A computer-based eye-movement controlled display system was developed for the study of perceptual processes in reading. A study was conducted to identify the region from which skilled readers pick up various types of visual information during a fixation while reading. This study involved making display changes, based on eye position, in the text pattern as the subject was in the act of reading from it, and then examining the effects these changes produced on eye behavior. The results indicated that the subjects acquired word-length pattern information at least 12 to 15 character positions to the right of the fixation point. and that this information primarily influenced saccade lengths. Specific letter-and word-shape information were acquired no further than 10 character positions to the right of the fixation point.

Sixty-six college students read two chapters from a contemporary novel while their eye movements were monitored. The eye movement data were analyzed to identify factors that influence the location of a reader's initial eye fixation on a word. When the data were partitioned according to the location of the prior fixation (i.e., launch site), the distribution of fixation locations on the word (i.e., landing site distribution) was highly constrained, normal in shape, and not influenced by word length. The locations of initial fixations on words can be accounted for on the basis of five principles of oculomotor control: A word-object has a specific functional target location, a saccadic range error occurs that produces a systematic deviation of landing sites from the functional target location, the saccadic range error is reduced somewhat for saccades that follow longer eye fixations, there exists oculomotor variability that is a second, non-systematic source of error in landing sites, and the oculomotor variability increases with distance of the launch site from the target.

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Previous research has found that words are identified most quickly when the eyes are near their center (the Optimal Viewing Position effect). A study was conducted to determine whether this same phenomenon is observed during reading, as revealed by a relationship between fixation position in a word and the duration of the fixation. An analysis of three large existing corpora of eye movement data, two from adults and one from children, showed a surprising inverted Optimal Viewing Position curve: mean fixation duration is greatest, rather than lowest, when the eyes were at the centers of words. From this phenomenon, we suggest an alternative explanation to the fixation duration trade-off effect in word refixations [O'Regan & Lévy-Schoen, Attention and performance XII: the psychology of reading (1987)]; the phenomenon also contradicts expectations of both oculomotor and cognitive theories of eye movement control. Attempts to test alternative explanations led to the discovery of another phenomenon, the Saccade Distance effect: mean fixation durations vary with the distance of the prior fixation from the currently-fixated word, being longer with greater distances. The durations of fixations in reading are complexly determined, with influences both from language and perceptual/oculomotor levels.

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As people visually examine their world, the proximal stimulus pattern changes position on their retinae with every saccade, but they still perceive the world as being stable. This phenomenon of space constancy or visual stability was explored by making changes in natural, full-color pictures during selected saccades as observers examined them for 20 s in preparation for a recognition test. In Experiment 1, the pictures were displaced up, down, left, or right by 03, 0.6, or 1.2 deg. In Experiment 2, the pictures were expanded or contracted in size by 10% or 20%. As a secondary task, subjects pressed a button whenever they detected a change in the picture. Three results from previous studies with simpler stimuli did not generalize to this situation. Evidence suggests that subjects' detection of image displacements as they examine complex pictures primarily involves the use of local information in the region of the saccade's landing position. A saccade target theory of visual stability is proposed.Visual Stability Across Saccades -2 VISUAL STABILITY ACROSS SACCADES WHILE VIEWING COMPLEX PICTURESMaking a saccadic eye movement causes a displacement of the light pattern across the retinae. If a similar retinal displacement occurs during an eye fixation, there is perception of movement: that is, the world appears to jump. However, the same pattern of motion on the retinae, occurring as a consequence of making a saccade, is not perceived and the world appears stable. 1 This phenomenon, referred to traditionally as space constancy, and which we will call visual stability, permits people to visually explore the world with a moving sensory matrix without mis-attributing self-induced stimulus motion on the matrix to the world itself. How the visual system achieves this stability has been a matter of speculation and research since Helmholtz (1866/1963) discussed the problem.Two classes of theories have been proposed to explain this visual stability. One class of theories assumes that the characteristics of the proximal stimulus alone are sufficient to distinguish between retinal change resulting from saccadic eye movements and change resulting from movement in the world. The other class of theories assumes that some additional, non-retinal information is required, though individual theories differ in the nature of the information proposed. Proximal Stimulus Alone: GibsonGibson (1966) argued that the transformation of the visual array over time that results from making a saccade is different from that which typically results from motion in the world. A saccadic eye movement produces a rigid displacement of the entire light pattern on the retinae. Thus, this type of transformation specifies a self-induced stimulus displacement rather than a change in the world. Furthermore, though not stated by Gibson, saccadic suppression (Volkman, Schick, & Riggs, 1968), together with visual masking from pre-and post-saccadic visual fields, prevents the perception of the stimulus motion on the retinae that results from a saccade-prod...

An analysis of over 40,000 eye fixations made by college students during reading indicates that the frequency of immediately refixating a word following an initial eye fixation on it varies with the location of that fixation. The refixation frequency is lowest near the center of the word and positively accelerating with distance from the center. The data are well fit by a parabolic function. Assuming that refixation frequency is related to the frequency of successful word identification, the observed curvilinear relation results naturally from models that postulate a linear decrease in acuity with retinal eccentricity. A single letter difference in fixation location in a word can make a sizeable difference in the likelihood of refixating that word. The effects of word length and cultural frequency on the frequency of refixating are also examined.McConkie, Kerr, Reddix, Zola, & Jacobs EYE MOVEMENT CONTROL DURING READING: II. FREQUENCY OF REFIXATING A WORDDuring reading, people fixate more frequently near the centers of words than near the beginnings and ends (Rayner, 1979). O'Regan (1981) proposed a Convenient Viewing Position hypothesis, stating that readers learn to send their eyes to the centers of words because, across the words in a language, that location is optimal for word identification. Due to the rapid drop in visual acuity with distance from the center of the fovea, together with the fact that letters bounded by spaces are more perceptible (Bouma, 1978;Jacobs, 1987), the letters of a word are maximally identifiable when the eyes are near the word's center. O'Regan further suggested that the further the eyes lie from the Convenient Viewing Position, the greater the probability that a second eye fixation on the word will be required for identification. This prediction was confirmed in a word identification study (O'Regan, 1984), which found that the frequency of making a second fixation on a word is minimized when the initial fixation is near the center of that word. Furthermore, the frequency of refixating increases as the distance of the first fixation from the center of the word increases. We refer to this relationship as the Word Refixation Frequency Curve, or simply as the word refixation curve. The existence of a word refixation curve in word identification tasks has been replicated (O'Regan, Levy-Schoen, Pynte, & Brugaillere, 1984) and there is some evidence that it may also be present in the eye fixation pattern made during reading (Blanchard & McConkie, cited by O'Regan & Levy-Schoen, 1987).

As people read continuous text, on occasional single eye fixations the text was replaced by one of six alternate stimulus patterns. Frequency distributions of the durations of these fixations were used to test predictions from four types of theories of saccadic eye movement control. Contrary to current cognitive theories, cognitive influences appeared to delay saccades rather than trigger them. Two saccade disruption times were identified, suggesting the existence of three distributions of saccades, labeled early, normal and late. The Competition-inhibition theory, an enhanced version of Findlay and Walker's (1999) theory, is proposed to account for eye movement control during reading.