The purpose of the proposed study is to examine the efficacy and safety of two doses of MK (Merck) -0777 GEM, 3 mg BID (twice daily) and 8 mg BID (twice daily), in the treatment of cognitive impairments in patients with schizophrenia. Secondary goals are to determine whether MK-0777 has beneficial effects on measures of functional capacity and patient self-report of cognitive function.