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)