TIME-FREQUENCY ANALYSES OF THYROARYTENOID MYOELECTRIC ACTIVITY IN NORMAL AND SPASMODIC DYSPHONIA SUBJECTS

Digital recordings of thyroarytenoid (TA) myoelectric activity (via pe rcutaneous hooked-wire electrodes) were obtained for 10 normal control subjects and 10 subjects with spasmodic dysphonia during performance of five tasks of varying complexity: quiet breathing, Valsalva maneuve r, whispered \i\, voiced \i\, and ''beep beep went the heap.'' Time-fr equency power spectral density functions, PSD(f, t), were determined f or a selected segment of the signals, and measures of median frequency , mean frequency, bandwidth, and center frequency of PSD(f, t) were de rived for each sample point. Statistical median, mean, standard deviat ion, minimum, maximum, and mode of the power spectral density measures were computed to compose feature vectors for each TA myoelectric reco rding. Statistical pattern recognition procedures using maximum likeli hood classification tests were applied to the feature space to discrim inate disordered from normal speakers for each task. Findings indicate a high level of discriminability between subject groups for phonated speaking tasks in contrast to low levels of discriminability for whisp ered and nonspeech tasks. Graphical presentations of three-dimensional PSD(f, t) plots are given that illustrate changes in spectral charact eristics of TA EMG at the onset of laryngospasm.