Download Eye-movement analysis in reading content words and function words

Eye-movement analysis in reading content words and
function words
Sophie Roussel1, Anne Rohr1, Eric Raufaste 2, Jean-Luc Nespoulous1
1
Laboratoire Lordat – CEA.1941- IFR N°96 - Université Toulouse-II, France
2
Laboratoire Travail et Cognition – UMR5551 du CNRS - Université Toulouse-II, France
Address for correspondence:
Sophie Roussel - Laboratoire Lordat
Université Toulouse-II
Maison de la Recherche
5, Allées A. Machado, 31058 Toulouse
Cedex
France
Email: [email protected]
Tel: (+33) 561-503-594
Fax: (+33) 561-504-918
Running Head: EYE-MOVEMENTS in READING
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ABSTRACT
Detection task studies and studies of eye-movement in reading all pointed
out a differential processing of content and function words. Several
determinants were proposed: grammatical class, word configuration, word
frequency, etc. Although function words are both “short” and “highly
frequent”,
interactions
between
those
factors
were
left
widely
underdetermined. Hence, the present eye-movement study aimed at isolate the
specific effect of grammatical class, controlling other factors, and specifically
frequency and form properties (e.g. word length). Results confirm that
grammatical class induces by itself different attentional patterns with more
fixations on content words than on function words. When words were gazed,
there were longer gaze durations and smaller pupil diameter on content words
than on function words.
Keywords: Reading - Eye-movements - content word – function words
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When reading a text, all words are not read in a similar way. The hypothesis
of a differential processing of content and function words in non-pathological
persons comes from the observation of aphasic patients with agrammatism.
This pathology is characterized by almost systematic omission and/or
substitution of function words in production. Although these typical errors are
present in agrammatic production (Kean, 1985; Menn & Obler, 1990), the
important variability in performances (within task and within subject)
exhibited by those patients suggests a role of factors other than genuinely
linguistic or psycholinguistic ones. It has been observed that an agrammatic
patient could produce function words provided that the experimenter had
drawn explicitly the patient’s attention towards those function words. Hence,
variability in performance might be explained by attentional strategies
(Nespoulous & Dordain, 1991). In other terms, any function word that does
not receive enough attention would be omitted or substituted by this patient. In
non-pathological subjects, studies based on detection tasks also showed a
differential processing of content and function words, the former giving fewer
detection errors than the second (Corcoran, 1966; Inhoff, 1984; Healy, 1994;
Moravcsik & Healy, 1995; Koriat & Greenberg, 1991, 1994; Saint-Aubin &
Poirier, 1997). This effect is known as “the missing letter effect”. The
processing time hypothesis, developed by Healy (1976, 1994; Moravcsik &
Healy, 1995) attribute this effect to the higher frequency of use of function
words. However, according to the structural account developed by Koriat and
Greenberg (1991, 1994), the higher level of omission on function words would
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be due to their grammatical role within the sentence. Function words would
enable the reader to establish a temporary syntactic structure, which would
enable accessing the meaning of text. This meaning is provided by content
words. In order to demonstrate the influence of syntactic factors at the letter
detection level, Saint-Aubin and Poirier (1997) compared omission rates when
a word is employed either as a conjunction or as a noun. Even when the noun
was as frequent as the conjunction, results showed more omissions on the
conjunction. Authors interpreted these results as a specific effect of syntactic
factors on the number of omissions in a letter detection task.
For about twenty years, eye-movement recording enabled a better
understanding of processes in subject’s reading. So, when reading a text, eyemovements may be considered as a spontaneous, direct, and measurable trace
of changes in the attentional focus. According to Posner (1980), any saccade is
preceded by a visual attention shift toward the desired gaze location. This
hypothesis was then developed by Fisher (1986; Fisher & Breitmeyer, 1987),
who suggested that gaze movements follow a series of steps: attentional
disengagement from start location, displacement of attention toward the target
location, and engagement of attention on the new target position. According
to Morrison (1984), access to the meaning of the fixated word (n) permits an
attentional shift toward the next word (n+1). For short function words, the
author emphasizes that the lag between preparation of the saccade toward n+1
and its realization would suffice for the reader to access the n+1 word
meaning. In such case, the saccade might be reprogrammed and n+1 skipped.
