Effect of Stimulation Rate on Speech Understanding in Older Cochlear-Implant Users

Cochlear implants (CIs) are considered a safe and effective intervention for more severe degrees of hearing loss in adults of all ages. Although older CI users ≥65 years of age can obtain large benefits in speech understanding from a CI, there is a growing body of literature suggesting that older CI users may not perform as well as younger CI users. One reason for this potential age-related limitation could be that default CI stimulation settings are not optimal for older CI users. The goal of this study was to determine whether improvements in speech understanding were possible when CI users were programmed with nondefault stimulation rates and to determine whether lower-than-default stimulation rates improved older CI users' speech understanding.

Sentence recognition was measured acutely using different stimulation rates in 37 CI users ranging in age from 22 to 87 years. Maps were created using rates of 500, 720, 900, and 1200 pulses per second (pps) for each subject. An additional map using a rate higher than 1200 pps was also created for individuals who used a higher rate in their clinical processors. Thus, the clinical rate of each subject was also tested, including non-default rates above 1200 pps for Cochlear users and higher rates consistent with the manufacturer defaults for subjects implanted with Advanced Bionics and Med-El devices. Speech understanding performance was evaluated at each stimulation rate using AzBio and Perceptually Robust English Sentence Test Open-set (PRESTO) sentence materials tested in quiet and in noise.

For Cochlear-brand users, speech understanding performance using non-default rates was slightly poorer when compared with the default rate (900 pps). However, this effect was offset somewhat by age, in which older subjects were able to maintain comparable performance using a 500-pps map compared with the default rate map when listening to the more difficult PRESTO sentence material. Advanced Bionics and Med-El users showed modest improvements in their overall performance using 720 pps compared with the default rate (>1200 pps). On the individual-subject level, 10 subjects (11 ears) showed a significant effect of stimulation rate, with 8 of those ears performing best with a lower-than-default rate.

Results suggest that default stimulation rates are likely sufficient for many CI users, but some CI users at any age can benefit from a lower-than-default rate. Future work that provides experience with novel rates in everyday life has the potential to identify more individuals whose performance could be improved with changes to stimulation rate.