Availability of binaural cues for bilateral implant recipients and bimodal listeners with and without preserved hearing in the implanted ear

Abstract

The purpose of this study was to examine the availability of binaural cues for adult, bilateral cochlear implant (CI) patients, bimodal patients and hearing preservation patients using a multiple-baseline, observational study design. Speech recognition was assessed using the Bamford-Kowal-Bench Speech-in-Noise (BKB-SIN) test as well as the AzBio sentences [Spahr AJ, et al: Ear Hear 2012;33:112-117] presented in a multi-talker babble at a +5 dB signal-to-noise ratio (SNR). Test conditions included speech at 0° with noise presented at 0° (S0N0), 90° (S0N90) and 270° (S0N270). Estimates of summation, head shadow (HS), squelch and spatial release from masking (SRM) were calculated. Though nonwwe of the subject groups consistently showed access to binaural cues, the hearing preservation patients exhibited a significant correlation between summation and squelch whereas the bilateral and bimodal participants did not. That is to say, the two effects associated with binaural hearing - summation and squelch - were positively correlated only for the listeners with bilateral acoustic hearing. This finding provides evidence for the supposition that implant recipients with bilateral acoustic hearing have access to binaural cues, which should, in theory, provide greater benefit in noisy listening environments. It is likely, however, that the chosen test environment negatively affected the outcomes. Specifically, the spatially separated noise conditions directed noise toward the microphone (mic) port of the behind-the-ear (BTE) hearing aid and implant processor. Thus, it is possible that in more realistic listening environments for which the diffuse noise is not directed toward the processor/hearing aid mic, hearing preservation patients have binaural cues for improved speech understanding.

FIGURE 1

Individual and mean audiometric thresholds (in dB HL) obtained on the day of testing for the non-implanted ears of the bimodal and hearing preservation patients as well as the implanted ear of the hearing preservation patients. Error bars represent ± 1 standard deviation.

FIGURE 2

Box and whisker plots for BKB-SIN (SNR-50) and AzBio at +5 dB (% correct) for the S₀N₀ listening condition (i.e. speech and noise at 0° azimuth). The box extends from the 25th to 75th percentiles with the horizontal line in the middle representing the median. The whiskers extend from the minimum to the maximum value for all individual data thus displaying the range of scores for any given condition. The shaded bars represent bilateral subjects, the unfilled bars represent bimodal subjects and the patterned bars represent hearing preservation subjects.

FIGURE 3

Box and whisker plots for BKB-SIN (in dB) and AzBio at +5 dB (in percentage points), in panels A and B, respectively. The box extends from the 25th to 75th percentiles with the horizontal line in the middle representing the median. The whiskers extend from the minimum to the maximum value for all individual data thus displaying the range of scores for any given condition. The shaded bars represent bilateral subjects, the unfilled bars represent bimodal subjects and the patterned bars represent hearing preservation subjects.

FIGURE 4

Box and whisker plots for BKB-SIN (SNR-50) for the bilateral (panel A), bimodal (panel B), and hearing preservation subjects (panel C) for the spatially separated listening conditions with speech at 0° and noise at 90° (S₀N₉₀) and speech at 0° degrees and noise at 270° (S₀N₂₇₀).

FIGURE 5

Box and whisker plots for AzBio sentences at +5 dB (percent correct) for the bilateral (panel A), bimodal (panel B), and hearing preservation subjects (panel C) for the spatially separated listening conditions with speech at 0° and noise at 90° (S₀N₉₀) and speech at 0° degrees and noise at 270° (S₀N₂₇₀).

FIGURE 6

Box and whisker plots displaying estimates of head shadow for BKB-SIN (in dB, panel A) and AzBio at +5 dB SNR (in percentage points, panel B) for the poorer ear, better ear, and best-aided conditions.

FIGURE 7

Box and whisker plots displaying estimates of spatial release from masking (SRM) for BKB-SIN (in dB, panel A) and AzBio at +5 dB SNR (in percentage points, panel B) for the best-aided condition.

FIGURE 8

Box and whisker plots displaying estimates of spatial release from masking (SRM) for BKB-SIN (in dB, panel A) and AzBio at +5 dB SNR (in percentage points, panel B) for the best-aided condition.

FIGURE 9

Hearing preservation patients’ individual squelch estimates are plotted as a function of summation for BKB-SIN (dB, panel A) and AzBio +5 dB (percentage points, panel B). Diagonal dashed lines represent a linear regression function representing the Pearson correlation coefficient shown in each panel.