The Effects of Frequency Response on Speech Perception for Cochlear Implant Users

Bimodal cochlear implantation in elderly patients

OBJECTIVE

Bimodal stimulation is a standard option for asymmetric hearing loss in adults. Questions have been raised whether receiving two stimulations may conflict in elderly listeners where the central integration of an acoustic/electrical signal may be very important to obtain benefit in terms of speech perception.

DESIGN

Clinical retrospective study.

STUDY SAMPLE

The outcomes from 17 bimodal cochlear implant (CI) users were analysed. The test material consisted of speech audiometry in quiet and in noise (STARR and Matrix).

RESULTS

Bimodal PTA and speech perception both in quiet and in noise were significantly better than CI or HA alone. Age showed a significant effect on bimodal STARR outcomes. Similarly, bimodal STARR scores improved significantly in comparison to Better Ear.

CONCLUSION

Both Matrix and STARR tests were very difficult for many elderly CI listeners from the present study group, especially in unilateral listening condition. The performance improved significantly, emphasising a good integration of acoustic and electric hearing in this group of elderly bimodal listeners. Overall results highlighted how a specific study, based on speech perception in noise in the elderly listeners, might shed light on the effect of speech test modality on bimodal outcomes.

Encoding speech in cochlear implants using simultaneous amplitude and rate modulation

To improve speech perception for cochlear implant (CI) users, it is essential to improve the transmission of temporal envelopes. The most common speech processors deliver temporal envelopes via the CI using fixed-rate amplitude modulated (AM) pulse trains. Psychophysical studies suggest that rate modulation (RM) and AM are perceived by a shared temporal integration mechanism, but the potential for them to constructively combine to encode temporal envelopes has yet to be explored. In this experiment, a speech processing strategy called amplitude and rate temporal modulation was developed to encode speech temporal envelopes with simultaneous AM and RM. The strategy was tested for perception of clean speech at 60 and 40 dBA, and 60 dBA speech in noise (+10 dB SNR). The amount of RM was varied and the amount of AM was held constant to determine whether the addition of RM could enhance the perception of temporal envelopes and improve speech understanding. At the lowest RM amount, speech scores were poorest for all speech conditions. For 60 dBA clean speech and speech in noise, speech scores were significantly better at the highest RM amounts, suggesting that RM combined with AM can be used to enhance perception of temporal envelopes.