Adaptation effects in facial expression recognition

The effect of adaptation on facial expression recognition was investigated by measuring how identification performance of test stimuli falling along a particular expression continuum was affected after adapting to various prototype emotional faces or a control pattern. The results showed that for recognition of fear, happiness, and sadness, inhibition effects were observed on recognition of test expressions following 5 s adaptation to the same emotion, suggesting different neural populations tuned for the encoding of fearful, happy, and sad expressions. Facilitation of recognition of test stimuli differing in emotion to the adapting stimulus was also sometimes observed. The nature of these adaptation effects was investigated by introducing a size transformation or a delay between adapting and test stimuli and was found to survive these changes. The results of a further experiment argued against a criterion effect being the major source by demonstrating the importance of adapting time in generating the effects. Overall, the present study demonstrates the utility of adaptation effects for revealing functional characteristics of facial expression processing.