When either real or simulated electric stimulation from a cochlear implant (CI) is combined with low-frequency acoustic stimulation (electric-acoustic stimulation [EAS]), speech intelligibility in noise can improve dramatically. We recently showed that a similar benefit to intelligibility can be observed in simulation when the low-frequency acoustic stimulation (low-pass target speech) is replaced with a tone that is modulated both in frequency with the fundamental frequency (F0) of the target talker and in amplitude with the amplitude envelope of the low-pass target speech (Brown & Bacon 2009). The goal of the current experiment was to examine the benefit of the modulated tone to intelligibility in CI patients.
Eight CI users who had some residual acoustic hearing either in the implanted ear, the unimplanted ear, or both ears participated in this study. Target speech was combined with either multitalker babble or a single competing talker and presented to the implant. Stimulation to the acoustic region consisted of no signal, target speech, or a tone that was modulated in frequency to track the changes in the target talker's F0 and in amplitude to track the amplitude envelope of target speech low-pass filtered at 500 Hz.
All patients showed improvements in intelligibility over electric-only stimulation when either the tone or target speech was presented acoustically. The average improvement in intelligibility was 46 percentage points due to the tone and 55 percentage points due to target speech.
The results demonstrate that a tone carrying F0 and amplitude envelope cues of target speech can provide significant benefit to CI users and may lead to new technologies that could offer EAS benefit to many patients who would not benefit from current EAS approaches.