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Biomedical subjects

L Mitrani

Publications and source records attributed to L Mitrani.

At least 55 records · Page 3Linked to original sources
PubMed1977

Visual extrapolation of a line segment to the point of its intersection with a straight line. II.

The article describes three experiments to study visual extrapolation of a line segment to the point of its intersection with a straight line. Eye movements are shown to play no significant role in solving problems involving visual spatial extrapolation. It is also indicated that systematic mislocations of the point of intersection sought in cases of acute angles are preserved even when the motor response is substituted by verbal estimation. When the test line segment is presented for a very short time (tau =20 ms), the estimations of the subjects manifest great individual differences and considerable dispersion. The results of the experiments show that the ability of visual extrapolation is influenced by different and numerous factors and this ability does not reflect only the functioning of simple detectors for direction in the visual system.

Adult↗
PubMed1977

Estimation of duration of an array of time interval and of its separate elements.

It is shown that when a human subject estimates verbally the duration of an array consisting of three intervals - two light intervals divided by a dark one - considerable underestimation is observed compared with estimates of the same duration in the control experiment. In case of separate estimation of the three intervals composing the array the sum of the estimates is much more precise even compared with estimates in the control. Perhaps in this case the system for time intervals estimation operates with two "internal clocks", each of which reads the duration of the dark and of the light intervals. In estimating the array of three intervals the subjects estimate the total array and they do not summate their separate estimations. It may be assumed that the system uses only one "clock" for measuring the duration of the total array.

Adult↗
PubMed1977

Estimation of short time intervals under different experimental conditions.

A complex experiment is carried out in order to study the human ability to estimate and reproduce short time intervals in the 100-1000 ms range presented with light stimuli. The estimation task consists in verbal nomination of the time intervals presented to the subject in random order after preliminary training. In the production task the subject is expected to press a telegraph key simultaneously with the end of the light interval presented the duration of which is announced to him in advance. In the reproduction task the subject is to press the key a given time after the onset of the stimulus which duration is of 2 sec. The results show that in spite of the relatively good achievements in tasks involving verbal estimation of the duration of the intervals, the reproduction tasks are performed with systematic errors. In the production task the mean values of the response times decrease upon increasing of the required interval, while in the reproduction task they increase parallel with the increase of the required interval. Consequently, one and the same short time interval is perceived differently depending on the task to be performed, namely: verbal nomination, coincidence between hand movement and the end of the interval, or reproduction after verbal nomination.

Adult↗
PubMed1977

Estimation of time intervals--elements of an array of three intervals.

The article reports the results of experiments on human ability to estimate time intervals separately or in groups of two intervals as elements of a three-interval array presented by two light signals separated by a dark interval. The first light interval is shown to be systematically overestimated compared with the second one. Moreover, the subjects usually ascribe a constant value to the dark interval. The double interval (light + dark or dark + light) proves to be underestimated compared with the case when estimation of the same intervals was required without estimation of a third interval. The additional task changes the estimations of the subjects. It may be claimed that the complexity of the problem is connected with definite changes in the average estimations of the subjects.

Darkness↗
PubMed1977

Visual extrapolation of a line segment to the point of its intersection with a straight line. I.

A study is made of the capacity of fifty subjects to estimate the position of the point of intersection between a straight line and the visually extrapolated extension of a line segment at three different angles between the line and the segment: 30 degrees, 60 degrees and 90 degrees. The results show systematic deviations in the estimation of acute angles. The point of intersection of the straight line and the segment is misperceived to be shifted inwards in the angle between them. It is also shown that the set of imaginary extensions of a line segment with a given length, until its intersection with the given straight line, is determined only by the angle between the straight line and the segment and does not depend on the distance between them. Various possible mechanisms which could determine the solution of the task facing the subjects are discussed.

Adult↗
PubMed1977

Localization of disappearance of a light target during tracking eye movements. I.

A light target moving at a constant velocity in horizontal direction and disappearing at a locus determined by the experimenter is presented to the subjects in the experiments. The task of the subjects is to track its movement with their eyes and to determine the place of its disappearance using a scale fixed on the screen. Under these conditions they systematically mislocate the locus of disappearance in the direction of the eye movement. The mislocation is in linear dependence on the velocity of tracking and, moreover, it depends on the locus of disappearance of the target. The error is smaller when the target disappears at the end of tracking. The theory that mislocation is due to perception time is rejected.

Adult↗
PubMed1976

Duration estimation of visual light and dark stimuli.

Estimation of visual light and dark stimuli duration is studied in eight subjects. The intervals are within the range of 100 to 1,100 ms. Three of the subjects were trained with intervals presented with light stimuli, the others - with dark stimuli. Time intervals presented in both ways were given for estimation to both groups of subjects. The extimates depend on the position of the time intervals in the range, on the type of the stimuli with which they are presented and on the way of training.

Darkness↗
PubMed1976

Estimation of time intervals in an array of intervals. I.

It has been shown that when man estimates the duration of separate brief time intervals(300-1,000ms), elements of a certain array of time intervals within the same range, the estimation is not affected by changes in the other elements of the array. The complex light and dark intervals are considerably underestimated. The separate estimation of two elements (light and dark interval) from the array has shown that the sum of the separate responses exceeds the estimation when the same two elements have to be estimated together as a total interval. The results could be explained by the existence of at least two "internal clocks".

Adult↗
PubMed1975

Various background pattern-effect on saccadic suppression.

It has been proved that the saccadic suppression is a phenomenon closely related to the presence of contours and structures in the visual field. Experiments were performed to clarify whether the structured background influences the pattern of attention distribution (making the stimulus detection more difficult) or whether the elevation of visual threshold is due to the "masking' effect of the moving background image over the retina. Two types of backgrounds were used therefore: those with symbolic meaning in the processing of which "psychological' mechanisms are presumably involved like picture reproductions of famous painters and photographs of nudes, and those lacking semantic significance like computer figures composed of randomly distributed black and white squares with different grain expressed as the entropy of the pattern. The results show that saccadic suppression is primarily a consequence of peripheral mechanisms, probably of lateral inhibition in the visual field occurring in the presence of moving edges over the retina. Psychological factors have to be excluded as being fundamental for saccadic suppression.

Eye Movements↗