Perception and Acoustic Studies of Vowel Intelligibility in Dysphonic Speech.

PURPOSE: This study aimed to (1) examine the effect of dysphonia and background noise on the identifiability of vowels, and (2) evaluate the relationship between the degree of vowel intelligibility and vowel-related acoustic measurements. METHOD: A speech perception experiment was conducted with speech samples collected from 10 adult females with healthy voices and 10 adult females with dysphonia. The speech material was 11 vowels of American English in /h/-vowel-/d/ format. Cafeteria noise was added to these samples at a signal-to-noise ratio of -6 dB. A total of 10 adults with normal hearing participated in a speech perception experiment, in which the vowels were presented with and without the noise. F1 and F2 frequencies of the vowels were measured, and their relationships with the vowel intelligibility were statistically evaluated. RESULTS: The group-level analysis showed that vowel intelligibility was lower in dysphonic speech than normal speech, both in quiet and at signal-to-noise ratio of -6 dB. The intelligibility was higher for the high vowels than the low vowels. In general, the vowel confusion pattern was similar between normal and dysphonic speech. However, data from a speaker with severe diplophonia showed a distinct confusion pattern. Voice quality ratings did not significantly correlate with the vowel intelligibility. There was a significant correlation between F2 and the vowel intelligibility in quiet. A post-hoc acoustic analysis revealed that vowels of the speakers with lower vowel intelligibility had lower acoustic energy above 1 kHz. CONCLUSION: Dysphonia negatively affects vowel intelligibility. Low vowels were more vulnerable to the effect of dysphonia than high vowels. Among different types of dysphonic voice qualities, diplophonia appears to be particularly detrimental to vowel intelligibility. F2 significantly correlated with vowel intelligibility; however, this result requires a careful interpretation. Given that the acoustic energy above 1 kHz resulted in better intelligibility in noise, a treatment strategy that targets this frequency region may help improve intelligibility in noise. Future studies should examine the generalizability of this finding to different age and gender groups, and intelligibility as a whole.

Agreement between Transcription- and Rating-Based Intelligibility Measurements for Evaluation of Dysphonic Speech in Noise.

Dysphonia negatively affects a speaker's intelligibility, especially in noisy environments. Previously, our study showed this effect of dysphonia with the transcription-based intelligibility measurement. While this finding indicates the importance of intelligibility assessment for this population, implementing the transcription-based measurement may be difficult in clinical settings due to its resource-demanding nature. Using the same speakers, this study examined the agreement between transcription- and rating-based intelligibility measurements. Six sentences from the Consensus of Auditory-Perceptual Evaluation of Voice (CAPE-V) were recorded from 18 individuals with dysphonia (6 adult females, 6 adult males, and 6 children). Their dysphonia severity was determined through auditory-perceptual evaluation by two speech-language pathologists. Cafeteria noise was added to these recordings at SNR0 and paired with a sample from a healthy speaker in their age and/or gender group. Forty-five listeners rated intelligibility of the dysphonic samples on a 7-point rating scale. Spearman's rank correlation tests were conducted to examine the correlations between rating-based intelligibility measurement and the transcription-based measurement from our previous study, as well as the voice quality ratings and the rating-based intelligibility measurements. There was a strong positive correlation between the transcription- and rating-based measurements at all noise levels. The correlation between rating-based intelligibility measurement and breathiness rating was also strong. Our findings suggest that the rating-based intelligibility measurement could potentially be used as a substitute for the transcription-based analysis. Furthermore, the intelligibility deficit may be particularly problematic to patients who present with breathy dysphonia.