Word Learning in Deaf Adults Who Use Cochlear Implants: The Role of Talker Variability and Attention to the Mouth.

Abstract

Although cochlear implants (CIs) facilitate spoken language acquisition, many CI listeners experience difficulty learning new words. Studies have shown that highly variable stimulus input and audiovisual cues improve speech perception in CI listeners. However, less is known whether these two factors improve perception in a word learning context. Furthermore, few studies have examined how CI listeners direct their gaze to efficiently capture visual information available on a talker's face. The purpose of this study was two-fold: (1) to examine whether talker variability could improve word learning in CI listeners and (2) to examine how CI listeners direct their gaze while viewing a talker speak. Eighteen adults with CIs and 10 adults with normal hearing (NH) learned eight novel word-object pairs spoken by a single talker or six different talkers (multiple talkers). The word learning task comprised of nonsense words following the phonotactic rules of English. Learning was probed using a novel talker in a two-alternative forced-choice eye gaze task. Learners' eye movements to the mouth and the target object (accuracy) were tracked over time. Both groups performed near ceiling during the test phase, regardless of whether they learned from the same talker or different talkers. However, compared to listeners with NH, CI listeners directed their gaze significantly more to the talker's mouth while learning the words. Unlike NH listeners who can successfully learn words without focusing on the talker's mouth, CI listeners tended to direct their gaze to the talker's mouth, which may facilitate learning. This finding is consistent with the hypothesis that CI listeners use a visual processing strategy that efficiently captures redundant audiovisual speech cues available at the mouth. Due to ceiling effects, however, it is unclear whether talker variability facilitated word learning for adult CI listeners, an issue that should be addressed in future work using more difficult listening conditions.