Telechargé par younes rami

pollatsek1981

publicité
BRAIN
AND
LANGUAGE
14, 174-180 (1981)
Asymmetries in the Perceptual Span for Israeli Readers
ALEXANDER POLLATSEK,SHMUELBOLOZKY,
ARNOLDD. WELL, AND KEITH RAYNER
University of Massachusetts
Native Israelireadersread Hebrew and English text as their eye movements
were monitored. A window of text moved in synchrony with their eye movements
and the window was either symmetrical about the fixation point or offset to the
left or right. When subjects were reading Hebrew, the perceptual span was
asymmetric to the left and when they were reading English it was asymmetric
to the right. The results point out the importance of attentional factors in reading.
A great deal of research has confirmed that for right-handed subjects,
individual words are processed more efficiently when presented in the
right visual field (to the right of a central fixation location) than in the
left visual field. Early explanations of this asymmetry centered oh scanning habits that result from experience with reading (Heron, 1957; Mishkin & Forgays, 1952). Inherent in much of the recent research on the
topic, however, is the assumption that the processing differences are due
to a functional asymmetry of the brain (Hecaen & Albert, 1978). According to this position, the left hemisphere is more specialized for verbal
processing and the right hemisphere is more specialized for spatial processing, so that words are better recognized when presented in the right
visual field and thus initially received by the left or language-specialized
hemisphere.
The scanning explanation
predicts that native readers of Hebrew
should show a left-visual-field
superiority for words since the direction
of reading is from right to left. However, readers of Hebrew, like readers
of left-to-right languages, show a marked right-visual-field
advantage for
the recognition of individual words (Orbach, 1967; Barton, Goodglass,
& Shai, 1956; Carmon, Nachson, & Starinsky, 1976; Silverberg, Bentin,
This research was supported by Grant HD12727 from the National Institute of Child
Health and Human Development (Keith Rayner, principal investigator). The authors thank
Jim Bertera and Robert Morrison for their assistance in conducting the study. Requests
for reprints should be addressed to Alexander Pollatsek, Department of Psychology,
University of Massachusetts, Amherst, MA 01003.
174
0093-934Xl81/050174-07$02.00/O
Copyright
All rights
0 1981 by Academic
Press. Inc.
of reproduction
in any form reserved.
ASYMMETRIES
IN PERCEPTUAL
SPAN
175
Gaziel, Obler, & Albert, 1979). Thus, it has generally been concluded
that although scanning habits may have some influence on perceptual
asymmetries, there is an overriding effect of left-hemisphere superiority
for reading tasks (Jonides, 1979).
It is not clear, however, to what extent conclusions can be made about
the reading of text from studies in which individual words are briefly
displayed to the left or right visual field. Experiments
(McConkie
&
Rayner, 1976; Rayner, Well, & Pollatsek, 1980) with readers of English
text have confirmed that the perceptual span (the area of text from which
useful information
is extracted during a fixation) is asymmetric,
with
little information
obtained from the left of the fixation point. In these
experiments, eye movement information was monitored and fed into a
computer controlling a cathode-ray tube (CRT) from which the subject
was reading. Changes were made on the CRT on the basis of the location
of the reader’s gaze. For example, a passage of mutilated text was initially
presented on the CRT with every letter from the original text replaced
by an X. However, whenever the reader fixated, a region around the
fixation point changed into readable test. This “window”
area moved
in synchrony with the eye movement so that wherever the reader fixated,
the real text was exposed, but everywhere outside the window area the
mutilated text remained. By varying how far the window extends to the
left and right of fixation, it has been possible to determine the extent to
which the perceptual span in reading is asymmetric. The data suggest
that English readers show no difference in performance between (a) a
symmetric window extending 14 characters to the left of fixation and 14
characters to the right of fixation and (b) an asymmetric window extending 14 characters to the right of fixation but only 4 characters to the
left. On the other hand, if the window extends 14 characters to the left
of the fixation point but only 4 characters to the right, the reading performance of English readers was considerably disrupted.
