A significant recent advance in medical technology has been the development of the cochlear implant. This is a device which is surgically attached to the cochlea, or inner ear, connecting electrodes to cochlear nerves. The wearer carries a small radio- like device outside the body which translates sounds into elec- trical impulses transmitted directly to cochlear nerves via the electrodes, and the impulses are "heard" by the brain in a way which the wearer is able to interpret. For people with certain kinds of deafness, cochlear implants have already provided significant enhancements in their ability to understand speech, most usually in conjunction with lip reading but sometimes even in the absence of visual cues. The growing success of cochlear implantation presents interesting challenges to the science of speech perception, since only a fraction of the information in the acoustical signal is actually translated into electrical impulses. To the extent that the user is able to interpret the impoverished signal accurately, this shows that key perceptual information is included in it, thus affording a new perspective on the fundamental problem of speech perception: what are the acoustic properties of speech which determine accurate perception? This research project is a systematic exploration of the nature of the signal received by cochlear implantees, and their perception of it. The research will focus on wearers of the newly developed "Australian nucleus" implant, which is a multi- channel device and carries much more information than earlier models. The researcher will examine the speech perception of implantees, the changes in their speech patterns over time, and the reactions of normal listeners to speech signals distorted in the ways which the implant device distorts them for its users. The principal research aim of the project is to identify the components of the distorted signal which enable correct percep- tion. A successful outcome will be an important contribution to speech science, as well as offering the possibility of further improvements in the design of cochlear implants.
