Effects of cochlear-implant simulation on processing of vowel sequences by young normal-hearing listeners

Abstract

To better understand the effects of listening environment on efficiency of phonetic processing, the present study examined the effects of signal degradation on phonetic processing of two-syllable sequences by normal-hearing listeners. Auditory temporal-order processing of American-English vowel sequences was compared across two listening conditions, each presented to a separate group of young, normal-hearing listeners: 1) unprocessed resynthesized stimuli and 2) stimuli that had been processed to simulate the signal produced by a 16-channel cochlear implant (CI). Using the methods of Fogerty, Humes and Kewley-Port [2010, J. Acoust. Soc. Am., 127, 2509-2520], 70-ms resynthesized versions of the syllables “pit, pet, put,” and “pot” were presented in a two-syllable temporal-order processing task. Task difficulty was increased by decreasing syllable-onset asynchrony (SOA), i.e., the duration between syllable onsets. SOA thresholds for accuracy of syllable-sequence identification were estimated using the method of constant stimuli on each of four 72-trial blocks. Data analyzed to date show a threshold difference of approximately 20 ms between the unprocessed and CI-processed listener groups, or a difference in threshold of a factor of two or greater. Results will be discussed with regard to implications for phonetic processing of speech in challenging listening environments and practical implications for CI users.