The Potential Role of the cABR in Assessment and Management of Hearing Impairment

Abstract

Hearing aid technology has improved dramatically in the last decade, especially in the ability to adaptively respond to dynamic aspects of background noise. Despite these advancements, however, hearing aid users continue to report difficulty hearing in background noise and having trouble adjusting to amplified sound quality. These difficulties may arise in part from current approaches to hearing aid fittings, which largely focus on increased audibility and management of environmental noise. These approaches do not take into account the fact that sound is processed all along the auditory system from the cochlea to the auditory cortex. Older adults represent the largest group of hearing aid wearers; yet older adults are known to have deficits in temporal resolution in the central auditory system. Here we review evidence that supports the use of the auditory brainstem response to complex sounds (cABR) in the assessment of hearing-in-noise difficulties and auditory training efficacy in older adults.

Figure 1

The stimulus /da/ (gray) is displayed with its response (black) in time and frequency domains. (a) Time domain. The response represents an average of 17 older adults (ages 60 to 67) all of whom have audiometrically normal hearing. The periodicity of the stimulus is reflected in the response with peaks repeating every ~10 ms (the F ₀ of the vowel /a/). (b) and (c) Frequency domain. Fast Fourier transforms were calculated over the steady-state region of the response, showing frequency energy at the F ₀ (100 Hz) and its integer harmonics for responses obtained by adding (b) and subtracting (c) responses to alternating polarities.

Figure 2

A phaseogram displaying differences in phase (radians, colorbar) in responses to /ba/ and /ga/ syllables, which have been synthesized so that they differ only in the second formant of the consonant-to-vowel transition. The top and bottom groups are children (ages 8 to 12) who differ on a speech-in-noise perception measure, the Hearing in Noise Test (HINT). The red color indicates greater phase difference, with /ga/ preceding /ba/, as expected given cochlear tonotopicity. Note that phase differences are only present in the transition, not in the steady state, during which the syllables are identical. Modified from [27].

Figure 3

Responses to the syllable /da/ are more robust in older adults with good speech-in-noise perception compared to those with poor speech-in-noise perception, demonstrated by greater RMS amplitude (a) and amplitude of the F ₀ in the good speech-in-noise group (b). The responses in the poor speech-in-noise group were more susceptible to the degrading effects of noise, as shown by greater differences in responses to the /da/ in quiet and noise (cross-correlations) (c). Relationship between speech-in-noise perception and the quiet-noise correlation (d). *P < 0.05, **P < 0.01. Modified from [38].

Figure 4

Self-perception of speech, assessed by the Speech Spatial Qualities Hearing scale (SSQ), is predicted by audiologic and cABR measures. The audiometric variables predict 15% of the variance in SSQ; the cABR variables predict an additional 16%. In the multiple linear regression model, only the contributions of the cABR onset time and morphology variables are significant. *P < 0.05, ***P < 0.01.

Figure 5

Young adults with normal hearing have greater representation of the F ₀ in subcortical responses to /da/ presented in noise after undergoing LACE auditory training. The F ₀ and the second harmonic have greater amplitudes in the postcondition when calculated over the transition (20–60 ms) (b) and the steady state (60–170 ms) (a). Modified from [66].

Figure 6

Responses were obtained to the stimulus /da/ presented at 80 dB SPL in sound field in aided (blue) versus unaided (black) conditions ((a) and (c)) and different settings in the same hearing aid ((b) and (d)). Responses show greater RMS and F ₀ amplitudes in aided versus unaided conditions and for setting 1 versus setting 2.