A continuously lit stimulus is perceived to be shorter than a flickering stimulus during a saccade (original) (raw)

Spatial Independency in Perceived Lengths of Saccade-Induced Images

PSYCHOLOGIA -An International Journal of Psychology in the Orient, 2005

When observers make a saccade across a flickering light dot at the same location, they usually perceive an array of dots (Hershberger, 1987). This phenomenon can be exploited for presenting two-dimensional images using only a single dimensional light source such as a single column of LEDs or laser projectors. In the present study, we investigated whether the perceived length of saccade-induced images is modulated by relative position of the light source and the observer. Participants were presented with a continuous laser-lit dot at several different locations adjacent to a saccade target. On each trial, they were required to make a saccade from a fixation point to the saccade target and then to localize the two endpoints of perceived line induced by the saccade. The results showed that the perceived length of the saccade-induced lines was approximately a half of the distance between the fixation point and the saccade target regardless of the light source location.

Perception of relation of stimuli locations successively flashed before saccade

Vision Research, 2001

Based on localization error for a single perisaccadic flash, eye position signal is supposed to change more slowly than physical eye position. Nevertheless, a flicker is not perceived as moving in accordance with localization error for a single flash. We carried out two experiments to investigate this problem. Experiment 1 examined how a single flash or a flicker presented before saccade was perceived. The results showed that the flicker was not perceived as moving, although mislocalization for the single flash increases gradually before saccade. Experiment 2 was a vernier test of two stimuli successively flashed before the saccade. The results showed that the point of subjective equality shifted in accordance with the mislocalization for a single perisaccadic flash when the interstimulus interval (ISI) was about 2 s; however, it did not shift when the ISI was 78 ms. Comparison between these results and previous studies suggests that the relation of the locations of successive flashes before saccade is perceived exocentrically when the ISI and stimulus onset asynchrony between flashes was short.

Saccades to remembered targets: The effects of saccades and illusory stimulus motion

Vision Research, 1998

In 10 human subjects, we measured the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display, while they tracked a spot of light that stepped between three vertical locations. The background was either stationary or stepping horizontally in synchrony with vertical motion of the spot of light, a condition that induced a strong illusion of diagonal target motion. Memory-guided saccades were less accurate horizontally, but not vertically, when the background moved compared with when it was stationary. The horizontal component of memory-guided saccades correlated better with the position of the background when the target was flashed than with the position of the background at the end of the memory period. We conclude that the visual illusion corrupted the working memory of target location, but had a lesser effect on the estimate of gaze at the end of the memory period, which seemed to depend more on extraretinal signals. Published by Elsevier Science Ltd.

The effect of Kanizsa’s compression illusion on reflexive saccades

Experimental Brain Research, 2006

When a horizontal line is occluded by a surface, subjects misperceive the line as being compressed, that is, they perceive it to be shorter than it really is (Kanizsa's compression illusion). The size of the compression effect usually ranges from approximately 5 to 10%. In this experiment, subjects executed reflexive saccades from one end of a line, presented at fixation, to the other end, with and without an occluding square. Saccade amplitude was reduced in all subjects in the presence of an occluding square; the effect averaged about 5%. These results demonstrate that saccade amplitude is modified by the Kanizsa compression illusion. They provide further evidence that reflexive saccade amplitude can be altered by illusion inducing stimuli, to the same degree as perceptual effects, even in circumstances in which other motor behaviours resist the illusion. They are difficult to reconcile with any strong version of the ''two visual systems hypothesis''.

Spatial compression: Dissociable effects at the time of saccades and blinks

Journal of Vision, 2015

Various studies have identified systematic errors, such as spatial compression, when observers report the locations of objects displayed around the time of saccades. Localization errors also occur when holding spatial representations in visual working memory. Such errors, however, have not been examined in the context of eye blinks. In this study, we examined the effects of blinks and saccades when observers reproduced the locations of a set of briefly presented, randomly placed discs. Performance was compared with a fixation-only condition in which observers simply held these representations in working memory for the same duration; this allowed us to elucidate the relationship between the perceptual phenomena related to blinks, saccades, and visual working memory. Our results indicate that the same amount of spatial compression is experienced prior to a blink as is experienced in the control fixation-only condition, suggesting that blinks do not increase compression above that occurring from holding a spatial representation in visual memory. Saccades, however, tend to increase these compression effects and produce translational shifts both toward and away from saccade targets (depending on the time of the saccade onset in relation to the stimulus offset). A higher numerosity recall capacity was also observed when stimuli were presented prior to a blink in comparison with the other conditions. These findings reflect key differences underlying blinks and saccades in terms of spatial compression and translational shifts. Such results suggest that separate mechanisms maintain perceptual stability across these visual events.

