Acoustic + Electric Speech Processing: Insights into the Future

Objective: Review hearing preservation results and outcomes in clinical trials of 166 subjects implanted with Nucleus Hybrid cochlear implants and a subset of the population that has been followed longitudinally for 15 years.

Patients: Adults with residual low frequency hearing no poorer than 70 dB HL through 500 Hz and severe high frequency hearing loss above 2kHz.

Outcome Measures: The residual acoustic hearing, speech perception scores in quiet and noise, and spatial hearing measures three, six, and 12 months post implantation with longitudinal data spanning more than 15 years (N=69).

Results: Immediate functional hearing preservation was accomplished in 98%. Over time (S8: 9 yr average, S12 and L24:4 yr average) hearing preservation has been maintained in 85% of the group. Hearing preservation is better with less invasive electrodes. The reasons are likely multifactorial, and possible mechanisms along with human temporal bone observations will be discussed. There does not appear to be a correlation between the level of preservation of acoustic hearing and speech perception improvement as long as acoustic hearing can be aided and is better than 90 dB PTA for 125, 250, and 500 Hz. Signal-to-noise ratios have improved more than 9 dB in some individuals. Performance on standardized sentence test at a signal to noise ratio of 5dB are improved more than 30% with acoustic + electric (A+E) speech processing. High density EEG data suggest restoration of near normal auditory central processing can be restored using A+E processing. These results provide evidence that those with more residual hearing might benefit from minimally invasive electrodes with the objective of activating and preserving a much more intact neural substrate for the lifetime of the subject. Expanding selection criteria for cochlear implants to those with poor word understanding in noise will be important, as this group of individuals struggle to communicate in daily life.

This research was sponsored in part by NIH grants DC 00242, DC 0037, RR00059, and Cochlear Limited