Perceptual differences between low and high rates of stimulation on single electrodes for cochlear implantees

Previous research has shown that increases in the rate of stimulation on a single electrode yield changes in pitch perception until the rate is increased beyond a given critical rate, after which changes in rate are only perceived as changes in loudness. The critical rate beyond which a rate increase no longer elicits a pitch change in most subjects is approximately 300 Hz, although a small number of subjects have been observed to have critical rates up to approximately 1000 Hz. In this article, we sought to determine if increasing the rate of stimulation beyond the critical rate (up to 12.8 kHz) would eventually result in new changes of perception (other than loudness.) Our data replicate the previously observed results that rates between approximately 300 and 1500 Hz are indistinguishable from each other. However, we observed the finding that a rate of stimulation well above the critical rate (starting between 1500 Hz and 12.8 kHz, depending on electrode and subject) can elicit changes in perception. The perceptual differences between these high rates were sometimes but not always labeled as pitch changes. This phenomenon needs further research to assess its potential relevance to speech perception using high rates of stimulation.