Source: http://www.readingonline.org/research/eyemove.html
, some sentences highlighted by P. Rösler
(23.03.2006)
Influential Studies in Eye-Movement Research
Eric J. Paulson
Kenneth S. Goodman
Authors' Note: The studies discussed here do not
constitute the entire corpus of useful and informative research in the area of
eye movement but were chosen because they are representative of the valid,
reliable, high-quality work that exists and because each has contributed
significantly to the body of knowledge about perceptual process in reading.
These studies form the base for research that continues to yield insight into
vision and perception in the reading process.
This review is divided into five parts:
Early
Research
In 1879,
Perhaps the first concrete insight into the reading process made
possible by eye-movement research was provided in 1891 by Landolt,
one of Javal's colleagues at the
Dodge (1900)
constructed an experiment to explore the type of information the eye picks up
while it moves. Two pieces of cardboard were positioned one behind the other,
and a slit measuring 4 mm wide was cut into the center
of the piece in front. Subjects, who sat before the cardboard pieces, were to
fixate first on a point to the left of the slit and then to make a single
eye-movement to a point to the right of the slit. The slit itself was not
visible from either fixation point. Six different colors
were placed on the rear screen five times each to determine whether the
subjects saw the color through the slit as they
executed the required eye movement. Dodge reported that "when the eye
movement was unbroken, the observer was unable to tell what had been exposed or
even that anything at all had broken the black of the perimeter" (p. 461).
His results indicated that since no useful information is received during the
movement of the eyes, research should concentrate on the pauses the eye makes.
Edmund
Burke Huey and His Contemporaries
Huey provided what is possibly the first physical record of readers' eye
movements. In a procedure that sounds more than a bit uncomfortable for the
subjects, a plaster of paris cup with a hole in the center was placed on the cornea of one eye, much as a
contact lens. The cup was attached to an aluminum
pointer which responded to the slightest eye movement. As a subject read, the
pointer traced the movement of the eye on a piece of paper. In addition to
demonstrating that the eye regresses a small
percentage of the time, Huey's study showed that the first fixation in a line is frequently not at the
first word but at the second or even third; likewise, the final fixation
is usually not at the last word. Huey's data also demonstrated that readers fixated on anywhere from
20 to 70 percent of the words in a line. This remarkable research,
undertaken more than 90 years ago, provided evidence that reading is not a
passive process of word-by-word identification, but that readers make choices about where and when to
fixate while reading.
Buswell and Judd
(Buswell, 1922,
1937;
Judd & Buswell,
1922) photographed readers' eye movements in what
was for their time a relatively nonintrusive manner.
The procedure consisted of photographing a beam of light reflected first to a
subject's cornea from silvered glass mirrors, and then from the cornea through
a camera lens to moving kinetoscope film. The
changing positions of the beam of light were recorded on the film, which
provided an "accurate record showing the position and duration of each
fixation of the eye while the subject reads" (Buswell, 1922,
p. 12).
Judd and Buswell also deserve acknowledgment
for the sheer amount of data they collected, analyzed, and disseminated. In
addition to providing copious illustrations of what the data look like (there
are 90 plates in Judd & Buswell,
1922, alone), they support their conclusions well.
Their findings include evidence that not only do different readers read
differently, but individual
readers read differently in different circumstances. Ever mindful of
pedagogical implications, they asserted that readers "need to be made aware of the fact that
reading habits should be flexible and properly adapted to the purpose
and the type of material which is read" (Buswell, 1937,
p. 143).
Judd and Buswell's contributions to our
understanding of the reading process are also significant. Their work led them
to conclude that reading
is not simply a matter of bottom-up word identification but a perceptual
process that involves
interpretations on the reader's part. On the subject of word
identification, even today a subject of great dispute, they argued for the
primacy of context in determining the meaning of a word:
[I]n real
life the word will always turn up as a part of a sentence and...will have a peculiar shade of meaning through its contrast
with other words or through its special relation in the total idea conveyed by
the sentence. The notion that a word and its meaning are two fixed pieces of
experience that can be tied together is a purely mechanical theory and not
adequate... (Judd & Buswell,
1922, p. 4).
Tinker's landmark 1936 study investigated the reliability and validity of eye-movement
research as it applies to reading. One of his primary concerns was whether the
artificial situation that necessarily accompanied eye-movement studies
conducted in the laboratory caused subjects to alter significantly their
reading strategies and processes. He had 57 college students read one version
of a reading test at a table away from the eye-movement apparatus and then read
another version of the test while under typical eye-movement recording
conditions. The results were encouraging for eye-movement researchers:
“Although some subjects did better and some poorer before the camera, the group
as a whole gave an entirely typical performance in the photographic situation”
(Tinker, 1936,
p. 742). Tinker's conclusion that eye-movement research can reveal authentic
reading behavior has allowed workers in this area to
extend their findings to situations outside the laboratory.
