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The pathophysiology underlying visual misperceptions and hallucinations in PD is not well-understood. Psychosis is commonly associated with dementia ( 1). Often, PD patients realize that they are hallucinating, though patients with dementia may lose this insight ( 3). In visual hallucinations and illusions, most common “people” are reported ( 10). Flickering, false impressions, and illusionary misperceptions precede the core syndrome of stereotyped, colorful hallucinatory images ( 9). Furthermore, in 35-40% of drug-naive “ de novo” PD patients, minor hallucinations were reported ( 7) with gray matter loss in MRI being a risk factor ( 8). In early disease, older patients with slight decline of cognitive function were at higher risk of developing hallucinations under treatment ( 6). They occur in more than half of all patients with advanced disease ( 1– 5). Illusions (misperceptions of real stimuli) and hallucinations (aberrant perceptions) are a major problem within non-motor symptoms of Parkinson's disease (PD). However, due to the deficient communication with the DAN in PD patients, the DAN would not direct attention to the correct location, identifying a face at a location where actually none is present. In photographs in which a face is present, the VAN may detect this as a behaviourally relevant stimulus. Furthermore, we speculate that our results observed in PD patients rely on disturbed interactions between the Dorsal (DAN) and Ventral Attention Networks (VAN). We conclude that our new embedded faces paradigm is a useful tool to distinguish face perception performance between HC and PD patients. Montreal Cognitive Assessment (MoCA) was a significant predictor for pareidolia production in PD patients in trials in which a face was embedded in another region. Linear regression analyses showed that gender, age, hallucinations, and Multiple-Choice Vocabulary Intelligence Test (MWT) score were significant predictors of face pareidolia production in PD patients. However, PD patients also perceived faces significantly more often in locations where none were actually present than controls.
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We found that PD patients were significantly less likely to recognize embedded faces than controls. Participants were asked to decide for each photograph whether a face was embedded or not. The likelihood to perceive the embedded faces was modified by manipulating their transparency. Thirty participants (15 PD patients and 15 HC) were presented with 47 naturalistic photographs in which faces were embedded or not. We aimed to examine, within the same experiment, face perception and the production of face pareidolia in PD patients and healthy controls (HC). Literature suggests that the perception of face pareidolia may be increased in patients with neurodegenerative diseases. Pareidolia, i.e., the tendency to perceive a specific, meaningful image in an ambiguous visual pattern, is a phenomenon that occurs also in healthy subjects. In Parkinson's disease (PD) patients, visual misperceptions are a major problem within the non-motor symptoms.