Recognition of time-distorted sentences by normal-hearing and cochlear-implant listeners

This study evaluated the effects of time compression and expansion on sente nce recognition by normal-hearing (NH) listeners and cochlear-implant (CI) recipients of the Nucleus-22 device. Sentence recognition was measured in f ive CI users using custom 4-channel continuous interleaved sampler (CIS) pr ocessors and five NH listeners using either 4-channel or 32-channel noise-b and processors. For NI I listeners, recognition was largely unaffected by t ime expansion, regardless of spectral resolution. However, recognition of t ime-compressed speech varied significantly with spectral resolution. When f ine spectral resolution (32 channels) was available, speech recognition was unaffected even when the duration of sentences was shortened to 40% of the ir original length (equivalent to a mean duration of 40 ms/phoneme). Howeve r, a mean duration of 60 ms/phoneme was required to achieve the same level of recognition when only coarse spectral resolution (4 channels) was availa ble. Recognition patterns were highly variable across CI listeners. The bes t CI listener performed as well as NH subjects listening to corresponding s pectral conditions; however, three out of five CI listeners performed signi ficantly poorer in recognizing time-compressed speech. Further investigatio n revealed that these three poorer-performing CI users also had more diffic ulty with simple temporal gap-detection tasks. The results indicate that li mited spectral resolution reduces the ability to recognize time-compressed speech. Some CI listeners have more difficulty with time-compressed speech, as produced by rapid speakers, because of reduced spectral resolution and deficits in auditory temporal processing. (C) 2001 Acoustical Society of Am erica. [DOI: 10.1121/1.1327578].