An Alternative Explanation for Difficulties with Speech in Background Talkers: Abnormal Fusion of Vowels Across Fundamental Frequency and Ears

In this study, using dichotic speech stimuli, we examined the relationship between speech fusion and vowel identification. Dichotic vowel perception was measured in NH and HI listeners, with across-ear fundamental frequency differences varied. Synthetic vowels /i/, /u/, /a/, and /ae/ were generated with three fundamental frequencies (F0) of 106.9, 151.2, and 201.8  Hz and presented dichotically through headphones. For HI listeners, stimuli were shaped according to NAL-NL2 prescriptive targets. Although the dichotic vowels presented were always different across ears, listeners were not informed that there were no single vowel trials and could identify one vow el or two different vowels on each trial. When there was noF0 difference between the ears, both NH and HI listeners were more likely to fuse the vowels and identify only one vowel. As ΔF0 increased, NH listeners increased the percentage of two-vowel responses, but HI listeners were more likely to continue to fuse vowels even with large ΔF0. Binaural tone fusion range was significantly correlated with vowel fusion rates in both NH and HI listeners. Confusion patterns with dichotic vowels differed from those seen with concurrent monaural vowels, suggesting different mechanisms behind the errors. Together, the findings suggest that broad fusion leads to spectral blending across ears, even for different ΔF0, and may hinder the stream segregation and understanding of speech in the presence of competing talkers.

Source: JARO - Journal of the Association for Research in Otolaryngology - April 20, 2021 Category: ENT & OMF Source Type: research