Brief articleRecognizing one's own face
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.
Section snippets
Subjects
Twenty healthy, male volunteers participated in the behavioural study (mean age 31 years, mean IQ estimate 113; National Adult Reading Test, Nelson & Willison, 1991). Exclusion criteria were history of brain injury, and past and current psychiatric or neurological illness. No subject was taking regular medication. Neither the subjects nor their female partners wore spectacles and none had facial hair. Subjects had known their partners for between 1 and 16 years (median 2.7).
Stimuli
Coloured, full face,
Behavioural experiments
We performed an analysis of the perceived categorical boundaries for each subject in each trial. When the responses for each trial are sorted from image 1 to 21, the categorical boundary is defined as the mean between the first image judged as ‘unknown’ and the image after the last image judged as ‘known’. In both the self/unknown and the partner/unknown conditions, subjects judged stimuli as belonging to distinct categories with a sharp boundary between them (see Fig. 1). A regression of
Discussion
In two independent sets of experiments, we investigated processing of two highly overlearned faces, one's own and one's partner's, on a behavioural and neural systems level. We found a reaction time advantage for the recognition of morphs of overlearned faces compared with strangers' faces. The morphing procedure as well as the order of presentation influenced the response times significantly. Facial identity appears to be perceived categorically. There was no difference in categorical
Conclusion
We have reported evidence of a distinct neural substrate underlying facial self-recognition involving the right limbic system and left prefrontal and temporo-parietal cortex. One's own face is a stimulus that activates unique self-referential processing. We suggest that the interplay of both emotional and associative cognitive processes is necessary for the unique perception of a coherent self. Further studies are needed to clarify the specific nature of the neural correlates of visual
Acknowledgements
T.K. was supported by the German Research Council (DFG), C.S. was supported by the Pilkington Family Trusts and the McDonnell Foundation in Cognitive Neuroscience, and E.T.B. and M.LP. were supported by the Wellcome Trust. We thank P.K. McGuire and P. Fletcher for advice on earlier versions of the manuscript, and S.C.R. Williams and C. Andrew for technical support.
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