Noise enhances modulation sensitivity in cochlear implant listeners: Stochastic resonance in a prosthetic sensory system?

Cochlear implants restore auditory sensitivity to the profoundly hearing-im paired by means of electrical stimulation of residual auditory nerve fibers . Sensorineural hearing loss results in a loss of spontaneous activity amon g the remaining auditory neurons and is accompanied by a reduction in the n ormal stochastic nature of neural firing in response to electric stimulatio n. It has been hypothesized that the natural stochasticity of the neural re sponse is important for auditory signal processing and that introducing som e optimal amount of noise into the stimulus may improve auditory perception through the implant. In this article we show that, for soft but audible st imuli, an optimal amount of "prosthetic" noise significantly improves sensi tivity to envelope modulation in cochlear implant listeners. A nonmonotonic function relates modulation sensitivity and noise level, suggesting the pr esence of stochastic resonance.