Discrimination of Schroeder-Phase Harmonic Complexes by Normal-Hearing and Cochlear-Implant Listeners |
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Authors: | Ward R Drennan Jeff K Longnion Chad Ruffin Jay T Rubinstein |
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Institution: | (1) Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology, Head and Neck Surgery, University of Washington, Box 357923, Seattle, WA 98195, USA;(2) Department of Bioengineering, University of Washington, Seattle, WA 98195, USA |
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Abstract: | The temporal fine structure (TFS) of sound contributes significantly to the perception of music and speech in noise. The evaluation
of new strategies to improve TFS delivery in cochlear implants (CIs) relies upon the assessment of fine structure encoding.
Most modern CI sound processing schemes do not encode within-channel TFS per se, but some TFS information is delivered through
temporal envelope cues across multiple channels. Positive and negative Schroeder-phase harmonic complexes differ primarily
in acoustic TFS and provide a potential test of TFS discrimination ability in CI users for current and future processing strategies.
The ability to discriminate Schroeder-phase stimuli was evaluated in 24 CI users and 7 normal-hearing listeners at four fundamental
frequencies: 50, 100, 200, and 400 Hz. The dependent variables were percent correct at each fundamental frequency, average
score across all fundamental frequencies, and a maximum-likelihood-predicted threshold fundamental frequency for 75% correct.
CI listeners scored better than chance for all fundamental frequencies tested. The 50-Hz, average, and predicted threshold
scores correlated significantly with consonant–nucleus–consonant word scores. The 200-Hz score correlated with a measure of
speech perception in speech-shaped noise. Pitch-direction sensitivity is predicted jointly by the 400-Hz Schroeder score and
a spectral ripple discrimination task. The results demonstrate that the Schroeder test is a potentially useful measure of
clinically relevant temporal processing abilities in CI users. |
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Keywords: | temporal processing fine structure phase discrimination cochlear implant |
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