Attentional processing and the subjective contour illusion.

To distinguish between bottom–up and top–down (TD) accounts of subjective contour (SC) perception, the present investigation used a dual-task paradigm to test the relative attentional demands of real SC perception. In the primary task, 16 undergraduates made speeded same–different discriminations of either paired SC forms or their real contour analogs. Half the Ss performed this primary task in conjunction with a 6-digit short-term memory load secondary task. If subjective forms impose a greater limited-capacity processing load than real forms, then the need to share processing capacity with a secondary task was expected to produce a greater increment in RT for subjective relative to real forms. Results indicate that the expected enhanced RT increment for subjective relative to real forms with the addition of a concurrent memory load was limited to same trials. This result implies that the nature of response indicators must be considered in assessing capacity requirements with the sort of dual-task paradigm used in the present investigation. Nevertheless, the fact that the increment in same RT with the addition of a concurrent memory load was greater for subjective relative to real forms accords with expectations derived from the notion that the perception of SCs is more attention-demanding than that of real contours. A comprehensive theory of SC perception will most likely be formulated within the TD perspective of conceptually driven visual information processing. (90 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)