THE STATISTICAL-ANALYSIS OF SPEECH ENVELOPES IN STUTTERERS AND NON-STUTTERERS

This work is a portion of a research project that is aimed at the development of an objective method for evaluating fluency. The present purpose focuses on acoustic characteristics of utterances that distinguish stuttered and fluent speech. Toward this end, we used sound envelopes of utterances by 30 stutterers and 30 non-stutterers, each 100 seconds in duration and under conditions of simultaneous auditory feedback (SAF) or with an echo (DAF). Specifically, the interdependence of phonation number (number of times a given sound level was crossed) and sound intensity level was determined in this study. In addition, average distributions of phonation times and pause durations as a function of sound intensity level were examined. The resulting data suggest that differences in speech envelopes of stutterers and non-stutterers may be used to evaluate the degree of speech non-fluency. The obtained results support the hypothesis that the cause of stuttering is a lack of synchronization between laryngeal functioning and vocalizing activities. The result is that transitional states between vowels and consonants are either prolonged or more abrupt than normal. The present results are suggestive for a disorder of timing in the stutterers' speech.