Despite the exciting work of these early investigators, the studies
undertaken at the beginning of the 20th century were followed by a long hiatus,
blamed by some on the influence of the prevailing behaviorist
doctrine of the time (Rayner & Pollatsek,
1989). By the late 1960s, however, eye-movement
recording apparatuses, while operating on the same basic principles as earlier
equipment, became much more sophisticated. Microanalyses of eye behavior now became possible. Accordingly, more recent
eye-movement research is characterized not by broad generalizations, but by
smaller scale contributions to our overall knowledge about the role of the eye
in reading.
The
Physiology of Eye Movements
A central question since the inception of eye-movement research concerns
the amount of information the eye can process with each fixation. This issue
became even more important when Dodge's conclusion that we see nothing when the
eye is actually in motion began to be replicated empirically (see, for example,
Wolverton & Zola, 1983).
This suggests, of course, that the only text information available is presented during fixations.
From physiological studies we know several basic facts about how the eye
processes information and about the physical constraints that limit how this
information is presented to the brain. During a fixation, the eye has access to
three regions for viewing
information: the foveal, parafoveal,
and peripheral. The foveal region is the area that we think of
as being in focus and includes 2 degrees of visual angle around the point of fixation, where 1 degree is equal to three or
four letters (thus, six to eight letters are in focus). The parafoveal
region extends to about 15
to 20 letters, and the peripheral region includes everything in the
visual field beyond the parafoveal region. The fovea
is concerned with processing detail, with anything beyond producing a marked
drop in acuity; words presented to locations removed from the fovea are more
difficult to identify (Rayner & Sereno,
1994).
Eye
Movements and Perception
Many studies have suggested that the shorter the word is, the more likely it is to be
skipped. In order to ascertain whether it was length or a syntactic feature that was
responsible for the likelihood of a word being skipped, O'Regan (1979)
recorded the eye movements of subjects, each of whom read a pair of sentences
that began in the same way but ended differently (for example, “The dog that
growled the most was friendly” vs. “The dog that growled ate many biscuits”;
“He claimed the ladies the maid knew lived in New York” vs. “He claimed the
ladies met many times to discuss”). In these sentences, subjects skipped the substantially more
often than they skipped three-letter verbs; for example, in the first
pair of sentences given, the was more likely to
be skipped in the first sentence than ate in the second. O'Regan summarizes as follows:
The
conclusions to be drawn from this experiment are, first, that local eye
movement parameters (saccade size, regression probability, number of fixations,
and perhaps fixation duration), are controlled sufficiently rapidly to be
influenced from moment to moment by information concerning the lexical category
of a word in peripheral vision.... [I]t is clear that some systematic influence
of sentence structure exists (p. 59).
It seems that when readers
use their implicit knowledge of the structure of language along with their
constant predictions about upcoming text, they
sample from the syntactic cueing system (Goodman, 1996).
This enables them to read more efficiently—to skip words that have been confirmed parafoveally.
In the early 1980s, Just and Carpenter recorded the eye-movements of 14
college students who read 15 short excerpts from Time and Newsweek
magazines. The subjects were asked only to read normally and to recall what
they could of each paragraph after it was finished. The researchers found that readers fixated an average of
67.8 percent of the words, with content words being fixated 83 percent of the
time and function words 38 percent of the time (Carpenter & Just, 1983;
Just & Carpenter, 1980).
This work provided further evidence that not only is every word in a text not fixated, but the
syntactic and semantic components of each word play a role in determining
whether fixation occurs. In addition, data from these studies concerning
the differing lengths of fixations provided evidence for two major assumptions:
first, with the
“immediacy” assumption, Just and Carpenter asserted that the reader tries to interpret
each word in a text as it is encountered rather than holding it in abeyance and
assigning meaning later; second, their “eye-mind” assumption holds that the
reader's eyes remain fixated on a word as long as the word is being processed.