No experiments dealing with the characteristics of the perceptual span
for readers of Hebrew text have been reported, although there have been
suggestions that the direction of reading and hemispheric specialization
may be important for Hebrew readers (Albert, 1975). If the perceptual
span when reading text is determined by the same factors that are responsible for asymmetries when processing individual words (presumably
hemispheric specialization),
then the perceptual span should be asymmetric to the right. On the other hand, if the asymmetry of the perceptual
span for readers of English text is due primarily to attentional considerations related to the pattern of eye movements, then the perceptual
span for readers of Hebrew text should be asymmetric to the left. In the
experiments reported here, the technique (Rayner et al., 1980) used
previously to investigate the asymmetry of the perceptual span for English readers was employed to determine if the perceptual span of Israeli
176
POLLATSEK
ET AL.
readers is asymmetric to the left or right or is possibly symmetric due
to the conflict between the direction of scanning and hemispheric
specialization.
Israeli readers who were also fluent in English were asked to read
Hebrew sentences and English sentences presented on a CRT as their
eye movements were monitored.
The window area around a fixation
point was either symmetric, extending 14 characters both left and right
of fixation, or asymmetric so that it extended either 14 characters left
and 4 right of fixation or 4 left and 14 right of fixation.
METHOD
Subjects
Six native Israeli subjects participated
of experience they had reading English
instruction in reading English beginning
subjects were right-handed and none of
mean age of the subjects was 30 (range
in the study. All were bilingual and the amount
varied from 3 to 29 years. They had all received
in at least the fifth year of school. All of the
them required corrective lenses for reading. The
= 15-39 years) and two of them were female.
Apparatus and Procedure
Eye movements were recorded with a dual Purkinje eye tracker (Stanford Research
Institute) that was interfaced with a Hewlett-Packard 2100 computer. The eye tracker has
a resolution of 10 arcmin, and the output is linear over the visual angle (14 deg) occupied
by the sentences. Subjects’ heads were fixed by a bite bar. The subject’s eye was 46 cm
from the CRT used to present the sentences; three characters equaled 1 deg of visual
angle. Details of the apparatus have been described by Rayner et al. (1980).
At the beginning of the experiment each subject read some warm-up sentences with the
window offset either to the left or right of fixation. Following the warm-up sentences, each
subject read 16 Hebrew sentences in each of the 3 experimental conditions. Sentences
were read in blocks of 8 with the window either being symmetrical around the fixation
point, asymmetric to the right or asymmetric to the left. Subjects returned to the laboratory
on another day and read 48 English sentences, 16 in each of the conditions in the same
manner as the Hebrew sentences had been read. The English sentences were similar in
length and structure to English translations of the Hebrew sentences. For both Hebrew
and English sentences, the order of the conditions and the sentences read were counterbalanced across subjects.
Subjects were instructed to read each sentence and then report the sentence to the
experimenter. They were instructed to report the sentence verbatim or to paraphrase it.
RESULTS AND DISCUSSION
With Hebrew text, reading performance (See Table 1 and Figure 1)
did not differ between the symmetric condition and the asymmetric condition in which the window was shifted to the left. Conversely, when
subjects read English text, their performance was similar to that of native
English readers in that the symmetric condition did not differ from the
asymmetric condition in which the window was shifted to the right. As
can be seen in Table 1, the Israeli subjects read English (in the symmetric
and asymmetric
right conditions) at the rate of 230 wpm (words per
ASYMMETRIES
IN PERCEPTUAL
TABLE
EFFECTIVE
HEBREW
1
READING
RATES IN WORDS
PER MINUTE
FOR THE ISRAELI
SUBJECTS
READING
SENTENCES
AND ENGLISH
SENTENCE<
COMPARED
TO AMERICAN
SUBJECTS
READING
COMPARABLE
ENGLISH
SENTENCES
Israeli subjects
Window
condition
14-14
14-4
4-14
177
SPAN
Hebrew
286
282
185
English
English speaking
subjects
233
131
221
350
218
336
minute). Native English-speaking
subjects’ typical reading rates are between 320 and 350 wpm on sentences of similar length and complexity.
We assume that the slower reading rate for the Israeli subjects on English
sentences is because English is not their native language. However, it
is instructive to note that for all of the variables shown in Table 1 and
Figure 1, the window offset had the same effect as it did for English
readers reading English. For both types of text, the asymmetric condition
in which the window was shifted in the direction opposite to that of
reading resulted in marked decrements in reading behavior.
