Some, but not all, cochlear implant users prefer music stimuli with congruent haptic stimulation.

Cochlear implant (CI) users often report being unsatisfied by music listening through their hearing device. Vibrotactile stimulation could help alleviate those challenges. Previous research has shown that musical stimuli was given higher preference ratings by normal-hearing listeners when concurrent vibrotactile stimulation was congruent in intensity and timing with the corresponding auditory signal compared to incongruent. However, it is not known whether this is also the case for CI users. Therefore, in this experiment, we presented 18 CI users and 24 normal-hearing listeners with five melodies and five different audio-to-tactile maps. Each map varied the congruence between the audio and tactile signals related to intensity, fundamental frequency, and timing. Participants were asked to rate the maps from zero to 100, based on preference. It was shown that almost all normal-hearing listeners, as well as a subset of the CI users, preferred tactile stimulation, which was congruent with the audio in intensity and timing. However, many CI users had no difference in preference between timing aligned and timing unaligned stimuli. The results provide evidence that vibrotactile music enjoyment enhancement could be a solution for some CI users; however, more research is needed to understand which CI users can benefit from it most.

Reducing preferred listening levels in headphones through coherent audiotactile stimulation.

Using headphones may expose the listener to potentially harmful levels of sound. This study examines whether introducing tactile vibrations to the listening experience would encourage them to reduce their headphone volume. Fifteen participants adjusted their preferred listening levels for four diverse music tracks under audio-only and audiotactile conditions. Results indicated a significant decrease in preferred audio levels with added tactile stimulation. This effect was particularly significant in songs featuring a strong beat. In contrast, only a minimal effect was observed for genres such as classical music, which typically lack a pronounced beat, at higher vibration intensities. These findings suggest that integrating tactile feedback could be a viable strategy for lowering sound exposure risk.

Cochlear Implantation in Sporadic Intralabyrinthine Schwannomas with Single-Sided Deafness: Implications for Binaural Hearing.

BACKGROUND AND OBJECTIVE: Intralabyrinthine schwannomas (ILSs) may have detrimental effects on ipsilateral hearing, commonly leading to single-sided deafness (SSD). Cochlear implantation in patients with ILSs is an option to partly restore ipsilateral hearing; however, the available literature fails to account for the binaural hearing benefits of a cochlear implant (CI) for ILSs. METHODS: We prospectively evaluated SSD patients with sporadic ILS undergoing cochlear implantation with simultaneous tumor resection (n = 10) or with tumor observation (n = 1). Patients completed the Speech, Spatial and Qualities Questionnaire (SSQ12) and the Nijmegen Cochlear Implant Questionnaire (NCIQ) pre- and postoperatively, as well as the Bern Benefit in Single-Sided Deafness (BBSSD) questionnaire postoperatively. Patients were also tested postoperatively with and without their CI to measure the effect on localization ability and binaural summation, squelch, and head shadow. RESULTS: Evaluation was completed for nine and six patients (subjective and objective data, respectively). The CI significantly improved the speech reception threshold (SRT) in the head shadow condition where the target signal was presented to the CI side and the noise to the front (SCIN0). On the other hand, the SRTs in the colocated condition (S0N0) and the condition where the target signal was presented to the front and the noise to the CI side (S0NCI) were unaffected by the CI. The mean localization error decreased significantly from 102° to 61° (p = 0.0031) with the addition of a CI. The scores from SSQ12 demonstrated nonsignificant changes. For NCIQ, the self-esteem and the social interaction domains increased significantly but insignificantly for the remaining domains. The BBSSD responses ranged from +0.5 to +3.5 points. CONCLUSION: After implantation, patients achieved significantly better scores across some of the patient-reported and objective parameters. In addition to reporting on a number of ILS cases where implantation was performed, the study is the first of its kind to document patient-reported and objective binaural hearing improvement after cochlear implantation in patients with ILS and, thereby, lends support to the active management of ILS.

