Behavioural, Electrophysiological and Neurostimulatory Investigations into Developmental Prosopagnosia

Developmental prosopagnosia (DP) is the difficulty or inability to recognise a face and may affect up to 2.9 percent of the population. There is controversy over whether these impairments are perceptual or memorial in nature, and uncertainty about their stability over time and how to remediate symptoms. In the first stage, a battery of ten tests was assembled to assess a wide range of face recognition skills in DP (n = 11) and compared to a control group (Chapter Two). The majority of DPs showed no signs of impaired face perception but profound face memory deficits. To seek electrophysiological corroboration of these impairments, the DPs (n = 8) were given three behavioural tasks known to elicit specific event related potentials (Chapter Three), assessing face perception (N170), face familiarity (N250r) and semantic access (N400). During the experiment, caloric vestibular stimulation (CVS) was also administered to see if it could reduce symptoms. The tasks revealed intact face perception and impaired accuracy in both memory based tasks, corroborated by an atypical N400. Subtle effects of CVS were observed in all measures of the face familiarity task but not at a level that was clinically relevant. To establish, for the first time, whether the impairments in DP are consistent over time, the effects in Chapter Three were replicated (n = 7)(Chapter Four). A similar pattern emerged and test-retest correlations showed high reliability overtime in the familiarity task but not the semantic access task. This implies that reliable 'diagnosis' of developmental prosopagnosia should be based on judgements of face familiarity and not associated with semantic activity. The beneficial effects of CVS were again present in the N250r behavioural measures and were limited to familiar faces only. This implies that CVS is optimising memory recall for face representations. The source of impairments was consistently shown to be memorial in nature and future studies may wish to explore further divisions of memory in DP such as whether impairments are associated with encoding or recall. The thesis also demonstrates the potential for CVS as both a therapeutic tool and cognitive enhancer, and justify more robust trials investigation.