COCHLEAR IMPLANTATION - RELATIONSHIPS WITH RESEARCH ON AUDITORY DEPRIVATION AND ACCLIMATIZATION

This paper reviews research an cochlear implantation relevant to depri vation and acclimatization with acoustical hearing aids. The term ''de privation'' is used in its everyday sense to refer to the bilateral ab sence of acoustic stimulation. Results are reviewed from several sourc es, with detailed evidence presented from three groups of postlinguall y deafened adult patients and one group of prelingually deafened child patients, all implanted at the University of Iowa. Outcomes from impl antation reveal consistent effects of deprivation, evidenced by signif icant negative correlations between accuracy of speech perception and the duration of profound/total deafness before implantation. Outcomes also show acclimatization in the form of significant improvements in p erformance over time after implantation. For adult patients, the level of performance measured shortly after implantation on average is abou t half the level measured eventually. Individually, 80% of the adult p atients implanted in Iowa show significant performance improvements wi th time. On average,performance reached asymptote after 30 to 40 mo of implant use, although individual differences in the rate and amount o f improvement are large. Absolute accuracy of speech perception with i mplants by adults is believed to be related to preoperative measures i n three domains: 1) the number and physiological responsiveness of aud itory ganglion cells and nerve fibers, indexed by measures of hearing sensitivity, duration of deafness, and age; 2) the responsiveness of t he central nervous system, indexed by measures of cognitive and Lingui stic ability, and possibly also by age and duration of deafness; and 3 ) the motivation to learn to use the implant. Preliminary analyses sug gest that the measures in the first domain are more strongly associate d with the immediate benefit from implantation than with the subsequen t improvement in performance over time.