LOCAL DIRECTION OF EDGE MOTION CAUSES AND ABOLISHES THE BARBERPOLE ILLUSION

The perceived direction of motion of a one-dimensional grating is meas ured in straight-edged rectangular and indented rectangular apertures. It is shown that the perceived direction of motion of the pattern is largely determined by the directions of motion at the edges, rather th an by the aspect ratio or global shape of the aperture. The edge motio n vectors appear to be calculated at a remarkably local scale. The bar berpole illusion is abolished when indentation size equals or exceeds one-quarter of the grating period. This critical size is scale invaria nt with grating period and corresponds well with a quadrature model of motion perception.