PubMed Health⌕ Search

Biomedical subjects

R Sekuler

Publications and source records attributed to R Sekuler.

10 recordsLinked to original sources
PubMed1992

Temporal and spatial integration in dynamic random-dot stimuli.

Random-dot cinematograms comprising many different, spatially intermingled local motion vectors can produce a percept of global coherent motion in a single direction. Thresholds for discriminating the direction of global motion were measured under various conditions. Discrimination thresholds increased with the width of the distribution of directions in the cinematogram. Thresholds decreased as the duration of area of the cinematogram increased. Temporal integration for global direction discrimination extends over about 465 msec (9.3 frames) while the spatial integration limit is at least as large as 63 deg2 (circular aperture diameter = 9 deg). The large spatial integration area is consistent with the physiology of higher visual areas such as MT and MST.

Discrimination, Psychological↗
PubMed1979

Mutual repulsion between moving visual targets.

When two spatially intermingled sets of random dots move in different directions, the direction of each set may be misperceived. Observers report that each set of dots appears to move in a direction displaced by as much as 20 degrees from the direction of its companion set. Probably the result of inhibitory interactions, this mutual repulsion occurs at a central site in the visual system and may normally enhance discrimination of direction.

Eye Movements↗
PubMed1977

Mental set alters visibility of moving targets.

An observer's knowledge of a moving target's direction and velocity enhances detectability. In addition, knowledge of direction and velocity speeds an observer's reaction to the motion of a previously stationary target. Since rival, nonperceptual hypotheses can be ruled out, these effects represent a direct modulation of vision by mental set.

Cognition↗
PubMed1977

Rapid measurement of contrast-sensitivity functions.

We have developed a reliable and valid procedure for determining a person's contrast sensitivity function in approximately 6 min. This rapid procedure, which resembles that used in the Bekesy sweep-frequency audiometer, has potential as a clinical tool for diagnostic assessment.

Humans↗
PubMed1975

The independence of channels in human vision selective for direction of movement.

1. Human visual selectivity for direction of movement was determined using a subthreshold summation technique. 2. The threshold contrast for detecting a drifting sinusoidal grating was found to be independent of the contrast of an added subthreshold grating which moved in the opposite direction. 3. The detection threshold for a counterphase flickering grating is twice that for a moving grating, suggesting that the visual system analyses a counterphase grating as the sum of two half-contrast gratings which move in opposite directions. 4. Threshold for a counterphase grating may be linearly reduced by the addition of subthreshold background gratings drifting in either direction. Additivity between counterphase grating and moving background is complete. 5. After adaptation to a drifting grating, the behaviour of counterphase detection threshold as a function of the contrast of a moving subthreshold background depends upon the direction of background movement. When the background moves in a direction opposite that of the adaptation stimulus, complete linear additivity results. When the background moves in the same direction as the adapting grating, counterphase threshold is constant for low background contrasts, but drops linearly for higher background contrasts. 6. The results support the hypothesis that directionally selective channels in human vision are independent contrast detectors. Counterphase gratings are detected by one or the other of these direction-specific mechanisms, whichever is momentarily the more sensitive.

Adaptation, Ocular↗