Willed action in schizophrenia.

This study examined stimulus-driven and willed action in schizophrenic patients and healthy controls using an easy finger-tap task and a more demanding peg-placement task under unimanual, bimanual and dual-task conditions. Peg-placement externally cued by a metronome was also examined, as were practice effects. Patients with marked negative symptoms placed fewer pegs unimanually with and without practice and benefited most from metronome-cueing. Under dual-task conditions, when the participants placed pegs while concurrently finger-tapping, finger-tapping slowed down relative to unimanual scores in patients more than controls. Number of pegs placed also dropped off in controls and the patients with fewer negative symptoms. However, patients with more severe negative symptoms placed just as many pegs, and sometimes more, in the dual-task, compared to the unimanual, condition. These patients appeared to be using their finger-tapping just like an 'external' pacing-stimulus for peg-placement, thus rendering their peg-placement more stimulus-driven than willed. In contrast, patients with fewer negative symptoms and controls tried to self-generate maximal performance on both finger-tapping and peg-placement, with deleterious effects on both tasks. That the patients with marked negative symptoms performed best when their actions were more stimulus-driven than willed strengthens the case that negative schizophrenic symptoms reflect a disorder of willed action.