Procedural learning in Parkinson's disease: intact and impaired cognitive components

Two experiments were carried out to study procedural learning in Parkinson's disease (PD) patients. In Experiment 1, ten patients and their normal controls participated in a classical mirror reading task and in an inverted reading task where word-stimuli made of non inverted letters had to be processed from right to left (e.g., ygoloruen). In both tasks, reading times for new stimuli were compared to reading times for stimuli that repeated over blocks. Although PD patients and their controls exhibited learning for repeated words in both tasks, PD patients did not respond faster with practice for new words in the inverted reading task. In Experiment 2, PD patients and their controls were presented with an original dot counting task in which participants were asked to process a horizontal series of black and white dots from right to left and to indicate whether a dot that had been designated by a number at the beginning of each trial was black or white. Results showed that PD patients, in contrast to controls, did not exhibit learning in this task. Results are discussed in terms of the cognitive components involved in these tasks. It is suggested that PD patients are impaired in the acquisition of a right-to-left visual scanning skill that could be studied directly in Experiment 2.