A clinical, neuropsychological, and forensic investigation of congenital aphantasia

Congenital aphantasia is a neurodevelopmental condition characterised by markedly impaired visual imagery determined from birth. For example, when asked to imagine a sunset, most people can ‘see’ an image of the scene within their mind’s eye. People with aphantasia do not experience an internal image, despite knowing what a sunset looks like. Aphantasia only entered mainstream science in recent years, meaning our understanding of the condition is relatively limited. Through four experimental studies, this thesis will enhance our understanding of aphantasia from a clinical, neuropsychological, and forensic perspective. Chapter 2 asks how often aphantasia occurs in the general population, providing a reliable prevalence estimate. Chapter 3 examines how aphantasia intersects with the clinical condition of autism, and the neuropsychological condition of synaesthesia – both traits themselves characterised by imagery differences. Here, I show that aphantasics tend to experience high levels of autistic traits, and have an unusual profile of (certain types of) synaesthesia. Chapter 4 examines the broader sensory/imagery profile of aphantasia. Here, I show that aphantasia is often tied to low imagery beyond the visual domain (weak auditory imagery, olfactory imagery, etc.), and I coin the term dysikonesia to characterise multi-sensory imagery weakness (where aphantasia is the visual subtype). I also show that aphantasics tend to experience lower levels of sensory sensitivity (i.e., differences in responsivity to incoming sensation) across multiple senses. These findings demonstrate for the first time that mental imagery and sensory sensitivity are linked. Finally, Chapter 5 explores the forensic question of whether imagery influences face processing. I show that aphantasia is linked to weak face recognition and perception, but intact abilities when constructing face composites. Overall, this thesis shows that aphantasia is linked to a distinct psychological profile, with clinical, neuropsychological, and forensic implications. Together, this body of work serves to enhance our understanding of aphantasia, and mental imagery more broadly.