Although some cochlear implant (CI) listeners can show good word recognition accuracy, it is not clear how they perceive and use the various acoustic cues that contribute to phonetic perceptions. In this study, the use of acoustic cues was assessed for normal-hearing (NH) listeners in optimal and spectrally degraded conditions, and also for CI listeners. Two experiments tested the tense/lax vowel contrast (varying in formant structure, vowel-inherent spectral change, and vowel duration) and the word-final fricative voicing contrast (varying in F1 transition, vowel duration, consonant duration, and consonant voicing). Identification results were modeled using mixed-effects logistic regression. These experiments suggested that under spectrally-degraded conditions, NH listeners decrease their use of formant cues and increase their use of durational cues. Compared to NH listeners, CI listeners showed decreased use of spectral cues like formant structure and formant change and consonant voicing, and showed greater use of durational cues (especially for the fricative contrast). The results suggest that although NH and CI listeners may show similar accuracy on basic tests of word, phoneme or feature recognition, they may be using different perceptual strategies in the process.
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The authors would like to thank the participants for their time and willingness to contribute to this study, as well as Rochelle Newman, Shu-Chen Peng, Nelson Lu, Ewan Dunbar, and Shannon Barrios for their helpful comments and expertise. We also express appreciation to Mitchell Sommers for his patience and helpful suggestions on this manuscript and to two anonymous reviewers for helpful comments on an earlier version of this manuscript. We are grateful to Qian-Jie Fu for the software used for the experiment. This research was supported by NIH Grant No. R01 DC004786 to M.C. M.B.W. was supported by NIH Grant No. T32 DC000046-17 (PI: Arthur N. Popper).