Pareidolias: complex visual illusions in dementia with Lewy bodies

Abstract

Patients rarely experience visual hallucinations while being observed by clinicians. Therefore, instruments to detect visual hallucinations directly from patients are needed. Pareidolias, which are complex visual illusions involving ambiguous forms that are perceived as meaningful objects, are analogous to visual hallucinations and have the potential to be a surrogate indicator of visual hallucinations. In this study, we explored the clinical utility of a newly developed instrument for evoking pareidolic illusions, the Pareidolia test, in patients with dementia with Lewy bodies-one of the most common causes of visual hallucinations in the elderly. Thirty-four patients with dementia with Lewy bodies, 34 patients with Alzheimer's disease and 26 healthy controls were given the Pareidolia test. Patients with dementia with Lewy bodies produced a much greater number of pareidolic illusions compared with those with Alzheimer's disease or controls. A receiver operating characteristic analysis demonstrated that the number of pareidolias differentiated dementia with Lewy bodies from Alzheimer's disease with a sensitivity of 100% and a specificity of 88%. Full-length figures and faces of people and animals accounted for >80% of the contents of pareidolias. Pareidolias were observed in patients with dementia with Lewy bodies who had visual hallucinations as well as those who did not have visual hallucinations, suggesting that pareidolias do not reflect visual hallucinations themselves but may reflect susceptibility to visual hallucinations. A sub-analysis of patients with dementia with Lewy bodies who were or were not treated with donepzil demonstrated that the numbers of pareidolias were correlated with visuoperceptual abilities in the former and with indices of hallucinations and delusional misidentifications in the latter. Arousal and attentional deficits mediated by abnormal cholinergic mechanisms and visuoperceptual dysfunctions are likely to contribute to the development of visual hallucinations and pareidolias in dementia with Lewy bodies.

Figure 1

(A) Numbers of illusory responses and correct responses on the Pareidolia test. Significance is denoted by an asterisk (P < 0.05/3). (B) Numbers of illusory responses in patients with dementia with Lewy bodies with and without delusional misidentifications and hallucinations. (C) Numbers of illusory responses in patients with dementia with Lewy bodies with and without delusional misidentifications and hallucinations, stratified by medication status.

Figure 2

(A) Locations of illusory responses. (B) Locations of first illusory responses.

Figure 3

(A) Contents of illusory responses on the Pareidolia test. Numbers denote a percentage of the total illusory responses in each patient group. (B) Examples of illusory responses. Patients with dementia with Lewy bodies often misidentified objects or patterns in the picture as real faces (yellow triangle) or as figures of people and animals (white triangle).