Abstract
The Sequential Surface Integration Process (SSIP) hypothesis posits that the visual system relies on its intrinsic bias and the external depth cues to construct the ground surface representation. We previously deduced that the intrinsic bias, revealed in the dark, takes the form of an implicit surface with its far-end slanted upward (Ooi et al, 2001). To investigate the slant of the intrinsic bias, we measured judged surface slant of a fluorescent L-shaped target in the reduced background(2×4 parallel array of fluorescent elements on the floor in the dark) and dark conditions. The L-shaped target was placed flat, either at the test(4m or 6m on the floor) or catch-trial locations. Observers performed three tasks: (i)aspect ratio matching; (ii)blind-walking to the remembered target location and gesturing its height and slant; (iii)adjusting by hand the slant of a palm-board to match the perceived target slant(while standing at the starting position). We found that for all three tasks, including the last two that directly measured the judged target slant, the L-shaped target was perceived as slanted upward in the dark condition. The perceived slant represents the intrinsic bias, since the ground surface is invisible in the dark. The L-shaped target was also perceived as slanted upward in the reduced background condition, although the perceived slant was significantly decreased compared to the dark condition. This suggests that with external depth cues, the ground surface representation is less influenced by the intrinsic bias, leading to a more veridical slant percept.
Support: NIH grant EY014821