Abstract
<p>Face recognition is a fundamental cognitive function that is essential for social interaction – yet not everyone has it. Developmental prosopagnosia is a lifelong condition in which people have severe difficulty recognising faces but have normal intellect and no brain damage. Despite much research, the component processes of face recognition that are impaired in developmental prosopagnosia are not well understood. Two core processes are face perception, being the formation of visual representations of a currently seen face, and face memory, being the storage, maintenance, and retrieval of those representations. Most studies of developmental prosopagnosia focus on face memory deficits, but a few recent studies indicate that face perception deficits might also be important. Characterising face perception in developmental prosopagnosia is crucial for a better understanding of the condition. In this thesis, I addressed this issue in a large-scale experiment with 108 developmental prosopagnosics and 136 matched controls. I assessed face perception abilities with multiple measures and ran a broad range of analyses to establish the severity, scope, and nature of face perception deficits in developmental prosopagnosia. Three major results stand out. First, face perception deficits in developmental prosopagnosia were severe, and could be comparable in size to face memory deficits. Second, the face perception deficits were widespread, affecting the whole sample rather than a subset of individuals. Third, the deficits were mainly driven by impairments to mechanisms specialised for processing upright faces. Further analyses revealed several other features of the deficits, including the use of atypical and inconsistent strategies for perceiving faces, difficulties matching the same face across different pictures, equivalent impact of lighting and viewpoint variations in face images, and atypical perceptual and non-perceptual components of test performance. Overall, my thesis shows that face perception deficits are more central to developmental prosopagnosia than previously thought and motivates further research on the issue.</p>
Highlights
Face recognition is a fundamental cognitive function that is essential for social interaction – yet not everyone has it
The N250 is maximally responsive to faces with long-term associative memory, such as pictures of one’s own face (Herzmann et al, 2004; Tanaka et al, 2006). These findings suggest that the N250 is a marker of face memory (Gosling & Eimer, 2011)
3.2 The severity of face perception deficits in developmental prosopagnosia First, I estimated the severity of face perception deficits in developmental prosopagnosia
Summary
I estimated the severity of face perception deficits in developmental prosopagnosia. Longer response times have been taken to indicate atypical face processing in developmental prosopagnosia (Behrmann et al, 2005; Dalrymple et al, 2014b) To check for these possibilities, I ran a two (group: prosopagnosic, control) by four (test: BFRT, GFMT, CFPT, CFMT-Aus) mixed-measures analysis of variance (ANOVA) on participants’ raw mean response times. To compare face perception deficits and face memory deficits, I ran a two (group: prosopagnosics, controls) by four (test: BFRT, GFMT, CFPT, CFMT-Aus) mixed-measures ANCOVA on accuracy (Figure 7). The significant interaction suggests that the group differences differ across tests, which is reflected by the effect sizes To explore this interaction, I ran three follow-up mixed-measures ANCOVAs comparing group accuracy on the CFMT-Aus against each of the three face perception tests, while adjusting for response times as a covariate. This result provides robust evidence that face perception deficits in developmental prosopagnosia are much more severe than previously thought
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