Speech recognition with varying numbers and types of competing talkers by normal-hearing, cochlear-implant, and implant simulation subjects

Hearing and Speech Laboratory, University of California, Irvine, 364 Med Surge II, Room 315, Irvine, California 92697, USA.
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 02/2008; 123(1):450-61. DOI: 10.1121/1.2805617
Source: PubMed


Cochlear-implant users perform far below normal-hearing subjects in background noise. Speech recognition with varying numbers of competing female, male, and child talkers was evaluated in normal-hearing subjects, cochlear-implant users, and normal-hearing subjects utilizing an eight-channel sine-carrier cochlear-implant simulation. Target sentences were spoken by a male. Normal-hearing subjects obtained considerably better speech reception thresholds than cochlear-implant subjects; the largest discrepancy was 24 dB with a female masker. Evaluation of one implant subject with normal hearing in the contralateral ear suggested that this difference is not caused by age-related disparities between the subject groups. Normal-hearing subjects showed a significant advantage with fewer competing talkers, obtaining release from masking with up to three talker maskers. Cochlear-implant and simulation subjects showed little such effect, although there was a substantial difference between the implant and simulation results with talker maskers. All three groups benefited from a voice pitch difference between target and masker, with the female talker providing significantly less masking than the male. Child talkers produced more masking than expected, given their fundamental frequency, syllabic rate, and temporal modulation characteristics. Neither a simulation nor testing in steady-state noise predicts the difficulties cochlear-implant users experience in real-life noisy situations.

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    • "This guarantees that, on average, noise will affect speech equally for every frequency band and also that it will closely resemble everyday environmental noises such as the babble resulting from several voices heard simultaneously. Multitalker babble is often cited as the environmental noise most frequently encountered by listeners (Cullington & Zeng, 2008; R. H. Wilson, Abrams, & Pillion, 2003). It can thus be said to have more ecological validity than steady-state noises such as white noise. "
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    • "Additionally, the negative correlation coefficients indicated that speech recognition scores decreased with higher RMS noise levels and higher crest factors. These results were consistent with previous reports that cochlear implant listeners generally had more difficulty understanding speech in environments with high masker levels (Skinner et al, 1994; Chung et al, 2006; Ricketts et al, 2006) and in noise with high temporal fluctuations (Kwon and Turner, 2001; Nelson et al, 2003; Qin and Oxenham, 2003; Nelson and Jin, 2004; Stickney et al, 2004; Cullington and Zeng, 2008; Luo et al, 2008). These behavioral patterns were also consistent with cochlear implant stimulation patterns shown in electrodograms where higher noise levels and higher temporal fluctuations result in less speechlike stimulation patterns. "
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    • "Culling et al. (2004) found that their data with triplets of speech maskers were predicted fairly well by the Bronkhorst model. However, it is possible that this result is specific to three-masker configurations as the number of maskers can be an important factor in speech-on-speech masking (Brungart et al., 2001; Hawley et al., 2004; Cullington and Zeng, 2008). Moreover, there was limited variation in the degree of asymmetry in the masker configurations tested by Culling et al. "
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