The effect of auditory training on listening effort in hearing-aid users: insights from a pupillometry study.

OBJECTIVE: The study investigated how auditory training affects effort exerted by hearing-impaired listeners in speech-in-noise task. DESIGN: Pupillometry was used to characterise listening effort during a hearing in noise test (HINT) before and after phoneme-in-noise identification training. Half of the study participants completed the training, while the other half formed an active control group. STUDY SAMPLE: Twenty 63-to-79 years old experienced hearing-aid users. RESULTS: Higher peak pupil dilations (PPDs) were obtained at the end of the study compared to the beginning in both groups of the participants. The analysis of pupil dilation in an extended time window revealed, however, that the magnitude of pupillary response increased more in the training than in the control group. The effect of training on effort was observed in pupil responses even when no improvement in HINT was found. CONCLUSION: The results demonstrate that using a listening effort metric adds additional insights into the effectiveness of auditory training compared to the situation when only speech-in-noise performance is considered. Trends observed in pupil responses suggested increased effort-both after the training and the placebo intervention-most likely reflecting the effect of the individual's motivation.

Improved speech intelligibility in the presence of congruent vibrotactile speech input.

Vibrotactile stimulation is believed to enhance auditory speech perception, offering potential benefits for cochlear implant (CI) users who may utilize compensatory sensory strategies. Our study advances previous research by directly comparing tactile speech intelligibility enhancements in normal-hearing (NH) and CI participants, using the same paradigm. Moreover, we assessed tactile enhancement considering stimulus non-specific, excitatory effects through an incongruent audio-tactile control condition that did not contain any speech-relevant information. In addition to this incongruent audio-tactile condition, we presented sentences in an auditory only and a congruent audio-tactile condition, with the congruent tactile stimulus providing low-frequency envelope information via a vibrating probe on the index fingertip. The study involved 23 NH listeners and 14 CI users. In both groups, significant tactile enhancements were observed for congruent tactile stimuli (5.3% for NH and 5.4% for CI participants), but not for incongruent tactile stimulation. These findings replicate previously observed tactile enhancement effects. Juxtaposing our study with previous research, the informational content of the tactile stimulus emerges as a modulator of intelligibility: Generally, congruent stimuli enhanced, non-matching tactile stimuli reduced, and neutral stimuli did not change test outcomes. We conclude that the temporal cues provided by congruent vibrotactile stimuli may aid in parsing continuous speech signals into syllables and words, consequently leading to the observed improvements in intelligibility.

Temporal Cues in the Judgment of Music Emotion for Normal and Cochlear Implant Listeners.

Several studies have established that Cochlear implant (CI) listeners rely on the tempo of music to judge the emotional content of music. However, a re-analysis of a study in which CI listeners judged the emotion conveyed by piano pieces on a scale from happy to sad revealed a weak correlation between tempo and emotion. The present study explored which temporal cues in music influence emotion judgments among normal hearing (NH) listeners, which might provide insights into the cues utilized by CI listeners. Experiment 1 was a replication of the Vannson et al. study with NH listeners using rhythmic patterns of piano created with congas. The temporal cues were preserved while the tonal ones were removed. The results showed (i) tempo was weakly correlated with emotion judgments, (ii) NH listeners' judgments for congas were similar to CI listeners' judgments for piano. In Experiment 2, two tasks were administered with congas played at three different tempi: emotion judgment and a tapping task to record listeners' perceived tempo. Perceived tempo was a better predictor than the tempo, but its physical correlate, mean onset-to-onset difference (MOOD), a measure of the average time between notes, yielded higher correlations with NH listeners' emotion judgments. This result suggests that instead of the tempo, listeners rely on the average time between consecutive notes to judge the emotional content of music. CI listeners could utilize this cue to judge the emotional content of music.

Effect of Vibrotactile Stimulation on Auditory Timbre Perception for Normal-Hearing Listeners and Cochlear-Implant Users.

