Dissociating Face Identity and Facial Expression Processing Via Visual Adaptation

Face identity and facial expression are processed in two distinct neural pathways. However, most of the existing face adaptation literature studies them separately, despite the fact that they are two aspects from the same face. The current study conducted a systematic comparison between these two aspects by face adaptation, investigating how top- and bottom-half face parts contribute to the processing of face identity and facial expression. A real face (sad, “Adam”) and its two size-equivalent face parts (top- and bottom-half) were used as the adaptor in separate conditions. For face identity adaptation, the test stimuli were generated by morphing Adam's sad face with another person's sad face (“Sam”). For facial expression adaptation, the test stimuli were created by morphing Adam's sad face with his neutral face and morphing the neutral face with his happy face. In each trial, after exposure to the adaptor, observers indicated the perceived face identity or facial expression of the following test face via a key press. They were also tested in a baseline condition without adaptation. Results show that the top- and bottom-half face each generated a significant face identity aftereffect. However, the aftereffect by top-half face adaptation is much larger than that by the bottom-half face. On the contrary, only the bottom-half face generated a significant facial expression aftereffect. This dissociation of top- and bottom-half face adaptation suggests that face parts play different roles in face identity and facial expression. It thus provides further evidence for the distributed systems of face perception