Page 60 - Spring2019

The Remarkable Cochlear Implant
Figure 5. Means and SEMs of scores for the recognition of monosyllabic words (Words), AzBio sentences presented in an otherwise quiet condition (Sent, quiet), and the sentences pre- sented in competition with speech-babble noise at the SNRs of +10 dB (Sent, +10 dB) and +5 dB (Sent, +5 dB). Measures were made with acoustical stimulation of the ear with residual hearing for each of the 15 subjects; electrical stimulation with the CI on the opposite side; and combined electric and acoustic stimulation. Data from Dorman et al. (2008).
opposite side or with acoustic stimulation, the latter for per- sons with useful residual hearing on either side or both sides.
The effects of the additional stimulation can be large, as seen in Figure 5, which shows the effects of combined electric and acoustic stimulation (combined EAS; also called “hybrid” or “bimodal” stimulation). The data are from Dorman et al. (2008). They tested 15 subjects who had a full insertion of a CI on one side; residual hearing at low frequencies on the opposite side; and 5 months to 7 years of experience with the CI and 5 or more years of experience with a hearing aid. The tests included recognition of monosyllabic words and the AzBio sentences with acoustic stimulation of the one ear only with the hearing aid, electric stimulation of the opposite ear only with the CI, and combined EAS. As in Figure 4, the sentences were presented in an otherwise quiet condition and in competition with noise (4-talker babble noise) at the SNRs of +10 and +5 dB.
Means and SEMs of the scores are presented in Figure 5 and demonstrate the large benefits of the combination for all tests. Compared with electric stimulation only, the combina- tion produces a jump up in the recognition of monosyllabic
58 | Acoustics Today | Spring 2019
words from 54 to 73% correct and a 2-fold increase in the recognition of the sentences in noise at the SNR of +5 dB. Thus, the barrier of ~55% correct for recognition of mono- syllabic words by experienced users of unilateral CIs (Figure 3) can be broken, and recognition of speech in noise can be increased with combined EAS. Excellent results also have been obtained with bilateral electrical stimulation, as shown for example in Müller et al. (2002).
In broad terms, both combined EAS and bilateral CIs can improve speech reception substantially. Also, combined EAS can improve music reception and bilateral CIs can en- able sound localization abilities. Furthermore, the brain can integrate the seemingly disparate inputs from electric and acoustic stimulation, or the inputs from the two sides from bilateral electrical stimulation, into unitary percepts that for speech are more intelligible, often far more intelligible, than either input alone. Step 5 was a major step forward.
Step 6?
In my view, the greatest opportunities for the next large step forward are
(1) increasing access worldwide to the marvelous technol- ogy that already has been developed and proven to be safe and highly beneficial;
(2) improving the performance of unilateral CIs, which is the only option for many patients and prospective patients and is the foundation of the adjunctive stimulation treat- ments; and
(3) broadening the eligibility and indications for CIs and the adjunctive treatments, perhaps to include the many millions of people worldwide who suffer from disabling hearing loss in their sixth decade and beyond (a condition called “presbycusis”).
Any of these advances would be a worthy step 6.
Increasing Access
As mentioned in the Introduction, slightly more than half a million people worldwide have received a CI or bilateral CIs to date. In contrast, approximately 57 million people worldwide have a severe or worse hearing loss in the better hearing ear (Wilson et al., 2017). Most of these people could benefit from a CI. Additionally, manyfold more, with some- what better hearing on the worse side or with substantially better hearing on the opposite side, could benefit greatly from combined EAS. A conservative estimate of the num- ber of persons who could benefit from a CI or the adjunctive stimulation treatments is around 60 million and the actual number is probably very much higher. Taking the conser-