Recognizing one's own face

Abstract

We report two studies of facial self-perception using individually tailored, standardized facial photographs of a group of volunteers and their partners. A computerized morphing procedure was used to merge each target face with an unknown control face. In the first set of experiments, a discrimination task revealed a delayed response time for the more extensively morphed self-face stimuli. In a second set of experiments, functional magnetic resonance imaging (fMRI) was used to measure brain activation while subjects viewed morphed versions of either their own or their partner's face, alternating in blocks with presentation of an unknown face. When subjects viewed themselves (minus activation for viewing an unknown face), increased blood oxygenation was detected in right limbic (hippocampal formation, insula, anterior cingulate), left prefrontal cortex and superior temporal cortex. In the partner (versus unknown) experiment, only the right insula was activated. We suggest that a neural network involving the right hemisphere in conjunction with left-sided associative and executive regions underlies the process of visual self-recognition. Together, this combination produces the unique experience of self-awareness.

Introduction

The face is our most characteristic external feature. Mirror recognition does not occur in humans before 18 months or in other primates, except adult great apes (Gallup, 1970, Parker et al., 1994). Several investigations have shown that the processing of self-relevant information differs from processing objective information. For example, in word recognition studies, self-referential encoding facilitates recall better than any other mnemonic strategy (Kihlstrom and Klein, 1997, Schacter, 1989). Listening to autobiographical episodes (Fink et al., 1996) or judging one's own personality traits (Kircher, Brammer, Simmons, Bartels, & David, 2000) has been shown to activate distinct cerebral areas. Specific operations underlying self-processing have been proposed (Schacter, 1989, Snodgrass and Thompson, 1997). In previous imaging studies, verbal material has been used to investigate semantic self-referential knowledge (Craik et al., 1999). However, a stronger and more direct cue for investigating self-information processing is one's own face, with which we are very familiar from mirror reflections and photographs. Understanding of how we recognize a familiar face has grown through experiments in cognitive psychology (Bruce & Young, 1986), neurophysiology (Seeck et al., 1993), neuroimaging (Haxby et al., 1996, Kapur et al., 1995), and neuropsychological studies of patients with face recognition deficits (prosopagnosia) (Sergent & Poncet, 1990). Surprisingly, little research has been devoted to facial self-recognition, presumably because it is assumed that this cannot be separated from familiar face recognition. Some patients with severe prosopagnosia (Sergent & Poncet, 1990) and Alzheimer's disease (Bologna & Camp, 1997) fail to recognize themselves in the mirror yet no pure cases of ‘autoprosopagnosia’ have been described. In an event-related potential (ERP) study by Ninomiya, Onitsuka, Chen, Sato, and Tashiro (1998) a larger P300 response to the subject's own face compared to familiar faces has been reported.

One major problem when studying self-face processing is to control for emotional salience and overlearnedness, since both are known to influence processing (Klatzky and Forrest, 1984, Phillips et al., 1997, Valentine and Bruce, 1986, Young et al., 1985). In our study, we tried to overcome this by using the face of each subject's partner for comparison. We used morphed versions of the subject's own face and their partner's face, each blended with an unknown, same sex identity, and conducted two sets of experiments. In the first set, we measured reaction time and categorical boundaries for recognition of the subject's own face and their partner's face. In the second set, we measured cerebral activation with fMRI while subjects viewed the same stimuli. We predicted a specific behavioural and neural response when subjects viewed their own face because of its outstanding subjective importance.