THE ELECTRICALLY-EVOKED ACOUSTIC CHANGE COMPLEX IN COCHLEAR IMPLANT USERS

Beynon A, Keck TN, Snik AFM.

Auditory Evoked Potential Lab, Radboud University Nijmegen Medical Centre Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Dept of Otorhinolaryngology. Nijmegen, The Netherlands.

Background: The Slow Vertex Potential (SVP) or N1-P2 complex is an electrophysiological stimulus detection response elicited after an abrupt change in an acoustical environment. Although SVP measurements are applied for objective determination of auditory thresholds in clinical settings, a second N1-P2 complex (referred to as the acoustic change complex or ACC) can be evoked by changing an acoustic parameter within one stimulus (Ostroff et al, 1998; Martin et al, 2000). Apparently, this complex reflects change detection within a stimulus at the cortical level.

Aims: Investigating the feasibility to obtain ACCs using different stimulation parameter via electrical stimulation (EACCs) in the sound field and via direct intracochlear electrode stimulation.

Method: Two experiments were carried out, i.e. Experiment 1 in 9 normal hearing subjects and Experiment 2 in 22 adult CI-users. The purposes of the first experiment were to test the practical applicability of the setup and to optimize the stimulation/recording parameters. The second experiment investigated the electrical variant in the soundfield (indirect) and via direct stimulation of intracochlear electrodes. Three stimulation parameters were changed, i.e. frequency (electrode allocation), stimulation level (loudness) and stimulation rate. Additionally, the influence of the magnitude of the acoustic change within the stimulus on the EACC was evaluated.

Results: It was possible to elicit (E)ACCs in either soundfield and via direct stimulation by stimulus changes in frequency, stimulation level or stimulation rate. Comparisons of EACC after direct and indirect stimulation showed different morphologies of the EACC, showing more robust responses via direct stimulation due to limited impact of electrical artefact.

Conclusion: ACCs can be elicited electrically by (in)direct stimulation in cochlear implant users and might be a tool for objective evaluation of (electrical) stimulus change detection.

E-mail: a.beynon@kno.umcn.nl