Visual masking by flickering surrounds.

Observers detected drifting sine-wave gratings presented in a circular 3 dia test field which was surrounded by a 3.25 degrees wide annulus. Forced choice contrast thresholds were measured with surrounds consisting of a steady field of light or uniform sinusoidal flicker. The flickering surround raised detection thresholds only for gratings with spatial frequencies below 2-4 c/deg. Variations on the basic experiment revealed that: (1) low spatial frequency gratings drifting through the surround masked detection of uniform flicker presented to the center; (2) masking did not depend greatly on the drift rate of the test grating but could not be obtained with stationary targets; (3) flicker restricted to either the top or side borders of the test field was a sufficient condition to produce masking; (4) the size of the masking effect decreased with center-surround separation. These results suggest a destructive interaction between transient mechanisms subserving neighboring regions of the visual field.