Role of Fundamental Frequency Differences in the Perceptual Separation of Competing Vowel Sounds by Listeners With Normal Hearing and Listeners With Hearing Loss

Kathryn.arehart{at}colorado.edu

This study compared the ability of listeners with normal hearing and listeners with moderate to moderately-severe sensorineural hearing loss to use fundamental frequency differences (F₀) in the identification of monotically presented simultaneous vowels. Two psychophysical procedures, double vowel identification and masked vowel identification, were used to measure identification performance as a function of F₀ (0 through 8 semitones) between simultaneous vowels. Performance in the double vowel identification task was measured by the percentage of trials in which listeners correctly identified both vowels in a double vowel. The masked vowel identification task yielded thresholds representing signal-to-noise ratios at which listeners could just identify target vowels in the presence of a masking vowel. In the double vowel identification task, both listeners with normal hearing and listeners with hearing loss showed significant F₀ benefit: Between 0 and 2 semitones, listeners with normal hearing showed an 18.5% average increase in performance; listeners with hearing loss showed a 16.5% average increase. In the masked vowel identification task, both groups showed significant F₀ benefit. However, the mean benefit associated with F₀ differences in the masked vowel task was more than twice as large in listeners with normal hearing 9.4 dB) when compared to listeners with hearing loss (4.4 dB), suggesting less F₀ benefit in listeners with hearing loss. In both tasks, overall performance of listeners with hearing loss was significantly worse than performance of listeners with normal hearing. Possible reasons for reduced F₀ benefit and decreased overall performance in listeners with hearing loss include reduced audibility of vowel sounds and deficits in spectro-temporal processing.

KEY WORDS: double vowel identification, hearing loss, fundamental frequency cues, speech perception

Submitted on August 5, 1996
Accepted on June 6, 1997

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