Recent studies of eye movements in reading and other information processing tasks, such as music reading, typing, visual search, and scene perception, are reviewed. The major emphasis of the review is on reading as a specific example of cognitive processing. Basic topics discussed with respect to reading are (a) the characteristics of eye movements, (b) the perceptual span, (c) integration of information across saccades, (d) eye movement control, and (e) individual differences (including dyslexia). Similar topics are discussed with respect to the other tasks examined. The basic theme of the review is that eye movement data reflect moment-to-moment cognitive processes in the various tasks examined. Theoretical and practical considerations concerning the use of eye movement data are also discussed.

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Eye movements in reading and information processing: 20 years of research.

During active vision, the eyes continually scan the visual environment using saccadic scanning movements. This target article presents an information processing model for the control of these movements, with some close parallels to established physiological pro- cesses in the oculomotor system. Two separate pathways are concerned with the spatial and the temporal programming of the move- ment. In the temporal pathway there is spatially distributed coding and the saccade target is selected from a "salience map." Both path- ways descend through a hierarchy of levels, the lower ones operating automatically. Visual onsets have automatic access to the eye control system via the lower levels. Various centres in each pathway are interconnected via reciprocal inhibition. The model accounts for a num- ber of well-established phenomena in target-elicited saccades: the gap effect, express saccades, the remote distractor effect, and the global effect. High-level control of the pathways in tasks such as visual search and reading is discussed; it operates through spatial se- lection and search selection, which generally combine in an automated way. The model is examined in relation to data from patients with unilateral neglect.

/pdf/a-model-of-saccade-generation-based-on-parallel-processing-r9ubg7wqfu.pdf

A model of saccade generation based on parallel processing and competitive inhibition.

The antisaccade: a review of basic research and clinical studies

One of the most intriguing and controversial observations in oculomotor research in recent years is the phenomenon of express saccades in monkeys and man. These are saccades with such short reaction times (100 msec in man, 70 msec in monkeys) that some experts on eye movements still regard them as artifacts or as anticipatory reactions that do not need any further explanation. On the other hand, some research groups consider them not only authentic but also a valuable means of investigating the mechanisms of saccade generation, the coordination of vision and eye movements, and the mechanisms of visual attention.This target article puts together pieces of experimental evidence in oculomotor and related research – with special emphasis on the express saccade – to enhance our present understanding of the coordination of vision, visual attention, and the eye movements subserving visual perception and cognition.We hypothesize that an optomotor reflex is responsible for the occurrence of express saccades, one that is controlled by higher brain functions involved in disengaged visual attention and decision making. We propose a neural network as the basis for more elaborate mathematical models or computer simulations of the optomotor system in primates.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00031575

Express saccades and visual attention

We measured saccadic eye movements in 168 normal human subjects, ranging in age from 5 to 79 years, to determine age-related changes in saccadic task performance. Subjects were instructed to look either toward (pro-saccade task) or away from (anti-saccade task) an eccentric target under different conditions of fixation. We quantified the percentage of direction errors, the time to onset of the eye movement (saccadic reaction time: SRT), and the metrics and dynamics of the movement itself (amplitude, peak velocity, duration) for subjects in different age groups. Young children (5–8 years of age) had slow SRTs, great intra-subject variance in SRT, and the most direction errors in the anti-saccade task. Young adults (20–30 years of age) typically had the fastest SRTs and lowest intra-subject variance in SRT. Elderly subjects (60–79 years of age) had slower SRTs and longer duration saccades than other subject groups. These results demonstrate very strong age-related effects in subject performance, which may reflect different stages of normal development and degeneration in the nervous system. We attribute the dramatic improvement in performance in the anti-saccade task that occurs between the ages of 5–15 years to delayed maturation of the frontal lobes.

/pdf/age-related-performance-of-human-subjects-on-saccadic-eye-1blp97txp2.pdf

Age-related performance of human subjects on saccadic eye movement tasks.

The saccadic eye movements of 20 naive adults, 7 naive teenagers, 12 naive children, and 4 trained adult subjects were measured using two single target saccade tasks; the gap and the overlap task. In the gap task, the fixation point was switched off before the target occurred; in the overlap task it remained on until the end of each trial. The target position was randomly selected 4° to the left or 4° to the right of the fixation point. The subjects were instructed to look at the target when it appeared, not to react as fast as possible. They were not given any feedback about their performance. The results suggest that, in the gap task, most of the naive subjects exhibit at least two (the teenagers certainly three) clearly separated peaks in the distribution of the saccadic reaction times. The first peak occurs between 100 and 135 ms (express saccades), the second one between 140 and 180 ms (fast regular), and a third peak may follow at about 200 ms (slow regular). Other subjects did not show clear signs of two modes in the range of 100 to 180 ms, and still others did not produce any reaction times below 135 ms. In the overlap task as well three or even more peaks were obtained at about the same positions along the reaction time scale of many, but not all subjects. Group data as well as those of individual subjects were fitted by the superposition of three gaussian functions. Segregating the reaction time data into saccades that over- or undershoot the target indicated that express saccades almost never overshoot. The results are discussed in relation to the different neural processes preceding the initiation of visually-guided saccades.

