At study start all volunteers will be discontinued from their current antipsychotic drug (APD) and switched to haloperidol 4mg for 5 days. At the end of this discontinuation period, all baseline symptom ratings and cognition testing will be done, as well as the baseline imaging procedures. At the end of the baseline procedures, volunteers will be blindly randomized, either to lurasidone at 40mg (N=12), or to haloperidol at 4mg/d or perphenazine at 16mg/d (N=12). Doses will increase to 80mg/d lurasidone, 8 mg/d haloperidol, or 32 mg/d of perphenazine at the beginning of week two. Dose should be stable for the last 3 weeks of treatment unless side effects are prominent, then the dose can be decreased to 40 lurasidone/4 haloperidol/16 perphenazine mg/d for optimal clinical management. The randomization strategy will be designed and implemented by the research pharmacist in four blocks of six volunteers; drug will be dispensed by the research pharmacy according to the randomization schedule. The randomization will be followed by a four week treatment period at optimal dose levels. On the last two days of the 4 week stable dosing period, the specified glutamate outcome measures will be completed (neuroimaging and cognitive testing) along with all the symptom outcome measures, testing for drug plasma levels, and usual blood safety measures. Patients will be seen weekly for clinical evaluation; suicidality will be monitored weekly. All medications other than study drugs will be discontinued, as much as possible, for the 24-48 hr assessment period. After the evaluation phase, patients will be cross-titrated back to their original treatment medication and dosing.