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Biomedical subjects

N Yakimoff

Publications and source records attributed to N Yakimoff.

13 recordsLinked to original sources
PubMed1978

Perceived orientation of dot patterns.

Fifty subjects were asked to assign orientation to different configurations of bright dots by means of an adjustable long line. Their performance of the task clearly demonstrates that the assigned orientation of each configuration coincides with the orientation of a line drawn through the dot pattern so that the sum of the squared distances between each dot and this line is minimum. Such a line remains invariant in respect to rotation of the set of dots. It is concluded that perceived orientation of dot patterns in the plane is an invariant characteristic of this kind of visual stimulus.

Humans↗
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↗
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

Visual extrapolation of two converging nonintersecting line segments.

Fifty subjects were tested to determine the point of intersection between two converging line segments. The angle between the two nonintersecting line segments was 30 degrees. The orientation of the display as well as the distance between the line segments and the point of their intersection was varied. Two-dimensional normal distributions can be accepted to describe the results - the 50 estimates of the point of intersection for each of the five displays presented. The parameters of these distributions are influenced mainly by two factors characterizing the test line segments: (1) proximity to one of the main axes - vertical and horizontal, and (2) distance to the actual point of intersection. The possible mechanisms that might be involved in the estimation of the point of intersection between two converging line segments are discussed.

Adult↗
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↗
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↗