Cortical neural activity underlying speech perception in postlingual adult cochlear implant recipients

Auditory event-related potentials (AERPs) and the simultaneously obtained behavioral measures (performance accuracy and reaction time) were used to study speech perception in postlingual adult cochlear implant (CI) recipients and in normal-hearing (NH) controls. AERPs were recorded while subjects were performing oddball discrimination tasks with increasing acoustic-phonetic demand. The tasks consisted of pairs of natural syllables that differed by one of the following phonetic contrasts: vowel place, voicing, vowel height, and place of articulation. Results indicated that the P3 potential was comparable in CI recipients and NH controls when the acoustic cues to the perception of the phonetic contrast were accessible. With the reduction in accessibility to the essential temporal and/or spectral cues, CI recipients exhibited delayed (prolonged P3 latency) and less synchronous (reduced amplitude) central speech-sound processing compared to NH controls. Among the phonetic contrasts used in the present study the place of articulation contrast yielded (1) the most prominent differences between CI recipients and NH controls across all measures, and (2) significant correlations between the neurophysiologic manifestation of speech discrimination (i.e. P3 latency), and conscious integration of perceptual information (i.e. performance accuracy and reaction time). Thus, P3 exposed the difficulties imposed on the impaired auditory system of CI recipients especially when elicited by speech contrasts that required processing of brief temporal-spectral cues. These findings support the P3 potential as a sensitive neural index of cortical processing that may provide information regarding accessibility and neural encoding of distinct acoustic-phonetic cues in CI recipients.