In 1981, McClelland and O'Regan explored whether the
usefulness of information available in the parafovea
was dependent on readers' expectations about what the next word in a text would
be. In one experiment whose paradigm simulated eye movements, they examined
target word-naming reaction time when preview information was used. A sentence
from which the last word was missing was displayed on a computer screen. The
sentences were of two types: those for which a group of judges (who did not
take part in the experiment) accurately predicted the missing word, and those
that the judges felt did not allow prediction of the word. When subjects
reached the last word, they pressed a button that initiated first a 100
millisecond (ms) display of a preview item, then a 100 ms blank space, and
finally the target word. Subjects were to name the target word as soon as they
read it. Preview items were of three types: a series of Xs, an item
similar to the target word except that the second and penultimate letters were
replaced by other letters of the same shape, or the same word as the target
word.
Results of this study demonstrate that the speed and ease with which
readers can name a target word from a parafoveal
preview depend on readers' expectations. As McClelland and O'Regan
state, "a priori
expectations and context greatly increase the benefit subjects gain from a
preview of a word in parafoveal vision" (1981,
p. 634). Further, they assert that "our experiments have clarified one
point: The ability to derive
benefit from the preview we receive of upcoming words in parafoveal
vision depends on a prepared mind" (p. 643). That is, readers are
able to make use of text information that they have not fixated on but which
they have predicted. Fuzzy input is enough to confirm a prediction.
To support the idea that unfixated words are
indeed perceived and processed, Fisher and Shebilske
(1985) performed an experiment that made use of a yoked
control group. Half of the 60 university undergraduate students who
participated had their eye movements monitored while reading sentences (as well
as short essays) such as “Pets have funny names such as my favorite
dog, Jingles.” If those subjects failed to fixate, for example, the words funny
and dog, the remaining subjects (the yoked controls) would be shown the
sentence as “Pets have _____ names such as my favorite
_____, Jingles.” The researchers then examined the percentage of skipped versus
unskipped words that subjects could report. They
reasoned that if words that are not fixated are not perceived, the first group
of subjects would recall as many of the skipped words as would the second
group. In fact, this was not the case—the ratios of reporting nonfixated words to fixated words in the first subject
group were 1.0 for sentences and .97 for essays, while the ratios for the yoked
control group were .40 and .45, respectively. That the yoked controls were able
to “recall” a word at all is a function of their ability to infer the words
from the context. The indication is that even though a word is not directly fixated, it is still
perceived. Fisher and Shebilske concluded that
their results “support the generality of the hypothesis that expectations based on contextual
constraints can interact with parafoveal information
to determine the guidance of fixations” (p. 154). In other words, predictions from context are
used by the brain to direct the eye to fixate or not to do so.
Balota, Pollatsek,
and Rayner (1985) used a
boundary technique to explore the influence of context and parafoveal
information that was either visually similar or dissimilar to a target word
that the reader would subsequently fixate. For example, in the sentence “Since
the wedding was today, the baker rushed the wedding cake to the reception,” cake
had as a parafoveal preview either cake, cahc, pies, picz,
or bomb; the preview was changed to cake during the reader's
saccade immediately preceding. The researchers found that readers were
significantly more likely to skip the visually identical or visually similar parafoveal previews (cake, cahc)
than the semantically related, visually dissimilar, or anomalous parafoveal previews (pies, picz,
bomb). They conclude that “the data imply that when the word is skipped, only the beginning two
or three letters of the parafoveal word were actually
identified. Thus, on these occasions, a strong context helps
readers to fill in information that is not totally available in their parafovea” (p. 374).
Readers are able to sample phonological and orthographic information in
the parafoveal field of vision and use it, together
with their expectations for the upcoming material to be read, either to skip
text or to fixate on it for a shorter than average period. It is this
sampling—as opposed to a thorough processing of each and every letter—that
makes possible the efficient use of the least amount of information necessary
to make sense of the text and move on.
Different parts of words carry different types of semantic information,
and some of these parts are more useful than others for the process of word
recognition. Underwood, Clews, and Everatt (1990) examined
the process whereby a fixation location is determined by the information
distribution of the word in the parafoveal preview.
For example, underneath is the only word of its length that ends in neath, which makes the end of the word a “zone of
high information.” The end of engagement, however, is “redundant,”
because ment can attach to a great number of
words. Underwood, Clews, and Everatt selected target
words with zones of high information at the beginning or end and embedded them
in short stories. The location of readers' fixations on the
target words were recorded. The researchers proceeded with the
expectation that if
readers consistently fixated on the zones of high information then they must be
processing morphological information parafoveally.
