temporal markers of segmentation reduce the availability of the
information in the first sentence. More importantly, this experiment indicated that
and signals a stronger continuity than when no marker is present.
Our results seem to contradict the observations by Caron et al. (1988) who found
that and did not facilitate the construction of an integrated representation when
compared to the no connective condition. Apart from important differences in the
procedure (cued and free recall versus a lexical decision task), the conflicting results
may be attributed to two important differences in the materials. First, there was no
obvious coherence relation nor cohesion between the sentences of Caron et al.'s
pairs while in our pairs of sentences the subject of the second sentence was always a
pronoun that referred to the subject of the first sentence. In this manner, our pairs of
sentences followed the constraint of common topic that, following Fillenbaum
(1977), is necessary to allow the natural processing of connectives. Second, the
tense of the two verbs in Caron et al.'s sentences contradicts the temporal orientation
of and, since the first verb of a sentence pair was in the simple past and the second
verb in the pluperfect. In our materials, the verbs were in the same tense and each
pair of sentences expressed a possible temporal sequence that agreed with the usual
meanings of and and then. At a theoretical standpoint, it is worth noting that the
20 Version finale dans Discourse Processes, 19 , 385-406..
conclusions drawn by Caron et al. (1988) and by ourselves are very similar:
Connectives are processing instructions that direct the reader in the task of
integrating subsequent information.
A further point of interest concerns the absence of effect for the relationship
between the two sentences of a pair. The kind of relatedness manipulation we used
could be crucial for explaining this absence of effect. Recall that all second
sentences, whether they were more highly related or less related, were about a
common topic: the actor who was the grammatical subject of the two sentences. The
first word of the second sentence in the unmarked condition, or the second word in
the and and then conditions, was always a pronoun referring to this actor, thus
stressing the referential continuity. It is probable that the manipulation of the
relatedness in just two sentences was too weak to impair readers in constructing an
integrated structure.
General discussion
In Experiment 1, words presented before a temporal marker of segmentation
were less accessible than if there was no such marker. Experiment 2 replicated this
observation, but also extended it by comparing four different ways to express the
temporal organization of narratives. It appears that the role of markers in
comprehension parallels their role in production: markers used to highlight the
strongest breaks in the discourse reduced more heavily the accessibility of previous
information while weaker markers had less effect on accessibility. Results of
Experiment 3 indicated, more specifically, that and acts as a continuity marker that
allows a better accessibility of old information as compared to the default strategy of
expressing time structure in narratives (i.e., the simple juxtaposition of two
sentences). These results were obtained in experiments with short narratives and
two-sentence paragraphs. We think that they would generalize to other texts for the
following two reasons. First, temporal markers are used by speakers and writers to
signal the structure of their discourse in experimental studies just as they are used in
naturally observed texts (Bestgen, 1992; Brown & Yule, 1983, pp.95-99;
Costermans & Bestgen, 1991). Furthermore, the observed reduction of availability
can be considered as a local phenomenon that affects the information closely
preceding the segmentation marker.
We were able to generalize the observations made by Vonk et al. (1992) on the
discourse function of overspecified referential expressions in expository texts to the
role of temporal markers in narratives. The theoretical conception underlying this
research is in agreement with Gernsbacher's recent proposals summarized in her
"structure building framework" (1990). Comprehension is seen as an oscillation
between the development of an ongoing structure and the shift to a new one.
Comprehenders integrate the new information with the preceding information as
long as the information is related. When there is a shift in theme, people use the new
information for laying the foundation of a new structure, in which subsequent
Temporal markers of discourse structure 21
related information will be mapped. Information integrated in a structure is more
accessible when people are building this structure. After a shift, information
belonging to the previous structure becomes less available.
In narratives, a few structural principles that lead to the construction of a new
structure have already been pointed out. For instance, Grimes (1975) proposed four
segmentation principles based on the units of time, space, character and theme. A
change in one of these introduces a discontinuity in the narrative. These changes,
together with signals, like hesitation and paragraph indentation, are expected to
announce a change of macroproposition (van Dijk and Kintsch, 1983). For
Gernsbacher (1990), adverbs like then or next can also play this role. Our results
confirm this idea and further suggest that a number of devices that express the
temporal relation between subsequent events play this function. Compared to the
default strategy (i.e., the simple juxtaposition), and signals a high continuity while
then and the anchorage marker signal a high discontinuity. Our data however did not
confirm the hypothesis that then is less powerful than the anchor in reducing the
availability of old information as predicted from production studies (Bestgen, 1992;
Bestgen & Costermans, 1994; Costermans & Bestgen, 1991). Experiments that
exclusively compare these two conditions could be useful to gain power in testing
this prediction. Further experiments are also needed to increase our understanding of
the discourse function of segmentation markers. Specifically, the on-line difficulties
met by readers when they encounter a theme shift should be studied (Bestgen &
Vonk, 1993). The theoretical framework outlined above predicts that theme shifts
should be processed more easily when they are signaled by a marker, because
readers can directly bypass the nextness principle and construct a new structure.
Conversely, a segmentation marker should impair the processing when there is no
theme shift, because it leads readers in something like a discourse garden-path: the
construction of an unneeded partition that must be canceled afterward.
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