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Some other works directed at the study of word recognition in peripheral
vision showed that the proactive processing of a word might be primed in
periphery, before gaze actually reaches it (O’Regan, 1975 ; Rayner, 1979).
Finally, in an overview of twenty years of research on eye-movements in
reading, Rayner concluded: "Although we can easily decouple the locus of
attention and eye-location in simple discrimination tasks (Posner, 1980), in
complex information processing tasks such as reading, the link between the
two is probably quite tight" (1998, p. 375).
A major finding of eye-movement studies is the fact that not all words are
fixated. Particularly, analyses showed that non-fixated words are essentially
function words (prepositions, conjunctions, articles). Even when function
words are fixated, they receive fewer fixations than content words– nouns,
verbs, adjectives (Rayner & McConkie, 1976 ; Rayner, 1977 ; Just &
Carpenter, 1980 ; Rayner & Duffy, 1988). Thus, content words are fixated
about 85% of the time, whereas function words are fixated about 35% of the
time (Carpenter & Just, 1983 ; Rayner & Duffy, 1988). Besides, there are
more multiple fixations (including forward and background fixations) on
content words than on function words. With regard to fixation durations,
function words receive shorter fixations than content words (Just & Carpenter,
1983; Rayner & Duffy, 1988). Studies that used eye-tracking data thus led
their authors to postulate a differential processing of content and function
words.
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The very fact that a reader is able to understand a sentence without having
fixated every word in it rises questions about criteria that determine fixations.
Although these results emphasize a differential processing of content and
function words during reading, variables other than grammatical class can
affect the number and duration of fixations. Actually, variables like word
length, frequency of use, expectancy, might also influence ocular patterns.
Just and Carpenter (1980), who considered gaze durations (i.e., cumulated
duration of all fixations made on the word, either forward or backward)
observed a negative correlation between word frequency and fixation duration.
More precisely, after translating word frequencies with a log function, they
observed a 53ms increase in gaze duration for each log unit decrease in
frequency. Inhoff (1984) reached a similar conclusion for gaze duration, but
not for first fixation duration. With regard to first fixation duration, Inhoff
found that frequent words receive longer fixations than less frequent words.
According to the author, this would be due to the fact that lexical access and
context-based word interpretation would occur simultaneously when
processing high frequency words, that is, during first fixations. To the
contrary, in low frequency words, first fixation durations would only reflect
the time necessary for lexical access, word interpretation being made during
subsequent fixations. Longer fixation durations on low frequency words would
be due to returns (in order to complete processing) and then to new fixations.
Low frequency words would then receive more multiple fixations than high
frequency words.
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Word length also influences the ocular pattern. Rayner and McConkie
(1976) showed that short words (up to three letters) are less fixated, receive
less multiple fixations, and shorter fixations durations than long words (six
letters and more). In order to control for word form (and word length) in
testing the effect of grammatical class, an efficient strategy consists in using
homographic words such that at least one meaning attached to the form
corresponds to a content word and one meaning corresponds to a function
word. From now on, we will name "bi-class" such forms. We also name
"single-class" the forms that are attached to only one class (whether functionor content-word class). An analysis of the crossed effect of grammatical class
and word form led Perrier et al. (1991) to conclude to an effect of grammatical
class on the number and duration of fixations. When confronting the function
word and content word acceptations of a bi-class form, it was found that the
content word was significantly more fixated, received more multiple fixations,
and longer fixations than the corresponding function word.
Despite the fact that those experiments showed an effect of frequency and
length on the number and duration of fixations, none of them demonstrated the
genuine effect of grammatical class controlling for frequency, word length and
word form as the same time. By neglecting the very fact that most function
words are also very frequent and short words, they may have attributed to
grammatical class the effects of frequency or word length.
The mere fact that function words essentially convey information about
structure whereas content words convey information about meanings seems
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sufficient to hypothesize a differential process. With regard to the fundamental
difference between the syntactic and semantic roles of function and content
words, we assume that grammatical class should have an effect by itself. The
experiment that is reported here was designed to provide more evidence of an
effect of grammatical class in reading, controlling for frequency, length, and
word-form.
