Spectrotemporal Modulation Detection and Speech Perception by Cochlear Implant Users.

Jong Ho Won,Won-Ho Chung,Yang-Sun Cho,Sunhwa Jin,Il Joon Moon,Heesung Park,Jihwan Woo,Sung Hwa Hong,Frederic Dick

doi:10.1371/journal.pone.0140920

Abstract

Spectrotemporal modulation (STM) detection performance was examined for cochlear implant (CI) users. The test involved discriminating between an unmodulated steady noise and a modulated stimulus. The modulated stimulus presents frequency modulation patterns that change in frequency over time. In order to examine STM detection performance for different modulation conditions, two different temporal modulation rates (5 and 10 Hz) and three different spectral modulation densities (0.5, 1.0, and 2.0 cycles/octave) were employed, producing a total 6 different STM stimulus conditions. In order to explore how electric hearing constrains STM sensitivity for CI users differently from acoustic hearing, normal-hearing (NH) and hearing-impaired (HI) listeners were also tested on the same tasks. STM detection performance was best in NH subjects, followed by HI subjects. On average, CI subjects showed poorest performance, but some CI subjects showed high levels of STM detection performance that was comparable to acoustic hearing. Significant correlations were found between STM detection performance and speech identification performance in quiet and in noise. In order to understand the relative contribution of spectral and temporal modulation cues to speech perception abilities for CI users, spectral and temporal modulation detection was performed separately and related to STM detection and speech perception performance. The results suggest that that slow spectral modulation rather than slow temporal modulation may be important for determining speech perception capabilities for CI users. Lastly, test–retest reliability for STM detection was good with no learning. The present study demonstrates that STM detection may be a useful tool to evaluate the ability of CI sound processing strategies to deliver clinically pertinent acoustic modulation information.

Highlights

Speech identification performance for cochlear implant (CI) users has been gradually improving over the past 20 years [1, 2] partly due to the advancement in CI coding strategy, front-end signal processing, electrode design, and the use of electro-acoustic stimulation
The results showed that the K-CID sentence recognition scores in quiet were significantly correlated with Spectrotemporal modulation (STM) detection thresholds for lower spectral densities of 0.5 and 1.0 c/o regardless of temporal modulation rates
When the effect of temporal modulation detection at 10 Hz was controlled for (Table 6), the partial correlation analyses produced little change in correlation coefficients, and more importantly, did not change the significance at the 0.05 level. These analyses suggest that detection abilities for slow spectral modulation patterns rather than temporal modulation patterns might have played a primary role for the relationship between STM detection performance and speech perception abilities for CI subjects

Summary

Introduction

Speech identification performance for cochlear implant (CI) users has been gradually improving over the past 20 years [1, 2] partly due to the advancement in CI coding strategy, front-end signal processing, electrode design, and the use of electro-acoustic stimulation. Spectral modulation sensitivity has been documented on spectral-ripple discrimination or spectral-ripple detection tasks for CI users In these tests, listeners are presented with one interval containing a spectrally modulated stimulus (i.e., test signal or “oddball”) and two other intervals containing a reference signal. For the spectral-ripple discrimination test, spectral modulation depth is fixed, and spectral-ripple density thresholds are measured using a spectral phase-reversed reference signal [3,4,5,6,7,8]. Spectral modulation frequency is fixed for the spectral ripple detection test, and thresholds are measured by determining the minimum spectral modulation depth required to discriminate a noise carrier with flat spectrum from that with a sinusoidally modulated spectrum [9,10,11]. Significant correlations were reported between spectral modulation sensitivity (measured using both techniques) and speech perception outcomes for CI users [3, 5, 7, 11, 12]

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