Biomedical subjects

J L Barbur

Publications and source records attributed to J L Barbur.

39 records · Page 3Linked to original sources

PubMed1980

Quantitative studies of some dynamic visual effects.

The viewing of rotating or rapidly approaching one-dimensional periodic structures results in the perception of a high-contrast band on a uniform structureless surround. For rotating gratings, the width of the generated band is inversely proportional to the angular speed of rotation and the orientation of the band lags behind the direction perpendicular to the grating lines for both clockwise and anticlockwise rotation of the pattern. The amount of lag is proportional to the angular speed of rotation. The width of the band perceived during the viewing of an approaching or receding grating is inversely proportional to its speed, and the orientation of the generated band is along the direction of the lines in the grating. A model is proposed which explains and predicts the effects observed during the viewing of one-dimensional periodic structures in terms of temporal luminance integration in the visual system. The extent to which temporal luminance integration is responsible for the perception of frame or element movement in multielement stimulus frames is also examined. The results obtained with monocularly or dichoptically presented multielement stimulus frames, as well as other relevant psychophysical and physiological data, suggest that the temporal integration responsible for the observed effects is associated with mechanisms of early-stage visual processing which must be located prior to the lateral geniculate nucleus level.

Brain Mapping↗

PubMed1980

Human visual responses in the absence of the geniculo-calcarine projection.

This paper describes an investigation of responses elicited by flashed and moving light stimuli presented to the 'blind'half-field of a hemianopic subject. The detection mechanism is significantly less sensitive than that for vision in the normal half-field, but the increment threshold varies with the background illumination level in a manner similar to that for normal vision. The responses of the 'blind' hemifield are characterized by low critical fusion frequency (less than or equal to 8 Hz), large spatial summation and high sensitivity to fast moving targets. Velocity discrimination for targets located in the 'blind' hemifield is normal, but neither the shape nor the size of the target is discriminated. It is shown that the experimental data cannot be attributed to light scattered from the 'blind' into the normal hemifield, and other mechanisms which may be responsible for the observed responses are examined.

Adult↗

PubMed1979

A colour-dependent abnormality in human visual detection of stimulus motion and spatial structure.

We have studied the wavelength dependence of visual responses in a single human subject, M.W., who has an unusual visual defect. It is shown that for red stimuli, both spatial resolution for grating patterns and detection of target movement are grossly abnormal. On the basis of these and other [8] experimental data, we argue that M.W.'s response pattern implies interdependent central visual processing of colour, movement and spatial structure. We examine this conclusion in relation to recent anatomical and electrophysiological findings.

Color Perception↗