Single-Channel Focused Thresholds Relate to Vowel Identification in Pediatric and Adult Cochlear Implant Listeners

Speech-evoked cortical activities and speech recognition in adult cochlear implant listeners: a review of functional near-infrared spectroscopy studies

Cochlear implants (CIs) are the most successful neural prostheses, enabling individuals with severe to profound hearing loss to access sounds and understand speech. While CI has demonstrated success, speech perception outcomes vary largely among CI listeners, with significantly reduced performance in noise. This review paper summarizes prior findings on speech-evoked cortical activities in adult CI listeners using functional near-infrared spectroscopy (fNIRS) to understand (a) speech-evoked cortical processing in CI listeners compared to normal-hearing (NH) individuals, (b) the relationship between these activities and behavioral speech recognition scores, (c) the extent to which current fNIRS-measured speech-evoked cortical activities in CI listeners account for their differences in speech perception, and (d) challenges in using fNIRS for CI research. Compared to NH listeners, CI listeners had diminished speech-evoked activation in the middle temporal gyrus (MTG) and in the superior temporal gyrus (STG), except one study reporting an opposite pattern for STG. NH listeners exhibited higher inferior frontal gyrus (IFG) activity when listening to CI-simulated speech compared to natural speech. Among CI listeners, higher speech recognition scores correlated with lower speech-evoked activation in the STG, higher activation in the left IFG and left fusiform gyrus, with mixed findings in the MTG. fNIRS shows promise for enhancing our understanding of cortical processing of speech in CI listeners, though findings are mixed. Challenges include test-retest reliability, managing noise, replicating natural conditions, optimizing montage design, and standardizing methods to establish a strong predictive relationship between fNIRS-based cortical activities and speech perception in CI listeners.

Cochlear-implant simulated spectral degradation attenuates emotional responses to environmental sounds

OBJECTIVE

Cochlear implants (CI) provide users with a spectrally degraded acoustic signal that could impact their auditory emotional experiences. This study evaluated the effects of CI-simulated spectral degradation on emotional valence and arousal elicited by environmental sounds.

DESIGN

Thirty emotionally evocative sounds were filtered through a noise-band vocoder. Participants rated the perceived valence and arousal elicited by each of the full-spectrum and vocoded stimuli. These ratings were compared across acoustic conditions (full-spectrum, vocoded) and as a function of stimulus type (unpleasant, neutral, pleasant).

STUDY SAMPLE

Twenty-five young adults (age 19 to 34 years) with normal hearing.

RESULTS

Emotional responses were less extreme for spectrally degraded (i.e., vocoded) sounds than for full-spectrum sounds. Specifically, spectrally degraded stimuli were perceived as more negative and less arousing than full-spectrum stimuli.

CONCLUSION

By meticulously replicating CI spectral degradation while controlling for variables that are confounded within CI users, these findings indicate that CI spectral degradation can compress the range of sound-induced emotion independent of hearing loss and other idiosyncratic device- or person-level variables. Future work will characterize emotional reactions to sound in CI users via objective, psychoacoustic, and subjective measures.

Similar gaze behaviour during dialogue perception in congenitally deaf children with cochlear Implants and normal hearing children

BACKGROUND

Perceptual and speech production abilities of children with cochlear implants (CIs) are usually tested by word and sentence repetition or naming tests. However, these tests are quite far apart from daily life linguistic contexts.

AIM

Here, we describe a way of investigating the link between language comprehension and anticipatory verbal behaviour promoting the use of more complex listening situations.

METHODS AND PROCEDURE

The setup consists in watching the audio-visual dialogue of two actors. Children's gaze switches from one speaker to the other serve as a proxy of their prediction abilities. Moreover, to better understand the basis and the impact of anticipatory behaviour, we also measured children's ability to understand the dialogue content, their speech perception and memory skills as well as their rhythmic skills, that also require temporal predictions. Importantly, we compared children with CI performances with those of an age-matched group of children with normal hearing (NH).

OUTCOMES AND RESULTS

While children with CI revealed poorer speech perception and verbal working memory abilities than NH children, there was no difference in gaze anticipatory behaviour. Interestingly, in children with CI only, we found a significant correlation between dialogue comprehension, perceptual skills and gaze anticipatory behaviour.

CONCLUSION

Our results extend to a dialogue context of previous findings showing an absence of predictive deficits in children with CI. The current design seems an interesting avenue to provide an accurate and objective estimate of anticipatory language behaviour in a more ecological linguistic context also with young children.

