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The Effect of Changes in Stimulus Level on Electrically Evoked Cortical Auditory Potentials

Kim, Jae-Ryong1,3; Brown, Carolyn J.1,2; Abbas, Paul J.1,2; Etler, Christine P.1; O’Brien, Sara1

doi: 10.1097/AUD.0b013e31819c42b7
Research Articles
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Objectives: The purpose of this study was to determine whether the electrically evoked acoustic change complex (EACC) could be used to assess sensitivity to changes in stimulus level in cochlear implant (CI) recipients and to investigate the relationship between EACC amplitude and rate of growth of the N1-P2 onset response with increases in stimulus level.

Design: Twelve postlingually deafened adults using Nucleus CI24 CIs participated in this study. Nucleus Implant Communicator (NIC) routines were used to bypass the speech processor and to control the stimulation of the implant directly. The stimulus consisted of an 800 msec burst of a 1000 pps biphasic pulse train. A change in the stimulus level was introduced 400 msec after stimulus onset. Band-pass filtering (1 to 100 Hz) was used to minimize stimulus artifact. Four to six recordings of 50 sweeps were obtained for each condition, and averaged responses were analyzed in the time domain using standard peak picking procedures.

Results: Cortical auditory change potentials were recorded from CI users in response to both increases and decreases in stimulation level. The amplitude of the EACC was found to be dependent on the magnitude of the stimulus change. Increases in stimulus level elicited more robust EACC responses than decreases in stimulus level. Also, EACC amplitudes were significantly correlated with the slope of the growth of the onset response.

Conclusions: This work describes the effect of change in stimulus level on electrically evoked auditory change potentials in CI users. The amplitude of the EACC was found to be related both to the magnitude of the stimulus change introduced and to the rate of growth of the N1-P2 onset response. To the extent that the EACC reflects processing of stimulus change, it could potentially be a valuable tool for assessing neural processing of the kinds of stimulation patterns produced by a CI. Further studies are needed, however, to determine the relationships between the EACC and psychophysical measures of intensity discrimination in CI recipients.

The purpose of this study was to determine whether the electrically evoked acoustic change complex (EACC) could be used to assess sensitivity to changes in stimulus level in cochlear implant recipients. Twelve postlingually deafened adults using Nucleus CI24 participated in this study. The stimulus consisted of an 800 msec burst of a 1000 pps biphasic pulse train. A change in the stimulus level was introduced 400 msec after stimulus onset. EACCs could be recorded from cochlear implant users in response to both increases and decreases in stimulation level. Increases in stimulus level elicited more robust EACC responses than decreases.

Departments of 1Otolaryngology – Head and Neck Surgery, 2Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa; and 3Department of Otolaryngology – Head and Neck Surgery, Inje University College of Medicine, Busan Paik Hospital, Busan, Korea.

This work was supported by grants from the NIH/NIDCD (DC00242), the NIH/NCRR (RR00059), and the Iowa Lions Sight and Hearing Foundation.

Portions of this paper were presented at the annual meeting of the American Auditory Society in March 2007.

Address for correspondence: Carolyn J. Brown, PhD, 127B SHC, Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA 52242. E-mail: carolyn-brown@uiowa.edu.

Received December 13, 2007; accepted December 6, 2008.

© 2009 Lippincott Williams & Wilkins, Inc.