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Little is known about how the auditory cortex adapts to artificial input as provided by a cochlear implant (CI). We report the case of a 71-year-old profoundly deaf man, who has successfully used a unilateral CI for 4 years. Independent component analysis (ICA) of 61-channel EEG recordings could separate CI-related artifacts from auditory-evoked potentials (AEPs), even though it was the perfectly time-locked CI stimulation that caused the AEPs. AEP dipole source localization revealed contralaterally larger amplitudes in the P1-N1 range, similar to normal hearing individuals. In contrast to normal hearing individuals, the man with the CI showed a 20-ms shorter N1 latency ipsilaterally. We conclude that ICA allows the detailed study of AEPs in CI users.

Conductive hearing loss, produced by otitis media with effusion, is widespread in young children. However, little is known about its short- or long-term effects on hearing or the brain. To study the consequences of a conductive loss for the perception and processing of sounds, we plugged the left ear canal of ferrets for 7-15 months during either infancy or adulthood. Before or during plugging, the ferrets were trained to perform a binaural task requiring the detection of a 500 Hz tone, positioned 90 degrees to the right, that was masked by two sources of broad-band noise. In one condition ("control"), both noise sources were 90 degrees right and, in the second condition ("bilateral"), one noise source was moved to 90 degrees left. Normal ferrets showed binaural unmasking: tone detection thresholds were lower (mean 10.1 dB) for the bilateral condition than for the control condition. Both groups of ear-plugged ferrets had reduced unmasking; the mean residual unmasking was 2.3 dB for the infant and 0.7 dB for the adult ear-plugged animals. After unplugging, unmasking increased in both groups (infant, 7.1 dB; adult, 6.9 dB) but not to normal levels. Repeated testing during the 22 months after unplugging revealed a gradual return to normal levels of unmasking. These results show that a unilateral conductive hearing loss, in either infancy or adulthood, impairs binaural hearing both during and after the hearing loss. They show scant evidence for adaptation to the plug and demonstrate a recovery from the impairment that occurs over a period of several months after restoration of normal peripheral function.

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