Spectral amplitude measures of adductor spasmodic dysphonic speech

Spectral amplitude measures are sensitive to varying degrees of vocal fold adduction in normal speakers. This study examined the applicability of harmonic amplitude differences to adductor spasmodic dysphonia (ADSD) in comparison with normal controls. Amplitudes of the first and second harmonics (HI, H2) and of harmonics affiliated with the first, second, and third formants (A1, A2, A3) were obtained from spectra of vowels /a/ and /i/ excerpted from connected speech. Results indicated that these measures could be made reliably in ADSD. With the exception of H1*-H2*, harmonic amplitude differences (H1*-A1, H1*-A2, and H1*-A3*) exhibited significant negative linear relationships (P < 0.05) with clinical judgments of overall severity. The four harmonic amplitude differences significantly differentiated between pre-BT and post-BT productions (P < 0.05). After treatment, measurements from /a/ detected significant differences between ADSD and normal controls (P < 0.05), but measurements from /i/ did not. LTAS analysis of ADSD patients' speech samples proved a good fit with harmonic amplitude difference measures. Harmonic amplitude differences also significantly correlated with perceptual judgments of breathiness and roughness (P < 0.05). These findings demonstrate high clinical applicability for harmonic amplitude differences for characterizing phonation in the speech of persons with ADSD, as well as normal speakers, and they suggest promise for future application to other voice pathologies.