Abstract
The detection threshold of a Gabor target can be reduced by the presence of collinear flanking Gabors. Such collinear facilitation is disrupted when the target and the flanker have different disparity (Huang et al, 2006, Vision Research). Here, we further investigated whether it is the depth or surface difference between the target and the flanker that causes the abolition of collinear facilitation. The target and the flankers were 2 cy/deg vertical Gabor patches. The distance between the target and the flankers was three wavelengths. There were three viewing conditions: target and flankers were set (1) in the same frontoparallel plane; (2) at different disparities in different frontoparallel planes; and (3) at different disparities but embedded in the same slanted plane as defined by the orientation difference in stimuli between the left and right eye images. The Zero disparity was maintained by reference squares presented at the edge of the display. We measured the target contrast detection threshold with and without the flankers present with a temporal 2AFC paradigm and the Psi staircase method. Strong collinear facilitation was observed when the target and the flankers were either in the same frontoparallel plane or embedded in the same slanted surface even though the target and the flankers were at different disparities. The facilitation disappeared when the stimuli at this disparity difference were in different frontoparallel planes. Noticed that, for all viewing conditions, the target and the flankers were always collinear when monocularly viewed and thus produced collinear facilitation. Even if the collinear facilitation was operating at the monocular level, once the target and flankers occupied different disparities, the collinear facilitatory effect was disrupted. Our results suggest that it is the difference in surface assignment, not the difference in disparity per se, that causes the disruption of collinear facilitation.
Supported by 96-2413-H-002-006-MY3 to CCC and AFOSR FA09-1-0678 to CWT.