Pupil changes to voluntary and involuntary visual imagery: A unified paradigm with implications for aphantasia research

This study examined both voluntary and involuntary visual mental imagery using pupillometry. We developed a unified experimental paradigm in which 50 participants either deliberately imagined visual scenes (voluntary imagery) or processed brightness-related words (involuntary imagery), while their pupil size was continuously recorded. Subjective vividness was assessed through questionnaires and self-reports. At the group level, brightness-related stimuli reliably elicited stronger pupil constriction than darkness-related stimuli, replicating prior findings. However, substantial inter-individual variability, combined with the absence of correlation with self-reported imagery measures, points to limitations in the protocol's sensitivity at the individual level. These results underscore the need to refine pupillometric paradigms before applying them to atypical populations, such as individuals with aphantasia. Our findings contribute to the development of objective, physiological tools for assessing visual mental imagery, and highlight the importance of individual-level analyses in future research on both typical and atypical imagery.