Effects Of Adaptation Paradigms On Face Identity And Expression Perception:Behavior And ERP Studies

Face perception is fundamentally important for judging the characteristic of individuals,such as recognition of their gender,expression,ethnicity,age or identity.Nevertheless,our perception of a given face is not necessarily identical at different points in time,as preceding visual experiences can influence it.The adaptation-related aftereffect is one such phenomenon,previous studies have shown that the attributes of a face can be biased significantly after prolong exposure to a face of the same attributes,which is also known as the face aftereffects(FAE).This paper mainly studies the adaptation aftereffects of face emotions and face identities under the adaptation paradigm.At the same time,it combines ERP techniques to explore the underlying neural mechanisms of adaptation-related aftereffects.In the first experiment,we morphed the faces of Adam and Bob to generate a continuum of face images,and asked subjects to judge the identity of those face images to be Adam or Bob after they were exposed to a face image within the continuum.We found that after adaptation to Bob,the subjects identified a subsequently presented ambiguous face likelier to be Adam,and vice versa,i.e.,the face identity aftereffect(FIAE).We also simultaneously recorded EEG during the task and analyzed the event-related potentials(ERPs)in response to the test faces.We found that adapting to a face identity(e.g.,Bob)suppressed the amplitude,and prolonged the latency,of the late positive potential(LPP)in response to subsequent faces of the same identity(e.g.,Bob).When we used profile face images(45° rotation)as adaptors and still used frontal images as test faces,we found that the FIAE and neural adaptation effects of LPP transferred across viewpoints as well.The modulations of LPP amplitude and latency by the identity similarity between the adaptor and test face strongly indicate that the suppressed and prolonged LPP activity serves a neural correlate of FIAE.In the second experiment,we morphed the faces with happy and sad expressions to generate a continuum of face images,and asked subjects to judge the face expression to be happy or sad after they were exposed to a face image within the continuum.Prolonged exposure to one facial expression,such as happiness,biases people's perceptional judgment of subsequent presented faces toward another expression,such as sadness,the facial expression aftereffect(FEAE).Here,we found that the FEAE is abolished across identities,i.e.,the expression judgment of a person's faces from a happy-sad continuum,was biased toward sad after adaptation to a happy face of the same person,but was not biased after adaptation to a happy face of a different person.We also simultaneously recorded EEG during the task and analyzed the event-related potentials(ERPs)in response to the test faces.There were two significantly attenuated ERP components(N250r and LPP)occurring at ~250 ms and ~ 400 ms respectively after the onset of happy test faces when the happy face of the same identity was used as the adaptor.However,these two modulations of ERP components were both vanished when happy faces of different identities were used as adaptors.Our study illustrates two things,first,the failure of aftereffect transferred across changes in identity suggested the involvement of identity-dependent neural populations;second,the attenuated N250 r and LPP components essentially differentiates the identical and non-identical face trials,in general,providing additional evidence that the N250 r and LPP components are related to the facial expression aftereffects.Our results provide the first direct evidence for the abolishment of cross-identity adaptation on the perception of facial expression,and its neural correlates.In this study,we combined the behavioral and ERP techniques to demonstrate the two kinds of visual aftereffects of face identity adaptation and face emotion adaptation.The results all showed that the late positive potentials was sensitive to the adaptation mechanism.It is believed that adaptation to high-level face information such as emotions and identities takes place at a later stage of face processing and is correlated with the fatigue model at the neural level.