Patients with early Parkinson's disease are not impaired on spatial orientating of attention

The shifting of attention to visual stimuli was studied in twenty patients with early Parkinson's disease (stage I or II as defined by the Hoehn and Yahr scale) and twenty normal controls matched for age, sex and intellectual status. Both groups were screened to exclude dementia, psychiatric disease and other neurological abnormalities. The speed of shifting attention to visual stimuli was measured using the cost and benefit paradigm. The results showed an overall increase in response latencies in patients with early Parkinson's disease compared to the Control group, but without a concomitant slowness to shift their attention toward a visual spatial target. This slowness which appears to reflect a delay in the decision-making process, regardless of the demands of the task, was independent of motor impairment, mood, intellectual status and Levodopa medication. While the Parkinson patients and normal controls showed a 38 msec benefit when the target stimulus was expected in a given location, all subjects failed to demonstrate a cost when the target stimulus was presented in an unexpected location. This may be a reflection of age. Alternatively, subjects may have learned to inhibit responses to the invalid cue.