Cochlear implantation: relationships with research on auditory deprivation and acclimatization.

This paper reviews research on cochlear implantation relevant to deprivation and acclimatization with acoustical hearing aids. The term "deprivation" is used in its everyday sense to refer to the bilateral absence of acoustic stimulation. Results are reviewed from several sources, with detailed evidence presented from three groups of postlingually deafened adult patients and one group of prelingually deafened child patients, all implanted at the University of Iowa. Outcomes from implantation reveal consistent effects of deprivation, evidenced by significant 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 performance over time after implantation. For adult patients, the level of performance measured shortly after implantation on average is about half the level measured eventually. Individually, 80% of the adult patients implanted in Iowa show significant performance improvements with time. On average, performance reached asymptote after 30 to 40 mo of implant use, although individual differences in the rate and amount of improvement are large. Absolute accuracy of speech perception with implants by adults is believed to be related to preoperative measures in three domains: 1) the number and physiological responsiveness of auditory ganglion cells and nerve fibers, indexed by measures of hearing sensitivity, duration of deafness, and age; 2) the responsiveness of the central nervous system, indexed by measures of cognitive and linguistic ability, and possibly also by age and duration of deafness; and 3) the motivation to learn to use the implant. Preliminary analyses suggest that the measures in the first domain are more strongly associated with the immediate benefit from implantation than with the subsequent improvement in performance over time.