Background: Delirium is a neuropsychiatric disorder characterised by severe cognitive impairment, but its specific neuropsychological profile has not yet been clearly delineated. Psychiatric symptoms of perceptual disturbance, such as hallucinations, illusions and misperceptions, are also common in delirium, suggesting that patients may have deficits in the cognitive systems underlying visual perception.
Methods: Five neuropsychological tests of visual perception were administered to 17 older patients with delirium, as well as to control groups of 14 patients with Alzheimer’s dementia and 18 cognitively healthy controls. The Mini Mental State Examination (MMSE) and the CERAD verbal memory test were also administered to assess the specificity of any perceptual impairments.
Results: Patients with delirium scored significantly lower than cognitively normal controls on all perceptual tasks, and significantly lower than dementia patients on three of these tasks. MMSE scores did not differ between the delirium and dementia groups, and patients with delirium showed significantly better verbal recognition performance than the dementia group.
Conclusions: Patients with delirium have specific visual perceptual deficits that cannot be accounted for by general cognitive impairment. These novel findings provide insights into the neural mechanisms underling delirium, and may help to improve clinical detection and management of the disorder. The results also support previous suggestions that cognitive perceptual deficits play a causal role in eliciting psychiatric symptoms of perceptual disturbance.