Dynamic Range Enhancement for Cochlear Implants

Hypothesis The addition of a continuous, unmodulated, high-rate pulse train to sinusoidal stimuli presented by the cochlear implant to implant recipients will result in increases in the psychophysical dynamic range. Background The hearing dynamic range of cochlear implant patients is markedly reduced compared with that of normal-hearing individuals. This has negative implications for both speech perception and sound quality in these patients. It has been suggested that the addition of an unmodulated high-rate pulse train to deafened auditory nerves could create spontaneous-like neural activity, similar to that recorded from normal ears, of which one significant benefit would be an increase in the dynamic range of cochlear implant users. Methods Twenty-nine patients who underwent implantation with the Clarion CII device participated in this single-blinded prospective study. The psychophysical dynamic range of 28 of these subjects was measured with sinusoidal stimuli in response to various levels of an additional unmodulated high-rate pulse train. Results All the tested subjects (n = 28) demonstrated an increase in dynamic range in response to an appropriate level of unmodulated high-rate pulse train. The largest increase in dynamic range for each subject had a mean value of 6.7 dB. Conclusion The addition of an unmodulated high-rate pulse train to the electric signal presented to cochlear implant patients results in significant increases in dynamic range for sinusoidal stimuli.