Abstract/Summary

Developmental prosopagnosia (DP) is a neurodevelopmental condition characterised by difficulties in recognising and discriminating between faces, occurring in individuals with no manifest brain injuries, and with normal low-level vision and intelligence. The nature of the impairment remains unclear. Mnemonic accounts propose that DPs form accurate structural representations of faces, but cannot maintain them in short-term memory. Alternatively, apperceptive accounts predict that DPs form imprecise structural representations of faces. Key models of face processing posit that an impairment at the initial structural encoding stage should inform subsequent judgments including identity, sex, and age. While it is known that DPs have impaired identity recognition, it is unclear whether sex and age perception is also impaired. Chapter 2 of this thesis explored sex perception in DP and found significantly less sensitivity to subtle differences relative to controls. Chapter 3 explored the relationship between facial identity, sex, and age recognition, finding an association between all three in the general population, along with evidence of impaired sex and age perception, and slower response times, in DP compared to controls. Chapter 4 explored how structural encoding unfolds over time, finding evidence of higher processing rates for upright and familiar faces versus inverted and unfamiliar faces in neurotypical adults. No group differences were found between DPs and controls on the orientation task, though the sample was smaller than planned due to the COVID-19 pandemic. Chapter 5 used drift diffusion modelling to explore differences in the rate of evidence accumulation and response caution in a sex categorisation task between DPs and controls. No significant group differences were found, despite replicating earlier findings using behavioural measures. In general, replicable deficits of facial sex processing were observed in DP, providing evidence for the apperceptive account. In Chapter 6, the implications of these findings on the characterisation of DP are discussed.