Functional neuroimaging with positron emission tomography (PET) was used to compare the brain activation patterns of normal-hearing (NH) with postlingually deaf, cochlear-implant (CI) subjects listening to speech and nonspeech signals. The speech stimuli were derived from test batteries for assessing 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, Time-reversed Sentence, and Multitalker Babble. Both groups showed bilateral activation in superior and middle temporal gyri to speech and backward speech. However, group differences were observed in the Sentence compared to Silence condition. CI subjects showed more activated foci in right temporal regions, where lateralized mechanisms for prosodic (pitch) processing have been well established; NH subjects showed a focus in the left inferior frontal gyrus (Brodmann's area 47), where semantic processing has been implicated. Multitalker Babble activated auditory temporal regions in the CI group only. Whereas NH listeners probably habituated to this multitalker babble, the CI listeners may be using a perceptual strategy that emphasizes 'coarse' coding to perceive this stimulus globally as speechlike. The group differences provide the first neuroimaging evidence suggesting that postlingually deaf CI and NH subjects may engage differing perceptual processing strategies under certain speech conditions.