Orientation illusion and masking in central and peripheral vision.

Abstract

Notes that a vertical line appears tilted when viewed following inspection of tilted lines (aftereffect) or against a background of tilted lines (illusion). In Exp. I with 16 undergraduates, the illusion obtained, as the orientation of the inducing lines was varied, differed between central and peripheral vision. The possibility that orientation-selective cells in the human visual system are more broadly tuned in peripheral than central vision was examined in Exp. II with 8 Ss using a contour masking paradigm. The detectability of a vertical line varied with the orientation of a grating exposed immediately before the line, but contrary to expectations, masking (threshold elevation) was obtained over a wider range of orientation values in central than peripheral vision. No evidence was obtained that perceptual facilitation (improved detection of the line following exposure to the grating) can occur in central vision in addition to masking. Results question whether aftereffect, illusion, and masking paradigms are equally effective in obtaining information about the tuning characteristics of feature analyzers in the human visual system. (23 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved).