Training changes processing of speech cues in older adults with hearing loss

Abstract

Aging results in a loss of sensory function, and the effects of hearing impairment can be especially devastating due to reduced communication ability. Older adults with hearing loss report that speech, especially in noisy backgrounds, is uncomfortably loud yet unclear. Hearing loss results in an unbalanced neural representation of speech: the slowly-varying envelope is enhanced, dominating representation in the auditory pathway and perceptual salience at the cost of the rapidly-varying fine structure. We hypothesized that older adults with hearing loss can be trained to compensate for these changes in central auditory processing through directed attention to behaviorally-relevant speech sounds. To that end, we evaluated the effects of auditory-cognitive training in older adults (ages 55-79) with normal hearing and hearing loss. After training, the auditory training group with hearing loss experienced a reduction in the neural representation of the speech envelope presented in noise, approaching levels observed in normal hearing older adults. No changes were noted in the control group. Importantly, changes in speech processing were accompanied by improvements in speech perception. Thus, central processing deficits associated with hearing loss may be partially remediated with training, resulting in real-life benefits for everyday communication.

Keywords: aging; auditory plasticity; hearing loss; speech envelope; speech perception; temporal coding; temporal fine structure.

Figure 1

Average hearing thresholds are plotted from 0.125–8 kHz for participants with normal hearing (gray circles) and with hearing loss (black squares), with error bars ± 1 SE.

Figure 2

A summary of the experimental design.

Figure 3

(A) The spectrogram of the 40-ms syllable [da]. Fast Fourier transforms were calculated from 20 to 42 ms for the stimulus (B) and in responses to the envelope (C) and the TFS (D) in noise. The average responses for the participants with normal hearing (gray) and with hearing loss (black) are displayed. The group with hearing loss has higher amplitudes in the envelope-dominated low frequencies (F₀–H₂) in noise relative to the group with normal hearing (C); conversely, the group with normal hearing has higher amplitudes in the fine structure dominated higher frequencies (H₃–H₆) than the group with hearing loss (D). ^*p < 0.05, ^**p < 0.01.

Figure 4

(A,B) A comparison of pre- (dotted lines) and post-training responses (solid lines) to speech in noise to the envelope (F₀–H₂) in the auditory training (red) and active control (blue) groups with hearing loss, demonstrating a significant reduction in response to the envelope in the auditory training group. (C,D) No reduction was seen in response to the envelope in either group with normal hearing. (E) A significant hearing × session interaction was noted in the auditory training group, demonstrating that the change was specific to the participants with hearing loss. (F) A significant group × session interaction in the groups with hearing loss indicating a reduction in the representation of the F₀ in the auditory training group only. ^*p < 0.05. Error bars: ± 1 SE.

Figure 5

(A,B) A comparison of pre- (dotted lines) and post-training responses (solid lines) to speech in noise to the fine structure (H₃–H₆) in the auditory training (red) and active control (blue) groups with hearing loss, demonstrating no change in either group. (C,D) No change was seen in response to the fine structure in either group with normal hearing.

Figure 6

Mean F_0ADD and H_2ADD amplitudes are displayed for individual pre- (open circles) and post-data (closed circles) for the auditory training (red) and active control (blue) groups. Visual observation of the data reveals that there is greater pre-training variability in both groups with hearing loss and in the degree of change in the auditory training group with hearing loss.

Figure 7

Mean H_3SUB and H_6SUB amplitudes are displayed for individual pre- (open circles) and post-data (closed circles) for the auditory training (red) and active control (blue) groups. Similar to the data for the envelope, the data demonstrates greater variability in both groups with hearing loss for pre-test data, but there is no systematic change with training as was found for the envelope.

Figure 8

Pre and post-training perceptual and cognitive scores for participants with both normal hearing and hearing loss (group × session interactions). The auditory training group improved in speech-in-noise perception (A), memory (B), and attention (C), whereas there were no changes in the active control group. ^*p < 0.05, ^**p < 0.01. Error bars: ± 1 SE.