Band importance functions of listeners with cochlear implants using clinical maps

Abstract

Band importance functions estimate the relative contribution of individual acoustic frequency bands to speech intelligibility. Previous studies of band importance in listeners with cochlear implants have used experimental maps and direct stimulation. Here, band importance was estimated for clinical maps with acoustic stimulation. Listeners with cochlear implants had band importance functions that relied more heavily on lower frequencies and showed less cross-listener consistency than in listeners with normal hearing. The intersubject variability observed here indicates that averaging band importance functions across listeners with cochlear implants, as has been done in previous studies, may not be meaningful. Additionally, band importance functions of listeners with normal hearing for vocoded speech that either did or did not simulate spread of excitation were not different from one another, suggesting that additional factors beyond spread of excitation are necessary to account for changes in band importance in listeners with cochlear implants.

Individualized frequency importance functions for listeners with sensorineural hearing loss

“…Bands 1 (100-300 Hz) and 10 (5300-7700 Hz) often had negative importance in listeners with NH, and at least seven out of the ten bands had positive importance across listeners with HI. As described in Bosen and Chatterjee (2016), negative importance can occur as a result of the fixed number of bands in each trial, and should be interpreted with caution. Negative importance could simply reflect a band taking the place of a band that would provide more speech information, rather than a true impairment of speech recognition by that band.…”

“…The number of times each band was included in a sentence was balanced across bands, so this approach included each band in 24 sentences per talker, and 96 times overall. This number of presentations was selected to balance experimental session length against measurement precision (see the supplemental material from Bosen and Chatterjee, 2016). Preliminary experimentation used only two of ten bands on each trial, but this was too difficult for many listeners to achieve reliable performance (>20% of keywords correct).…”

“…These selection goals ensured that each band was sampled an equal number of times, and that the contribution of each band was averaged across its synergetisic interactions with all other bands. Details of how band combinations were selected are described in Bosen and Chatterjee (2016). Band combinations for each sentence were randomized across listeners to avoid systematic interactions between band combinations and sentences across listeners.…”

“…Recently, techniques have been developed to measure frequency importance functions for individual listeners (Bosen and Chatterjee, 2016;Shen and Kern, 2018). These techniques vary the combination of frequency bands that contain speech energy on a trial-by-trial basis, and regress speech recognition accuracy against the presence or absence of each band across trials.…”

“…The purpose of the current study was to determine the shape of frequency importance functions for individual listeners with sensorineural hearing impairment, and to determine if these functions deviate from functions observed in listeners with normal hearing. Individual frequency importance functions were estimated using an adapted version of the method described in Bosen and Chatterjee (2016), and from hereafter referred to as the "random combination strategy." To approximate the spectral shape and level of audibility (amount of speech information available to the listener based on that listener's audiometric thresholds) that would be provided by an individual's hearing aid, a standard hearing aid prescription formula (NAL-R) was applied for each listener to amplify the speech signal.…”