Different patterns of perceptual learning on spectral modulation detection between older hearing-impaired and younger normal-hearing adults

Abstract

Young adults with normal hearing (YNH) can improve their sensitivity to basic acoustic features with practice. However, it is not known to what extent the influence of the same training regimen differs between YNH listeners and older listeners with hearing impairment (OHI)--the largest population seeking treatment in audiology clinics. To examine this issue, we trained OHI listeners on a basic auditory task (spectral modulation detection) using a training regimen previously administered to YNH listeners (≈ 1 h/session for seven sessions on a single condition). For the trained conditions on which pretraining performance was not already at asymptote, the YNH listeners who received training learned more than matched controls who received none, but that learning did not generalize to any untrained spectral modulation frequency. In contrast, the OHI-trained listeners and controls learned similar amounts on the trained condition, implying no effect of the training itself. However, surprisingly the OHI-trained listeners improved over the training phase and on an untrained spectral modulation frequency. These population differences suggest that learning consolidated more slowly, and that training modified an aspect of processing that had broader tuning to spectral modulation frequency, in OHI than YNH listeners. More generally, these results demonstrate that conclusions about perceptual learning that come from examination of one population do not necessarily apply to another.

FIG. 1

Tasks. Schematic diagrams of the stimuli used in the two tested tasks. A In the spectral modulation detection task, listeners had to distinguish a noise with a sinusoidal spectral shape over a logarithmic frequency axis (solid line signal) from one with a flat spectrum (dotted line reference). The modulation depth was varied adaptively to determine the spectral modulation detection threshold. The noise ranged from 400 to 3,200 Hz. The spectral modulation frequency of the displayed stimulus is 2 cyc/oct (the trained condition). B In the ripple reversal task, listeners had to distinguish a stimulus with a full wave rectified sinusoidal shape on a logarithmic frequency axis (solid line signal) from one in which the peaks and valleys were interchanged with those of the signal stimulus (dotted line reference). The spectral modulation frequency was varied adaptively to determine the ripple reversal threshold. The stimulus ranged from 100 to 5,000 Hz. The spectral modulation frequency of the displayed stimulus is 5.6 cyc/oct.

FIG. 2

Learning curves. A The group average spectral modulation detection threshold on the trained condition (2 cyc/oct) as a function of testing session for the trained listeners (filled squares, n = 8) and controls (open circles, n = 8). Values are adjusted using individual differences in pre-test performance as a covariate (Eq. 1). The schematic illustrates the trained stimulus, with audiofrequency on the abscissa and magnitude on the ordinate (axes not shown; see Fig. 1). Error bars 1 standard error of the mean. B Individual performance for the trained listeners (lines) and controls (circles). Five of the controls improved between the pre- and post-tests (solid-line circles) while three others did not (dashed circles). Note that while the data are plotted on a linear scale, the regression analyses of performance across sessions were computed using log₁₀ of the session number. Trained listeners improved gradually over the training phase, but controls improved by a comparable amount.

FIG. 3

Within-session performance. The group-average spectral modulation detection thresholds toward the beginning and end of each training session. The averages of the first three (left square) and last three (right square) adjusted threshold estimates from the same training session are connected by a line. Values are adjusted using individual differences in pre-test performance as a covariate. Error bars 1 standard error of the mean. Trained listeners showed a rapid within-session improvement during the first training session and a gradual improvement across the remaining sessions.

FIG. 4

Pre- and post-tests. A Adjusted post-test spectral modulation detection thresholds for each tested condition for the trained listeners (squares) and controls (circles). Results are shown as group averages (filled symbols) and for each individual listener (unfilled symbols). As in Fig. 2, dashed circles represent the individual controls who did not improve on the 2 cyc/oct condition. Values are adjusted using individual differences in pre-test performance as a covariate (Eq. 1). For these conditions, lower values indicate better performance. Performance was evaluated for the trained (left column) and untrained (middle and right columns) spectral modulation frequencies. A schematic of the tested stimulus is displayed above each column. The dashed lines represent the mean pre-training performance across groups, and the horizontal boxes represent the 95 % confidence interval of the adjusted post-test performance of the controls. Error bars 1 standard error of the mean. Asterisks indicate a significant (p < 0.05) difference between trained listeners and controls based on an analysis of covariance using pre-test performance as a covariate. B As in A, but for the ripple-reversal condition. For this condition, higher values indicate better performance. C Raw (unadjusted) pre-test performance (x-axis) and pre-test minus post-test improvement (y-axis) is plotted for each listener in the trained (filled squares) and control (open circles) groups. Each panel is a different spectral modulation frequency. D As in C, but for the ripple reversal condition. Trained listeners learned more than controls on the untrained 1 cyc/oct condition. Both groups improved by similar amounts on the trained 2 cyc/oct and the untrained 4 cyc/oct conditions, and neither group improved on the untrained task.

FIG. 5

Comparison to young normal hearing listeners. A–D Adjusted learning curves, plotted as in Fig 2. Data are shown for three sets (A–C) of trained younger listeners with YNH (filled symbols) and corresponding YNH controls (open symbols; data from Sabin et al. 2012b) as well as for D the older listeners with hearing impairment (OHI; replotted from Fig. 2). E–H Summary of training-induced learning across all conditions. Each bar indicates the eta-squared effect size of a two group (trained vs control) ANCOVA, with pre-test performance as the covariate, computed separately for each condition in each experiment (indicated by x-axis labels). Larger bars indicate larger differences between trained and control listeners, and asterisks indicate significant differences (p < 0.05). The key result is that the patterns of improvement in the OHI listeners is different from those of each of the groups of YNH listeners.