The study tests the hypothesis that vibrotactile stimulation can affect timbre perception. A multidimensional scaling experiment was conducted. Twenty listeners with normal hearing and nine cochlear implant users were asked to judge the dissimilarity of a set of synthetic sounds that varied in attack time and amplitude modulation depth. The listeners were simultaneously presented with vibrotactile stimuli, which varied also in attack time and amplitude modulation depth. The results showed that alterations to the temporal waveform of the tactile stimuli affected the listeners' dissimilarity judgments of the audio. A three-dimensional analysis revealed evidence of crossmodal processing where the audio and tactile equivalents combined accounted for their dissimilarity judgments. For the normal-hearing listeners, 86% of the first dimension was explained by audio impulsiveness and 14% by tactile impulsiveness; 75% of the second dimension was explained by the audio roughness or fast amplitude modulation, while its tactile counterpart explained 25%. Interestingly, the third dimension revealed a combination of 43% of audio impulsiveness and 57% of tactile amplitude modulation. For the CI listeners, the first dimension was mostly accounted for by the tactile roughness and the second by the audio impulsiveness. This experiment shows that the perception of timbre can be affected by tactile input and could lead to the developing of new audio-tactile devices for people with hearing impairment.

The effect of phoneme-based auditory training on speech intelligibility in hearing-aid users.

OBJECTIVE: Hearing loss commonly causes difficulties in understanding speech in the presence of background noise. The benefits of hearing-aids in terms of speech intelligibility in challenging listening scenarios remain limited. The present study investigated if phoneme-in-noise discrimination training improves phoneme identification and sentence intelligibility in noise in hearing-aid users. DESIGN: Two groups of participants received either a two-week training program or a control intervention. Three phoneme categories were trained: onset consonants (C1), vowels (V) and post-vowel consonants (C2) in C1-V-C2-/i/ logatomes from the Danish nonsense word corpus (DANOK). Phoneme identification test and hearing in noise test (HINT) were administered before and after the respective interventions and, for the training group only, after three months. STUDY SAMPLE: Twenty 63-to-79 years old individuals with a mild-to-moderate sensorineural hearing loss and at least one year of experience using hearing-aids. RESULTS: The training provided an improvement in phoneme identification scores for vowels and post-vowel consonants, which was retained over three months. No significant performance improvement in HINT was found. CONCLUSION: The study demonstrates that the training induced a robust refinement of auditory perception at a phoneme level but provides no evidence for the generalisation to an untrained sentence intelligibility task.

Effect of audio-tactile congruence on vibrotactile music enhancement.

Music listening experiences can be enhanced with tactile vibrations. However, it is not known which parameters of the tactile vibration must be congruent with the music to enhance it. Devices that aim to enhance music with tactile vibrations often require coding an acoustic signal into a congruent vibrotactile signal. Therefore, understanding which of these audio-tactile congruences are important is crucial. Participants were presented with a simple sine wave melody through supra-aural headphones and a haptic actuator held between the thumb and forefinger. Incongruent versions of the stimuli were made by randomizing physical parameters of the tactile stimulus independently of the auditory stimulus. Participants were instructed to rate the stimuli against the incongruent stimuli based on preference. It was found making the intensity of the tactile stimulus incongruent with the intensity of the auditory stimulus, as well as misaligning the two modalities in time, had the biggest negative effect on ratings for the melody used. Future vibrotactile music enhancement devices can use time alignment and intensity congruence as a baseline coding strategy, which improved strategies can be tested against.

The effects of aging and musicianship on the use of auditory streaming cues.

Auditory stream segregation, or separating sounds into their respective sources and tracking them over time, is a fundamental auditory ability. Previous research has separately explored the impacts of aging and musicianship on the ability to separate and follow auditory streams. The current study evaluated the simultaneous effects of age and musicianship on auditory streaming induced by three physical features: intensity, spectral envelope and temporal envelope. In the first study, older and younger musicians and non-musicians with normal hearing identified deviants in a four-note melody interleaved with distractors that were more or less similar to the melody in terms of intensity, spectral envelope and temporal envelope. In the second study, older and younger musicians and non-musicians participated in a dissimilarity rating paradigm with pairs of melodies that differed along the same three features. Results suggested that auditory streaming skills are maintained in older adults but that older adults rely on intensity more than younger adults while musicianship is associated with increased sensitivity to spectral and temporal envelope, acoustic features that are typically less effective for stream segregation, particularly in older adults.

