The effects of Parkinson's disease on the capacity to generate information randomly

In two experiments, the capacity of Parkinson patients and normal controls to generate letters randomly was investigated using a dual task. The task was based on Baddeley's work (Baddeley, A. D., Quarterly Journal of experimental Psychology 18, 119-129, 1966) where participants vocalize letters of the alphabet in random order. The task was performed under two conditions where letters were (a) vocalized at a specified rate (0.5, 1, 2 and 4 sec); and (B) letters were vocalized at the same rates but with a secondary task of sorting cards into one, two, four and eight categories. The aim was to test the notion of non-specific slowing in response selection processing in Parkinson's disease. Results showed that randomness decreased as generation rate increased in both groups, but with the patient group significantly impaired in comparison to controls. The notion of a limited capacity response selector based on disruption to the Supervisory Attentional System is invoked to account for the impaired capacity of the patient group to generate information internally.