Discriminability and Perceptual Saliency of Temporal and Spectral Cues for Final Fricative Consonant Voicing in Simulated Cochlear-Implant and Bimodal Hearing

Abstract

Multiple redundant acoustic cues can contribute to the perception of a single phonemic contrast. This study investigated the effect of spectral degradation on the discriminability and perceptual saliency of acoustic cues for identification of word-final fricative voicing in “loss” versus “laws”, and possible changes that occurred when low-frequency acoustic cues were restored. Three acoustic cues that contribute to the word-final /s/-/z/ contrast (first formant frequency [F1] offset, vowel–consonant duration ratio, and consonant voicing duration) were systematically varied in synthesized words. A discrimination task measured listeners’ ability to discriminate differences among stimuli within a single cue dimension. A categorization task examined the extent to which listeners make use of a given cue to label a syllable as “loss” versus “laws” when multiple cues are available. Normal-hearing listeners were presented with stimuli that were either unprocessed, processed with an eight-channel noise-band vocoder to approximate spectral degradation in cochlear implants, or low-pass filtered. Listeners were tested in four listening conditions: unprocessed, vocoder, low-pass, and a combined vocoder + low-pass condition that simulated bimodal hearing. Results showed a negative impact of spectral degradation on F1 cue discrimination and a trading relation between spectral and temporal cues in which listeners relied more heavily on the temporal cues for “loss-laws” identification when spectral cues were degraded. Furthermore, the addition of low-frequency fine-structure cues in simulated bimodal hearing increased the perceptual saliency of the F1 cue for “loss-laws” identification compared with vocoded speech. Findings suggest an interplay between the quality of sensory input and cue importance.

Acoustic Context Alters Vowel Categorization in Perception of Noise-Vocoded Speech

“…This would be consistent with the findings of Stilp and Alexander (2016), who attributed larger SCEs for listeners with sensorineural hearing loss to broadened auditory filters. Additionally, as many acoustic cues to speech are degraded or eliminated in vocoder processing, normal-hearing listeners displayed increased reliance on cues that remained compared to their usage of those cues in intact speech (Winn et al 2012;Winn and Litovsky 2015;Moberly et al 2014Moberly et al , 2016Kong et al 2016). For example, Winn and Litovsky 2015showed that normal-hearing listeners' weighting of formant transitions decreased and weighting of spectral tilt changes increased when categorizing voiced stop consonants that were noise -vocoded with simulated current spread compared to their cue weighting in full-spectrum speech.…”