The perception of visual ambiguous figures in schizophrenia and Parkinson's disease

The frequency of reversal and dominance of aspect of three versions of an ambiguous Schröder staircase were studied in patients with a diagnosis of either schizophrenia or Parkinson's Disease (PD), and in a mixed group of psychiatric patients before and after prolonged neuroleptic therapy. It was found that schizophrenics perceived the staircases from above for significantly less time, and had a (nonsignificant) tendency to have more reversals than controls. PD patients saw the staircases from above for significantly more time, and also had (nonsignificantly) more reversals than controls. In the psychiatric patients, long term neuroleptic therapy had no significant effect on either reversal rate or dominance of aspect. When the contrast and the luminance of the stimulus were manipulated, normal subjects reported significantly less reversals and significantly increased dominance of the superior aspect when the contrast of the stimulus was reduced. Changing the luminance had no significant effect. The implications of these results for visual abnormalities in schizophrenia and Parkinson's Disease are discussed.