LOCAL AND GLOBAL FACTORS IN SPATIALLY-CONTINGENT COLORED AFTEREFFECTS

Dodwell and O'Shea's [(1987) Vision Research, 27, 569-580] conclusions that contingent coloured aftereffects (CAEs) depend on gobal pattern organization were investigated in four experiments, In Expt 1, we repl icated findings that CAEs can be induced with complex patterns (concen tric circles; radial spokes) under conditions of systematic eye moveme nts, Contrary to Dodwell and O'Shea's argument that eye movements shou ld uniformly cancel local orientation-colour contingencies, leaving on ly global effects, we reduced CAE magnitude by halving the diameter of the test stimuli. This suggests that cancellation did not occur unifo rmly over whole patterns, and that CAEs observed on these patterns are the residuals of uncancelled local orientation-colour contingencies. In Expt 2 we used central-fixation induction procedures to demonstrate that it is possible to induce CAEs with randomly-organized and locall y-orthogonal orientation components. These findings are inconsistent w ith Dodwell and O'Shea's failure to observe CAEs under these condition s, and with their conclusion that global organization is necessary for CAE induction, However, CAEs induced with randomly-organized componen ts were significantly weaker than those induced with globally-organize d components. We examined the contribution of global organization in t wo additional experiments. In Expt 3 we induced CAEs with randomly-org anized components under conditions in which the need for central fixat ion was removed, and found that CAE strength was directly related to t he organization as well as the density of local-orientation components . In Expt 4, we found that the global organization of local-orientatio n components enhanced CAE strength only in regions away from the edges of these components: pattern organization did not affect the strength of CAEs at edges. We interpret these findings as evidence that CAEs m ay involve separate edge- and spread-colour components, and conclude t hat such components may account for observations previously attributed to global pattern geometry.