Our general hypothesis, called “attentional hypothesis” was that the specific
processing of grammatical class influences the reader’s ocular pattern by
determining the level of visual attention. In order to test this hypothesis,
various measures of eye-movements were analyzed. These measures can be
divided into three general categories: (1) number of fixations; (2) gaze
durations; (3) pupil diameters; (4) In addition, we computed a fourth type of
measures, “elusion”, reflecting the degree to which words are skipped. All
those dependent variables relate to visual attention: more fixations, longer
gaze durations are generally considered as cues for strengthened visual
attention. Under controlled conditions of light and emotion, pupil diameters
generally decrease with attention focus.
All variables were computed using the following procedure. Each text was
built around a "target word", either function or content word. First, an area of
interest was defined around the target word of each text. Then variables were
computed for each area of interest and each participant: the number of
fixations that felt in the area of interest, and the cumulated duration of those
fixations (i.e., gaze duration). When the area of interest received at least one
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fixation, the variation in pupil diameter was also computed, otherwise it was
set to zero. Pupil diameter parameters for a particular subject were the mean
and standard deviation in pupil diameter, computed over all the fixations of
this participant. Then for each recorded fixation, a standardized variation was
computed by dividing the difference (current pupil diameter minus mean pupil
diameter) by the standard deviation. For the sake of simplicity, this variable
was labeled “pupil diameter” but was actually a standardized pupil diameter
variation: zero means no variation from the base level, a positive value means
a dilated pupil and a negative value a narrowed pupil. It should be noted that
pupil diameters could only be computed for target items that were fixated
because without at least one fixation, this information is unknown (and is not
relevant).
The forth dependent variable was elusion degree, which represents the
degree to which the word is skipped. To compute elusion degrees, it was first
distinguished between fixations done before and after the participant reached
the end of the text. Let us call “first reading” the former, and “second reading”
the later. Hence, there are three elusion degrees. The strongest, called “total
elusion”, was attributed when the word was completely skipped and coded
“2”. “Partial elusion” was attributed when the word was fixated during either
first or second readings but not both. It was coded “1”. The lowest, called “no
elusion”, is attributed when the word is fixated in both first and second
readings. It was coded “0”.
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Using the four dependent variables, and under the general hypothesis of a
less visual attention granted to function words, we expected to observe (a)
fewer fixations on function words than on content words, (b) shorter fixation
durations on function words, (c) pupil diameters thinner when fixating content
words than when fixating function words, and (d) a higher degree of elusion
on function words than on content words.
METHOD
Participants. Forty students at University of Toulouse II participated in the
experiment on a voluntary basis. All had normal, uncorrected vision.
Materials. The stimuli consisted in a series of seventy-eight short texts (3 to
5 lines; 26.5 words on average). Participants were instructed to read for
meaning. In order to prevent the effects of text order presentation, three
pseudo-random orders were built and each participant read the text in only one
of those orders.
Thirty-six target words and as many distracters were used to elaborate the set
of texts proposed in the experiment. All target words were centered at the 22sd
character of the second line. The second line was chosen because this position
corresponds to the location where reading is disturbed the less: the first line is
generally considered as the reading priming and the last one as its fall.
Moreover, target words were centered at the 22d character because vision
adjustments as a function of field depth complicate the interpretation of ocular
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data from the first and last words in the line: in fact, it may be biased by eye
jumps between lines.
Three lists of target words were built. One list was constituted of 6 bi-class
forms, that is, homographic couples where each form can be interpreted either
as a content word or as a function word. For example, the orthographic
sequence “car” can be interpreted in French as a noun (bus in English) or a
conjunction (for in English). The other two lists have been included 6 couples
of non homographic short words (3-4 letters). Each couple was composed by
one content word and one function word, matched with regard to frequency,
length, and syllabic structure. The normative frequency of words in French
was obtained from the “Brulex” norm (Content, Mousty, & Radeau, 1990). In
order to estimate the role of word frequency in ocular processing, control lists
have been built so that the mean frequency of first control list words (105676
according to Brulex norm) was higher than the mean frequency of words in
the second one (154 according to Brulex norm). For example the content word
"cas" (case), which frequency is 28414, was matched with the function word
"dont" (which), which frequency is 70315, in the first control list and the
content word "cal" (callus), which frequency is 38 was matched with the
function word "via" (via), which frequency is 199, in the second control list.
