Temporal envelope perception in Cochlear Implant users

Background: In timbre and especially instrument perception the attack time is known to hold crucial information to detect differences between instruments. The excitation mechanism by which an instrument is made to sound, is reflected by the first 50 to 150 ms of sound onset. As auditory processing and especially music perception in Cochlear Implant users is known to be hampered we conducted an EEG study with an oddball paradigm to evaluate processing of small differences in musical sound onset manipulations. Auditory evoked potential as elicited in an EEG study yield objective information about processing of auditory stimuli and thus allow to draw conclusions about general hearing abilities of the respective participants. Method: We therefore manipulated a cornet sound in the first 60 ms to examine whether these differences will be detectable for CI users (n=12) and a normal hearing control group (n=12). Our analysis focused on the N1 as an exogenous component known to reflect physical stimuli properties and the Mismatch Negativity (MMN), a component known to reflect detection of any discriminable changes in an ongoing auditory stimulation. Results: We found N1 latencies to differ significantly depending on the onset manipulations in both groups, MMN could be elicited in the normal hearing control group alone and not for the CI users. Conclusions: Our findings suggest that lower order processing as seen in the N1 latencies reflected the manipulation of the attack time in both groups. Higher order processing, such as the MMN, is hampered in the CI user group but robust in the normal hearing control group. These findings might give additional explanation to the general musical impairment of CI users.

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