Level discrimination of speech sounds by hearing-impaired individuals with and without hearing amplification

Abstract

Objectives: The current study was designed to see how hearing-impaired individuals judge level differences between speech sounds with and without hearing amplification. It was hypothesized that hearing aid compression should adversely affect the user's ability to judge level differences.

Design: Thirty-eight hearing-impaired participants performed an adaptive tracking procedure to determine their level-discrimination thresholds for different word and sentence tokens, as well as speech-spectrum noise, with and without their hearing aids. Eight normal-hearing participants performed the same task for comparison.

Results: Level discrimination for different word and sentence tokens was more difficult than the discrimination of stationary noises. Word level discrimination was significantly more difficult than sentence level discrimination. There were no significant differences, however, between mean performance with and without hearing aids and no correlations between performance and various hearing aid measurements.

Conclusions: There is a clear difficulty in judging the level differences between words or sentences relative to differences between broadband noises, but this difficulty was found for both hearing-impaired and normal-hearing individuals and had no relation to hearing aid compression measures. The lack of a clear adverse effect of hearing aid compression on level discrimination is suggested to be due to the low effective compression ratios of currently fit hearing aids.

Figure 1

Average pure-tone audiometric thresholds as a function of frequency. Error bars show ±1 standard deviation; shaded area shows range of values. Gray lines show individual audiograms of the three lowest and highest four-frequency average thresholds. Hearing losses varied from sloping normal-to-mild to flat moderate to severe-to-profound

Figure 2

Compression ratio as a function of frequency computed from measured outputs at 60- and 80-dB SPL input, averaged across bilateral fittings. Lines represent medians, boxes represent lower and upper quartile of data, bars represent 1.5 × inter-quartile range. Outliers outside 1.5 × inter-quartile range are marked with crosses.

Figure 3

Frequency histograms of level-discrimination thresholds for hearing-impaired participants grouped in 0.5-dB bins for unaided (left panel) and aided (right panel) conditions with long-term-average speech-spectrum noise (a), mono-syllabic words (b) and sentences (c). Median values are given in parentheses. For aided word and sentence stimuli, there were several thresholds that were much greater than the general distribution.

Figure 4

Retest level-discrimination thresholds (ΔLs) as a function of test (original) ΔLs for twelve unaided participants. Stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. Pearson product-moment correlations, showing significant correlations between test and re-test values for each stimulus type, are given in the legend. The identity plot (test = retest; solid line) is shown for reference.

Figure 5

Mean level-discrimination (ΔL) thresholds as a function of stimulus type for normal-hearing (NH), hearing-impaired (HI) unaided and aided. Error bars show 95% confidence intervals. The ability to discriminate level differences between different words and sentences was significantly more difficult than discriminating level differences in noises.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.

Figure 6

Upper left panel (a) shows unaided level-discrimination thresholds (ΔL) as a function of four-frequency average (4FA) pure-tone thresholds. Upper right panel (b) shows aided ΔL as a function of 4FA pure-tone thresholds. Middle left panel shows aided ΔL as a function of average hearing-aid standardised compression ratio (x:1). Middle right panel shows aided ΔL as a function of average compressor attack time. Bottom left panel shows aided ΔL as a function of average compressor release time. Bottom right panel shows aided ΔL as a function of unaided ΔL. For all plots, stimulus conditions are separated by symbol: dots (●) for stationary noises, circles (○) for words, and crosses (+) for sentences. None of the stimulus thresholds systematically change with any of the audiometric, hearing-aid or other measures.