A psychophysical analog to cortical receptive-field
end-stopping has been demonstrated previously in spatial
filters tuned to a wide range of spatial frequencies (Yu
& Levi, 1997a). The current study investigated
tuning characteristics in psychophysical spatial filter
end-stopping. 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 masks)
was measured at various spatial frequencies and orientations
of end-zone masks. End-stopping reached its maximal strength
when the spatial frequency and/or orientation of the end-zone
masks matched the spatial frequency and/or orientation
of the target and center mask, showing spatial-frequency
tuning and orientation tuning. The bandwidths of spatial-frequency
and orientation tuning functions decreased with increasing
target spatial frequency. At larger orientation differences,
however, end-zone masks induced a secondary facilitation
effect, which was maximal when the spatial frequency of
end-zone masks equated the target spatial frequency. This
facilitation effect might be related to certain types of
contour and texture perception, such as perceptual pop-out.