Objective: To investigate color discrimination ability and complex visual illusions known as pareidolias, and their associating factors in patients with iRBD compared to PD and healthy controls.

Background: Visuoperceptual dysfunction is a common manifestation of Lewy body disease (LBD) and is also reported in its prodromal phase, isolated REM sleep behavior disorder (iRBD). Current findings suggest that visuoperceptual impairment, although insufficient on its own, may be involved in the development of pareidolias. However, no studies up to date have simultaneously assessed color discrimination and pareidolic responses along with its possible inter-relationship.

Method: 46 iRBD, 43 PD patients, and 32 healthy controls underwent the Farnsworth–Munsell 100 hue and noise pareidolia tests in succession. We aimed to explore any relationship between those two visual functions and their associations with prodromal motor and non-motor manifestations, evaluated by the MDS-Unified Parkinson’s Disease Rating Scale (UPDRS) part I and III, Cross-Cultural Smell Identification Test (CCSIT), sleep questionnaires, and comprehensive neuropsychological assessment.

Results: iRBD and PD patients both performed worse on the Farnsworth–Munsell 100 hue test and had greater number of pareidolias compared with healthy controls. No correlations were found between the extent of impaired color discrimination and pareidolia scores in either group. In iRBD patients, the number of pareidolias was associated with worse global cognition score and frontal executive dysfunction, while impaired color discrimination was associated with visuospatial dysfunction, hyposmia, and higher MDS-UPDRS-III scores. Pareidolias in PD patients correlated with worse global cognition and verbal memory recall whereas color perception deficits were associated with frontal executive dysfunction.

Conclusion: Color discrimination deficits and pareidolias are frequent but does not correlate with each other from prodromal to clinically established stage of PD. The different pattern of clinical associates with both visual symptoms suggests that evaluation of color and pareidolic illusions may aid in revealing the course of LBD-related neurodegeneration.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pareidolias-and-color-discrimination-deficits-differently-correlate-with-cognitive-dysfunction-in-prodromal-lewy-body-disease/