Amplitude modulation and loudness in cochlear implantees.

The effect of amplitude modulation of pulse trains on the loudness perceived by cochlear implantees was investigated for different overall levels of the signal, modulation depth and the carrier rate of the pulse train. Equally loud and threshold levels were determined for a variety of signal levels, modulation depths and carrier rates in six cochlear implantees. The pattern of results was consistent with the predictions of a previously published loudness model of McKay et al. (J Acoust Soc Am 113:2054-2063, 2003). The degree to which the loudness of modulated stimuli differed from the loudness elicited by an unmodulated pulse train with equivalent average current depended on the modulation depth and the absolute current level of the unmodulated stimulus. The effect of carrier rate on this measure was predictable solely from the effect of rate on absolute current level for equal loudness. The results have important implications for the interpretation of experiments measuring modulation detection that do not control loudness cues. We show that several previously published results regarding the effect of carrier rate and added noise on modulation detection could be reinterpreted in the light of these findings.