Effects of broad binaural fusion and hearing loss ondichotic concurrent vowel identification

Abstract

Many hearing-impaired (HI) individuals have abnormally broad binaural pitch fusion, such that tones differing in pitch by up to 3-4 octaves are fused between ears (Reiss et al., 2017). Broad binaural fusion leads to averaging of the monaural pitches (Oh and Reiss, 2017), and may similarly lead to fusion and averaging of speech streams across ears. In this study, we examined the relationship between binaural fusion range and dichotic vowel identification in normal-hearing (NH) and HI listeners. 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. Listeners identified 1 vowel or 2 different vowels on each trial. Preliminary results indicate that NH listeners improved their percentage of both vowels identified as the ΔF0 increased, but HI listeners did not. HI listeners were more likely to fuse two vowels together even with large ΔF0. NH listeners with broad fusion also had poorer overall performance than those with sharp fusion. The findings suggest that broad binaural fusion can impede separation of voices and speech streams in both NH and HI listeners. [Work supported by NIH-NIDCD grant R01 DC013307.]

Binaural pitch fusion: Effects of sound level in listeners with normal hearing

“…Broad fusion is also correlated with reduced release from masking due to voice-pitch differences in multitalker listening environments, potentially because the different voices are fused together instead of segregated as they normally would be on the basis of pitch (Oh et al, 2019). While voice pitch is thought to be conveyed by different cues than place-pitch, referring to the changes in place-of-stimulation along the basilar membrane thought to be involved with pitch perception of high frequency tones (for review, see Oxenham, 2008), preliminary findings suggest that abnormal fusion of dichotic tones is correlated with abnormal fusion of dichotic vowels at different fundamental frequencies, and thus fusion of voices of different pitch in HI listeners (Reiss et al, 2018). Such speech fusion leads to spectral averaging of different vowels similar to that demonstrated for consonants (Cutting, 1976).…”

Factors underlying masking release by voice-gender differences and spatial separation cues in multi-talker listening environments in listeners with and without hearing loss

“…Generally, binaural pitch fusion is narrow in NH listeners because the two ears provide essentially matched spectral information for a given signal. In contrast, HI listeners can exhibit abnormally broad binaural pitch fusion, i.e., can fuse stimuli with pitches differing by up to 3–4 octaves across ears into a single percept ( Reiss et al, 2014 , 2017 , 2018a , b ; Oh and Reiss, 2017b , 2020 ). Thus, broad binaural pitch fusion appears to be detrimental, and could negatively impact the ability to segregate out multiple voices of different pitches in complex environments.…”