isual hallucinations are a common, distressing, and disabling symptom of Lewy body and other diseases. Current models\udsuggest that interactions in internal cognitive processes generate hallucinations. However, these neglect external factors.\udPareidolic illusions are an experimental analogue of hallucinations. They are easily induced in Lewy body disease, have\udsimilar content to spontaneous hallucinations, and respond to cholinesterase inhibitors in the same way. We used a\udprimed pareidolia task with hallucinating participants with Lewy body disorders (n = 16), non-hallucinating participants\udwith Lewy body disorders (n = 19), and healthy controls (n = 20). Participants were presented with visual “noise” that\udsometimes contained degraded visual objects and were required to indicate what they saw. Some perceptions were\udcued in advance by a visual prime. Results showed that hallucinating participants were impaired in discerning visual\udsignals from noise, with a relaxed criterion threshold for perception compared to both other groups. After the\udpresentation of a visual prime, the criterion was comparable to the other groups. The results suggest that participants\udwith hallucinations compensate for perceptual deficits by relaxing perceptual criteria, at a cost of seeing things that are\udnot there, and that visual cues regularize perception. This latter finding may provide a mechanism for understanding the\udinteraction between environments and hallucinations.
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