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Xin Zheng, Catherine J. Mondloch, Sidney J. Segalowitz; Delineate the temporal sequence and mechanisms for perceiving individual faces. Journal of Vision 2010;10(7):670. doi: 10.1167/10.7.670.
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In two event-related potential (ERP) studies, we examined neural correlates of individual face perception. In Study 1, 36 individual female and 9 male faces were randomly presented, and participants were instructed to press a button for male faces. Based on similarity ratings from a previous behavioral study, the female faces could be located in a multidimensional “face-space”. The facial characteristics representing the “face-space” and therefore important for judging face similarities include eye color, face width, eye size and top-of-face height. The face-sensitive N170 component was affected by all these factors. In addition, there was a hemisphere difference: the right N170 amplitude was related to eye color and face width, while the left N170 amplitude was related to eye size and top-of-face height when bottom-of-face height was small. In Study 2, we created a set of faces that varied in identity strength by morphing each of the 36 female faces with an average face formed from the entire set; the relative weighting of an original face ranged from 100% to 0% in 10% decrements. Participants were instructed to press a button whenever they detected a target identity. Accuracy data indicated an ambiguous region between 30% and 60% identity strength. Neither the P1 nor the N170 to non-target faces were influenced by identity strength. However, the amplitude of the P2 component (230-270 ms) became smaller as identity strength decreased, with no categorical boundary effect. Collectively, these results provide electrocortical evidence of structural decoding of individual faces before 200 ms that involves rather fine-tuned analyses of multiple facial characteristics, which might be carried out separately by two hemispheres. Following structural decoding, the electrocortical evidence of individual face identification occurs around 250 ms with minimal response to “average” faces.
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