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Biomedical subjects

L Mitrani

Publications and source records attributed to L Mitrani.

At least 37 records · Page 2Linked to original sources
PubMed1983

Estimation of brief time intervals presented in the right and left visual half-fields.

The perception of visually presented duration is studied depending on the visual half-field in which the light stimulation has been presented. Light stimuli of the order of 200-1000 ms, of equal duration, divided by a 10 ms interval, were presented in random order, one in the left, the other in the right visual half-field. The subjects' task was to determine which of the pair of stimuli seemed longer. The response "equal in duration" was not allowed. It was found that two light stimuli of equal duration, consecutively presented in the left and right visual half-fields, are perceived as different owing to their time order. This difference reveals the effect of hemispheric differences in duration perception--the second of the pair of stimuli was reported by the subjects as longer in 70% of the cases when it was presented in the left visual half-field, while the second--in the right visual half-field was reported as longer in 60% of the cases.

Adult↗
PubMed1982

Visual localization during eye tracking on steady background and during steady fixation on moving background.

Experiments were performed to clarify the role of the background motion on the retina in the phenomenon of mislocation of brief visual stimuli during smooth eye tracking. It was found that these visual stimuli were mislocated also relative to a moving background during steady eye fixation. The magnitude of mislocation during pursuit eye movements and during steady fixation was influenced by the stimulus intensity, the background/eye velocity and the place of stimulus presentation in respect to the background; the influence having the same features in both cases. However, the magnitudes of mislocation under the two conditions were quantitatively different. The validity of a hypothesis that the eye movement itself plays no role in the process of localization, and, that this process is based on retinal information only, is considered.

Adult↗
PubMed1982

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.

Adult↗
PubMed1982

Retinal location and visual localization during pursuit eye movement.

Experiments were performed to measure the mislocation of a brief visual stimulus presented during pursuit eye movements in different places over the retina. The results obtained show that the mislocation for regions 5 degrees from fovea in the direction of motion is greater than in fovea. This fact shows that some kind of reorganization takes place in the visual localization mechanisms during pursuit eye movements. The results cast doubts on the concept of "perception time" which is often used to explain the visual mislocation phenomenon.

Adult↗
PubMed1982

Half-field asymmetry in visual perception of distance.

Distances were presented to the right and left halves of the visual field during steady fixation of a central point. Two methods of evaluation were used: direct scaling and the method of limits. A small but statistically significant difference was found between the estimates of distances presented to the left and to the right of the fixation point by direct scaling. No difference was found when the method of limits was used. The results are interpreted as evidence for the existence of functional asymmetry connected with the computation-and-speech ability of the hemispheres. No evidence for perception asymmetry could be found.

Adult↗
PubMed1982

Direct scaling of short time intervals presented with moving and stationary visual stimuli.

The subjective duration of moving and stationary stimuli was compared by the method of magnitude estimation. The psychophysical functions for both types of stimuli differ in shape. The psychophysical function in the case of stationary stimuli is linear as it has been shown in earlier investigations. The psychophysical function in the case of moving stimuli is not linear because for certain velocities there appear inversions in it. Above a certain velocity the duration of moving stimuli is perceived as longer than that of the stationary ones.

Adult↗
PubMed1981

Visio-motor prediction of collision.

Visually presented moving stimuli were used in a collision prediction experiment aimed at revealing the ability of human subjects to estimate the velocity of motion. Spatial extent, velocity and exposure duration of movement were varied so that the correlation between these characteristics of the stimuli was low (about 0.5). The moving stimulus disappeared at a certain place on the screen. By pressing a button the subject had to estimate the moment the stimulus would reach a target in the visual field. A linear dependence between estimated and actual duration of concealed motion was obtained. It is concluded that spatial extent and duration of motion do not influence the performance of the task. Velocity estimation and individual characteristics of the mechanisms controlling the motor response are supposed to determine the linear dependences obtained for all subjects tested.

Accidents↗
PubMed1981

Localization of brief light stimuli on differently labelled reference patterns during smooth eye tracking.

Experiments are reported in which the mislocation of brief visual stimuli during tracking eye movements was measured in respect to three kinds of reference patterns placed in the horizontal plane--A) a scale with numbered divisions, B) a bar consisting of seven differently hatched regions; and C) two single markings, the distance between them being equal to the length of patterns A and B. A mislocation of a magnitude up to 2 degrees was obtained in all experiments. The mislocation on reference patterns A and C was the same, the presence of numbered markings did not influence it. The mislocation magnitude tended to decrease when reference pattern B was applied. Conclusion was made that clearly labelled structures near the place of stimulus presentation were a visual cue which affects localization; a scale with identical numbered markings, despite their proximity to the test stimulus, was not a structure of this type.

Eye Movements↗
PubMed1981

Scaling spatial extent, velocity and duration of motion.

