Cognitive substrates of thought disorder, II: Specifying a candidate cognitive mechanism

Objective: In part I of this series, the authors found that semantic knowle dge and organization accounted for most of the variance in thought disorder in a group of chronic schizophrenic patients. In the present study, they e xamined a possible cognitive mechanism within the semantic system that migh t produce thought disorder. Method: Twenty patients with chronic schizophre nia and 21 normal comparison subjects were assessed on priming (the ability to respond to a stimulus word more quickly when it is preceded by a semant ically related word than when it is preceded by an unrelated word). The pat ients were divided into subgroups with high (N=9) and low (N=11) levels of thought disorder. The word pairs in the priming paradigm differed in their degree of association but shared a categorical membership. The paradigm inv olved short stimulus onset asynchronies to maximize automatic processing an d required pronunciation of words to minimize decision making. All subjects were also administered neuropsychological tests to assess language, execut ive function, real-world knowledge, and mental status. Results: Comparison subjects showed appropriate priming in stepwise fashion at the three differ ent fevers of word association, as did the patients with mild thought disor der. The patients with high thought disorder showed inhibited responses to high and medium associates compared with their baseline reaction times. Cor relations between priming and cognitive variables were significant only wit h measures of semantic processing. Priming abnormalities were uniformly rel ated to ratings of global thought disorder. Conclusions: These results sugg est that aberrations in the automatic spread of activation or facilitation in semantic networks may be a candidate cognitive mechanism in semantic acc ounts of thought disorder.