Assessment of procedural learning and problem solving in schizophrenic patients by Tower of Hanoi type tasks.

Two versions of the Tower of Hanoi task were used to investigate different components of learning and problem solving in schizophrenia. Prior studies have suggested that a three-disk version (Tower 3), which involves primarily problem-solving abilities and planning, is preferentially sensitive to frontal lobe lesions and that the more difficult four-disk version (Tower 4), which involves "learning by doing," is sensitive to basal ganglia disease. Schizophrenic patients performed significantly worse than normal subjects on Tower 3 and Tower 4. However, they performed at least as well relatively on Tower 4 as on Tower 3, indicating that level of difficulty per se does not account for their poor performance on these tasks. Moreover, they eventually attained perfect or near-perfect performance after four days of repeated administration. Their relatively stronger performance on Tower 4 may have reflected an ability to acquire a procedure and, as such, suggests greater preservation of basal ganglia function than of prefrontal function.