EEG responses to facial contrast-chimeras

Abstract

Contrast negation greatly diminishes the identifiability of a facial image. Recent results have shown that much of this performance reduction can be compensated for if contrast relationships in the neighborhood of the eyes are restored. Chimeric faces that contain positive eyes on negative faces are almost as well recognized as fully positive faces. Here we examine the neural correlates of this behavioral finding. Given that positive and chimeric faces lead to similar behavioral performance, do they also elicit similar neural responses? Specifically, we investigate early event-related potential components in response to these two kinds of images. Past studies have shown that the N170 is significantly affected by contrast negation. However, we find that the simple chimeric transformation has a profound effect on this and two other event-related potential components associated with face perception. Consistent with our behavioral results, we find that the N170, P100 and P250 components for positive and chimeric faces are statistically indistinguishable, but differ significantly from those corresponding to the fully negative faces. We discuss the implications of these results regarding the nature of facial representation underlying behavior as well as the event-related potential components.