Authors: Sil Zoest¹, Floris Rotteveel¹, Bert Maat¹, Deniz Başkent¹, Etienne Gaudrain²
¹Department of Otorhinolaryngology, University Medical Center Groningen
²Lyon Neuroscience Research Center, Université Lyon
Objective/Background: In addition to the well documented limitations in pitch perception, it has been shown that cochlear implant (CI) users also suffer from difficulties with perceiving another voice characteristic: vocal-tract length (VTL) (Gaudrain et al, 2017, doi: 10.1097/AUD.0000000000000480). In normal hearing (NH) listeners, the VTL percept is associated with the size of a speaker and is used in combination with voice pitch to, e.g., discriminate between competing talker voices or categorize voice gender. However, CI users seem entirely unable to use VTL information for voice gender categorization and rely solely on voice pitch (Fuller et al, 2014, doi:10.1007/s10162-014-0483-7). A possible explanation for this is that during the signal processing in the CI, VTL information is degraded. Another likely contributing factor to this decreased VTL perception in CI users is the current spread in the cochlea, which increases the spectrotemporal degradation already induced by the reduced number of frequency bands of the CI. The objective in the current study is to assess the effect of CI processing and current spread on VTL discrimination.
Methods: Psychometric functions for VTL discrimination were measured using speech tokens in a 3AFC odd-one-out task. Unlike previous studies using simpler vocoders, the current study employs stimuli that are reconstructed by vocoding stimulation patterns generated by an actual CI, then presented to NH listeners. To simulate current spread in the cochlea, we filtered noise band carriers with lower-order bandpass filters, artificially inducing spectral smearing across neighbouring frequency bands (Bingabr et al, 2008, doi:10.1016/j.heares.2008.04.012).
Results & Conclusions: Data collection is ongoing. Preliminary findings suggest that CI processing might have a small effect on usable VTL information, while current spread could be responsible for a larger decrement in VTL discriminability.
