Abstract
Psychological models suggest that perceptual similarity can be subdivided into geometric effects, such as metric distance in stimulus space, and non-geometric effects such as stimulus-specific biases. However, the time course of neural similarity processing remains unclear. We investigated this question using a neural adaptation paradigm to study event-related potentials (ERP) related to facial similarity. We find an ERP component between the “face-selective” N170 and N250 responses (the “P200”) that is modulated by transitions of face appearance, consistent with neural adaptation to the geometric similarity of face transitions. In contrast, the N170 and N250 reflect non-geometric stimulus bias, with different degrees of adaptation depending upon the direction of face transition within the stimulus space. Thus, the behavioral distinction between geometric and non-geometric similarity effects is consistent with dissociable neural responses across the time course of face perception. In line with prior results implicating the N170 and N250 in perception and memory, respectively, these data support an intermediate role of the P200 in consolidation of the perceptual representation. Together, these results demonstrate that the neural coding of perceptual similarity, in terms of both geometric and non-geometric representation, occurs rapidly and from relatively early in the perceptual processing stream.
This work was supported by K08 MH 7 2926-01 and a Burroughs-Wellcome Career Development Award.