Spectro-temporal cues enhance modulation sensitivity in cochlear implant users

Abstract

Although speech understanding is highly variable amongst cochlear implants (CIs) subjects, the remarkably high speech recognition performance of many CI users is unexpected and not well understood. Numerous factors, including neural health and degradation of the spectral information in the speech signal of CIs, likely contribute to speech understanding. We studied the ability to use spectro-temporal modulations, which may be critical for speech understanding and discrimination, and hypothesize that CI users adopt a different perceptual strategy than normal-hearing (NH) individuals, whereby they rely more heavily on joint spectro-temporal cues to enhance detection of auditory cues. Modulation detection sensitivity was studied in CI users and NH subjects using broadband “ripple” stimuli that were modulated spectrally, temporally, or jointly, i.e., spectro-temporally. The spectro-temporal modulation transfer functions of CI users and NH subjects was decomposed into spectral and temporal dimensions and compared to those subjects’ spectral-only and temporal-only modulation transfer functions. In CI users, the joint spectro-temporal sensitivity was better than that predicted by spectral-only and temporal-only sensitivity, indicating a heightened spectro-temporal sensitivity. Such an enhancement through the combined integration of spectral and temporal cues was not observed in NH subjects. The unique use of spectro-temporal cues by CI patients can yield benefits for use of cues that are important for speech understanding. This finding has implications for developing sound processing strategies that may rely on joint spectro-temporal modulations to improve speech comprehension of CI users, and the findings of this study may be valuable for developing clinical assessment tools to optimize CI processor performance.

Relationship between spectrotemporal modulation detection and music perception in normal-hearing, hearing-impaired, and cochlear implant listeners

“…354–5664 Hz) 15 . STM stimuli have been used for assessing psychoacoustic capabilities in recent studies 31 , 32 . …”

Spectrotemporal Modulation Sensitivity in Cochlear-Implant and Normal-Hearing Listeners: Is the Performance Driven by Temporal or Spectral Modulation Sensitivity?

“…Won et al (2015) did not find any strong evidence that spectrotemporal modulation detection, that is, the minimum modulation depth required to detect the STM, was correlated with either the subjects' ability to detect AM or static spectral ripples. Zheng et al (2017) also reported that the spectrotemporal modulation transfer functions cannot be predicted by the temporal, or spectral modulation transfer functions. In fact, the spectral transfer function, decomposed from a spectrotemporal modulation transfer function, was better than the measured values, especially for stimuli with higher ripple density.…”

“…(2015) did not find any strong evidence that spectrotemporal modulation detection, that is, the minimum modulation depth required to detect the STM, was correlated with either the subjects’ ability to detect AM or static spectral ripples. Zheng et al. (2017) also reported that the spectrotemporal modulation transfer functions cannot be predicted by the temporal, or spectral modulation transfer functions.…”

The effect of presentation level on spectrotemporal modulation detection

“…For example, STMD paradigms have been used to explore perceptual learning mechanisms in the auditory system (Sabin et al, 2012). SMD/STMD tests have also used spectral/spectrotemporal resolution successfully as an outcome measure in different fields of audiological research: prediction of speech understanding in noise of hearing-aid users (Bernstein et al, 2016), assessment of cochlear implant candidacy, parameter fitting, and new sound processing strategies (Langner et al, 2017;Choi et al, 2016;Croghan and Smith, 2018;Zheng et al, 2017), evaluation of bimodal hearing benefit (Zhang et al, 2013), and music perception (Choi et al, 2018).…”