Congenital aphantasia is a variation of the human experience, characterised by a life-long inability to generate voluntary mental imagery, and so far, has been examined in the visual domain. In a series of 10 experiments, this thesis took an experimental approach to examine the possible explanations of congenital aphantasia and the nature of the experience in the visual and non-visual domains, using objective measures and matched samples. Chapter 2 examines the findings of the early published studies within larger experimental designs, and the results confirmed self-reported differences in object imagery but not spatial imagery. Chapter 3 investigates whether aphantasia may be associated with differences in personality or deficits in broader cognitive functions. The results showed no evidence of a difference between individuals with aphantasia and neurotypical imagers on personality or selected neuropsychological measures. Aphantasic participants were slower in a task during trials that had greater working memory load, however, individual differences in performance were apparent and four aphantasic subgroups identified. Chapter 4 showed no difference in accuracy or response time in complex visuospatial working memory tasks requiring allocentric and egocentric transformations. However, aphantasic participants exhibited greater variability in their response times for front/back orientations within an egocentric task. In Chapter 5, a task that attempted to isolate ‘visual’ from spatial imagery showed no difference in performance across visual and spatial features. Nevertheless, self-reports of nonvisual sensory imagery showed variability in the range of imagery experience across the other senses. Chapter 6 extended exploration of mental imagery in aphantasia beyond the visual modality by examining behavioural performance in two auditory imagery tasks, in which no differences in accuracy or reaction time were evident. Taken together, this research shows that despite the differences in self-reported experience, limited group differences are found between aphantasic and neurotypical participants on a range of imagery and visuospatial working memory tasks. Nevertheless, individual differences in performance were apparent. Further research should investigate the processes adopted by these subgroups, or whether (or not) individuals with aphantasia have unconscious mental imagery
