Reduced Negative Priming Does Indicate Reduced Cognitive Inhibition in Schizophrenia

Abstract

Introduction. Negative priming (NP) refers to the slowing of reaction times (RTs) that occurs when an ignored distractor in a first trial (prime) becomes the target in the subsequent trial (probe). Unlike normal controls, patients with schizophrenia fail to show significant NP. It has been proposed that delayed RTs in NP studies may be a result of perceptual mismatch rather than active inhibition, since the prime distractor and the probe target differ. The aim of this study was to examine spatial NP in schizophrenia using a new paradigm without perceptual mismatch. Methods. Twelve patients with schizophrenia and 17 normals were tested on a spatial NP task. Prime distractors and probe targets matched in terms of colour and location or did not match. Results. Normals showed significant spatial NP whether the probe target matched the prime distractor in terms of colour or not. In contrast, patients with schizophrenia did not show significant spatial NP. Conclusions. In normals, NP can be observed even when prime and probe stimuli are identical while patients with schizophrenia fail to show NP in conditions with or without perceptual mismatch. This is the first unequivocal demonstration of impaired inhibitory processes in schizophrenia based on reduced NP effects.