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Comparative Study
. 2012 Dec;132(6):3925-34.
doi: 10.1121/1.4763999.

Assessing the role of spectral and intensity cues in spectral ripple detection and discrimination in cochlear-implant users

Elizabeth S Anderson  1 , Andrew J Oxenham, Peggy B Nelson, David A Nelson
Affiliations
Comparative Study

Assessing the role of spectral and intensity cues in spectral ripple detection and discrimination in cochlear-implant users

Elizabeth S Anderson et al. J Acoust Soc Am. 2012 Dec.

Abstract

Measures of spectral ripple resolution have become widely used psychophysical tools for assessing spectral resolution in cochlear-implant (CI) listeners. The objective of this study was to compare spectral ripple discrimination and detection in the same group of CI listeners. Ripple detection thresholds were measured over a range of ripple frequencies and were compared to spectral ripple discrimination thresholds previously obtained from the same CI listeners. The data showed that performance on the two measures was correlated, but that individual subjects' thresholds (at a constant spectral modulation depth) for the two tasks were not equivalent. In addition, spectral ripple detection was often found to be possible at higher rates than expected based on the available spectral cues, making it likely that temporal-envelope cues played a role at higher ripple rates. Finally, spectral ripple detection thresholds were compared to previously obtained speech-perception measures. Results confirmed earlier reports of a robust relationship between detection of widely spaced ripples and measures of speech recognition. In contrast, intensity difference limens for broadband noise did not correlate with spectral ripple detection measures, suggesting a dissociation between the ability to detect small changes in intensity across frequency and across time.

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Figures

Figure 1
Figure 1
Spectral modulation transfer functions (SMTFs) for 15 CI subjects. Ripple detection threshold (in dB) for each of seven different spectral ripple frequencies (0.25, 0.5, 0.75, 1.0, 1.5, 2.0, and 3.0 rpo) is depicted.
Figure 2
Figure 2
SMTFs for Clarion-I, Clarion-II, and Nucleus subjects (top, middle, and lower panels, respectively) over an extended range of spectral ripple rates. The dotted horizontal lines correspond to a ripple detection threshold of 30 dB.
Figure 3
Figure 3
Interpolated ripple frequency (in rpo) for ripple detection threshold, or spectral modulation threshold (SMT) = 30 dB, as a function of spectral ripple discrimination threshold (rpo).
Figure 4
Figure 4
RAU scores for sentence recognition (A) and vowel recognition (B) as a function of average SMT for 0.25 and 0.5 rpo. (C), (D) SNR50% for sentences and vowels, respectively, as a function of the average of ripple detection thresholds at 0.25 and 0.5 rpo.
Figure 5
Figure 5
Individual SMTF (ripple detection threshold as a function of spectral ripple frequency) for subject D10. The vertical line indicates the spectral ripple discrimination threshold for this listener.
Figure 6
Figure 6
SMTFs for three normal-hearing subjects. Ripple detection thresholds (in dB) for each of 15 different spectral ripple frequencies (0.25–60 rpo) is displayed. Spectral ripple discrimination thresholds are indicated by vertical lines.
Figure 7
Figure 7
Intensity difference limens (ΔL) for each subject. Error bars represent 1 s.d.
See this image and copyright information in PMC

References

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