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Objective and psychoacoustic measurements as indicators of peripheral and/or central filtar

Speech processor map parameters determine the acoustic to electric stimuli conversion thus influencing peripheral entry to hearing pathway. The base for optimal map are correctly set thresholds (T) and comfortable levels (C levels) for each channel along the electrode array. Levels can be set behaviourally or in cases of inadequate cooperation, hearing field could be supposed acording to neural response telemetry (NRT) values. Beside information useful for mappings, response morphology, amplitudes and latencies also provide information on functional status of spiral ganglion cells (SGC), neccessary for the transmission of electrical stimuli to more central parts of hearing pathway (1). Hearing deprivation results in degenerative changes in hearing pathway including SGC (2). The effect of these changes should be less with shorter duration of hearing loss. According to literature indicators of better SGC survival could be lower NRT levels, bigger amplitudes and shorter response latencies, higher T and C levels and better T/C and TNRT correlation (1, 3, 4). The aim of this study was to assess the influence of preoperative deafness duration on NRT and psychophysical measurements in two groups of children operated at different age: (1) 20 prelingually deaf children operated in optimal age – mean age 2.3 y ; (2) 20 prelingually deaf children operated in school age – mean age11.3 y. The following parameters were compared: NRT thresholds, N1P2 amplitudes, N1 latencies, response morphology, T and C map levels, dynamic ranges, T-NRT as a percentage of the map dynamic range, correlation between T-NRT and map T, and C levels. The overall results indicate more pronounced degenerative effects in basal then in apical cochlear segments. As this was especially noticed in the group of school children the effect of intense preoperative rehabilitation, will be discussed.

cochlear implant ; neural response telemetry ; verbotonal method

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