Broad binaural fusion impairs segregation of speech based on voice pitch differences in a ‘cocktail party’ environment

Abstract

words)In the normal auditory system, central auditory neurons are sharply tuned to the same frequency ranges for each ear. This precise tuning is mirrored behaviorally as the binaural fusion of tones evoking similar pitches across ears. In contrast, hearing-impaired listeners exhibit abnormally broad tuning of binaural pitch fusion, fusing sounds with pitches differing by up to 3-4 octaves across ears into a single object. Here we present evidence that such broad fusion may similarly impair the segregation and recognition of speech based on voice pitch differences in a 'cocktail party' environment. Speech recognition performance in a multi-talker environment was measured in four groups of adult subjects: normal-hearing (NH) listeners and hearing-impaired listeners with bilateral hearing aids (HAs), bimodal cochlear implant (CI) worn with a contralateral HA, or bilateral CIs. Performance was measured as the threshold target-to-masker ratio needed to understand a target talker in the presence of masker talkers either co-located or symmetrically spatially separated from the target. Binaural pitch fusion was also measured.Voice pitch differences between target and masker talkers improved speech recognition performance for the NH, bilateral HA, and bimodal CI groups, but not the bilateral CI group. Spatial separation only improved performance for the NH group, indicating an inability of the hearing-impaired groups to benefit from spatial release from masking. A moderate to strong negative correlation was observed between the benefit from voice pitch differences and the breadth of binaural pitch fusion in all groups except the bilateral CI group in the co-located spatial condition. Hence, tuning of binaural pitch fusion predicts the ability to segregate voices based on pitch when acoustic cues are available. The findings suggest that obligatory binaural 3 fusion, with a concomitant loss of information from individual streams, may occur at a level of processing before auditory object formation and segregation.

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

“…Results from listeners HI25, HI38, and HI40 were based on the average of two different fusion range estimates where the left and right ear were each used as the reference ear, while all others only used one reference ear and fusion function. The results indicate that fusion ranges tended to be larger for listeners with HI compared to NH, as in previous experiments with listeners who use bilateral hearing aids (Oh et al, 2019;Reiss et al, 2017Reiss et al, , 2016. Only 4/9 of the HI data points indicate fusion ranges at or below the greatest NH fusion range.…”

“…The present experiment investigated whether sound level affected the interaural frequency disparity over which two pure tones are heard as one pitch (fusion range). It was hypothesized that if increased sound level contributes to the larger fusion ranges observed in previous studies in listeners with HI who use hearing aids compared to NH (Oh et al, 2019;Reiss et al, 2017Reiss et al, , 2016, then fusion range would also increase for higher sound levels in listeners with NH. The results of the present experiment contradict this hypothesis and suggest that increases in sound level alone do not lead to consistent increases in fusion range.…”

“…5 since their fusion range was 0 Hz in the loud condition, which implies an infinitely small value on the y-axis, and is therefore impossible to show in a correlation plot. Results from listeners with HI were previously published in Oh et al (2019), Oh and Reiss (2018), Oh and Reiss (2017), and Reiss et al (2017).…”

Low-Intensity Steady Background Noise Enhances Pitch Fusion Across the Ears in Normal-Hearing Listeners

“…In addition, studying this further may lead to another path for intervention to help with the rehabilitative care of hearing-impaired listeners. As proposed by Oh et al (2019) , abnormally broad binaural fusion which is often observed in hearing-impaired listeners could interfere with the segregation of auditory objects based on pitch differences, such as multiple voices in a multi-talker listening environment. Increased understanding of abnormal binaural fusion in hearing-impaired listeners can provide information for future design and training with device-based rehabilitative strategies to enhance the benefits of binaural processing for speech perception in noise.…”

“…One recent study by Oh et al (2019) suggested that broad fusion is associated with greater difficulty in using voice pitch difference cues to separate a target voice from other interfering voices in both NH and HI listeners. In other words, the broader the pitch fusion, the smaller the benefit from voice pitch differences because broad fusion could lead to abnormal spectral fusion and blending of words from voices of different pitches.…”