Apparatus. The experiment took place in a room with no window, under a
dim and constant light. Texts were shown on a 21 inches screen with a
640*480 resolution. Eye-movement recording was made with a monitoring
system manufactured by Applied Science Laboratories (ASL5000). The infra-
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red camera was remote, so that participants’ heads remained free, contrary to
most older studies, where participants had to wear a helmet. Thus, the
apparatus is somewhat more “natural”. The remote optics provided a sample
every 20ms (50Hz). Each sample contains the Cartesian coordinates of the
point of regard, the pupil diameter, and some other information that are not
relevant to the present study (e.g., data about saccades). Fixations were
computed using the EYENAL program provided by ASL with the eye-tracker.
It aggregates contiguous samples that fall within a same location (1° of
vertical and horizontal angles).
Procedure. At the beginning of the experiment, the participant was seated in
front of the computer and was asked to read texts silently, as long as needed
for understanding. They were told that, after reading each text, they would be
required to alert the experimenter and to answer verbally a question about the
text. A first calibration phase was run. Then a text was presented and eyemovement recording started. The participant read the text, alerted the
experimenter who clicked a button to remove the text from the screen and to
stop eye-movement recording. The computer then showed a window with the
first question about the text. The participant answered the question. The
experimenter then sent the next text. Every ten texts, the program
automatically interrupted the experiment in order to make a new calibration
phase. In addition, the experimenter could, at any moment, trigger a
calibration phase. This procedure was repeated until all 78 texts were
processed.
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Analysis. The main independent variable was grammatical class (content vs.
function words). However, in order to control for other variables that may
affect attention, other variables were introduced in statistical analyses: bi-class
membership (bi-class vs. single-class forms) and frequency. Frequency was
computed using the decimal logarithm of the normative frequency of each
word, according to the procedure defined by Just and Carpenter (1980).
Analyses were conducted separately for each dependent variable. The
combined effects of grammatical class, bi-class membership, and frequency
were analyzed using separate univariate ANOVAs on number of fixations,
gaze durations, and pupil diameters. The effects of grammatical class on
elusion degrees were analyzed using three Kolmogorov-Smirnov tests, one for
each level of elusion.
RESULTS
First, 61,4% of content words were fixated vs. 47,9% of function words.
Although content and function words had a significant effect on fixations
numbers, gaze durations and pupil diameters (see Table 1), it would be
premature to conclude that grammatical class actually has an effect on the
observed ocular pattern. In fact, it would neglect the fact that a function words
is also a short and a highly frequent word. For example, Among the target
words of the experiment, there was a significant difference between frequency
in content word and function words, the later being more frequent (3.27 vs.
4.28, t(38) = 2,44; p=.019) and grammatical class. In the sequel of this section,
other variables are controlled.
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--------- Insert Table 1 about here ---------Number of fixations. The analysis of conjoined effects of grammatical class
and frequency on the mean number of fixations on all target words showed a
significant effect of both variables ([F(1,1589) = 5.86; p = .008] and
[F(1,1589) = 19.31; p < .0005]
for
frequency
and
grammatical
class
respectively). This analysis indicated a clear relation between this measure of
frequency and the number of fixation. The number of fixations decreased by
0.04 for each log unit of increase in word frequency (p = .008).
Another variable that is potentially to be controlled is word form. The
analysis limited to fixations on bi-class forms showed fewer fixations on
function words than on content words (0.55 vs. 0.91). The ANOVA showed a
significant effect of frequency and grammatical class on the mean number of
fixations (F(1, 33) = 8.16; p = .002 and F(1, 633) = 10.46; p = .0005, for
frequency and grammatical class respectively). Therefore, grammatical class
still has an effect on fixation numbers independently of both frequency and
word length. Nevertheless, the new variable we introduced, bi-class
membership, is another property of forms that might also have an effect on
global analyses.
The analysis of the conjoined effect of grammatical class and bi-class
membership on the mean number of fixations, controlling for frequency,
showed a significant effect for each variable: F(1, 1587) = 16.15 for
frequency, F(1, 1587) = 18.78 for grammatical class, and F(1, 1587) = 9.21
for bi-class membership (all ps < .001).
