<qa>  What is donepezil?The present study will specify and delineate the separate components of cognitive deficits and examine the effects of adjunctive cholinergic augmentation on these cognitive deficits as well as psychopathology in schizophrenic patients treated with an antipsychotic compound with no aberrant binding affinity for the cholinergic receptor system. The hypothesis is that cholinergic augmentation using donepezil will improve cognitive deficits, sensory gating deficits, and psychopathology in schizophrenic patients treated with an atypical antipsychotic ziprasidone. 