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Romina Palermo, Davide Rivolta, C. Ellie Wilson, Linda Jeffery; Abnormal adaptive coding of identity in congenital prosopagnosia. Journal of Vision 2011;11(11):572. doi: https://doi.org/10.1167/11.11.572.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive face coding mechanisms are believed to generate face norms, which represent the average characteristics of faces that have been experienced. Individual faces are coded relative to these norms, which are continually updated by experience. We investigated whether individuals with congenital prosopagnosia (CP), who report difficulty recognising faces and perform poorly on face recognition tests, have abnormal adaptive face coding mechanisms. We administered two face adaptation measures to 14 CPs to pinpoint their face processing impairments. The figural aftereffect reflects the dynamic updating of face norms, e.g., viewing ‘contracted’ faces shifts the norm in that direction, so that subsequently viewed undistorted faces are perceived as somewhat ‘expanded’. The figural aftereffect reflects adaptation to general distortions of shape and may not directly tap coding of facial identity. The performance of CPs was indistinguishable from that of controls on this task, consistent with evidence that CPs process some shape-based information from faces e.g., gender. In contrast, the face identity aftereffect directly taps the mechanisms involved in the discrimination of different face identities. Adapting to an individual face temporarily shifts the norm closer to that face, facilitating identification of a computationally opposite identity. CPs demonstrated a significant identity aftereffect, consistent with the figural aftereffect results. However, unlike controls, CPs impression of the identity of the neutral average face was not significantly shifted by adaptation, suggesting that the adaptive coding of identity is abnormal in CP. Further, the strength of the identity aftereffect for the average face correlated significantly and positively with performance on face recognition tests. CPs therefore show reduced aftereffects but only when the task directly taps the use of face norms used to code individual identity. These results are consistent with the finding that individuals with ASD, a developmental disorder associated with face identification difficulties, also show reduced face identity aftereffects.
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