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Biomedical subjects

E Levinson

Publications and source records attributed to E Levinson.

At least 19 recordsLinked to original sources
PubMed1988

Apparent motion can be perceived between patterns with dissimilar spatial frequencies.

Many recent models of movement processing in the human visual system predict that the perception of apparent motion requires stimuli that are similar in spatial frequency. The data presented here provide an example of the perception of apparent motion between patterns with nonoverlapping harmonic content. When patterns presented in alternate frames are dissimilar, motion can be perceived as long as the velocity is not too high.

Form Perception↗
PubMed1977

Visual movement perception in the cat is directionally selective.

Behavioral experiments show that the visual system of cat contains mechanisms which are selective for direction of stimulus movement. The cat's contrast detection threshold for a drifting grating is unaffected by the addition of a grating moving in the opposite direction; this same pattern of results is found for human observers. The convergence of cat and human psychophysical data suggests that man's brain may hold direction-specific neurons, similar to those known to exist in the cat brain.

Animals↗
PubMed1977

Spatial properties of binocular neurones in the human visual system.

The spatial properties of human binocular mechanisms were investigated using the technique of subthreshold summation. Isolation of binocular mechanisms was achieved by means of interocular stimulus presentation. The contrast detection threshold for a sinusoidal test grating viewed by one eye was found to be reduced by a subthreshold grating of the same spatial frequency and orientation seen by the other eye. The interaction between the gratings was approximately linear. Threshold increased as the spatial frequencies or orientations of test and subthreshold gratings were made increasingly different. Spatial stimulus specificities measured in this way were as great for interocular presentation as for simultaneous monocular presentation. The results suggest that human contrast sensitivity for gratings may depend upon binocularly-activated neurones similar to those found in cat and monkey visual cortex.

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↗