WHAT THIS PAPER ADDS

What is already known on the subject Children with cochlear implants seem to have difficulties extracting structure from and learning sequential input patterns, possibly due to signal degradation and auditory deprivation in the first years of life. They also seem to have a reduced use of contextual information and slow language processing among children with hearing loss. What this paper adds to existing knowledge Here we show that when adopting a rather complex linguistic context such as watching a dialogue of two individuals, children with cochlear implants are able to use the speech and language structure to anticipate gaze switches to the upcoming speaker. What are the clinical implications of this work? The present design seems an interesting avenue to provide an accurate and objective estimate of anticipatory behaviour in a more ecological and dynamic linguistic context. Importantly, this measure is implicit and it has been previously used with very young (normal-hearing) children, showing that they spontaneously make anticipatory gaze switches by age two. Thus, this approach may be of interest to refine the speech comprehension assessment at a rather early age after cochlear implantation where explicit behavioural tests are not always reliable and sensitive.

On the interplay between speech perception and production: insights from research and theories

The study of spoken communication has long been entrenched in a debate surrounding the interdependence of speech production and perception. This mini review summarizes findings from prior studies to elucidate the reciprocal relationships between speech production and perception. We also discuss key theoretical perspectives relevant to speech perception-production loop, including hyper-articulation and hypo-articulation (H&H) theory, speech motor theory, direct realism theory, articulatory phonology, the Directions into Velocities of Articulators (DIVA) and Gradient Order DIVA (GODIVA) models, and predictive coding. Building on prior findings, we propose a revised auditory-motor integration model of speech and provide insights for future research in speech perception and production, focusing on the effects of impaired peripheral auditory systems.

The Relationship Between Cochlear Implant Speech Perception Outcomes and Electrophysiological Measures of the Electrically Evoked Compound Action Potential

OBJECTIVE

This study assessed the relationship between electrophysiological measures of the electrically evoked compound action potential (eCAP) and speech perception scores measured in quiet and in noise in postlingually deafened adult cochlear implant (CI) users. It tested the hypothesis that how well the auditory nerve (AN) responds to electrical stimulation is important for speech perception with a CI in challenging listening conditions.

DESIGN

Study participants included 24 postlingually deafened adult CI users. All participants used Cochlear Nucleus CIs in their test ears. In each participant, eCAPs were measured at multiple electrode locations in response to single-pulse, paired-pulse, and pulse-train stimuli. Independent variables included six metrics calculated from the eCAP recordings: the electrode-neuron interface (ENI) index, the neural adaptation (NA) ratio, NA speed, the adaptation recovery (AR) ratio, AR speed, and the amplitude modulation (AM) ratio. The ENI index quantified the effectiveness of the CI electrodes in stimulating the targeted AN fibers. The NA ratio indicated the amount of NA at the AN caused by a train of constant-amplitude pulses. NA speed was defined as the speed/rate of NA. The AR ratio estimated the amount of recovery from NA at a fixed time point after the cessation of pulse-train stimulation. AR speed referred to the speed of recovery from NA caused by previous pulse-train stimulation. The AM ratio provided a measure of AN sensitivity to AM cues. Participants' speech perception scores were measured using Consonant-Nucleus-Consonant (CNC) word lists and AzBio sentences presented in quiet, as well as in noise at signal-to-noise ratios (SNRs) of +10 and +5 dB. Predictive models were created for each speech measure to identify eCAP metrics with meaningful predictive power.

RESULTS

The ENI index and AR speed individually explained at least 10% of the variance in most of the speech perception scores measured in this study, while the NA ratio, NA speed, the AR ratio, and the AM ratio did not. The ENI index was identified as the only eCAP metric that had unique predictive power for each of the speech test results. The amount of variance in speech perception scores (both CNC words and AzBio sentences) explained by the eCAP metrics increased with increased difficulty under the listening condition. Over half of the variance in speech perception scores measured in +5 dB SNR noise (both CNC words and AzBio sentences) was explained by a model with only three eCAP metrics: the ENI index, NA speed, and AR speed.

CONCLUSIONS

Of the six electrophysiological measures assessed in this study, the ENI index is the most informative predictor for speech perception performance in CI users. In agreement with the tested hypothesis, the response characteristics of the AN to electrical stimulation are more important for speech perception with a CI in noise than they are in quiet.

Consonant bias in adult lexical processing under acoustically degraded listening conditions

Consonants facilitate lexical processing across many languages, including French. This study investigates whether acoustic degradation affects this phonological bias in an auditory lexical decision task. French words were processed using an eight-band vocoder, degrading their frequency modulations (FM) while preserving original amplitude modulations (AM). Adult French natives were presented with these French words, preceded by similarly processed pseudoword primes sharing their vowels, consonants, or neither. Results reveal a consonant bias in the listeners' accuracy and response times, despite the reduced spectral and FM information. These degraded conditions resemble current cochlear-implant processors, and attest to the robustness of this phonological bias.