This study is a confirmatory, double-blind, placebo-controlled randomized clinical trial (RCT) testing whether gamma EEG neurofeedback (EEG-NFB) improves working memory in adults with schizophrenia or schizoaffective disorder. Participants are randomly assigned to receive either active gamma EEG-NFB (real-time feedback of frontal gamma brain activity) or sham EEG-NFB (false pre-recorded feedback), twice weekly for 12 weeks. Working memory (N-back task), brain gamma coherence, and everyday community functioning are assessed at baseline, mid-treatment, end of treatment, and follow-up.