Vocal expression in schizophrenia: Less than meets the ear

Abstract

Abnormalities in nonverbal communication are a hallmark of schizophrenia. Results from studies using symptom rating scales suggest that these abnormalities are profound (i.e., 3-5 SDs) and occur across virtually every channel of vocal expression. Computerized acoustic analytic technologies, used to overcome practical and psychometric limitations with symptom rating scales, have found much more benign and isolated abnormalities. To better understand vocal deficits in schizophrenia and to advance acoustic analytic technologies for clinical and research applications, we examined archived speech samples from 5 separate studies, each using different speaking tasks (patient N = 309; control N = 117). We sought to: (a) use Principal Component Analysis (PCA) to identify independent vocal expression measures from a large set of variables, (b) quantify how patients with schizophrenia are abnormal with respect to these variables, (c) evaluate the impact of demographic and contextual factors (e.g., study site, speaking task), and (d) examine the relationship between clinically-rated psychiatric symptoms and vocal variables. PCA identified 7 independent markers of vocal expression. Most of these vocal variables varied considerably as a function of context and many were associated with demographic factors. After controlling for context and demographics, there were no meaningful differences in vocal expression between patients and controls. Within patients, vocal variables were associated with a range of psychiatric symptoms-though only pause length was significantly associated with clinically rated negative symptoms. The discussion centers on explaining the apparent discordance between clinical and computerized speech measures.

Figure 1

Vocal properties examined in this study.

Figure 2

Standardized means of vocal variables plotted as a function of study (combined patients and controls).

Figure 3

Standardized means of vocal variables plotted as a function of patients with No (Non), Mild and High clinically-rated negative symptoms and controls.