Lexical Diversity and Other Linguistic Measures in Schizophrenia: Associations With Negative Symptoms and Neurocognitive Performance.

ABSTRACT: Straightforward linguistic measures may be indicators of reduced language production and lexical diversity among individuals with schizophrenia with negative symptoms and neurocognitive impairments. We compared 98 patients with schizophrenia to 101 unaffected controls on six language variables ( e.g. , number of relationships between objects, use of complex transitions in the narrative structure), number of words produced, and lexical diversity computed as the moving average type-token ratio from both speaking and writing tasks. Patients differed from controls on nearly all of the linguistic measures; number of words produced had the strongest effect, with an average Cohen's d of 0.68; values pertaining to lexical diversity were 0.50 and 0.32, respectively, for the speaking tasks and the writing tasks. Most measures were correlated with alogia and other domains of negative symptoms (including avolition-apathy and anhedonia-asociality), as well as with diverse neurocognitive domains, especially those pertaining to working memory, verbal learning, and verbal category fluency. Further work is needed to understand longitudinal changes in these linguistic variables, as well as their utility as measures of alogia.

Initial evidence of vowel space reduction in a subset of individuals with schizophrenia.

OBJECTIVE: Acoustic phonetic measures have been found to correlate with negative symptoms of schizophrenia, thus offering a path toward quantitative measurement of such symptoms. These acoustic properties include F1 and F2 measurements (affected by tongue height and tongue forward/back position, respectively), which determine a general "vowel space." Among patients and controls, we consider two phonetic measures of vowel space: average Euclidean distance from a participant's mean F1 and mean F2, and density of vowels around one standard deviation of mean F1 and of F2. METHODS: Structured and spontaneous speech of 148 participants (70 patients and 78 controls) was recorded and measured acoustically. We examined correlations between the phonetic measures of vowel space and ratings of aprosody obtained using two clinical research measures, the Scale for the Assessment of Negative Symptoms (SANS) and the Clinical Assessment Interview for Negative Symptoms (CAINS). RESULTS: Vowel space measurements were significantly associated with patient/control status, attributed to a cluster of 13 patients whose phonetic values correspond to reduced vowel space as assessed by both phoenetic measures. No correlation was found between phonetic measures and relevant items and averages of ratings on the SANS and CAINS. Reduced vowel space appears to affect only a subset of patients with schizophrenia, potentially those on higher antipsychotic dosages. CONCLUSIONS: Acoustic phonetic measures may be more sensitive measures of constricted vowel space than clinical research rating scales of aprosody or monotone speech. Replications are needed before further interpretation of this novel finding, including potential medication effects.