Adaptation Aftereffect In The Face Animacy Perception

The animate monitoring hypothesis considers that the animacy perception is an instinct evolved by human beings.For survival,the ancestors need to quickly judge whether the object in the visual field is animate or inanimate.Because the living thing means that it may be a threatening enemy,a normal animal,or a prey.For social connection,animate object means that it may be potential social objects.So,animacy perception which distinguishes animate object and inanimate object is an important ability for human.With the rapid development of technology,more and more artificial objects appear,such as simulation robots,computer generated characters,simulation dolls,wax figures,these objects are more and more lifelike,and some can have social interaction with people.The complexity and obscure of the animacy boundary caused by these is a great challenge to people’s animacy perception ability.Long-term observation of a stimulus will cause a perceptual bias.This is because our visual system will make adaptive adjustment with the changes of the external environment and this kind of visual adaptation is a common visual phenomenon in daily life.For example,the classical “waterfall aftereffect”,after we watch the water cascaded for a while,it is easier for us to perceive the standing stones nearby as “flying up”.The explanation of this phenomenon is that the perception of movement direction depends on the balance of the activities of the groups of neurons processing in different movement directions.When the “motor” neurons adapt to the downward movement,they will reduce the response to the downward movement,so the balance will be changed and the upward movement will become easier to perceive.Previous studies have shown that our visual system can adapt to many features of the face.When people look at a face for a while,they tend to produce opposite perceptual judgment of the adaptive feature of the subsequent face,which is a face adaptation aftereffect.As a basic feature dimension of face,animacy can also produce an adaptation aftereffect,like face animacy adaptation aftereffect(FAAE).However,the neural mechanism of the FAAE is not clear.Moreover,there is still controversy about the mechanism of adaptation.Generally speaking,the shape-similarity between the adaptor and the test stimulus is the basic mechanism of adaptation.However,recent studies have shown that there may be another mechanism of feature association in the occurrence of adaptation.That is,when the adaptor and the test stimulus have feature association could produce adaptation,such as cross-category gender aftereffect.Therefore,this paper will mainly explore the neural mechanism of face animacy adaptation aftereffect and the produce mechanism of the face animacy adaptation.Study 1 mainly explored the neural mechanism of the face animacy adaptation aftereffect.We used human and artificial faces as adaptors.A series of test stimuli were generated by morphing the human face(animate = 1)and the artificial face(inanimate =0).The identity of adaptor was different from the test faces.There were three experiment conditions: a baseline condition which did not has an adaptor and two adaptation conditions with different animacy property.In adaptation condition,subjects watched a human face or an artificial face for a while then they were asked to judge whether the subsequent test face was animate or inanimate.We found that after adaptation to a real face,the subjects were inclined to judge a subsequently ambiguous face to be inanimate,whereas after adaptation to an artificial face,the subjects were inclined to judge a subsequently ambiguous face to be animate,i.e.,the face animacy aftereffect.As the identities were different across the adaptors and the test faces,the results showed that the FAAE could transfer across different identities.EEG data were recorded when the psychophysical task was completed,and analyzed the event-related potentials(ERP)in response to the test stimulus.We found that the amplitude of LPP and the latencies of the N250 r and LPP were modulated by the animacy-congruent of the adaptor and the test face.In the animacy-congruent conditions,the latencies of N250 r and LPP were prolonged and the amplitude of LPP were suppressed.However,in the animacy-incongruent conditions,the latencies of N250 r and LPP were shortened and the amplitude of LPP were enhanced.Those modulations of N250 r and LPP activities indicated that they were neural correlates of the FAAE.Study 2 and study 3 were mainly explored the produce mechanism of the FAAE.By studying whether the face animacy adaptation aftereffect can transfer across the human body parts,we explored the produce mechanism of the FAAE.In study 2,the upper bodies(human body / silicone human body)without head were used as adaptor,while the faces were used as test stimuli.In Study 3,faces(human face / doll face)were used as adaptor,while the upper bodies without head was used as test stimulus.The results showed that neither "body-to-face" nor "face-to-body" can produce face animacy aftereffect,which indicated that the FAAE was not based on the principle of feature association.However,we found significant FAAE in study 1 which used faces as the adaptor and the test stimuli.Therefore,we inferred that the FAAE is more likely based on the principle of shape similarity,and the feature association between the adaptor and the test stimulus is not enough to produce cross-category aftereffect.In a word,by combine the psychophysical methods and the ERP techniques we found that the N250 r and LPP are sensitive to the FAAE,and FAAE can transfer across identities,but not across body parts,indicating that the FAAE is more likely based on the shape similarity principle of the adaptor and the test stimulus.