This is indeed what happened, as the researchers explain:
The target
words used in our sentences varied in their distribution of information. Being
given the first few letters of some words would not be sufficient to identify
them, and, likewise, the final few letters of some words did not provide a
unique suggestion as to the identity of the word. The distribution of the
information had its effect upon the location of the first fixation upon the
target.... A redundant
beginning induced a first fixation further from the word's beginning. This
variation in the initial landing position is evidence of parafoveal
processing of the distribution of information in the word, because until that
fixation had been made only parafoveal processing
could deliver the information necessary to guide the eyes to one location or
another (p. 58).
This conclusion indicates that readers are able to sample semantic
information from the parafoveal field, which enables
them to use as textual cues the most informative part of a word—a good example
of one of the numerous ways readers make efficient use of text.
To demonstrate the importance of phonological information, Pollatsek, Lesch,
Morris, and Rayner (1992)
undertook a project designed to determine whether homophones provide a better parafoveal preview than do visually similar words. Of
interest was fixation duration on the target word in a sentence. Each target
word had one of four corresponding preview words, either a homophone, a
visually similar word, a completely different word, or an identical word to the
target. The text was displayed on a computer screen. When subjects began reading
the sentence, one of the preview words would be in the target word's position
until their eyes crossed the boundary point (the parafoveal
preview), at which time the preview word would be replaced with the target
word. In other words, the preview word would be in the sentence until the
readers began the saccade that would take them to that word, at which time the
computer would change the preview word to the target word; because the eye
picks up no information during a saccade, the reader would not be aware that
there had been a change. The dependent variable was processing time of the
target word once it was reached, with a shorter duration of fixation being
attributed to the usefulness of the parafoveal
preview. The results
indicate that readers fixated for less time after a homophone preview than
after a visually similar preview. The authors' central finding was that
“when a parafoveal preview word was a homophone of a
target word, there was a greater preview benefit than when the preview was a
non-homophonic control word that was as visually similar to the target word as
was the homophone” (p. 158).
To further confirm the effects of contextual constraint, or
predictability, of text, Rayner and Well (1996)
asked subjects to read sentences that contained a target word classified as
high, medium, or low constraint. Their method of determining the predictability
of the target words was similar to that already described of Fisher and Shebilske
(1985): judges who did not participate in the study
were given a cloze sentence or paragraph and asked to fill in the blank. Target
words that were produced by the judges over 60 percent of the time were
considered highly constrained, or predictable, and target words that were
produced less than 10 percent of the time were considered unconstrained. The
eye movements of eighteen adult participants were recorded as they read a range
of sentences, from highly constrained to relatively unconstrained, with word
length and frequency controlled. The study's results indicate that the
low-constraint words yielded longer fixation times than the medium- and
high-constraint words, and that readers were more likely not to fixate on
high-constraint target words than on medium- or low-constraint target words.
This work effectively confirms findings of other eye-movement studies
that show that “highly
constrained target words are skipped (i.e., not directly fixated) more
frequently than unconstrained words...(and) when
target words are fixated, fixation time is shorter on constrained than
unconstrained words” (Rayner & Well, 1996,
p. 504). The researchers conclude that "predictability of a word (or the amount of contextual
constraint for that word)...will affect both fixation time and word skipping"
(p. 507).
The
Past, Present, and Future of Eye-Movement Studies
The long, barren gaps in a century of research are not a unique phenomenon
in studies in education. In part, they reflect the changes in research
paradigms, research methodologies, and views popular during each period. Most
of the research of the 1980s and '90s, for example, is rooted in a view of
reading as rapid, automatic, word recognition, and eye movements are studied
within a set of assumptions arising from that view of the reading process.
In the decades from the 1930s to the late '60s, reading research was
dominated by views that put little focus on how the eyes functioned in reading.
The feeling was that we already knew what we needed to know. Still, there is a
remarkable continuity over the long history of eye-movement research. There is
a tangible reality to eye movement that transcends researchers' assumptions.
Interpretations of findings are certainly affected by the vantage point of the
researcher, but the eyes provide data that ultimately must be accommodated.
In some graduate programs, students are advised not to read or cite
research that is more than five years old. That leaves these young researchers
ignorant of a knowledge base that has provided a foundation for many
investigations and findings. It is also unfortunate when workers in the field
come to know a body of research only from reports of it in the current
literature. Relying on third-party interpretations alone can lead to widespread
misunderstanding or misrepresentation of the original researchers' actual data
and findings.
Summaries of the findings of eye-movement research are now being used to
argue for a word-recognition, as opposed to a meaning-construction, view of
reading (e.g., Adams & Bruck,
1995). To put this current view into context, we
need instead to look directly at the research of the past and present and think
about what new research directions could help us more completely to understand
how the eyes work in reading.
Author
Information
Paulson can be contacted at the Department of Language,
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