Effect of Channel Interaction on Vocal Cue Perception in Cochlear Implant Users

Abstract

Speech intelligibility in multi-talker settings is challenging for most CI users. One possibility for this limitation is the suboptimal representation of vocal cues in implant processing, such as the fundamental frequency (F0), and the vocal tract length (VTL). Previous studies suggested that while F0 perception depends on both spectral and temporal cues, VTL perception relies largely on spectral cues. To investigate how spectral smearing in CIs affects vocal cue perception in speech-on-speech (SoS) settings, parallel channels were simultaneously stimulated in 14 Advanced Bionics users to simulate channel interaction. Three such patterns were created: Sequential (stimulation of 2 simultaneous electrodes), Paired (4 electrodes), and Triplet stimulation (6 electrodes). F0 and VTL just-noticeable differences (JNDs; task 1), in addition to SoS intelligibility (task 2) and comprehension (task 3) were measured for each stimulation strategy. In tasks 2 and 3, four maskers were used: the same female talker, a male voice obtained by manipulating both F0 and VTL (F0+VTL) of the original female speaker, a voice where only F0 was manipulated, and a voice where only VTL was manipulated. JNDs were measured relative to the original voice for the F0, VTL, and F0+VTL manipulations. When spectral smearing was increased, a significant deterioration in performance was observed for all tasks, with no differences between Sequential and Paired stimulation. These results imply that CI users may tolerate certain amounts of channel interaction without significant reduction in performance on tasks relying on voice perception. This points to possibilities for utilizing parallel stimulation in CIs for reducing power consumption.