Impairment of semantic composition in schizophrenia: An ERP study with lexical stimuli

Abstract

The ability of taking advantage of contextual constraints to facilitate semantic composition is impaired in schizophrenia, especially when control demands are high. This study examined the deficit using a primed lexical decision task with low control demands. Furthermore, two types of two-character Chinese words, binding nouns and compound nouns representing different levels of compositional difficulty, were employed to explore processing differences between schizophrenic (N = 35) and healthy (N = 18) participants. With the initial character of each word serving as the prime (context), participants judged as quickly and accurately as possible whether the final character, presented subsequently (SOA = 1000 ms) as the target, could combine and form a real word. Analyses of the N400 effect indicated that, even when integrating a one-character target into a one-character context, schizophrenic patients demonstrated lower efficiency than healthy controls, possibly due to deficiency in sustained attention and memory maintenance. However, their sensitivity to different levels of compositional difficulty seemed to be preserved. Specifically, as the initial characters of binding nouns could generate strong expectancies for their respective final characters, there was a processing advantage (greater N400 effect) of binding nouns over compound nouns, which was observed in both healthy and schizophrenic participants. Implications for the mechanisms underlying impairment of semantic composition in schizophrenia are discussed.