Dependence of plaid motion coherence on component grating directions

We measured motion coherence for plaids composed of two different spatial frequency (SF) cosine grating components moving at various relative angles. The component SFs were in a ratio of 6:1, and several component motion directions were chosen to produce small to large angular differences. For angles of less than +/- 45 deg all subjects perceived rigid coherent motion, while for angles of +/- 45 deg or greater the components were perceived to slide transparently. The results were not altered when we changed the ratio of component contrasts or speeds over a factor of 2 and varied the SF ratio up to 9:1. These results show that transparency or coherence of moving plaids in different spatial scales depends on the relative component motion directions and is relatively independent of contrast, speed, and SF difference between the components. This angular dependence also explains recent data previously thought to be based on a visual computation of multiplicative transparency. A quantitative model in which the resultant motion on each scale provides a facilitative biasing signal to units tuned to similar directions (within +/- 30 deg) on other scales explains the experimental results.