PROCESSING OF AMBIGUOUS INFORMATION DERIVED FROM FACE REVEALED BY ERP STUDY
 
Nomura, M., Matsumoto, A. and Ohira, H., Nagoya University, Japan
 
Much information such as gender, age, personality, and emotional state can be derived from facial expression (Bruce and Young, 1988). An event-related brain potential (ERP) study investigated how different processing stages involved in categorization of facial expression and gender were reflected in ERP modulations and how ambiguity of each information set influenced such effects. Fifteen subjects performed two tasks. One task required the subjects to label the facial expression as positive or negative, and the other was to label the gender (male or female). Each trial lasted 6.5 s with 0.5s of presentation, followed by a 6s interval. An ANOVA (task x ambiguity) for reaction time showed a main effect of ambiguity that the ambiguous stimuli were judged more slowly than the clear ones. Ambiguous stimuli gave rise to N480 ms component with front-central (Fz) and temporal electrodes (T5, T6) irrespective of the task., that The onset of N480 component was much later in temporal than in front-central. The mean amplitude in 600-740ms time window from onset of the stimuli showed an effect of ambiguity suggesting that the ambiguous stimuli evoked larger positive potential., Furthermore the effect was larger in the facial expression task than in the gender task at posterior temporal area. Our results revealed involvement of differential neural network between in processing of ambiguity of facial expression and that of gender.