Can global field power be an objective tool to assess cortical responses to acoustic change? A study with cochlear implant users

Introduction: The aim of the present study was to record and analyse acoustic change complex (ACC) response with Global Field Power (GFP) in cochlear implant users. Materials and Methods: Event- related potentials were recorded from 12 CI users. Study participants were tested in sound-treated electrically shielded test booth in the Auditory Electrophysiology Laboratory at the Hacettepe University. For acoustic change complex recording /ui/ stimulus was used. The magnitude of the acoustic change complex was expressed as the ratio of GFP amplitude of ACC response to GFP amplitude of onset response and GFP measures. Results: Recordings from each participant's 20 electrodes were plotted as butterfly plots and GFPs were computed. The GFP waveform of each subject was analyzed in terms of the peaks corresponding to suspected latency ranges of onset, ACC and off-set responses. Moreover ratio of GFP amplitude of ACC response to GFP amplitude of onset response was computed for each subject. Discussions: In this study a new tool for adding objectivity to ACC response identification was applied, which was GFP measures. In addition, ratio of GFP peak amplitude corresponding to suspected ACC and onset response was computed, in order to find a cut-off score that differentiates a clear ACC response from a questionable one. Copyright 2005