The effects of lexical content, acoustic and linguistic variability, and vocoding on voice cue perception

Deniz Başkent,Thomas Koelewijn,Terrin Tamati,Etienne Gaudrain

doi:10.1121/10.0005938

Abstract

Perceptual differences in voice cues, such as fundamental frequency (F0) and vocal tract length (VTL), can facilitate speech understanding in challenging conditions. Yet, we hypothesized that in the presence of spectrotemporal signal degradations, as imposed by cochlear implants (CIs) and vocoders, acoustic cues that overlap for voice perception and phonemic categorization could be mistaken for one another, leading to a strong interaction between linguistic and indexical (talker-specific) content. Fifteen normal-hearing participants performed an odd-one-out adaptive task measuring just-noticeable differences (JNDs) in F0 and VTL. Items used were words (lexical content) or time-reversed words (no lexical content). The use of lexical content was either promoted (by using variable items across comparison intervals) or not (fixed item). Finally, stimuli were presented without or with vocoding. Results showed that JNDs for both F0 and VTL were significantly smaller (better) for non-vocoded compared with vocoded speech and for fixed compared with variable items. Lexical content (forward vs reversed) affected VTL JNDs in the variable item condition, but F0 JNDs only in the non-vocoded, fixed condition. In conclusion, lexical content had a positive top-down effect on VTL perception when acoustic and linguistic variability was present but not on F0 perception. Lexical advantage persisted in the most degraded conditions and vocoding even enhanced the effect of item variability, suggesting that linguistic content could support compensation for poor voice perception in CI users.

Highlights

Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands. c) at: Department of Otorhinolaryngology/Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. d)ORCID: 0000-0003-0490-0295. e)ORCID: 0000-0002-6560-1451.acoustic manipulation has indicated that two acoustic voice cues are important for speech-on-speech performance (Baskent and Gaudrain, 2016; Darwin et al, 2003; Vestergaard et al, 2011): fundamental frequency (F0), which arises from the glottal–pulse rate, and vocal tract length (VTL), which shapes the spectral parameters, such as formant frequencies.Individual talkers can control their F0 by applying more or less tension on their glottal folds as they speak or sing
The lexical content factor is represented with hatches: just-noticeable differences (JNDs) for forward words are shown with plain boxes, whereas JNDs for reversed words are shown with striped boxes
We investigated the effect of lexical content, item variability, and vocoding on the JNDs of the F0 and VTL voice cues

Summary

Introduction

Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands. C) at: Department of Otorhinolaryngology/Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. F0 varies with testosterone levels (Dabbs and Mallinger, 1999), whereas both F0 and VTL are known to vary with actual body size and shape (Evans et al, 2006). The morphology of the male and female VTL differs, resulting in an overall greater VTL for men (Fitch and Giedd, 1999). This variance in VTL leads to the variation in formant patterns observed for different talkers (Hillenbrand et al, 1994). For NH listeners, the F0 and VTL voice cues greatly

Methods

Results

Conclusion