Sequence learning in Parkinson's disease: a comparison of spatial-attention and number-response sequences.

The serial reaction time (SRT) task has been frequently used to assess procedural learning of sequences. Patients with Parkinson's disease (PD) have been reported to show deficits on this task, but it is as yet unclear whether this impairment reflects a general sequencing deficit or a deficit in the sequencing of motor-output responses. In order to examine this issue, PD patients and controls were administered an SRT task which allowed the simultaneous and independent assessment of the procedural learning of spatial regularities and the learning of motor-response regularities. PD patients were unimpaired at learning a sequence of spatial locations, but showed a deficit at learning a stimulus-to-motor-response sequence. The results suggest that sequencing impairments in PD are not general, but specific to the type of sequential information inherent in a task.