QPR Final: Final Report for NIH Project N01-DC-8-2105 (September 30, 1998 through March 30, 2002) -- Speech Processors for Auditory Prostheses
The main objective of this and prior projects in the “speech processors” series at the Research Triangle Institute (RTI) has been to design, develop, and evaluate speech processors for implantable auditory prostheses. Ideally, such processors represent the information content of speech in a way that it can be perceived and utilized by implant patients. An additional objective of recent projects has been to record responses of the auditory nerve to a variety of electrical stimuli in studies with patients. Results from such recordings can provide important information on the physiological function of the nerve, on an electrode-by-electrode basis, and also can be used to evaluate the ability of speech processing strategies to produce desired spatial or temporal patterns of neural activity. Work in the project just completed has included a wide range of psychophysical, electrophysiological, and speech reception studies. Many of those studies are described in our progress reports for the project (see Table 1) and in recent publications. As indicated in section II of this report, results from these and prior studies provide a foundation for the further development of cochlear implant systems. Some specific achievements and activities of the project included • Completion of an extensive series of studies to evaluate effects of changes in stimulus rate and envelope cutoff frequency for continuous interleaved sampling (CIS) processors, across many combinations of the two parameters and for four subjects • Completion of an extensive series of studies to evaluate effects of manipulations in mapping functions for CIS processors, across many choices of power-law mapping function exponents and for five subjects • A large advancement in our knowledge about the factor or factors underlying the high variability in outcomes with implants, through comparisons among psychophysical, electrophysiological and speech reception measures in studies with each of six Ineraid subjects, and through comparisons between psychophysical and speech reception measures in studies with each of two Clarion subjects • Completion of a series of longitudinal studies with five Ineraid subjects, to measure performance over time following substitution of a portable CIS processor for the clinical compressed analog (CA) processor previously used by these subjects • Completion of an initial series of psychophysical and speech reception studies with thirteen recipients of bilateral implants, one with Cochlear Ltd. CI22 implants on both sides, four with Cochlear Ltd. CI24M implants on both sides, two with Med El COMBI 40 implants on both sides, four with COMBI 40 implants on both sides, one with a COMBI 40 implant on one side and a COMBI 40 implant on the other side, and one with a short-electrode version of a COMBI 40 implant on one side and standard COMBI 40 implant on the other side (the studies included measures of sensitivities to interaural timing and amplitude differences, and evaluation of various processing strategies designed to represent cues for sound localization or to exploit the availability of bilateral electrodes in other ways, e.g., to increase the number of perceptually separable channels) • Initiation of the above studies with an additional recipient of COMBI 40 implants on both sides • Initial design and evaluation of "conditioner pulses" processors, in psychophysical and speech reception studies with three subjects (see Rubinstein et al., 1999).