-Hebrew
.i‘%j
:------r;,:
2
Asymmtrlc
Left
Symmetric
Asymmatric
Right
FIG. 1. Mean saccade length, mean fixation duration,
Hebrew and English text.
and number of fixations for
178
POLLATSEK
ET AL.
When reading Hebrew, performance m the 14L-4R condition was
superior to that in the 4L-14R condition for each of the six subjects with
the exception of a reversal for a single subject on the fixation duration
measure. For reading rate, mean saccade length and mean number of
fixations per line, the results were highly significant, t(5) = 4.10, 7.45,
and 4.61, respectively, p < .Ol, whereas for average fixation duration,
the difference was not significant, t(5) = 1.26, p > .20. When reading
English, performance in the 4L-14R condition was superior to that in
the 14L-4R condition for each of the six subjects, with the exception
of a reversal for a single subject on the fixation duration measure. For
mean saccade length and mean number of fixations per line, the differences were highly significant, t(5) = 3.39 and 4.04, respectively, p <
.02, while for reading rate and mean fixation duration the results failed
to reach conventional
levels of significance, t(5) = 2.39 and 2.52, respectively, .05 < p < .10. However, this reduced level of significance
for reading rate was due to one subject who had a much larger difference
than the others which inflated the error term. If this subject who showed
the largest asymmetry (a difference of 292 wpm vs. an average difference
of 57 wpm for the other five subjects) is removed from the analysis, then
the difference in reading rate for the other five subjects is highly significant, t(4) = 5.16, p < .Ol.
These results provide an unambiguous demonstration
that during the
reading of meaningful text, the direction of reading (and not hemispheric
specialization)
primarily
determines the asymmetry of the perceptual
span. For each of the six bilingual subjects, the perceptual span was
asymmetric to the left when Hebrew was read and asymmetric to the
right when English was read.
It is interesting to note that Hebrew varies structurally and orthographically from English in some important ways that are relevant to our
experiment. In Hebrew, many function words are clitic, i.e., are attached
like prefixes or suffixes to content words. Furthermore, unlike English,
not all vowels are represented in Hebrew orthography. The net effect
of these differences is that Hebrew sentences normally contain fewer
words than their English counterparts. In our case, for example, the
Hebrew sentences were translations of English sentences, and the Hebrew sentences were shorter than the English versions by approximately
1.3 words per sentence. Thus while the Israeli readers reading Hebrew
are markedly slower than American readers reading English (see Table
l), when measured by words per minute, this may be accounted for by
the above structural and orthographic differences. As a quick check that
there was nothing abnormally slow about our Hebrew readers, we computed the reading rate in Hebrew based on the number of words contained
in the English translations of the Hebrew sentences. Using this measure,
the average reading rate for our native Israeli subjects reading Hebrew
ASYMMETRIESINPERCEPTUALSPAN
179
in the 14-14 condition was 348 words per minute, a rate almost identical
to that of a group of 9 native English speaking subjects reading similar
English sentences under similar conditions (see Table 1).
While the above analysis suggests that Hebrew readers acquire meaning from text in their native language about as rapidly as their American
counterparts,
a considerably more ambitious study would clearly be
needed to compare the efficiency of the two languages in terms of information transmission.
However, it is clear that Hebrew readers are
reading their native language more slowly in terms of surface measures
such as words per minute. Inasmuch as more information is condensed
into less space in Hebrew because of the greater use of clitics and because
of the omission of many vowels, it is not surprising that the average
saccade length found for the readers of Hebrew in the 14-14 condition
(5.5 characters) is smaller than the average saccade length (7-9 characters) typically found for readers of English (Rayner, 1978). In experiments similar to that described here, carried out with English speaking
subjects, we have obtained average saccade lengths of approximately
7
characters and average fixation durations of about 220 msec (Rayner et
al., 1980). The finding that the average saccade length varies as a function
of the writing system is consistent with studies of Japanese and Chinese
readers @hen, 1927; Ikeda & Saida, 1978; Stern, 1978). Our data also
show that the average saccade length of Israeli subjects when reading
English is much shorter than is the case for native English readers. While
this might simply reflect the fact that Israeli subjects are not as fluent
in reading English, a more intriguing possibility is that there is some
carryover from their experience with Hebrew. It is also interesting to
note that the Israeli readers’ average fixation duration while reading
Hebrew in the 14-14 condition (265 msec) is about 45 msec longer than
the average fixation duration we have obtained for English speaking
readers in a number of studies in our laboratory. On the other hand, the
265-msec average does not differ markedly from the range of 200-250
msec that is typically described as the average fixation time in reading
(Rayner, 1978). Our results suggest that languages can be characterized
by their density (in terms of such measures as the ratio of morphemes
to graphemes or syllables to graphemes) and as density increases, subjects will shorten their saccades and lengthen their fixations. Clearly this
study is not definitive since it compares readers of different languages
and texts in different languages that have not been equated in precise
ways. We are pursuing these ideas using variations of text within a given
language.
