Effect of photographic negation on face expression aftereffects.

Our visual representation of facial expression is examined in this study: is this representation built from edge information, or does it incorporate surface-based information? To answer this question, photographic negation of grey-scale images is used. Negation preserves edge information whilst disrupting the surface-based information. In two experiments visual aftereffects produced by prolonged viewing of images of facial expressions were measured. This adaptation-based technique allows a behavioural assessment of the characteristics encoded by the neural systems underlying our representation of facial expression. The experiments show that photographic negation of the adapting images results in a profound decrease of expression aftereffect. Our visual representation of facial expression therefore appears to not just be built from edge information, but to also incorporate surface information. The latter allows an appreciation of the 3-D structure of the expressing face that, it is argued, may underpin the subtlety and range of our non-verbal facial communication.