In this article, we review the literature on practice effects in schizophrenia, an underappreciated confound in interpreting cognitive improvement in clinical trials. We first examine claims regarding first- and second-generation antipsychotic medications as cognitive enhancers, and follow it with a discussion of recent studies demonstrating how practice or placebo effects may drive ‘positive’ findings. Thus, this review suggests that many previous findings can be reinterpreted in this light.

Goldberg TE, Keefe RS, Goldman RS, Robinson DG, Harvey PD. Circumstances under which practice does not make perfect:  A review of the practice effect literature in schizophrenia and its relevance to clinical treatment studies.  Neuropsychopharmacology, 2010; 35(5): 1053-1062.