Direction repulsion between components in motion transparency

Abstract

We measured the perceived direction of one motion component as a function of the contrast and speed of a second component for three pattern classes: plaids with two different spatial frequency components, multi-aperture patterns, and contrast-modulated (CM) patterns. The components were moving at +/-63.4 or +/-71.6 deg to the vertical, angles where motion transparency always occurred under our conditions. For multi-aperture and CM patterns on a single spatial scale, the components were perceived to deviate from the component motion directions by up to 20 deg at high contrasts or high speeds of the second component. However, for plaids with components on different spatial scales, the test components were perceived moving in the component directions regardless of the contrast or the speed of the second component. Our data show that this direction repulsion between components occurs within a single spatial scale but not between widely separated spatial scales. This implies that two different mechanisms are involved in motion transparency.