Neuropsychological approaches to understanding visual hallucinations

Hallucinations are a subjective experience with phenomenologically distinct characteristics, which are most likely to be a result of distinct neuronal origins. The mechanisms of the experience are investigated using a range of cognitive tests designed to examine characteristics such as memory, visual ability and executive function, which have generally been designed for general cognition evaluations rather than to specifically investigate hallucinations. Hallucination research from the perspective of cognitive neuropsychology focuses on the mechanisms integral to both hallucinations and veridical perception, in an attempt to identify the specific cognitive mechanisms which underlie hallucinations as well as their associated neural basis. For instance, although hallucinations are one of the main symptoms of schizophrenia, they are not experienced by all people with schizophrenia. In theory, the internal generation of images, along with compensatory visual processing, could be caused by relatively impaired visual processing in patients with PD who are experiencing visual hallucination (VHs).