Abstract
It has been proposed the visual system represents a texture surface by first constructing the boundary contour (BC) and surface texture adjacent to the BC, whereupon the process spreads interiorly until completion. To further verify this border-to-interior hypothesis, we tested the prediction that representing the central area of a disc image takes less time if the disc diameter is small. We used a monocular boundary contour (MBC) rivalry stimulus, comprising of a grating disc surrounded by orthogonal grating square in one eye and the same orthogonal grating square in the other eye. With this stimulus, the MBC disc is rendered dominant for surface representation while the orthogonal grating in the other eye is suppressed. We measured detection of a monocular Gabor probe (20 msec) presented at the center of the MBC disc (1.5 or 3.0 deg diameter), or its corresponding retinal location, at various SOA between the probe and MBC rivalry stimulus (30, 50, 80, 120 msec). If the surface representation of the MBC disc spreads inwardly from the MBC (border) to the disc center, the central disc area is expected to be completely represented at a shorter SOA when the MBC disc is small. This will be revealed as a reliable threshold difference between the two eyes (interocular suppression). Our results confirm the prediction. For example, at the 30 msec SOA, there is a significant interocular suppression with the 1.5 deg stimulus, which does not occur until 80 msec with the 3.0 deg stimulus. Besides confirming the border-to-interior hypothesis, the observation that interocular suppression occurs as early as 30 msec suggests the inhibitory mechanism becomes effective almost immediately upon stimulus onset and is much quicker than previously thought (150 msec).