Abstract
Behavioral, computational, and physiological theorists have suggested that intermediate-level medium-span configurations play a role in shape perception. Which behavioral tasks probe medium-span configurations rather than local configurations or global shapes? Figure-ground tasks show effects of experience with previously seen shapes only when representations are accessed quickly, consistent with intermediate-level representations. Here we show that the relevant representations are medium-span configurations by altering a paradigm used previously to assess past experience effects implicitly. We measured the time needed for figure assignment when past experience competes with, but does not dominate, other cues. Novel shapes with three straight and one (vertical) stepped edge were shown on prime trials. On probe trials subjects judged whether two vertically aligned shapes were the same as or different from each other. On experimental probe trials, the stepped edge of the prime was repeated but other cues (closure, small area) specified that the figure lay on the opposite side of the edge. Consequently, the perceived shape of the probe differed from that of the prime. On control probe trials the probe shapes were completely novel. Competition from past experience led to longer RTs on experimental than control probes. Thus, repeating just the stepped edge of the prime activated the memory of where the figure was the first time the edge was encountered; repeating the whole prime was unnecessary. Here, we ask whether repeating a smaller span (only the top or the bottom half) of the continuous stepped edge was sufficient to trigger the effects of past experience. Again, we found that RTs were longer on experimental than control probe trials, p < .05. Surprise recognition trials showed that subjects were unaware that the experimental probes were related to the primes. The results are consistent with a distributed shape representation system with medium-span configurations lying at intermediate levels.
Research supported by NSF BCS 0425650 to MAP.