A Study to Evaluate ABT-126 for the Treatment of Cognitive Deficits in Schizophrenia

* Has a current Diagnostic and Statistical Manual of Mental Disorders-, 4th Edition, Text Revision (DSM-IV-TR) diagnosis of schizophrenia confirmed by the Mini-International Neuropsychiatric Interview (M.I.N.I.). * Is clinically stable while receiving a regimen of one or two allowable antipsychotic medications: lack of hospitalizations in 4 months prior to initial screening visit; taking the same antipsychotic medication(s) for at least 8 weeks prior to baseline visit; core positive symptoms of Positive and Negative Syndrome Scale (PANSS) no worse than moderate in severity throughout screening period of at least 4 weeks. * Has been diagnosed with or treated for schizophrenia for at least 2 years prior to initial screening visit. * Has had continuity in psychiatric care (e.g., mental health system, clinic or physician) for at least 6 months prior to initial screening visit. * Has an identified contact person (e.g., family member, social worker, case worker, or nurse) that can provide support to the subject to ensure compliance with protocol requirements.

* In the Investigator's judgment, has a current or past diagnosis of schizoaffective disorder, bipolar disorder, manic episode, dementia, post traumatic stress disorder, or obsessive-compulsive disorder, or the subject has a current major depressive episode. * Has a positive urine drug screen for cocaine, phencyclidine (PCP), opiates (unless duly prescribed), benzodiazepines (unless duly prescribed), marijuana, or amphetamines during the Screening Period. * Has a current or past history of seizures, with the exception of a single febrile seizure occurring prior to 6 years of age. * Has a clinically significant abnormal electrocardiogram (ECG) at Screening Visit 1 as determined by the Investigator. * Has any risk factors for Torsades de Pointes (TdP)