Abstract
Differences in voice pitch (F0) and vocal tract length (VTL) improve intelligibility of speech masked by a background talker (speech-on-speech; SoS) for normal-hearing (NH) listeners. Cochlear implant (CI) users, who are less sensitive to these two voice cues compared to NH listeners, experience difficulties in SoS perception. Three research questions were addressed: (1) whether increasing the F0 and VTL difference (ΔF0; ΔVTL) between two competing talkers benefits CI users in SoS intelligibility and comprehension, (2) whether this benefit is related to their F0 and VTL sensitivity, and (3) whether their overall SoS intelligibility and comprehension are related to their F0 and VTL sensitivity. Results showed: (1) CI users did not benefit in SoS perception from increasing ΔF0 and ΔVTL; increasing ΔVTL had a slightly detrimental effect on SoS intelligibility and comprehension. Results also showed: (2) the effect from increasing ΔF0 on SoS intelligibility was correlated with F0 sensitivity, while the effect from increasing ΔVTL on SoS comprehension was correlated with VTL sensitivity. Finally, (3) the sensitivity to both F0 and VTL, and not only one of them, was found to be correlated with overall SoS performance, elucidating important aspects of voice perception that should be optimized through future coding strategies.
Highlights
Cochlear implant (CI) users have more difficulties understanding speech in multi-talker settings compared to normal hearing (NH) listeners (e.g., Cullington and Zeng, 2008; Stickney et al, 2004; Stickney et al, 2007), yet the relationship between this difficulty and voice cue perception remains relatively unknown
EXPERIMENT 1: THE EFFECT OF DF0 AND DVTL ON SOS INTELLIGIBILITY. This experiment, along with experiment 2, was designed to answer the first research question posed in this study, which is whether CI users, similar to NH listeners, could benefit from increasing DF0 and DVTL between target and masker voices in a SoS sentence intelligibility task
A trend for improvement in comprehension performance as a function of increasing DF0 or DVTL could be seen in the data (Fig. 4), this trend was not significant. These findings indicate that the setup for the sentence verification task (SVT) might not have been adverse enough for the NH participants, such that they mostly performed nearly at ceiling levels and no additional benefit could be drawn from the voice cue differences
Summary
Cochlear implant (CI) users have more difficulties understanding speech in multi-talker settings compared to normal hearing (NH) listeners (e.g., Cullington and Zeng, 2008; Stickney et al, 2004; Stickney et al, 2007), yet the relationship between this difficulty and voice cue perception remains relatively unknown. Previous literature has shown that when stimuli were sufficiently degraded using acoustic vocoder simulations of CI processing, NH listeners became less sensitive to both F0 and VTL differences, compared to listening in the non-vocoded condition (Gaudrain and Baskent, 2015) In line with these findings, NH listeners exposed to vocoded SoS were shown to benefit differently from voice cue differences between target and masker speakers, depending on the type of vocoder used. The range for F0 and VTL differences was chosen to encompass CI users’ typical sensitivity thresholds reported in the literature (Gaudrain and Baskent, 2018; Zaltz et al, 2018) This range was chosen to ensure that the F0 and VTL differences introduced between target and masker voices would be detected by the CI users tested. The hypothesis was that higher sensitivity to F0 and VTL differences would correlate with higher SoS overall performance
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