L. Mitrani

Is saccadic suppression really saccadic

Abstract Visual thresholds were measured during voluntary saccades of 8° under different conditions. From the experimental data the contributions of the “smearing” and the propre suppression were evaluated. It was found that the suppression disappears when the luminance of the screen was 4 × 10 −2 nt. On the contrary, the suppression increases when the screen was made nonuniform by means of black figures on it. Conclusion is made that the “saccadic suppression” is not saccadic but merely depends on the motion of the entire visual pattern on the retina.

Smearing of the retinal image during voluntary saccadic eye movements

Abstract Voluntary saccades of 13° arc are made and temporal thresholds for two kinds of stimuli—horizontal and vertical bands—are obtained. A quantitative estimation of “smearing” contribution in the process of decrease in vision during voluntary saccade is made. Data, that “smearing” of the retinal image plays a definite role are given.

Oculomotor and perceptual localization during smooth eye movements.

The mislocation of brief flashes presented during smooth tracking eye movements has been known since the work of Hazelhoff and Wiersma (1924). Mateeff (19773 has criticized their explanation of this penomenon based on the concept of visual latency. In another study, Mitrani and Dimitrov (1978) showed that the smooth eye movement persisted for some time after the disappearance of the moving target pursued with the eyes. This is what we shall call “overtracking”. The present letter is aimed at revealing to what extent the overtracking and the mislocation of a disappearing moving target are interrelated and whether the misIocation can be determined by the ocutomotor behavior during performance of the localization task.

Temporal and spatial characteristics of visual suppression during voluntary saccadic eye movement

Abstract An experimental arrangement enables the presentation of stimuli on different places of the retina with variable delays during voluntary saccades. The percentage of stimuli seen in a trial under definite conditions is taken as a measure of vision. Distribution of the visual suppression during voluntary saccade on different places of the retina was obtained. The fovea centralis is not always the most sensitive part of the retina. Data, that both the degree and the time-course of the suppression of different parts of the retina vary during the saccade are given.

Dependence of visual suppression on the angular size of voluntary saccadic eye movements.

Abstract Voluntary saccades of 17°, 15°, 13°, 11° and 8.30 min arc were made and a 20 msec stimulus presented as the saccade began. The percentage of trials in which the subject reported that he had seen the stimulus was taken as a measure for the vision suppression. A linear dependence between the size of the saccade and the percentage has been observed. The larger the saccade the smaller the percentage of stimuli perceived. This linear dependence gives clear evidence that the simple “smearing” of the retinal image can not be the only cause for the decrease in vision during a voluntary saccade.

Some characteristics of the visual masking by moving contours.

Abstract The visual threshold elevation caused by jerk movements of a vertical grating in the visual field is considered. The dependence of the effect on the movement durations and the spatial background distribution are investigated. The main conclusions are that the masking is due to the movement of the grating and not to its displacement from one retinal locus to another one; the masking range is about 4° and only the parts of the grating near to the stimulus produce an essential masking effect.

Deterioration of vision due to contour shift over the retina during eye movements.

It has been pointed out (MacKay. 1970; hlitrani. bfateeff and Yakimoff. 1971; Mitrani. Yakimoff and bfateeff. 1973) that shifts of the retinal image due either to eye movements or swift displacement of the picture a subject is looking at cause an elevation of visual thresholds. One possible explanation of this effect is connected with the assumption that movement of contours over the retina is the source of the observed visual suppression. However, two independent interpretations are possible: either the displacement of contours (i.e. their continuous movement is the cause of the suppression) or the disappearance of a given structure in one place and its appearance in another place on the retina. In an attempt to obtain more data concerning the two points of vievv we performed some new experiments with saccadic eye movements.

Scanning open and closed polygons

The process of selection of target points during voluntary eye movements when contoured polygonal shapes with open and closed angles are observed was analysed in humans by means of an eye recording technique. It has been found for both types of stimuli that the majority of fixation points where located at angles and that the mean value of distribution was found to be more distant from the vertex for acute angles than for obtuse ones. In this respect a difference was found between open and closed contours. In the former case the mean values of fixation point distribution were more distant from the vertex and the dispersion of eye fixation was greater.