SPATIAL-FREQUENCY AND ORIENTATION TUNING IN PSYCHOPHYSICAL END-STOPPING

A psychophysical analog to cortical receptive-field end-stopping has b een demonstrated previously in spatial filters tuned to a wide range o f spatial frequencies (Yu & Levi, 1997a). The current study investigat ed tuning characteristics in psychophysical spatial filter end-stoppin g. When a D6 (the sixth derivative of a Gaussian) target is masked by a center mask (placed in the putative spatial filter center), two end- zone masks (placed in the filter end-zones) reduce thresholds. This '' end-stopping'' effect (the reduction of masking induced by end-zone ma sks) was measured at various spatial frequencies and orientations of e nd-zone masks. End-stopping reached its maximal strength when the spat ial frequency and/or orientation of the end-zone masks matched the spa tial frequency and/or orientation of the target and center mask, showi ng spatial-frequency tuning and orientation tuning. The bandwidths of spatial-frequency and orientation tuning functions decreased with incr easing target spatial frequency. At larger orientation differences, ho wever, end-zone masks induced a secondary facilitation effect, which w as maximal when the spatial frequency of end-zone masks equated the ta rget spatial frequency. This facilitation effect might be related to c ertain types of contour and texture perception, such as perceptual pop -out.