PET imaging of cochlear-implant and normal-hearing subjects listening to speech and nonspeech

Functional neuroimaging with positron emission tomography (PET) was used to compare the brain activation patterns of normal-hearing (NH) with postling ually deaf, cochlear-implant (CI) subjects listening to speech and nonspeec h signals. The speech stimuli were derived from test batteries for assessin g speech-perception performance of hearing-impaired subjects with different sensory aids. Subjects were scanned while passively listening to monaural (right ear) stimuli in five conditions: Silent Baseline, Word, Sentence, Ti me-reversed Sentence, and Multitalker Babble. Both groups showed bilateral activation in superior and middle temporal gyri to speech and backward spee ch. However, group differences were observed in the Sentence compared to Si lence condition. Ct subjects showed more activated foci in right temporal r egions, where lateralized mechanisms for prosodic (pitch) processing have b een well established; NH subjects showed a focus in the left inferior front al gyrus (Brodmann's area 47), where semantic processing has been implicate d. Multitalker Babble activated auditory temporal regions in the Ct group o nly. Whereas NH listeners probably habituated to this multitalker babble, t he CI listeners may be using a perceptual strategy that emphasizes 'coarse' coding to perceive this stimulus globally as speechlike. The group differe nces provide the first neuroimaging evidence suggesting that postlingually deaf Ct and NH subjects may engage differing perceptual processing strategi es under certain speech conditions. (C) 1999 Elsevier Science B.V. All righ ts reserved.