Cognitive deficits present in almost all patients with schizophrenia, and account for considerable functional disability, but as typically measured in schizophrenia are unrelated to hallucinations and delusions.

Keefe RSE, Kraus MS, Krishnan RR. Failures in learning-dependent predictive perception as the key cognitive vulnerability to psychosis in schizophrenia.  Neuropsychopharmacology, 2011; 36(1): 367-380.  (PMCID:  PMC3055500).