Priming effects between two-dimensional shapes.

The role of reference frames in shape perception was examined by investigating priming effects between two-dimensional shapes. Ambiguous shapes and shapes with an unambiguous axis were used, and primes and targets could be orientationally transformed so that for ambiguous shapes, different axes aligned with the vertical. Reliable priming effects were established that were dependent on the structural similarity of primes and targets, the informativeness of the prime, and the interval between the stimuli. Most interestingly, with short interstimulus intervals, differential priming effects were found between ambiguous shapes and unambiguous shapes when an orientational transformation aligned different axes in the ambiguous shape with the vertical. The result was interpreted as demonstrating that priming was determined by the similarity of the frame-based descriptions of primes and targets. The finding occurred irrespective of the informativeness of the prime, suggesting that it reflects obligatory processes in shape perception. Further data showed that under some circumstances prespecifying the orientation of a shape also facilitated its processing; this provided direct evidence that shapes are represented relative to a perceptual reference frame.