“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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