Discriminability and perceptual saliency of acoustic cues for final consonant voicing in simulations of cochlear-implant and electric-acoustic stimulation

Abstract

Multiple redundant acoustic cues can contribute to the perception of a single class of speech sounds. This study investigates the effect of spectral degradation on the discriminability and perceptual saliency of acoustic cues for phonetic identification of word-final fricative voicing in “loss” versus “laws,” and possible changes that occur when low-frequency acoustic cues are 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 modified natural speech syllables. The first experiment measured listeners' ability to discriminate differences among stimuli within a single cue dimension. The second experiment 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 8-channel noise-band vocoder to approximate CI spectral degradation, or low-pass (LP) filtered to simulate low-frequency residual hearing. They were tested in four listening conditions: unprocessed, vocoder alone, LP alone, and vocoder + LP where low-frequency fine-structure cues could enhance F1 perception and voicing cues. The impact of listening condition on discriminability and weighting of different acoustic cues will be discussed.