Modeling adaptations in the face-processing system
Individuation in primates primarily relies on face recognition. Consequently, the visual system seems specialized for perception of faces since psycho-physical and neuro-imaging studies found that the right but not the left hemisphere of the brain is predominantly involved (Campanella et al., 2001; Dien, 2009; Grill-Spector et al., 2004; Levy et al., 1972; Morris et al., 2007).
Mechanistically, face recognition is thought be based on a number face features extracted from the visual input of a face, such as the distance of the two eyes, length of the mouth, etc. In fact, such features extraction can be in part located in high visual areas and specialized nuclei (Freiwald et al., 2009). Comparison with successful face-recognition algorithms from machine learning suggests that many simple face features might get combined together to form an ensemble having high performances in the recognition of faces (Viola and Jones, 2001). However, a possible neural implementation of this features extraction process in the visual system remains unknown.
One hypothesis is that the left hemisphere is involved in analytic processing and the right hemisphere in configural processing (Bradshaw et al., 1981), thus supporting a view of a lateralization of the face features extraction system (Hsiao et al., 2008; Robertson and Ivry, 2000). However, if this lateralization emerges because of anatomical constraints or because of the specific structure of faces (i.e. the invariance of faces for mirroring at the mid-line between the eyes) remains unclear.
Similarly, development and adaptation of face perception is relatively unclear. There is, however, evidence for an early developmental mechanism, that is an early sensory period of perceptual narrowing when the recognition system tunes towards the predominant race (Kelly et al., 2007) and species (Pascalis et al., 2002). On the other hand, it goes without saying that individuals with lifelong intense exposure to faces “know more” about faces than newborns do. Representations qualitatively change with experience (Goldstone, 1998; Palmeri and Gauthier, 2004; Schyns et al., 1998; Tanaka, 2001).
Indeed, our recent behavioral studies in chimpanzees suggest (Dahl et al., 2013) that the face recognition system is dependent and shaped by life-long experience. In particular, after extensive exposure of chimpanzees to other-species (human) faces, individuals learn to discriminate this new face class, while discrimination performance on con-specific faces deteriorates.
In this sub-project, we propose to investigate possible mechanisms of life-long adaptive changes of the face recognition system as well as possible roles of symmetry of faces in the development of hemispheric lateralization of the face feature extraction system.