Recharacterising Face Recognition Deficits in Developmental Prosopagnosia.

Abstract

Developmental prosopagnosia (DP) is a neurodevelopmental condition characterised by a relatively selective deficit in face recognition. Current approaches to diagnose the condition vary within the field, making comparisons across studies difficult. Furthermore, theoretical inferences rely on accurate identification of people with DP and, combined with the fact that some individuals also report moderate-to-severe psychosocial consequences of the condition, the methods used to diagnose DP have been under increasing scrutiny. Thus, the present thesis aimed to address contemporary issues relating to the diagnosis of DP. Specifically, the thesis begins by investigating the utility of self-report, and presents a list of empirically-driven hallmark symptoms of the condition which can aid the identification of DP in children and adults, both in oneself and in others. The thesis then explores objective measures of face processing; Chapter Four presents, for the first known time, the test-retest reliability for the Cambridge Face Memory Test (CFMT) – the leading test of unfamiliar face recognition. Interestingly, this value falls just short of accepted psychometric protocols, and recommendations for using two separate tests of the same subprocess of face processing are suggested. With this in mind, Chapter Five supported the diagnostic utility of repeat assessment for face perception. We present a new test of face matching and, in combination with the original Benton Facial Recognition Test, advocate the use of identifying face perception deficits in DP by administering two separate tests. Finally, we come away from behavioural measures to consider more nuanced means of dissociating DP from other developmental conditions that are commonly associated with face recognition difficulties. For instance, many people with autistic spectrum conditions (ASCs) struggle with face recognition, and many DPs avoid social situations – an outward symptom that may be confused with ASCs. Given face recognition difficulties likely have different underpinnings in the two conditions, Chapter Six employs eye-tracking methods to differentially diagnose face recognition impairments in DP versus ASCs. Whilst sample size is low due to the interruption of data collection by COVID- 19, we find that those with ASC look more towards non-social stimuli than DP participants, particularly when the scene is more social and interactive. Those with DP look more towards extrafacial information, such as hair and bodies, than ASC participants. The thesis concludes with a summary of recommendations for the future diagnosis of DP.