In summary, we find clear and striking evidence that during the reading
of Hebrew, the perceptual span of Israeli subjects is asymmetric to the
left. Thus, while in experiments (Hecaen & Albert, 1978) in which stimuli
are presented tachistoscopically
to the left and right visual fields the
180
POLLATSEK
ET AL.
typical conclusion is that hemispheric specialization is the major factor
underlying processing asymmetries, our experiments indicate that in an
ongoing reading task, attentional factors and factors associated with the
direction of eye movements are crucial. Finally, our results are consistent
with a case study (Dessoff, 1957) of a Hebrew-English
bilingual suffering
from brain damage that resulted from right hemifield homonymous hemianopia. The subject could not read English as the fovea1 and parafoveal
regions were affected by the damage. However, since the brain damage
affected the right visual field only, he apparently could read Hebrew
without difficulty.
REFERENCES
Albert, M. L. 1975. Cerebral dominance and reading habits. Nature, 256, 403-404.
Barton, M. I., Goodglass, H., & Shai, A. 1965. Differential recognition of tachistoscopically
presented English and Hebrew words in right and left visual fields. Perceptual
and
Motor
Skills, 21, 431-437.
Cannon, A., Nachson, I., & Starinsky, R. 1976. Developmental aspects of visual hemifield
differences in perception of verbal material. Brain and Language,
3, 463-464.
Dessoff, J. 1957. Paracentral homonymous hemianopic scotoma. Archives
of Ophtholmology,
58, 452-454.
Hdcaen, H., & Albert, M. L. 1978. Human neuropsychology.
New York: Wiley.
Heron, W. 1957. Perception as a function of retinal locus and attention. American
Journnl
of Psychology,
70, 38-48.
Ikeda, M., & Saida, S. 1978. Span of recognition in reading, Vision Research,
18, 83-88.
Jonides, J. 1979. Left and right visual field superiority for letter classification. Quarterly
Journal
McConkie,
Bulletin
Mishkin,
Journal
of Experimental
Psychology,
31, 423-439.
G. W., Jr Rayner, K. 1976. Asymmetry of the perceptual span in reading.
of the Psychonomic
Society,
8, 365-368.
M., & Forgays, D. G. 1952. Word recognition
of Experimental
Psychology,
as a function of retinal locus.
43, 43-48.
Orbach, J. 1967. Differential recognition of English and Hebrew words in right and left
visual fields as a function of cerebral dominance and reading habits. Neuropsychologia,
5, 127-134.
Rayner, K. 1978. Eye movements in reading and information processing. Psychological
Bulletin,
85, 618-660.
Rayner, K., Well, A. D., & Pollatsek, A. 1980. Asymmetry of the effective visual field
in reading. Perception
& Psychophysics,
27, 537-544.
Shen, E. 1927. An analysis of eye movements in the reading of Chinese. Journal
of
Experimental
Psychology,
10, 158-183.
Silverberg, R., Bentin, S., Gaziel, T., Obler, L. K., & Albert, M. L. 1979. Shift of visual
field preference for English words in native Israeli speakers. Bruin and Language,
8, 184-190.
Stem, J. A. 1978. Eye movements, reading, and cognition. In J. W. Senders, D. F. Fisher,
& R. A. Monty (Eds.), Eye movements
and the higher psychologicalfunctions.
Hillsdale, NJ: Erlbaum.
Téléchargement
Explore flashcards