Structured visual hallucinations (VH) in Parkinson’s disease (PD) are predominantly social, yet most accounts ignore this bias. In a home-based web study, 170 patients with PD and 45 controls completed a human numerosity estimation (NEH) task and a matched object control, plus brief measures of anthropomorphism and loneliness. After prespecified exclusions, 28 PD hallucinators (PD-VH), 55 PD without hallucinations (PD-nH), and 38 controls were analyzed. PD-VH showed a robust, selective overestimation of human crowds (≈+2.4 people on average), which scaled with numerosity and exceeded biases in PD-nH and controls; the effect was absent for non-human objects.
PD-VH also reported higher anthropomorphism and greater loneliness than both comparison groups; these traits correlated with each other but not with the NEH bias, suggesting partially independent mechanisms. Together, the findings indicate a selective impairment of social visual perception in PD-VH—consistent with dysfunction in social-vision circuitry—and help explain why VH so often feature animate figures. The NEH overestimation emerges as a simple, scalable digital marker of VH risk/severity, while elevated anthropomorphism/loneliness highlight a complementary, socially driven pathway for assessment and intervention.
Reference: Albert L, Vehar N, Potheegadoo J, Bernasconi F, Blanke O. Visual hallucinations in Parkinson’s disease are associated with deficits in social perception. J Parkinsons Dis. 2025;15(4):892-903. doi: 10.1177/1877718X251336196.