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-------------- Insert Table 2 about here -------------Data showed a significant effect of bi-class membership on the mean
number of fixations on content words [F(1, 831) = 16.11; p < .0001], but not
on the mean number of fixations on function words [F(1, 755) = .015;
p > .90]. Besides, results yielded a significant interaction (Figure 1) between
bi-class membership and grammatical class effects [F(1, 1587) = 12.35;
p < .0005].
-------------- Insert Figure 1 about here -------------Gaze duration. Computations about gaze durations are limited to the cases
where the target word were actually fixated. The effects of grammatical class
and frequency on gaze durations were also analyzed. Whether one considers
the whole fixation set or only fixations on bi-class forms, results did not yield
any significant effect of frequency on gaze duration (p > .66 and p > .16 for
all data, and bi-class form data only, respectively).To the contrary there was a
significant effect of grammatical class with content word targets gazed during
454ms vs. 404ms for function word targets [F(1, 873) = 7.26 ; p = .003].
“Elusion” degree. According to our hypothesis, function words tended to
receive no fixation during reading whereas content words tended to be gazed
several times. More precisely, whereas more than 58% of partially eluded
words (n=782) were content words, more than 55% of completely eluded
words (n=717) were function words (Figure 2). Also, 60,2% of completely
eluded words were content words (n=93). Kolmogorov-Smirnov tests showed
a significant difference between function and content word in each of the three
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degrees of elusion (p < .001 for each degree). Anyway, this result is clearly in
favor of our hypothesis: when a word is totally eluded, it is most likely a
function word whereas when a word is not eluded it is most likely a content
word.
--------- insert Figure 2 about here -----------Pupil diameter. Like the number of fixations and gaze duration data, pupil
diameter data showed a differential processing of content and function words.
Pupil diameters were narrowed more on content words than on function
words: in normalized data (calculated for each subject separately), the mean
pupil diameter was -0.011σ for function words and -0.1054σ for content
words. There was no significant effect of frequency on pupil diameters,
whether one considers all the data (p > .95) or only first reading data (p = .75).
In contrast, the effect of grammatical class was significant for first reading
data: the mean pupil diameter was -0.071σ (SE = 0.04σ) when gazing function
words and -0.185σ (SE = 0.04σ) when gazing content words [t(812) = 2.01;
p = .023 one-tailed]. Although smaller for all reading data, the effect was still
significant [t(1, 873) = 1.75; p = .041 one-tailed].
--------- insert Figure 3 about here -----------DISCUSSION
Summary of results. The general hypothesis of this paper is that grammatical
class influences the reader’s ocular pattern by determining the level of visual
attention, independently of other factors such as frequency and word form.
Along with previous studies (Carpenter & Just, 1983; Rayner & Duffy, 1988),
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results showed the expected effect of grammatical class on the number of
fixations and gaze durations. As expected from our attentional hypothesis, we
observed an effect of grammatical class on pupil diameters (i.e., pupil
diameters were larger on function words than on content words). We also
defined an “elusion degree” with "total elusion" for skipped words, "part
elusion" for words fixated during either first or second reading but not both,
and "no elusion" for words that were fixated in both first and second readings).
The later variable showed that most eluded words were more likely function
words whereas less eluded words were most likely content words. In previous
literature, the effects of grammatical class were not dissociated from
frequency effects. To the contrary, in the present experiment, both frequency
and form were controlled. More specifically, two features of word form were
controlled: shape and "bi-class membership". The later feature corresponds to
the fact that a single form may refer either to a single class (function or
content word) or to the two classes. By using bi-class forms, it is possible to
control for the effects of word form. In addition, by combining bi-class and
single-class forms, it is possible to control also bi-class membership. Results
showed (1) fewer fixations on function words than on content words, even
when frequency and form were controlled; (2) shorter gaze durations on
function words than on content words, even when frequency and shape were
controlled; (3) The main effects of both grammatical class and bi-class
membership were significant, even when frequency was controlled. There was
also a significant interaction between grammatical class and bi-class
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membership on the number of fixations: in function words, there was no
significant difference between single- and bi-class forms whereas, in content
words, bi-class forms received significantly more fixations than single-class
forms .