The Perception of Ramped Pulse Shapes in Cochlear Implant Users.

The electric stimulation provided by current cochlear implants (CI) is not power efficient. One underlying problem is the poor efficiency by which information from electric pulses is transformed into auditory nerve responses. A novel stimulation paradigm using ramped pulse shapes has recently been proposed to remedy this inefficiency. The primary motivation is a better biophysical fit to spiral ganglion neurons with ramped pulses compared to the rectangular pulses used in most contemporary CIs. Here, we tested the hypotheses that ramped pulses provide more efficient stimulation compared to rectangular pulses and that a rising ramp is more efficient than a declining ramp. Rectangular, rising ramped and declining ramped pulse shapes were compared in terms of charge efficiency and discriminability, and threshold variability in seven CI listeners. The tasks included single-channel threshold detection, loudness-balancing, discrimination of pulse shapes, and threshold measurement across the electrode array. Results showed that reduced charge, but increased peak current amplitudes, was required at threshold and most comfortable levels with ramped pulses relative to rectangular pulses. Furthermore, only one subject could reliably discriminate between equally-loud ramped and rectangular pulses, suggesting variations in neural activation patterns between pulse shapes in that participant. No significant difference was found between rising and declining ramped pulses across all tests. In summary, the present findings show some benefits of charge efficiency with ramped pulses relative to rectangular pulses, that the direction of a ramped slope is of less importance, and that most participants could not perceive a difference between pulse shapes.

Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users.

The effect of the relative timing between pairs of same-polarity monophasic pulses has been studied extensively in single-neuron animal studies and has revealed fundamental properties of the neurons. For human cochlear implant listeners, the requirement to use charge-balanced stimulation and the typical use of symmetric, biphasic pulses limits such measures, because currents of opposite polarities interact at the level of the neural membrane. Here, we propose a paradigm to study same-polarity summation of currents while keeping the stimulation charge-balanced within a short time window. We used pairs of mirrored pseudo-monophasic pulses (a long-low phase followed by a short-high phase for the first pulse and a short-high phase followed by a long-low phase for the second pulse). We assumed that most of the excitation would stem from the two adjacent short-high phases, which had the same polarity. The inter-pulse interval between the short-high phases was varied from 0 to 345 µs. The inter-pulse interval had a significant effect on the perceived loudness, and this effect was consistent with both passive (membrane-related) and active (ion-channel-related) neuronal mechanisms contributing to facilitation. Furthermore, the effect of interval interacted with the polarity of the pulse pairs. At threshold, there was an effect of polarity, but, surprisingly, no effect of interval nor an interaction between the two factors. We discuss possible peripheral origins of these results.

The Effect of Phantom Stimulation and Pseudomonophasic Pulse Shapes on Pitch Perception by Cochlear Implant Listeners.

It has been suggested that a specialized high-temporal-acuity brainstem pathway can be activated by stimulating more apically in the cochlea than is achieved by cochlear implants (CIs) when programmed with contemporary clinical settings. We performed multiple experiments to test the effect on pitch perception of phantom stimulation and asymmetric current pulses, both supposedly stimulating beyond the most apical electrode of a CI. The two stimulus types were generated using a bipolar electrode pair, composed of the most apical electrode of the array and a neighboring, more basal electrode. Experiment 1 used a pitch-ranking procedure where neural excitation was shifted apically or basally using so-called phantom stimulation. No benefit of apical phantom stimulation was found on the highest rate up to which pitch ranks increased (upper limit), nor on the slopes of the pitch-ranking function above 300 pulses per second (pps). Experiment 2 used the same procedure to study the effects of apical pseudomonophasic pulses, where the locus of excitation was manipulated by changing stimulus polarity. A benefit of apical stimulation was obtained for the slopes above 300 pps. Experiment 3 used an adaptive rate discrimination procedure and found a small but significant benefit of both types of apical stimulation. Overall, the results show some benefit for apical stimulation on temporal pitch processing at high pulse rates but reveal that the effect is smaller and more variable across listeners than suggested by previous research. The results also provide some indication that the benefit of apical stimulation may decline over time since implantation.

