The human face displays mild asymmetry, with measurements of facial structure differing from left to right of the meridian by an average of three percent.Presently this source of variation is of theoretical interest primarily to researchers studying the perception of beauty, but a very limited amount of research has addressed the question of how this variation contributes to the cognitive processes underlying face recognition. This is surprising given that measurement of facial asymmetry can reliably distinguish between even the most similar of faces. Furthermore, brain regions responsible for symmetry detection support face-processing regions, and detection of symmetry is superior in upright faces relative to inverted and contrast-reversed face stimuli. In addition, facial asymmetry provides a useful biometric for automatic face recognition systems, and understanding the contribution of facial asymmetry in human face recognition may therefore inform the development of these systems. In this thesis the extent to which facial asymmetry is implicated in the process of recognition in human participants is quantified. By measuring the effect of left-right reversal on various tasks of face processing, the degree to which facial asymmetry is represented by memory is investigated. Marginal sensitivity to mirror reversal is demonstrated in a number of instances, and it is therefore concluded that cognitive representations of faces specify structural asymmetry. Reversal effects are typically slight however and on a number of occasions no reliable effect of this stimulus manipulation is detected. It is likely that a general tendency to treat mirror reversals as equivalent stimuli, in addition to an inability to recall lateral orientation of objects from memory, somewhat obscure the effect of reversal. The findings are discussed in the context of existing literature examining the way in which faces are cognitively represented.
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