Neurophysiological and psychophysical measures of duration discrimination in normal-hearing adults and adults with cochlear implants

The ability to discriminate duration contrasts (a first approximation of voice onset time differences) was evaluated in adult cochlear implant users and normal-hearing adults using a neurophysiological response (the mismatch negativity—MMN). The MMN is an evoked response generated by a deviant stimulus when embedded in a series of standard homogeneous stimuli. Magnitude of the MMN correlates with psychophysical discrimination thresholds indicating that the MMN provides a measure of perceived acoustic change [Kraus et al. (1996)]. The MMN thus provides a neurophysiological correlate of acoustic discrimination. The present study compared an objective statistical measure of MMN magnitude to psychophysical measures in response to duration differences of brief auditory stimuli. A ten-click train was paired with shorter trains to create an oddball sequence. The selected duration differences were similar to voice onset time differences that distinguish voiced from voiceless speech phonemes. The MMN magnitude was measured at four scalp-electrode locations. The relationship between neurophysiological and psychophysical thresholds was determined and comparisons were made between the normal-hearing adults and adults with cochlear implants. While some similarities were found, the results suggest that the sensitivity to duration differences differs between normal-hearing and cochlear implant subjects.