The sound sensation of a pure tone in cochlear implant recipients with single-sided deafness.

Ten cochlear implant (CI) users with single-sided deafness were asked to vary the parameters of an acoustic sound played to their contralateral ear to characterize the perception evoked by a pure tone played through the direct audio input of their CI. Two frequencies, centered on an apical and a medial electrode, were tested. In six subjects, the electrode positions were estimated on CT scans. The study was divided in 3 experiments in which the parameters of the acoustic sound varied. The listeners had to vary the frequency of a pure tone (Exp.1), the center frequency and the bandwidth of a filter applied to a harmonic complex sound (Exp.2), and the frequency of the components and the inharmonicity factor of a complex sound (Exp.3). Two testing sessions were performed at 3 and 12 months after activation. The mean results of Exp. 1 showed that the frequency of the matched tone was significantly lower for the apical than for the medial stimulus. In Exp.2, the mean center frequencies of the filters were also significantly lower for the apical than for the medial stimulus. As this parameter modifies the energy ratio between the high and low-frequency components, this result suggests that the medial stimulus was perceived with a brighter timbre than the apical stimulus. In Exp.3, the mean frequencies of the components were not significantly different between the sounds resulting from the stimulation of the two electrodes, but were significantly lower at the12-month session compared to the 3-month visit. These results suggest that a change in place of excitation may be perceived as a change in timbre rather than a change in pitch, and that an effect of adaptation can be observed.

The effect of a coding strategy that removes temporally masked pulses on speech perception by cochlear implant users.

Speech recognition in noisy environments remains a challenge for cochlear implant (CI) recipients. Unwanted charge interactions between current pulses, both within and between electrode channels, are likely to impair performance. Here we investigate the effect of reducing the number of current pulses on speech perception. This was achieved by implementing a psychoacoustic temporal-masking model where current pulses in each channel were passed through a temporal integrator to identify and remove pulses that were less likely to be perceived by the recipient. The decision criterion of the temporal integrator was varied to control the percentage of pulses removed in each condition. In experiment 1, speech in quiet was processed with a standard Continuous Interleaved Sampling (CIS) strategy and with 25, 50 and 75% of pulses removed. In experiment 2, performance was measured for speech in noise with the CIS reference and with 50 and 75% of pulses removed. Speech intelligibility in quiet revealed no significant difference between reference and test conditions. For speech in noise, results showed a significant improvement of 2.4 dB when removing 50% of pulses and performance was not significantly different between the reference and when 75% of pulses were removed. Further, by reducing the overall amount of current pulses by 25, 50, and 75% but accounting for the increase in charge necessary to compensate for the decrease in loudness, estimated average power savings of 21.15, 40.95, and 63.45%, respectively, could be possible for this set of listeners. In conclusion, removing temporally masked pulses may improve speech perception in noise and result in substantial power savings.

Ramped pulse shapes are more efficient for cochlear implant stimulation in an animal model.

