The RTI's Perspective On Bilateral Cochlear Implantation

Wilson, B

The RTI perspective on bilateral cochlear implants will be offered in this talk, through a review of findings from our laboratories and elsewhere. In broad terms, findings from studies with the first 13 subjects at RTI include the following:

	Subjects with bilateral implants show a wide range of sensitivities to interaural time delays (ITDs), from 25 microseconds to more than a millisecond (one of the 13 subjects was unable to lateralize on the basis of any of the ITD conditions tested with him, including ITDs greater than 2 ms)
	However, most of the studied subjects demonstrated sensitivities of 50 microseconds or better for at least some of the tested conditions; such excellent sensitivities indicate intact pathways in the central auditory system for processing binaural inputs
	In general, sensitivities to interaural amplitude differences (IADs) are good, and in many cases at least as good as the minimum step size for increments or decrements in current with present implant devices
	Recipients of bilateral implants can integrate information across the two sides, e.g., from "interlaced” channel-to-electrode assignments
	Independent (and asynchronous) processors can confer an advantage for at least some subjects, especially in noisy conditions (the greatest benefits have been observed for speech presented in competition with high levels of noise and with the noise and speech coming from different directions)
	Many subjects show head-shadow advantages, and some show binaural squelch and/or binaural summation effects as well
	Full preservation of ITD sensitivities, where present, probably will require a matching of stimulus sites across the two sides (i.e., results with three tested subjects indicate that ITD sensitivity can be sensitive to matches or mismatches in places of stimulation across the two sides)

Preliminary results also suggest that temporal coordination of stimulus pulses across the two sides may not be important or necessary, especially with high-rate carriers. However, studies with more subjects and with more conditions are needed to affirm or refute this tentative conclusion.
Where comparisons can made, these findings from studies at RTI are largely consistent with results from other laboratories. Bilateral implantation is a highly promising approach, which provides better speech reception and sound localization abilities for many of its users.

Contact Information

Blake Wilson
Research Triangle Institute, Research Triangle Park, NC 27709, and
Duke University Medical Center, Durham, NC 27710
E-mail: bsw@rti.org