N. Yakimoff

Selective directional sensitivity in visual motion perception

We present two experiments demonstrating that: (i) the latency of perception of the position of a small visual target moving towards the fovea is shorter than that of the same target moving away from the fovea; (ii) the reaction time (RT) to onset of motion of the same type of target is also shorter when it moves towards the fovea; and (iii) the RT to onset of motion away from the fovea may be shorter when larger, textured stimuli are employed. The relation of the findings to the existence of two systems for visual motion information processing and to recent neurophysiological findings is discussed.

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.

Localization of brief visual stimuli during pursuit eye movements

Experimental findings concerning the properties of the phenomenon of mislocation of brief visual stimuli during smooth eye tracking are described. One of these, which cannot be explained by existing hypotheses, is that under certain conditions the mislocation magnitude tends to have zero or even negative values. A model is developed for explanation of the mislocation phenomenon. It is suggested that localization is based on: (1) information about the current eye position and (2) information about the stimulus locus on the retina. They both arrive at the localization centre with non-zero delays. The mode of information processing in this centre leads to a magnitude of mislocation which is proportional to the difference between the two delays and which could be positive, zero or negative. Factors which influence either delay should also influence the mislocation magnitude.

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.

Motion Extrapolation Performance: A Linear Model Approach:

Researchers have obtained similar results from different visual motion extrapolation experiments despite the large variety of motion stimuli used. With respect to the ability of human subjects to judge the moment at which an occluded moving stimulus arrives at a predetermined position along its motion path, the general conclusion has been that errors increase with the duration of the occluded motion. However, substantial individual differences are often obscured within this statement. We propose a linear model to describe the performance of human observers in motion extrapolation tasks. The results from an experiment on centrifugal and centripetal motion extrapolation are examined in terms of this model. We discuss the restrictions imposed by the model on conclusions drawn after converting estimated arrival times to velocity estimates or accuracy scores. The parameters of the linear regression describing the individual performance in motion extrapolation tasks might be appropriate measures of interindividual differences.

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.

A constant latency difference determines directional anisotropy in visual motion perception.

In a recent paper in this journal (Mateeff, Yakimoff, Hohnsbein, Ehrenstein, Bohdanecky & Radil, 1991) we reported a new visual anisotropy: inward (foveopetal) motion of a small visual target was perceived with a latency shorter than the perceptual latency of outward ( foveofugal) motion. The latency difference was demonstrated by a simultaneity judgement task. A visual target moved horizontally toward or away from a fixation point. Another stationary target was positioned just above the path of the moving target at a distance of 16 deg from the fixation. A fovea1 light signal was given during the motion and the observer had to judge whether the moving and stationary peripheral target were aligned at the moment the signal occurred. Under the condition of inward motion apparent alignment occurred more than 100 msec earlier than in the case of outward motion. The possibility that the different performance under the two directions of motion might be due to less accurate localization of targets in the visual periphery was ruled out by the results of a control task. In this task the moving target disappeared and the observers had to localize the place of disappearance relative to the stationary target. Although their accuracy in determining the position of the moving target at the moment of its disappearance was not perfect, the mislocations obtained could not explain quantitatively the data from the simultaneity judgement task. It was concluded that centripetal motion of visual targets is indeed perceived faster than centrifugal motion, There is another way to distinguish the effects of spatial and temporal factors in the localization of moving targets: by measuring the moment of subjective alignment between the stationary and the moving targets for different target velocities. If performance is determined only by a constant perceptual delay, the latency difference between inward and outward motion should remain the same as velocity is varied. Correspondingly, the localization errors should increase with increasing velocity. On the other hand, if performance is determined only by a constant spatial error, then the mislocation should remain the same at different velocities, implying that the latency difference between inward and outward motion diminishes with increasing velocity. In the two experiments reported here the main and the control tasks of the first experiment described by Mateeff et al. (1991) were replicated for different motion velocities.

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.