In all commercial cochlear implant (CI) devices, the electric stimulation is performed with a rectangular pulse that generally has two phases of opposite polarity. To date, developing new stimulation strategies has relied on the efficacy of this shape. Here, we investigate the potential of a novel stimulation paradigm that uses biophysically-inspired electrical ramped pulses. Using electrically-evoked auditory brainstem response (eABR) recordings in mice, we found that less charge, but higher current level amplitude, is needed to evoke responses with ramped shapes that are similar in amplitude to responses obtained with rectangular shapes. The most charge-efficient pulse shape had a rising ramp over both phases, supporting findings from previous in vitro studies. This was also true for longer phase durations. Our study presents the first physiological data on CI-stimulation with ramped pulse shapes. By reducing charge consumption ramped pulses have the potential to produce more battery-efficient CIs and may open new perspectives for designing other efficient neural implants in the future.

Perception of Musical Tension in Cochlear Implant Listeners.

Despite the difficulties experienced by cochlear implant (CI) users in perceiving pitch and harmony, it is not uncommon to see CI users listening to music, or even playing an instrument. Listening to music is a complex process that relies not only on low-level percepts, such as pitch or timbre, but also on emotional reactions or the ability to perceive musical sequences as patterns of tension and release. CI users engaged in musical activities might experience some of these higher-level musical features. The goal of this study is to evaluate CI users' ability to perceive musical tension. Nine CI listeners (CIL) and nine normal-hearing listeners (NHL) were asked to rate musical tension on a continuous visual analog slider during music listening. The subjects listened to a 4 min recording of Mozart's Piano Sonata No. 4 (K282) performed by an experienced pianist. In addition to the original piece, four modified versions were also tested to identify which features might influence the responses to the music in the two groups. In each version, one musical feature of the piece was altered: tone pitch, intensity, rhythm, or tempo. Surprisingly, CIL and NHL rated overall musical tension in a very similar way in the original piece. However, the results from the different modifications revealed that while NHL ratings were strongly affected by music with random pitch tones (but preserved intensity and timing information), CIL ratings were not. Rating judgments of both groups were similarly affected by modifications of rhythm and tempo. Our study indicates that CI users can understand higher-level musical aspects as indexed by musical tension ratings. The results suggest that although most CI users have difficulties perceiving pitch, additional music cues, such as tempo and dynamics might contribute positively to their experience of music.

A modification of the scale illusion into a detection task for assessment of binaural streaming.

Binaural streaming by frequency-proximity was investigated without subjective listener-feedback by modifying the scale illusion of Deutsch [J. Acoust. Soc. Am. 57, 1156-1160 (1975)] into a detection-task. Nineteen listeners had to detect one deviation within a repeating melody stream, while simultaneously presented with a randomized distractor stream. Every second note in each stream was presented to the opposite ear, requiring binaural streaming to detect the deviant. Listeners performed well in this test but adding interaural delay or timbre-difference let the listeners group by lateralization instead. This confirms the grouping by frequency-proximity. The method could be used to investigate binaural streaming in hearing-impaired patients, where interaural percepts might differ.

Auditory Stream Segregation Can Be Modeled by Neural Competition in Cochlear Implant Listeners.

Auditory stream segregation is a perceptual process by which the human auditory system groups sounds from different sources into perceptually meaningful elements (e.g., a voice or a melody). The perceptual segregation of sounds is important, for example, for the understanding of speech in noisy scenarios, a particularly challenging task for listeners with a cochlear implant (CI). It has been suggested that some aspects of stream segregation may be explained by relatively basic neural mechanisms at a cortical level. During the past decades, a variety of models have been proposed to account for the data from stream segregation experiments in normal-hearing (NH) listeners. However, little attention has been given to corresponding findings in CI listeners. The present study investigated whether a neural model of sequential stream segregation, proposed to describe the behavioral effects observed in NH listeners, can account for behavioral data from CI listeners. The model operates on the stimulus features at the cortical level and includes a competition stage between the neuronal units encoding the different percepts. The competition arises from a combination of mutual inhibition, adaptation, and additive noise. The model was found to capture the main trends in the behavioral data from CI listeners, such as the larger probability of a segregated percept with increasing the feature difference between the sounds as well as the build-up effect. Importantly, this was achieved without any modification to the model's competition stage, suggesting that stream segregation could be mediated by a similar mechanism in both groups of listeners.