Radial bias for orientation and direction of motion modulates access to visual awareness during continuous flash suppression.

Abstract

Two types of radial bias have been demonstrated in the primate visual cortex: for orientation and for direction of motion. Considering that a visual neuron's directional selectivity is generally perpendicular to its preferred orientation, it is counterintuitive that radial biases for orientation and direction of motion coexist in retinotopic cortex including primary visual cortex. The current study measured the influence of radial bias for orientation and direction of motion on the access to visual awareness during continuous flash suppression. Strength of static and moving target stimuli, inferred by time to breakup of suppression, was modulated by the orientation and motion direction of the suppressed target stimulus according to its spatial location, indicating radial biases for both orientation and motion direction. However, orientation dominated over direction of motion when they were perpendicular to each other. These results indicate that, first, orientation-specific neural responses may be stronger than direction-specific neural responses at the stage of visual processing where interocular suppression is resolved. Second, the preferential processing of both orientation and direction of motion may result from anisotropic distribution of orientation- and direction-selective cells. Third, the neural substrate of the radial direction bias may reflect an orientation-specific neural response induced by fast-moving random dot patterns.