Validation of a clinical assessment of spectral-ripple resolution for cochlear implant users

Abstract

Objectives: Nonspeech psychophysical tests of spectral resolution, such as the spectral-ripple discrimination task, have been shown to correlate with speech-recognition performance in cochlear implant (CI) users. However, these tests are best suited for use in the research laboratory setting and are impractical for clinical use. A test of spectral resolution that is quicker and could more easily be implemented in the clinical setting has been developed. The objectives of this study were (1) To determine whether this new clinical ripple test would yield individual results equivalent to the longer, adaptive version of the ripple-discrimination test; (2) To evaluate test-retest reliability for the clinical ripple measure; and (3) To examine the relationship between clinical ripple performance and monosyllabic word recognition in quiet for a group of CI listeners.

Design: Twenty-eight CI recipients participated in the study. Each subject was tested on both the adaptive and the clinical versions of spectral ripple discrimination, as well as consonant-nucleus-consonant word recognition in quiet. The adaptive version of spectral ripple used a two-up, one-down procedure for determining spectral ripple discrimination threshold. The clinical ripple test used a method of constant stimuli, with trials for each of 12 fixed ripple densities occurring six times in random order. Results from the clinical ripple test (proportion correct) were then compared with ripple-discrimination thresholds (in ripples per octave) from the adaptive test.

Results: The clinical ripple test showed strong concurrent validity, evidenced by a good correlation between clinical ripple and adaptive ripple results (r = 0.79), as well as a correlation with word recognition (r = 0.7). Excellent test-retest reliability was also demonstrated with a high test-retest correlation (r = 0.9).

Conclusions: The clinical ripple test is a reliable nonlinguistic measure of spectral resolution, optimized for use with CI users in a clinical setting. The test might be useful as a diagnostic tool or as a possible surrogate outcome measure for evaluating treatment effects in hearing.

Figure 1

Amplitude spectra (magnitude, in dB, as a function of frequency) of spectral-ripple stimuli used in the spectral-ripple discrimination tasks. Standard and inverted ripples for ripple densities of 1, 2, and 4 ripples/octave are displayed.

Figure 2

Adaptive ripple discrimination thresholds (rpo) as a function of clinical ripple performance (average proportion correct across all ripple densities). Panel a: first repetition of clinical ripple test. Panel b: average of two repetitions of clinical ripple test.

Figure 3

Performance on second repetition of clinical ripple test as a function of performance on first repetition, for 27 subjects. The diagonal line represents perfect correspondence.

Figure 4

Histogram showing the differences scores between the 1^st and 2^nd run of the clinical spectral ripple discrimination test. A normal curve is shown fit to the data.

Figure 5

Word recognition (rau scores) as a function of clinical ripple performance (proportion correct) for all subjects. Panel a: first repetition of clinical ripple test. Panel b: average of two repetitions of clinical ripple test.

Figure 6

Word recognition (rau scores) as a function of adaptive spectral-ripple discrimination thresholds (rpo). A logarithmic fit is displayed.