Separate populations of visually guided saccades in humans: reaction times and amplitudes.

The saccadic eye movements of three humans and one non-human primate (a male rhesus monkey) have been measured for target eccentricities between 0.3 and 15 deg. With a gap task (fixation point offset precedes target onset by 200 ms) and a target at 4 deg, all subjects produced reasonable amounts of express saccades as indicated by a clear peak in the distribution of their saccadic reaction times (SRT): about 100 ms in human subjects and 70 ms in the monkey. This peak disappeared with decreasing target eccentricity below 2 deg, but saccades of longer (regular) reaction times were still present. Thus it was found that there exists a dead zone for express saccades. In addition, small saccades have a much stronger tendency to overshoot the target and their velocity falls above the main sequence as defined by the least square fit of an exponential v=vo(1-exp(-a/ao)) to the maximal velocity (v) versus amplitude (a) relationship (vo and ao are constants fitted). It is concluded that for small saccades the express way is blocked functionally or does not exist anatomically.

Dead zone for express saccades.

Twenty-four children made saccades in five noncognitive tasks. Two standard tasks required saccades to a single target presented randomly 4 deg to the right or left of a fixation point. Three other tasks required sequential saccades from the left to the right. 75 parameters of the eye-movement data were collected for each child. On the basis of their reading, writing, and other cognitive performances, twelve children were considered dyslexic and were divided into two groups (D1 and D2). Group statistical comparisons revealed significant differences between control and dyslexic subjects. In general, in the standard tasks the dyslexic subjects had poorer fixation quality, failed more often to hit the target at once, had smaller primary saccades, and had shorter reaction times to the left as compared with the control group. The control group and group D1 dyslexics showed an asymmetrical distribution of reaction times, but in opposite directions. Group D2 dyslexics made more anticipatory and express saccades,...

Saccadic Eye Movements of Dyslexic and Normal Reading Children

Saccadic reaction times (SRTs) of three human subjects were analyzed. The gap paradigm was used (i.e. fixation point offset precedes target onset) to obtain high proportions of express saccades (i.e. saccades of extremely short reaction times) in the SRT distributions. In one set of experiments, the luminance of the (red) saccade target was varied from brighter to darker than the (green) background including an isoluminance condition. Express saccades were obtained in response to pure color contrast stimuli with about the same frequency and reaction time as to stimuli with both color and luminance contrast. In a second experiment, the luminance contrast of a white target on a white background was lowered below 10%. Again the number of express saccades was not reduced. Thus, in contrast to other perceptual phenomena the visual neural mechanisms underlying the generation of express saccades are not affected by isoluminance nor low contrast luminance.

Occurrence of express saccades under isoluminance and low contrast luminance conditions.

The eye movements of three human subjects have been measured when they made saccades to single targets at eccentricities between 0.3 and 15 degrees. If the fixation point disappeared 200 ms before a target at 4 degrees was presented (Gap condition), all subjects produced reasonable amounts of express saccades as indicated by a clear peak in the distribution of the saccadic reaction times (SRT) located at about 100 ms ( Fischer & Ramsperger, 1984 ). The peak disappeared when the target eccentricity decreased below 2 degrees, but saccades of longer (regular) reaction times were still present. Thus it was found that there exists a dead zone for express saccades. Yet there was a clear gap effect for small saccades, i.e., the latencies were shortened when the fixation point was extinguished before the onset of the target (Gap condition) as compared to the Overlap condition where it remained visible throughout the trials. In addition, small saccades had a much stronger tendency to overshoot the target and their velocity falls above the main sequence as defined by the least square fit of an exponential v = vo [1 – exp(-a/ao)] to the maximal velocity (v) versus amplitude (a) relationship (vo and ao are constants fitted). It is concluded that for small saccades the express way is blocked functionally or does not exist anatomically.

Franz Aiple

Papers

Separate populations of visually guided saccades in humans: reaction times and amplitudes.

Dead zone for express saccades.

Saccadic Eye Movements of Dyslexic and Normal Reading Children

Occurrence of express saccades under isoluminance and low contrast luminance conditions.

Reaction Time and Velocity of Small Saccades in Man