Voice quality in patients suffering from bipolar disease

People suffering from bipolar disease are more and more common. Such pathology can severely affect patients' lifestyle by wide, and sometimes extreme, mood swings. Biosignals can be very useful to understand this disease. Specifically, speech-related features have been seen to vary in depressed people with respect to healthy subjects. Usually prosodic, spectral and energy-related features are studied. Some further information, instead, can be provided studying voice quality. According to Laver's model, voice quality is sensitive and depends on both anatomic/physiologic issues and long-term muscular adjustments of the larynx or the supraglottal vocal tract. A pilot study on both bipolar patients and healthy control subjects, performed by means of the Long-Term Average Spectrum (LTAS) is presented. The effects on LTAS estimation of a F0-correction procedure are discussed. Pairwise statistical comparisons between subjects in euthymic and depressed states and euthymic and hypomanic states were performed. Significant differences were found in some frequency intervals in both cases. The F0-correction procedure modified the values of the significant frequency intervals in the euthymic/depressed comparison, that also was characterized by a change of F0. Noticeably, no statistically significant differences were found in control subjects acquired in the same mood state. Though the number of subjects is small, the results are encouraging given their coherence across patients and the lack of differences in the control group. Finally, this work suggests that particular vocal settings might be involved in different mood states.