Eye Movements in Reading 559eye movement measures can also be used to infer moment-to-
moment cognitive processes in reading such as the difficulty
in identifying a word.
There is now a large body of evidence, however, that the
time spent fixating a word is influenced by word frequency:
Fixation times are longer for words of lower frequency (i.e.,
words less frequently seen in text) than for words of higher
frequency, even when the low-frequency words are the same
length as the high-frequency words (Hyönä & Olson, 1995;
Inhoff & Rayner, 1986; Just & Carpenter, 1980; Kennison &
Clifton, 1995; Rayner, 1977; Rayner & Duffy, 1986; Rayner
& Fischer, 1996; Raney & Rayner, 1995; Rayner & Raney,
1996; Rayner et al., 1996; Sereno & Rayner, 2000; Vitu,
1991). As with words in isolation, this is presumably because
the slower direct access process for words of lower frequency
increases the time to identify them. Furthermore, there is a
spillover effectfor low-frequency words (Rayner & Duffy,
1986; Rayner, Sereno, Morris, Schmauder, & Clifton, 1989).
When the currently fixated word is of low frequency, cogni-
tive processing may be passed downstream in the text, lead-
ing to longer fixation times on the next word. A corollary to
the spillover effect is that when words are fixated multiple
times within a passage, fixation durations on these words de-
crease, particularly if they are of low frequency (Hyönä &
Niemi, 1990; Rayner, Raney, & Pollatsek, 1995). Finally, the
nature of a word’s morphology also has a mediating effect on
fixation times. Lima (1987), for example, found that readers
tend to fixate for longer periods of time on prefixed words
(e.g.,revive) as compared to pseudoprefixed words (e.g.,
rescue). More recently Hyönä and Pollatsek (1998) found
that the frequency of both the morphemes of compound
words influenced fixation time on the word for compound
words that were equated on the frequency of the word. How-
ever, the timing was different; the first morpheme influenced
the duration of the initial fixation on the word, whereas the
second morpheme only influenced later processing on the
word. Similarly, Niswander, Pollatsek, and Rayner (2000)
found that the frequency of the root morpheme of suffixed
words (e.g. governingovernment) affected the fixation time
on the word. Thus, at least some components of words, in ad-
dition to the words themselves, are influencing fixation times
in reading.
The Perceptual Span
A central question in reading is how much information we
can extract from text during a single fixation. As mentioned
earlier, the data show that our eyes move approximately once
every quarter of a second during normal reading, suggesting
that only a limited amount of information is typically
extracted from the text on each fixation. This, coupled with
the physical acuity limitations inherent in the visual system,
suggests that the region of text on the page from which useful
information may be extracted on each fixation is relatively
small.
Although a number of different techniques have been used
in attempts to measure the size of the effective visual field (or
perceptual span) in reading, most of them have rather severe
limitations (see Rayner, 1975, 1978 for a discussion). One
method which has proven to be effective, however, is called
themoving window technique(McConkie & Rayner, 1975;
Rayner, 1986; Rayner & Bertera, 1979; N. R. Underwood &
McConkie, 1985). This technique involves presenting read-
ers with a window of normal text around the fixation point on
each fixation, with the information outside that window de-
graded in some manner. In order to accomplish this, readers’
eye movements and fixations are continuously monitored and
recorded by a computer while they read text presented on a
computer monitor, and, when the eyes move, the computer
changes the text contingent on the position of the eyes. In a
typical experiment, an experimenter-defined window of nor-
mal text is presented around the fixation point, while all the
letters outside the window are changed to random letters. The
extent of the perceptual span may be examined by manipulat-
ing the size of the window region. The logic of this technique
is that if reading is normal for a window of a particular size
(i.e., if people read both with normal comprehension and at
their normal rate), then information outside this window is
not used in the reading process.
Figure 20.2 illustrates a typical example of the moving
window technique. In this example, a hypothetical reader is
presented with a window of text that consists of 4 letters to
the left of fixation and 14 letters to the right of fixation (fixa-
tion points are indicated by asterisks). As can be seen in theFigure 20.2 Examples of the moving window and boundary paradigms.
The moving window example consists of a window that extends 4 characters
to the left of fixation and 14 characters to the right of fixation on the two fix-
ations shown (fixation locations are marked by asterisks). In the boundary
paradigm example, a word (in this case, the word previews) is present in a
target location prior to a reader’s moving over an invisible boundary location
(the letter einthe). When the eyes cross this boundary location, the preview
word is replaced by the target word (in this case, the word boundary).Moving Window Paradigm
xx xxample of a moving xxxxxx pxxxxxxx* (fixation 1)
xx xxxxxxx xx a moving window paxxxxxx (fixation 2)
*Boundary Paradigm
an example of the previous paradigm* (fixation 1)
an example of the boundary paradigm (fixation 2)
*