Lateralized deficits and drug influences on the dichotic listening of schizophrenic patients.

Recall of dichotically presented digit strings was compared between normal controls and 18 chronic schizophrenic patients tested over 12 weeks on chlorpromazine, placebo, and chlorpromazine reinstatement. Patients were subgrouped according to (i) arousal as indexed by orienting responses in a tone-habituation sequence and (ii) paranoid diagnosis. Digits were of equal intensity or differed by 20 dB between the ears and were reported in any order or one ear before the other. Overall, patients performed as well as controls and withdrawal or reinstatement of drug did not reduce accuracy. Patient-control differences occurred when the louder digits were to be reported second and left-hemisphere inhibitory mechanisms were involved, especially when patients were on chlorpromazine. Some lateralized differences in serial position effects found only in patients were interpreted as reflecting left-hemisphere processing impairments. The more aroused patients showed poorer accuracy than the less aroused group due to reduced recall in the left ear. Paranoid patients had superior recall and showed less shifting of attention away from the right ear than nonparanoids. The results are discussed in the context of neurophysiological theories of brain disturbance in schizophrenia.