Comparison with previous studies. The comparison with previous studies
shows some points of convergence, but also some differences. Along with
previous studies, a significant effect of grammatical class was observed for all
dependent variables.
According to Rayner’s review (1998), content words are generally fixated
85% of the time, whereas function words are generally fixated 35% of the
time. In the present study, we found 61% and 48% respectively, which is
sensibly different. The main difference, the one in content words, might be
explained by word lengths. In the present study, all target words were short
(ranging from 2 to 5 letters), which is generally not the case in content words.
Therefore, based on word length effect, we can expect fewer fixations on
content words than in an experiment where length of target words is left
uncontrolled. An explanation of the difference with regard to function words is
less clear. However, the difference is also smaller (14%).
Another difference with previous studies lies in the length of fixations, and
in gaze durations. Most studies obtained fixations that lasted about 225 to
250ms on average. Here, we obtained 346ms on average for one fixation.
Experimental condition peculiarities are probably involved in this difference.
First passages used in Just and Carpenter’ study (1980) contained 132 words
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on average whereas passages used in the present study contained only 26.5
words on average. Therefore, subjects in our study were not under time
pressure when compared to other studies. This may explain why we did not
find a significant effect of frequency on gaze durations, although we had a
significant effect of frequency on the number of fixations: frequency is used to
determine whether a word will be fixated or not. But once a word is fixated,
frequency adds no measurable effect. It does not mean that frequency actually
has no effect but simply that even if there is an effect, it is little in comparison
to other factors. In other words, if subjects are ready to spend enough time
processing a single word, then the additional time that usually accompanies
lower frequency may be masked by overall processing. For example, a longer
time spent on content words might be linked to their semantic content, a
feature that is almost missing in function words. With regard to the main
purpose of this article, the absence of significant frequency effects on gaze
durations is not a problem since the effect of the grammatical class was
significant even when the effect of frequency was not. Therefore, we can
conclude to an effect of grammatical class independently of frequency.
Explaining the interaction between bi-class membership and grammatical
class. Results showed a significant effect of grammatical class by itself:
content words were more fixated than function words. Bi-class membership
also had an effect by itself: content words received more fixations when they
had a bi-class form than when they had not. In addition to those two main
effects, there was a significant interaction between bi-class membership and
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grammatical class: function words were fixated equally, whether they have a
single- or a bi-class form, whereas content words where more fixated when the
had a bi-class form. To put it differently, bi-class membership influenced the
number of fixations on content words whereas it had no measurable influence
on the number of fixations on function words. Although letter detection and
silent reading tasks are different, the data presented here may be analysed in
the terms of to the debate between processing time hypothesis (Healy, 1976,
1994) and the structural account (Koriat & Greenberg, 1991, 1994). Two main
explanations of these results seem possible:
The first explanation is based on frequency effects (close to Healy's
processing time hypothesis) and on inhibition. When a form is ambiguous
(several meanings are possible), its most frequent meaning is generally
selected first. In general, the most frequent meaning of a bi-class form
corresponds to the function word since this acceptation is generally the most
frequently encountered. Hence, when the word in the text actually corresponds
to the function word interpretation of the bi-class form, automatic processing
is sufficient. Thus, in function words, there is no reason for a difference
between single- and bi-class forms. To the contrary, the content-word
interpretation of a bi-class form has a higher cognitive cost because selecting
this interpretation first requires an inhibition of the automatically selected
meaning, which is most likely the function word interpretation. Thus, this
inhibition in content words generates a difference between single- and bi-class
forms. In function words, the ambiguity generated by bi-class membership is
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automatically solved by activation of the mot frequent meaning whereas in
content words, solving ambiguity requires a new interpretation of the form.
Thus, combining frequency effects and inhibition may explain the interaction
observed between bi-class membership and grammatical class.
The second explanation of the results is based on the FAN effect (Anderson,
1974, 1983) and the role of function words in the sentence, (close to the
structural account, Koriat & Greenberg, 1991, 1994). The FAN effect consists
in a greater latency in processing forms that are related to many concepts, just
like bi-class forms are. This effect has been explained in terms of associative
strength in semantic networks. The FAN effect may explain why polysemous
forms may receive more fixations that non polysemous forms. Thus, it might
explain why words receive more fixations when they are bi-class: being
activated less due to the FAN effect, words attached to a bi-class form would
require more deliberate processing than words attached to a single-class form.
