Phonetic identification in quiet and in noise by listeners with cochlear implants

This study examined the effect of noise on the identification of four synthetic speech continua (/ra/-/la/, /wa/-/ja/, /i/-/u/, and say-stay) by adults with cochlea implants (CIs) and adults with normal-hearing (NH) sensitivity in quiet and noise. Significant group-by-SNR interactions were found for endpoint identification accuracy for all continua except /i/-/u/. The CI listeners showed the least NH-like identification functions for the /ra/-/la/ and /wa/-/ja/ continua. In a second experiment, NH adults identified four- and eight-band cochlear implant stimulations of the four continua, to examine whether group differences in frequency selectivity could account for the group differences in the first experiment. Number of bands and SNR interacted significantly for /ra/-/la/, /wa/-/ja/, and say-stay endpoint identification; strongest effects were found for the /ra/-/la/ and say-stay continua. Results suggest that the speech features that are most vulnerable to misperception in noise by listeners with CIs are those whose acoustic cues are rapidly changing spectral patterns, like the formant transitions in the /wa/-/ja/ and /ra/-/la/ continua. However, the group differences in the first experiment cannot be wholly attributable to frequency selectivity differences, as the number of bands in the second experiment affected performance differently than suggested by group differences in the first experiment.