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Abstract
Conclusion. Amplitude weighting using the bell-shaped filter design within the OPUS speech processors allows the creation of pitches intermediate to those of two adjacent electrodes. This mechanism can be used for both sequential and simultaneous stimulation. Objectives. This paper describes frequency discrimination experiments which are based on amplitude weighting of two adjacent electrodes. The effects of sequential versus simultaneous stimulation of the electrode pair were investigated. Materials and methods. The experiment was performed using a laboratory system emulating the signal processing using bell-shaped filters in the MED-EL speech processors. The system transformed input files (wav-files) into the stimulation data stream which was transmitted to the implant via the OPUS processor coil. Pitch discrimination was assessed for up to three electrode pairs in each subject, using an adaptive test method. Results for sequential stimulation were collected in eight subjects, a comparison between sequential and simultaneous stimulation was made in five subjects. Results. Results show an average frequency discrimination of 8.8% for sequential stimulation and 11.2% for simultaneous stimulation, of the nominal test frequency. Frequency discrimination ability varied across subjects and test electrode pairs. The difference in performance between sequential and simultaneous stimulation was not statistically significant.