Rate Discrimination Training May Partially Restore Temporal Processing Abilities from Age-Related Deficits

Abstract

The ability to understand speech in complex environments depends on the brain's ability to preserve the precise timing characteristics of the speech signal. Age-related declines in temporal processing may contribute to the older adult's experience of communication difficulty in challenging listening conditions. This study's purpose was to evaluate the effects of rate discrimination training on auditory temporal processing. A double-blind, randomized control design assigned 77 young normal-hearing, older normal-hearing, and older hearing-impaired listeners to one of two treatment groups: experimental (rate discrimination for 100- and 300-Hz pulse trains) and active control (tone detection in noise). All listeners were evaluated during pre- and post-training sessions using perceptual rate discrimination of 100-, 200-, 300-, and 400-Hz band-limited pulse trains and auditory steady-state responses (ASSRs) to the same stimuli. Training generalization was evaluated using several temporal processing measures and sentence recognition tests that included time-compressed and reverberant speech stimuli. Results demonstrated a session × training group interaction for perceptual and ASSR testing to the trained frequencies (100 and 300 Hz), driven by greater improvements in the training group than in the active control group. Further, post-test rate discrimination of the older listeners reached levels that were equivalent to those of the younger listeners at pre-test. Generalization was observed in significant improvement in rate discrimination of untrained frequencies (200 and 400 Hz) and in correlations between performance changes in rate discrimination and sentence recognition of reverberant speech. Further, non-auditory inhibition/attention performance predicted training-related improvement in rate discrimination. Overall, the results demonstrate the potential for auditory training to partially restore temporal processing in older listeners and highlight the role of cognitive function in these gains.

Keywords: Aging; Auditory Training; Auditory steady-state response; Speech perception; Temporal processing.

Fig. 1

Average rate discrimination difference limens (DLs) are displayed for 100 and 300 Hz (left panels) and 200 and 400 Hz (right panels) in young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners who completed nine sessions of rate discrimination training (experimental group, EXP) or tone-in-noise detection training (active control group, AC). There were significant improvements in performance (smaller DLs) in the EXP group that were not observed in the AC group. *P < 0.05, **P < 0.01, ***P < 0.001. Error bars = ± 1 S.E

Fig. 2

Average pre- and post-training phase-locking factor (PLF) are displayed for 100 and 300 Hz (left panels) and 200 and 400 Hz (right panels) in young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (EXP) and active control (AC) groups. There were significant increases in PLF in the training group, especially in the YNH listeners that were not observed in the active control group. *P < 0.05, **P < 0.01. Error bars = ± S.E

Fig. 3

Pre- and post-training phase-locking factor (PLF) for 100- and 300-Hz rates is displayed in the time–frequency domain for young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (top three panels) and active control (bottom three panels) groups

Fig. 4

Average pre- and post-training gap detection thresholds (A) and gap duration DLs (B) are displayed for young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (EXP) and active control (AC) groups. No changes in performance were noted from pre-test to post-test in any group. Error bars = ± S.E

Fig. 5

Average relative difference limens (DL) are displayed as a function of 100- and 600-ms inter-onset intervals (IOIs) obtained in young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (EXP) and active control (AC) groups. No changes in performance were noted in any group. Error bars = ± S.E

Fig. 6

Average percent correct sentence recognition scores are displayed for pre- and post-training for clean (undistorted) speech, 40 % time-compressed speech (40 % TC), 60 % time-compressed speech (60 % TC), and 0.6-s and 1.2-s reverberation time (0.6s REV, 1.2s REV, respectively) in young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (EXP) and active control (AC) groups. No changes in performance were noted in any listener group. Error bars = ± S.E

Fig. 7

Scatter plots demonstrating relationships among training-related changes in relative phase-locking factor (PLF) (left two panels) and differences limens (DLs right two panels) to the 300-Hz rate and sentence recognition in young normal-hearing (YNH, cyan squares), older normal-hearing (ONH, red triangles), and older hearing-impaired (OHI, black circles) listeners. Improvement in 300-Hz PLF and 300-Hz DLs was related to improvement in sentence recognition in the 0.6-s reverberation condition. *P < 0.05, **P < 0.01