T-junctions in inhomogeneous surrounds

In an inhomogeneous checkerboard surround, the lighter check darkens;an inc remental test patch more than the darker check lightens it. However, decrem ental test patches are influenced equally [Schirillo & Shevell, 1996. Visio n Research, 36, 1783-1796]. In the current study, we manipulate the spatial arrangement of a checkerboard surround to produce T-junctions that percept ually group the checks with the test patch. These stimuli alter the inducin g effects of the checks. For one modified surround, increments appeared sim ilar to 8% darker and decrements appeared similar to 10% lighter over the o riginal checkerboard surround prior to modification. In a second modified s urround, that resembled White's illusion [White, 1979. Perception, 8, 413-4 16], increments again appeared similar to 8% darker, while decrements appea red a dramatic similar to 23% lighter over the original checkerboard surrou nd prior to modification. These enhanced induction effects are postulated t o result from the addition of specific T-junctions. However, these grouping effects remain subservient to the asymmetrical induction effects found by Schirillo and Shevell (1996). (C) 2000 Published by Elsevier Science Ltd.