Objective and subjective experiences of developmental prosopagnosia

Abstract

In this thesis, I investigated objective and subjective experiences of developmental prosopagnosia (DP), a neurodevelopmental condition that results in severe face recognition difficulties. To assess objective face processing, I first screened for general cognitive deficits that could explain poor face test performance. Participants completed a fluid reasoning task using abstract shapes. Potential DPs were more accurate than controls but significantly slower, suggesting speed-accuracy trade-off in non-face tasks. To address this, I calculated the Balanced Integration Score (BIS). Results showed no group differences, highlighting that DPs clearly adopted a different strategy from controls. I next investigated which face memory measures best classified DP. Participants completed two face memory tests, the Cambridge Face Memory Test (CFMT) and Old New Faces, a bicycle memory task and a famous faces recognition test. I directly compared how well accuracy and (BIS) classified DP. BIS was a more sensitive measure than accuracy alone on these tasks, classifying 83% vs 58% of DPs respectively and produced larger group effect sizes. I next systematically tested which subprocesses of face perception were impaired in DP. Single case analysis, group comparisons and intraclass correlations showed that face perception ability was highly heterogenous. Data showed evidence for two sub types of DP; an apperceptive subtype, in which both face perception and face memory are impaired and a mnemonic subtype (in which only face memory is impaired). Finally, I explored subjective experiences of living with DP using a mixed methods survey. Responses provided further evidence of the heterogeneity of the condition and highlighted the types of difficulties that DPs experienced in everyday life and their priorities for future research. Being unable to recognise close friends and family was a common experience and lower CFMT scores were not associated with the ability to recognise friends and family.