Non-linear Dynamic Analysis of Inter-word Time Intervals in Psychotic Speech

D Todder, S Avissar, and G Schreiber, Ben Gurion University of the Negev

Non-linear Dynamic Analysis of Inter-word Time Intervals in Psychotic Speech

“Language is a form and not a substance” Ferdinand de Saussure

Objective: Analyses of speech processes in schizophrenia have been invariably focused on words as vocal signals. However, the results of such analyses are strongly related to content, and may be language-and culture-dependent. Little attention was paid to a pure measure of the form of speech, unrelated to its content: inter-words time intervals.

Method: 15 patients with schizophrenia and 15 healthy volunteers were recorded spontaneously speaking for 10-15 minutes. Recordings were analyzed for inter-words time intervals using the following non-linear dynamical methods: unstable periodic orbits; correlation dimension; bi-spectral analysis, and symbolic dynamics.

Results: The series of inter-word time intervals in normal speech had characteristics of a low-dimensional chaotic attractor with correlation dimension of 3.2±1.1. Deconstruction of the attractor appeared in psychosis with re-establishment after anti-psychotic treatment. Shannon entropy, a measure of the complexity in the time series, calculated from symbolic dynamics, was higher for psychotic speech, which was also characterized by higher levels of phase coupling: higher bicoherence, obtained using bi-spectral analysis.

Conclusions: Non-linear dynamical methods applied to inter-word time intervals thus enable a content-independent, pure measure of the form of normal thought, its distortion in psychosis, and its restoration under treatment.

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See complete bios of the authors in the full version of this article.

D Todder
Ben Gurion University of the Negev

S Avissar
Ben Gurion University of the Negev

G Schreiber
Ben Gurion University of the Negev

Editorial Comments

We expect the impact of this paper to be high. This approach has not been used to this effect prior to this investigation. The results provide a meaningful insight into brain function that should be correlated with other measures such as fMRI and neuropsych testing in subsequent experiments and should form the basis for a larger multi-modality study.

JTEHM 2013Issue

This article appeared in the 2013 issue of IEEE Journal of Translational Engineering in Health and Medicine.
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