Syntactic and semantic processing in schizophrenic patients evaluated by lexical-decision tasks

Two lexical-decision tasks with 500-ms stimulus-onset asynchrony were conducted with 34 schizophrenic patients. This group consisted of 24 schizophrenic patients with thought disorder (TD) and 10 schizophrenic patients without thought disorder (NTD), 14 psychiatric controls (depressive illness), 20 hospitalized controls, and 20 normal controls. One lexical-decision task with semantic relations (related vs. unrelated, Experiment 1) and 1 task with syntactic relations (congruent vs. incongruent; Experiment 2) were used to evaluate processing of different lexical information. In Experiment 1, although all control groups and NTD schizophrenic patients showed semantic priming, TD schizophrenic patients did not. In Experiment 2, all groups showed a significant syntactic effect. These findings provide evidence for an abnormality in semantic processing and the preservation of syntactic processing in TD schizophrenic patients, thus suggesting a deficit in the processing of semantic information under certain conditions when compared with normal syntactic processing.