Neural noise caused by executive dysfunction accounts for lexical-semantic deficits in first-episode psychosis

Lexical-semantic deficits in first-episode psychosis have been relatively explored, but few questions remain answered. The aim of this study was to investigate the preservation of category relations in the mental lexicon of first-episode psychosis patients with schizophrenic symptoms or symptoms similar to schizophrenia. The study recruited 24 first- episode psychosis patients from the University Psychiatric Hospital “Vrapče” in Zagreb and 24 matched control subjects. Subjects performed a lexical-semantic categorization task where they had to determine which of the four possible answers was a hyponym of the given lexical- semantic category. The task consisted of 10 categories, and each category was tested using 5 different exemplar hyperonyms. Other than the target word, three distractors were presented: a semantical-pragmatically related distractor, meronym and lexical-semantically unrelated word. Research was guided by two hypotheses: (1) the patient group would show significantly less correct answers compared to the control group, and (2) the patients would choose significantly more semantical- pragmatically related distractors, but not other distractors. Our hypotheses were modeled after the recent findings of Berberian et al. (2016) and Gabrić et al. (in press) who suggest stronger neural noise during lexical-semantic processing and a dysfunction of automated connections in the mental lexicon of first- episode psychosis and schizophrenia patients due to deficits in executive functioning. Both hypotheses were confirmed. Our results support the hypothesis that there is no significant damage to the mental lexicon in first-episode psychosis and that lexical-semantical deficits can be attributed to stronger neural noise in the mental lexicon of patients. This further implies that lexical-semantic deficits in first-episode psychosis are largely due to deficits in executive functioning and specifically inhibition. In addition, our results suggest that stronger neural noise in first-episode psychosis causes an outward shift of lexical-semantic category boundaries, but doesn’t include meronyms and semantically unrelated words.