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Three experiments examined normal-hearing and cochlear-implant listeners' abilities to perceive and use talker-specific information in the speech signal. In Experiment 1 voice similarity judgments were gathered from normal-hearing listeners to maximize variability across talkers used in Experiment 2. These judgments were submitted to a multidimensional scaling (MDS) analysis; this solution was used to select the talkers of Experiment 2.
Experiment 2 was an approximate replication of Nygaard and Pisoni's (1998) work. In this study cochlear-implant and normal-hearing listeners were trained to recognize 6 different voices. The cochlear-implant users recognized the voices with 59.31% accuracy and the normal-hearing listeners achieved 92.64% accuracy. After training the listeners completed a sentence recognition task in noise. In the task 6 familiar talkers spoken half of the sentences and 6 novel talkers spoke the other half. It was predicted that sentences spoken by the familiar talkers would be more accurately perceived than those spoken by the novel talkers. However, there was no difference in accuracy, nor was there a difference in performance across the groups of listeners. The factors contributing to these null results were discussed at length.
Experiment 3 gathered voice similarity judgments from the normal-hearing and cochlear-implant listeners of Experiment 2. These data were submitted to both classical and weighted MDS analyses. The voice maps showed notable differences in the perceptual spaces of the two groups of listeners. The participant space yielded from the weighted MDS showed great variation across all of the participants' judgments, but no clear trend supporting the listeners' group membership.
In conclusion, despite listening via a constrained, electric signal, the cochlear-implant users were trained to recognize voices with notable accuracy (as were the normal-hearing listeners). Nevertheless, Experiment 2 failed to provide insight into talker familiarity's effect on the sentence recognition skills of cochlear-implant and normal-hearing listeners. These results are contrary to research with normal-hearing listeners that suggests talker familiarity facilitates speech processing in noise. The present studies did show, though, that cochlear-implant users appear to perceive and use talker-specific information differently than normal-hearing listeners.