Experiments on magnitude estimation of spatial extent, velocity and duration of 11 moving stimuli which had low correlations between the stimulus attributes revealed psychophysical curves of different slopes and shapes for the three attributes of motion. A psychophysical power function with an exponent almost equal to 1.0 described the magnitude estimation of distance. Deviations in velocity judgments were observed with shortening the spatial extent of motion. Duration estimation determined by moving stimuli was found to differ significantly from the estimation of time intervals of the same range presented with stationary light stimuli (Marinova, Mitrani, Yakimoff, 1980). The results indicate that velocity cannot be regarded as a directly perceived attribute of motion. Distance only seems to be directly perceived.

Distance Perception↗
PubMed1981

Estimating the velocity of briefly presented moving stimuli.

The ability of human subjects to estimate the velocity of briefly presented moving stimuli was studied in a prediction-of-collision experiment. After the disappearance of the moving target the subject had to press a button at the moment the target would reach a predetermined position in the visual field. Four velocities of the moving target were used -6 degrees/s, 10 degrees/s, 14 degrees/s, and 20 degrees/s. For each velocity there were five exposure distances: 0.5, 1.0, 2.0, 3.0 and 4.0 degrees and four concealment distances: 6, 8, 10 and 12 degrees. For the large exposure distances a linear dependence of the response time on the concealment time was observed. This dependence was not linear for exposure durations less than 100 ms. The response time increased in these cases. Despite the common character of the results obtained with different subjects there were clear individual differences most probably due to differences in subjective velocity scales and individual mechanisms of motion extrapolation and organization of motor responses.

Humans↗
PubMed1980

Dependence of the delay time for smooth pursuit eye movements in man on the velocity of the visual target.

Experiments were performed to measure the dependence of the delay time of the appearance of the first saccade preceding smooth eye movement on the velocity of the target. A clear hyperbolic dependence was found meaning that the delay time is composed of at least two components, i.e. the time needed to measure the stimulus velocity and the time to select one program for the smooth eye movement. The results are interpreted on the assumption that these movements are preprogrammed rather than of servomotor type.

Eye Movements↗
PubMed1980

Time estimation of visually presented increment and decrement stimuli: the filled-duration illusion.

Experiments were carried out to estimate the duration of time intervals in the 100-1100 ms range, using the direct scaling method. Time intervals were filled: (a) by increment visual stimuli on a light background, (b) by decrement visual stimuli on a light background, (c) only by background illumination. The results obtained show that increment stimuli are perceived as equal in duration to the decrement stimuli. Both increment and decrement stimuli are perceived to be longer than the intervals during which only the background was presented. These results make it possible to generalize the concept of filled and unfilled intervals. A hypothesis is raised that the filled-duration illusion is due not to the properties of the on- and off-effects in the visual system but to processes in the iconic memory connected with the presence of an image (increment or decrement) in the filled intervals.

Humans↗
PubMed1980

Influence of the standard stimulus in magnitude estimation of time intervals.

Visually presented time intervals between 100 and 1100 ms were scaled directly. Six different standards within the same range were used. The dependence between the reports and the presented time intervals was found to be linear. Different standards led to estimates lying on different straight lines. The slope of these straight lines decreases upon increasing the standard. Nevertheless the ratio between two neighbouring estimates of each straight line remains invariant with respect to the changes in the standard.

Adult↗
PubMed1980

Some temporal characteristics of eye tracking.

The frequency of occurence and the latency of eye tracking determined by moving stimuli of different velocities (5, 10 and 15 degrees/s) and different durations (between 50 and 400 ms) were measured. The result was that eye movement can occur only if the duration of the stimulus exceeds a critical value. This value depends on the stimulus velocity. The difference between the latency of the movement and the critical duration of the stimulus however remains constant. This difference is interpreted as the time necessary for selecting and releasing the appropriate programme for eye movement.

Adult↗
PubMed1979

Localization of the change in intensity of a visually pursued light target.

The aim of the subjects was to track a moving light target and to locate the change in its intensity (its disappearance or dimming). It is shown experimentally that: (1) mislocation of target disappearance is smaller than mislocation when the target is dimmed three times; (2) the distance at which the eyes move after the target is darkened does not influence localization. The data disprove possible influence of "overtracking" on localization. They are in favour of the hypothesis about the dependence of localization on stimulus intensity.

Adult↗
PubMed1977

Localization of the disappearance of a light target during tracking eye movements. II.

A light target moving with constant velocity and disappearing at a place determined by the experimenter, is presented to the subjects who track it visually and determine the locus of its disappearance with respect to a scale mounted on the screen. The result is that the disappearance of the target is systematically mislocated in the direction of the eye movement. The value of the mislocation depends on the target intensity. Under different experimental conditions the subjects localize target disappearance by steady fixation of the eyes. The resulting mislocation has entirely different characteristics compared with the first conditions. The theory that the phenomenon of mislocation is due only to wgnal latency in the visual pathways is rejected. A hypothesis is proposed concerning the participation of psychological factors in the process of localization.

Eye Movements↗