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Biomedical subjects

S Mateeff

Publications and source records attributed to S Mateeff.

17 recordsLinked to original sources
PubMed1991

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.

Adult↗
PubMed1991

Perceptual constancy during ocular pursuit: a quantitative estimation procedure.

Perceptual constancy of visual motion is usually described as the degree of correspondence between physical and perceived characteristics of motion in the external world. To study it, one has to assess the relationship between physical motion, its retinal image, and its perception. We describe a quantitative estimation procedure for a measure K denoting the degree of perceptual constancy of background target motions noncollinear to the eye movements during ocular pursuit. The calculation of K is based on three vectors describing the target motion (1) as it is physically, (2) as it is mapped to the retina, and (3) as it is perceived, but only the direction of the perceptual motion vector has to be determined experimentally. K allows for quantitative comparison between experiments with a variety of parameters in visual motion displays.

Eye Movements↗
PubMed1990

Visual localization and estimation of extent of target motion during ocular pursuit: a common mechanism?

The ability to localize a visual target and to estimate the distance through which it moves was studied during ocular pursuit. In the first experiment observers had to localize the position of a visually tracked moving target when they heard an acoustic signal. The signal was sounded near the beginning or near the end of the motion. The distance between the perceived positions was shorter than the distance between the corresponding physical positions of the target. The 'shortening' became more pronounced with higher tracking velocity. In another condition the observers estimated the length of the motion path between two successive sound signals, one presented near the beginning and one near the end of the motion. The length of path travelled was underestimated, the effect being stronger with higher tracking velocity. In the second experiment this effect of velocity on the underestimation of distance was shown to exist only during ocular pursuit and not during steady fixation. The hypothesis that localization and estimation of distance during ocular pursuit share a common mechanism is discussed.

Acceleration↗
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↗
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↗
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↗