The Contribution of a Frequency-Compression Hearing Aid to Contralateral Cochlear Implant Performance

Abstract

Frequency-lowering signal processing in hearing aids has re-emerged as an option to improve audibility of the high frequencies by expanding the input bandwidth.However, few studies have investigated the usefulness of the scheme as a bimodal option for cochlear implant users. In this study, that question was posed. It was hypothesized that, following fitting and a period of adjustment to a frequency-compression hearing aid, sound localization and speech perception would be improved compared to conventional amplification. More specifically, more high-frequency cues would be perceived in the hearing aid ear using frequency compression, thereby providing better sensitivity to interaural level differences when a cochlear implant is used contralaterally.There were two experiments in this study. In the first experiment, the goal was to determine if frequency compression was a better bimodal option than conventional amplification. Performance was assessed on tests of sound localization, speech perception in a background of noise, and using questionnaires. Ten subjects with a cochlear implant plus hearing aid participated in experiment one. In the second experiment, the goal was to determine the impact of frequency compression on speech perception in quiet. Consonant and vowel perception in quiet was assessed using the frequency-compression and conventional hearing aid. Seventeen adult subjects participated in the second experiment.In both experiments, subjects alternated daily between a frequency-compression and conventional hearing aid for two months. The parameters of frequency compression were set individually for each subject and audibility was measured for the frequency compression and conventional hearing aid programs by comparing estimations of the Speech Intelligibility Index (SII) using a modified algorithm (Bentler, R., Cole, B., Wu, Y-H. (2011, March). Deriving an audibility index for frequency-lowered hearing aids.Poster session presented at the meeting of the American Auditory Society, Scottsdale, 2 AZ). In both experiments, the outcome measures were administered following the hearing aid fitting to establish baseline performance and after two months of use.Results revealed no significant difference between the frequency-compression and conventional hearing aid on tests of localization and consonant recognition. Spondee-innoise and vowel perception scores were significantly higher with the conventional hearing aid compared to the frequency-compression hearing aid after two months of use.These results suggest that, for the subjects in this study, frequency compression is not a better bimodal option than conventional amplification. In addition, speech perception may be negatively influenced by frequency compression because formant frequencies are too severely compressed and can no longer be distinguished.

Effect of extreme adaptive frequency compression in bimodal listeners on sound localization and speech perception

“…These studies reported no benefit of FC for speech perception or sound localization either (Davidson et al, 2015;McDermott and Henshall, 2010;Park et al, 2012;Perreau et al, 2013). Perreau et al (2013) reported impaired vowel perception, in contrast to our results, even though we used FC across a much broader frequency range. This discrepancy most likely is a consequence of our signal-adaptive variant of FC, specifically aiming at preserving the vowels ( Figure 2B).…”

“…So far, only a few studies have investigated FC in bimodal listeners, but no significant benefits were found. Yet, speech and consonant perception remained unaffected in those studies (Davidson et al, 2015;Hua et al, 2012;McDermott and Henshall, 2010;Park et al, 2012;Perreau et al, 2013). Perreau et al (2013) and Davidson et al (2015) investigated bimodal sound localization of daily sounds or words, but found no improvement as a result of FC in the HA.…”

“…The switching between consonants and vowels was based on the energy content of the input signal: fricative consonants are characterized by their non-harmonic broadband frequency content, in which the high-frequency part contains potentially strong ILD information. We hypothesized that adaptive FC would also avoid the decrement in vowel perception of bimodal users equipped with a HA with FC (Perreau et al, 2013). Therefore, besides localization performance in the horizontal plane (which might improve with FC), we also performed additional psychophysical tests to determine the effects of adaptive FC on speech perception (which should not deteriorate).…”

Benefit from non-linear frequency compression hearing aids in a clinical setting: The effects of duration of experience and severity of high-frequency hearing loss

“…Glista et al (2009) and Wolfe et al (2010;2011) found that consonant recognition was signifi cantly better when NLFC was enabled, although McDermott and Henshall (2010) and Perreau et al (2013) did not. A possible reason for the discrepancy in the results is that the studies that did not fi nd a benefi t from NLFC for consonant recognition both tested listeners with a hearing aid in one ear and although only fi ve subjects were tested and one subject showed a large improvement which accounted for most of the mean improvement.…”

“…Several studies assessed the effect of NLFC on consonant recognition in quiet using closed set vowel-consonant-vowel (VCV) identifi cation tasks, either at a fi xed level (Glista et al, 2009;McDermott & Henshall, 2010;Perreau et al, 2013) or by using an cochlear implant in the contralateral ear. It is possible that NLFC is less benefi cial in this situation, as the listener may already have adequate access to high-frequency information from their cochlear implant.…”