Discrimination of Voice Pitch and Vocal-Tract Length in Cochlear Implant Users

Abstract

Objectives:When listening to two competing speakers, normal-hearing (NH) listeners can take advantage of voice differences between the speakers. Users of cochlear implants (CIs) have difficulty in perceiving speech on speech. Previous literature has indicated sensitivity to voice pitch (related to fundamental frequency, F0) to be poor among implant users, while sensitivity to vocal-tract length (VTL; related to the height of the speaker and formant frequencies), the other principal voice characteristic, has not been directly investigated in CIs. A few recent studies evaluated F0 and VTL perception indirectly, through voice gender categorization, which relies on perception of both voice cues. These studies revealed that, contrary to prior literature, CI users seem to rely exclusively on F0 while not utilizing VTL to perform this task. The objective of the present study was to directly and systematically assess raw sensitivity to F0 and VTL differences in CI users to define the extent of the deficit in voice perception.Design:The just-noticeable differences (JNDs) for F0 and VTL were measured in 11 CI listeners using triplets of consonant–vowel syllables in an adaptive three-alternative forced choice method.Results:The results showed that while NH listeners had average JNDs of 1.95 and 1.73 semitones (st) for F0 and VTL, respectively, CI listeners showed JNDs of 9.19 and 7.19 st. These JNDs correspond to differences of 70% in F0 and 52% in VTL. For comparison to the natural range of voices in the population, the F0 JND in CIs remains smaller than the typical male–female F0 difference. However, the average VTL JND in CIs is about twice as large as the typical male–female VTL difference.Conclusions:These findings, thus, directly confirm that CI listeners do not seem to have sufficient access to VTL cues, likely as a result of limited spectral resolution, and, hence, that CI listeners’ voice perception deficit goes beyond poor perception of F0. These results provide a potential common explanation not only for a number of deficits observed in CI listeners, such as voice identification and gender categorization, but also for competing speech perception.

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

“…For the bimodal CI+HA users, residual acoustic hearing in the HA ear allows the separation of different voice pitches due to better encoding of spectral information than in the CI ear. In contrast, bilateral CI users, who lack an acoustic hearing ear, have less access to this cue and have difficulty discriminating voice gender (Cleary and Pisoni, 2002;Fu et al, 2005;Gaudrain and Başkent, 2018). The way the CI processor is programmed does not provide sufficient spectral resolution to distinguish F 0 and thus gender.…”

Perceptual grouping in the cocktail party: contributions of voice-feature continuity

“…Furthermore, while normal-hearing listeners make use of both GPR and VTL differences for 541 talker sex categorization, CI users seem to rely exclusively on differences in GPR (Fuller et al,542 2014; Meister et al, 2016) which has been attributed to their limited access to VTL cues 543 (Gaudrain and Başkent, 2018). 544…”

Effect of frequency mismatch and band partitioning on vocal tract length perception in vocoder simulations of cochlear implant processing

“…Both analysis and synthesis filters were given the same filter order for a given condition. This choice of filter orders was based on data from Gaudrain and Başkent (2015), which showed that shallower filters, simulating larger channel interaction, yielded VTL JNDs that were close to those obtained from actual CI users (Gaudrain and Başkent, 2018). It is expected that frequency shift might play a larger role with sharper filters than with shallower filters because shallow filters effectively become more similar to each other, which should manifest as an interaction effect between filter order and frequency shift.…”

“…It is expected that frequency shift might play a larger role with sharper filters than with shallower filters because shallow filters effectively become more similar to each other, which should manifest as an interaction effect between filter order and frequency shift. In experiments 2 and 3, 16 analysis filter bands of 12th-order were used instead because pilot data revealed that 4th-and 8th-order filters, when combined with the synthesis filter models used in experiment 3, yielded unrealistically large VTL JNDs compared to those of actual CI users (Gaudrain and Başkent, 2018).…”

“…For example, not only do CI users demonstrate poor sensitivity to differences in both F0 and VTL compared to NH listeners (Gaudrain and Başkent, 2018), but they are also unable to use the latter to correctly judge a speaker's gender (Fuller et al, 2014;Meister et al, 2016).…”