Auditory feature conjunction in patients with schizophrenia.

The neural mechanisms supporting performance during single feature and feature conjunction tasks were investigated in patients with schizophrenia and age-matched controls using event-related brain potentials. In different blocks of trials, participants responded to auditory targets defined by one of two pitches, one of two locations, or both pitch and location. All participants were faster and more accurate in detecting targets defined by a single feature than for targets defined by a conjunction of features. Compared with the single feature conditions, conjunction targets were associated with enhanced negativity between 200 and 250ms (N2) post-stimulus and showed a delayed P3b latency. Compared with controls, patients with schizophrenia showed reduced N1 and N2 amplitude elicited by single and conjunctive targets. The results are consistent with defective perceptual mechanisms in schizophrenia. The fact that both performance and P3b amplitude were similar in patients and controls suggests that controlled processes compensate for processes normally carried out by early perceptual mechanisms.