Although Galton recognised in 1880 that some individuals lack visual imagery, this phenomenon was largely neglected over the following century. We recently coined the terms ‘aphantasia’ and ‘hyperphantasia’ to describe visual imagery vividness extremes, unlocking a sustained surge of public interest. Aphantasia is associated with subjective impairment of face recognition and autobiographical memory. Here we report the first systematic, wide-ranging neuropsychological and brain imaging study of people with aphantasia (n=24), hyperphantasia (n=25) and mid-range imagery vividness (n=20). Despite equivalent performance on standard memory tests, there were marked group differences on measures of autobiographical memory and imagination, participants with hyperphantasia outperforming controls who outperformed participants with aphantasia. Face recognition difficulties were reported more commonly in aphantasia. The Revised NEO Personality Inventory highlighted reduced extroversion in the aphantasia group and increased openness in the hyperphantasia group. Resting-state fMRI revealed stronger connectivity between prefrontal cortices and the visual network among hyperphantasic than aphantasic participants. In an active fMRI paradigm, there was greater anterior parietal activation among hyperphantasic and control than aphantasic participants when comparing visualisation of famous faces and places with perception. These behavioral and neural signatures of visual imagery vividness extremes validate and illuminate this significant but neglected dimension of individual difference.