Visual hallucinations in Parkinson's disease are associated with deficits in social perception.

BackgroundMost structured visual hallucinations (VH) in Parkinson's disease (PD) involve animate-social objects, yet current theories fail to account for the prominent social component of VH in PD.ObjectiveTo study social perception in PD patients with VH in a behavioral task and its relationship with social traits such as perceived social isolation and anthropomorphism (tendency to ascribe human-like characteristics to non-human stimuli).MethodsIn this online web-based study, 28 PD with visual hallucinations (PD-VH), 55 PD patients without hallucinations (PD-nH), and 45 age-matched healthy controls (HC) performed a visual social task (human numerosity estimation), a control task, and filled an anthropomorphism and a loneliness questionnaire.ResultsOur data reveal a deficit in social visual perception characterized by a larger overestimation bias in human numerosity estimation in PD-VH versus control PD-nH and HC. Moreover, PD-VH had higher social traits of anthropomorphism and loneliness versus control PD-nH and HC and the overestimation bias was absent for non-human control stimuli.ConclusionsThese data describe a stronger social visual deficit and higher social traits in PD patients with VH, suggesting that neurodegenerative changes in PD-VH predominantly affect structures involved in social visual perception.