However, this explanation would predict the same effect in function and
content words, which is not the case since in function words, single- and biclass forms are equally fixated. Therefore we have to explain why the FAN
effect is blocked in function words. Let us turn to the structural account.
Koriat and Greenberg assume that function words are processed prior to
content words, so that syntactic information processing facilitates semantic
information processing. The reader would use sentence-building patterns to
reconstruct the "skeletal structure" of the sentence. Recognizing familiar
patterns would enable predicting the locus of structure cues, what function
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words fundamentally are. In other words, recognizing a skeletal structure
would facilitate automatic processing of function words by making them
predictable. Being predicted, function words would be skipped, whichever
form they actually have (single- or bi-class). Hence, the structural account
may explain why bi-class membership plays no role in the number of fixations
on function words. Indeed, the structural account does not apply to content
words so the FAN effect still applies. Thus, combining FAN effects and the
structural account may explain the interaction observed between bi-class
membership and grammatical class.
Finally, the two explanations that we proposed are non incompatible since
they tap on different processes: It may well be that they both concur to
produce the effects that are reported in this paper. For example, the FAN
effect and inhibition of the most activated meaning can both concur to
lengthen the processing of a content word having a bi-class form, compared to
a content with a single-form. Similarly, having activated a structural pattern on
one hand and frequency on the other hand may concur in preventing the reader
to place attention on the word, whether its form is bi-class or not.
Conclusion. Our general hypothesis, called “attentional hypothesis” was that
the specific processing effect of grammatical class influences the reader’s
ocular pattern by determining the level of visual attention. Contrary to
previous studies, the present one controlled frequency, bi-class membership
and form length in testing the effect of grammatical class in reading. Results
yielded that grammatical class actually had a specific effect on the reader
ROUSSEL
EYE-MOVEMENTS in READING
22
ocular pattern. The interaction between bi-class membership and grammatical
class may receive several explanations, which will deserve more studies.
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23
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AUTHORS' NOTES
Requests for reprints may be sent to Sophie Roussel, Laboratoire Lordat,
Maison de la Recherche, Université de Toulouse - Le Mirail, 31058 Toulouse
Cedex, France.
Email: [email protected]
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Table 1: Effects of grammatical class on fixation numbers, gaze
durations, and pupil diameters with no control on frequency or bi-class
form
Grammatical class
Function words
Content words
M (SE) N
M (SE) N
Fixation numbers (all readings)
0.59 (0.02) 758
0.81 (0.02) 834
5.67
<.0005
Gaze durations in ms (all readings)
403 (7.9) 363
453ms (8.6) 512
2.96
.001
Pupil Ø variation in σ (first readings)
-0.07 (0.04) 334
-0.19 (0.04) 480
2.01
.023
Pupil Ø variation in σ (all readings)
-0.01 (0.04) 363
-0.10 (0.04) 512
1.75
.042
* all tests are one-tailed
t value
Sig.*
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EYE-MOVEMENTS in READING
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Table 2: Fixation numbers depending on grammatical class and bi-class
membership
N
Mean
SE
Single-class form
956
0.69
(0.02)
Bi-class form
636
0.73
(0.03)
Bi-class membership
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Figure Captions
Figure 1. Interaction between grammatical class and bi-class
membership effects controlling for frequency
Figure 2. Elusion degree according to grammatical class
Figure 3. Pupil diameter during first reading (with standard errors)
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mean number of fixations
1
0,95
0,9
0,85
0,8
single-class form
0,75
bi-class form
0,7
0,65
0,6
0,55
0,5
Function words
Content words
grammatical class
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percentage of words within each
elusion degree
32
65%
60,20%
60%
58,30%
55,10%
55%
50%
Function words
Content words
45%
44,90%
40%
39,80%
41,70%
35%
30%
no elusion
(n=93)
part elusion total elusion
(n=782)
(n=717)
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33
Mean pupil diameter variation
0
-0,05
-0,072
-0,1
-0,15
-0,185
-0,2
-0,25
Function word
Content word
Grammatical class