Neural Correlates of Phonetic Learning in Adult Listeners with Cochlear Implants

Abstract

Speech perception is a product of an individual's linguistic experience. Postlingually deafened cochlear implant (CI) recipients, persons who acquired speech and language with normal acoustic hearing, need to learn to remap degraded electric inputs provided by the implant to previously learned language patterns. The mechanisms underlying the perceptual remapping and whether formal auditory training can promote phonetic learning in CI users remain unclear. This dissertation used behavioral and auditory event-related potential (ERP) methods to examine phonetic learning of the difficult /ba/-/da/ and /wa/-/ja/ speech contrasts in adult CI recipients. Behavioral and neural measures were collected before and after high variability identification training. Behavioral experiments employed identification and discrimination tasks, and the ERP experiments used an oddball paradigm to elicit the mismatch negativity (MMN) response associated with preattentive phonetic categorization. The results indicated substantial neural plasticity for phonetic learning in adult postlingually deafened CI listeners can be induced by high variability identification training. The training protocol significantly improved perception of naturally produced speech in postlingually deafened CI recipients, and listeners generalized their learning to unfamiliar talkers. Fine scale behavioral and neural measures suggest enhanced phonetic categorization skills supported the observed improvements in phonetic perception. These findings have potential clinical implications related to the aural rehabilitation process following receipt of a cochlear implant device.