Temporal uncertainty separates flashes from their background during saccades

The Journal of Neuroscience, 2011

It is known that spatial localization of flashed objects fails around the time of rapid eye movements (saccades). This mislocalization is often interpreted in terms of a combination of shifts and deformations of the brain's representation of space to account for the eye movement. Such temporary remapping of positions in space should affect all elements in a scene, leaving ordinal relationships between positions intact. We performed an experiment in which we presented flashes on a background with red and green regions to human subjects. We found that flashes that were presented on the green part of the background around the time of a saccade were readily reported to have been presented on the red part of the background and vice versa. This is inconsistent with the notion of a temporary shift and deformation of perceived space. To explain our results, we present a model that illustrates how temporal uncertainty could give rise to the observed spatial mislocalization. The model combines uncertainty about the time of the flash with a bias to localize targets where one is looking. It reproduced the pattern of mislocalization very accurately, showing that perisaccadic mislocalization can best be explained in terms of temporal uncertainty about the moment of the flash.

The Phantom Array: A Perisaccadic Illusion of Visual Direction

The Psychological Record

Naive observers (N = 75) were asked to saccade in the dark across a point light source blinking on and off at 200 Hz and to describe the resultant phantom array . The vast majority represented this perisaccadic illusion of visual direction essentially as Hershberger described it. Replicable features of the phantom array imply that the perisaccadic shift of retinal local signs (i.e., spatiotopic coordinates) is discontinuous, comprising two separate parts, a discrete partial shift that occurs before the eyes start to move, and a continuous partial shift that is completed at about the same time as the eye movement. Although these implications are consistent with recent experimental findings, they are inconsistent with the received view that retinal local signs shift sluggishly. The phantom array implies that the faster, presaccadic, partial shift has a time constant of 5 ms or less.

Perisaccadic perception of continuous flickers

Vision Research, 2005

To realize perceptual space constancy, the visual system compensates for the retinal displacement caused by eye movements. It has been reported that the compensation process does not function perfectly around the time of a saccade--a perisaccadic flash is systematically mislocalized. However, observations made with transient flash stimuli do not necessarily indicate a general perisaccadic failure of space constancy. To investigate how the visual system realizes perisaccadic space constancy for continuous stimuli, we examined the time course of localization for a perisaccadic 500 Hz flicker with systematic variation of the onset timing, the offset timing and the duration. If each flash in the flicker is localized individually in the same way as a single flash, the apparent position and length of the flicker should be predicted from the time course of mislocalization of a perisaccadic flash. However, the results did not support this prediction in many respects. A dot array (of half the length of the retinal image) was perceived when the flicker was presented during a saccade, while only a single dot was perceived when the flicker was presented only before or after the saccade. A flash in a flicker was localized at a different position, depending on the onset timing, the offset timing and the duration of the flicker, even if the flash was presented at the same timing to the saccade. In general, our results support a two-stage localization in which the local geometrical configuration is first generated primarily based on the retinal information, and then localized as a whole in the egocentric or exocentric space. The localization is based on the eye position signal sampled at a time temporally distant from the saccade, which enables precise localization and space constancy for continuous stimuli.

Influence of visual perception on spatial coding of saccadic eye movements and fixation

Neuro-Ophthalmology, 2004

The Müller-Lyer illusion produces differences in visual length perception when lines of equal length are presented as doublearrows with inward-pointing and outward-pointing arrowheads, respectively. The aim of this study was to investigate the influence of length perception on the amplitude of saccadic eye movements and on postsaccadic fixation positions. Video recordings of eye movements were obtained from 35 healthy volunteers (age: 20-30 years) while they scanned the endpoints of Müller-Lyer targets. The targets were presented in horizontal and vertical orientations with an arrow length of 15 •. Fixation periods between the saccades were adjusted at 1 s and 4 s. The final saccadic amplitudes between the endpoints of Müller-Lyer figures reflect the visually perceived length differences: lines with outward-pointing arrowheads were scanned with smaller saccades than lines with inwardpointing arrowheads. This bias in final saccadic amplitude was equal in both the horizontal and vertical target orientations as well as for 1-s and 4-s fixation periods. Postsaccadic drift after initial saccadic movements reduced the effect of the Müller-Lyer illusion depending on arrowhead and target orientation: outward-pointing horizontal arrows caused hypometric pulses, while inward-pointing vertical arrows caused hypermetric pulses. The results of this study demonstrate that spatial coding of both saccadic eye movements and fixation is strongly influenced by visual perception. While the influence of the Müller-Lyer illusion on final saccadic amplitudes did not depend on target orientation or fixation period, an additional pulse-step mismatch appeared in the horizontal (hypometria) and vertical (hypermetria) direction.

The use of the saccade target as a visual reference when localizing flashes during saccades

Journal of …, 2010

Flashes presented around the time of a saccade are often mislocalized. Such mislocalization is influenced by various factors. Here, we evaluate the role of the saccade target as a landmark when localizing flashes. The experiment was performed in a normally illuminated room to provide ample other visual references. Subjects were instructed to follow a randomly jumping target with their eyes. We flashed a black dot on the screen around the time of saccade onset. The subjects were asked to localize the black dot by touching the appropriate location on the screen. In a first experiment, the saccade target was displaced during the saccade. In a second experiment, it disappeared at different moments. Both manipulations affected the mislocalization. We conclude that our subjects' judgments are partly based on the flashed dot's position relative to the saccade target.