Use of amplitude modulation cues recovered from frequency modulation for cochlear implant users when original speech cues are severely degraded

Electro-Haptic Stimulation: A New Approach for Improving Cochlear-Implant Listening

Cochlear implants (CIs) have been remarkably successful at restoring speech perception for severely to profoundly deaf individuals. Despite their success, several limitations remain, particularly in CI users' ability to understand speech in noisy environments, locate sound sources, and enjoy music. A new multimodal approach has been proposed that uses haptic stimulation to provide sound information that is poorly transmitted by the implant. This augmenting of the electrical CI signal with haptic stimulation (electro-haptic stimulation; EHS) has been shown to improve speech-in-noise performance and sound localization in CI users. There is also evidence that it could enhance music perception. We review the evidence of EHS enhancement of CI listening and discuss key areas where further research is required. These include understanding the neural basis of EHS enhancement, understanding the effectiveness of EHS across different clinical populations, and the optimization of signal-processing strategies. We also discuss the significant potential for a new generation of haptic neuroprosthetic devices to aid those who cannot access hearing-assistive technology, either because of biomedical or healthcare-access issues. While significant further research and development is required, we conclude that EHS represents a promising new approach that could, in the near future, offer a non-invasive, inexpensive means of substantially improving clinical outcomes for hearing-impaired individuals.

Nonlinguistic Outcome Measures in Adult Cochlear Implant Users Over the First Year of Implantation

OBJECTIVES

Postlingually deaf cochlear implant users' speech perception improves over several months after implantation due to a learning process which involves integration of the new acoustic information presented by the device. Basic tests of hearing acuity might evaluate sensitivity to the new acoustic information and be less sensitive to learning effects. It was hypothesized that, unlike speech perception, basic spectral and temporal discrimination abilities will not change over the first year of implant use. If there were limited change over time and the test scores were correlated with clinical outcome, the tests might be useful for acute diagnostic assessments of hearing ability and also useful for testing speakers of any language, many of which do not have validated speech tests.

DESIGN

Ten newly implanted cochlear implant users were tested for speech understanding in quiet and in noise at 1 and 12 months postactivation. Spectral-ripple discrimination, temporal-modulation detection, and Schroeder-phase discrimination abilities were evaluated at 1, 3, 6, 9, and 12 months postactivation.

RESULTS

Speech understanding in quiet improved between 1 and 12 months postactivation (mean 8% improvement). Speech in noise performance showed no statistically significant improvement. Mean spectral-ripple discrimination thresholds and temporal-modulation detection thresholds for modulation frequencies of 100 Hz and above also showed no significant improvement. Spectral-ripple discrimination thresholds were significantly correlated with speech understanding. Low FM detection and Schroeder-phase discrimination abilities improved over the period. Individual learning trends varied, but the majority of listeners followed the same stable pattern as group data.

CONCLUSIONS

Spectral-ripple discrimination ability and temporal-modulation detection at 100-Hz modulation and above might serve as a useful diagnostic tool for early acute assessment of cochlear implant outcome for listeners speaking any native language.

Mandarin Tone Identification in Cochlear Implant Users Using Exaggerated Pitch Contours

OBJECTIVE

To determine whether exaggerating the variations in fundamental frequency (F0) contours of Mandarin-based pitch fluctuations could improve tone identification by cochlear implant (CI) users.

METHODS

Twelve normal-hearing (NH) listeners and 11 CI users were tested for their ability to recognize F0 contours modeled after Mandarin tones, in 4- or 5-alternatives forced-choice paradigms. Two types of stimuli were used: computer-generated complex tones and voice recordings. Four contours were tested with voice recordings: flat, rise, fall, and dip. A fifth contour, peak, was added for complex tones. The F0 range of each contour was varied in an adaptive manner. A maximum-likelihood technique was used to fit a psychometric function to the performance data and extract threshold at 70% accuracy.

RESULTS

As F0 range increased, performance in tone identification improved but did not reach 100% for some CI users, suggesting that confusions between contours could always be made even with extremely exaggerated contours. Compared with NH participants, CI users required substantially larger F0 ranges to identify tones, on the order of 9.3 versus 0.4 semitones. CI users achieved better performance for complex tones than for voice recordings, whereas the reverse was true for NH participants. Confusion matrices showed that the "flat" tone was often a default option when the tone contour's F0 range presented was too narrow for participants to respond correctly.

CONCLUSION

These results demonstrate markedly impaired ability for CI users to identify tonal contours, but suggest that the use of exaggerated pitch contours may be helpful for tonal language perception.

Spectrotemporal Modulation Detection and Speech Perception by Cochlear Implant Users

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.

Consonant identification in noise using Hilbert-transform temporal fine-structure speech and recovered-envelope speech for listeners with normal and impaired hearing

Consonant-identification ability was examined in normal-hearing (NH) and hearing-impaired (HI) listeners in the presence of steady-state and 10-Hz square-wave interrupted speech-shaped noise. The Hilbert transform was used to process speech stimuli (16 consonants in a-C-a syllables) to present envelope cues, temporal fine-structure (TFS) cues, or envelope cues recovered from TFS speech. The performance of the HI listeners was inferior to that of the NH listeners both in terms of lower levels of performance in the baseline condition and in the need for higher signal-to-noise ratio to yield a given level of performance. For NH listeners, scores were higher in interrupted noise than in steady-state noise for all speech types (indicating substantial masking release). For HI listeners, masking release was typically observed for TFS and recovered-envelope speech but not for unprocessed and envelope speech. For both groups of listeners, TFS and recovered-envelope speech yielded similar levels of performance and consonant confusion patterns. The masking release observed for TFS and recovered-envelope speech may be related to level effects associated with the manner in which the TFS processing interacts with the interrupted noise signal, rather than to the contributions of TFS cues per se.