title: Non-Linear Dynamic Analysis of Inter-Word Time Intervals in Psychotic Speech.
abstract: "Language is a form and not a substance" - Ferdinand de Saussure Objective: Analyses of speech processes in schizophrenia are invariably focused on words as vocal signals. The results of such analyses are, however, strongly related to content, and may be language- and culture-dependent. Little attention has been paid to a pure measure of the form of speech, unrelated to its content: inter-words time intervals.
  
  
  METHODS
  15 patients with schizophrenia and 15 healthy volunteers are recorded spontaneously speaking for 10-15 min. Recordings are 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 have the characteristics of a low-dimensional chaotic attractor with a correlation dimension of [Formula: see text]. Deconstruction of the attractor appears in psychosis with re-establishment after anti-psychotic treatment. Shannon entropy, a measure of the complexity in the time series, calculated from symbolic dynamics, is higher for psychotic speech, which is also characterized by higher levels of phase coupling: higher bicoherence, obtained using bi-spectral analysis.
  
  
  CONCLUSIONS
  Non-linear dynamical methods applied to ITIs thus enable a content-independent, pure measure of the form of normal thought, its distortion in psychosis, and its restoration under treatment.
authors.affiliation: Ben Gurion University of the Negev Psychiatry Department Beer Sheva Israel 84105.
authors.forename: Doron
authors.initials: D
authors.lastname: Todder
authors.affiliation: Ben Gurion University of the Negev Clinical Pharmacology Department Beer Sheva Israel 84105.
authors.forename: Sofia
authors.initials: S
authors.lastname: Avissar
authors.affiliation: Ben Gurion University of the Negev Faculty of Health Sciences Beer Sheva Israel 84105.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Schreiber
keywords: Schizophrenia; cognitive neuroscience; inter-words time intervals (ITIs); nonlinear dynamics; psychotic speech; speech form