Continuous Interleaved Sampling Research Articles

Effects of Number of Filters and Frequency Cutoff in Continuous Interleaved Sampling and Frequency Amplitude Modulation Encoding Schemes in Cochlear Implant

Cochlear implants are devices designed to transform sound into electrical signals perceived by the brain, making them vital prostheses for deaf individuals. This study examines two schemes used in cochlear implants, namely Continuous Interleaved Sampling (CIS) and Frequency Amplitude Modulation Encoding (FAME), to compare their performance while varying the number of bandpass filters and cutoff frequencies used. Both schemes were simulated using 8 and 5 bandpass filters, and cutoff frequencies of 2000 Hz and 200 Hz. Results show that the CIS scheme can maintain signal intelligibility despite the loss of some frequency components when the number of bandpass filters is lowered. Conversely, FAME retains more frequency details but presents perceptible delays. With a cut off frequency of 200 Hz, signals processed with CIS loses intelligibility significantly, whereas FAME-processed signals remain intelligible both at 200 Hz and 2000 Hz cut off frequencies. It is therefore concluded that FAME can provide better cochlear implant performance despite the lower number of bandpass filters and lower frequency cutoff.

Effect of interaural electrode insertion depth difference and independent band selection on sentence recognition in noise and spatial release from masking in simulated bilateral cochlear implant listening

PurposeInter-aural insertion depth difference (IEDD) in bilateral cochlear implant (BiCI) with continuous interleaved sampling (CIS) processing is known to reduce the recognition of speech in noise and spatial release from masking (SRM). However, the independent channel selection in the ‘n-of-m’ sound coding strategy might have a different effect on speech recognition and SRM when compared to the effects of IEDD in CIS-based findings. This study aimed to investigate the effect of bilateral ‘n-of-m’ processing strategy and interaural electrode insertion depth difference on speech recognition in noise and SRM under conditions that simulated bilateral cochlear implant listening.MethodsFive young adults with normal hearing sensitivity participated in the study. The target sentences were spatially filtered to originate from 0° and the masker was spatially filtered at 0°, 15°, 37.5°, and 90° using the Oldenburg head-related transfer function database for behind the ear microphone. A 22-channel sine wave vocoder processing based on ‘n-of-m’ processing was applied to the spatialized target-masker mixture, in each ear. The perceptual experiment involved a test of speech recognition in noise under one co-located condition (target and masker at 0°) and three spatially separated conditions (target at 0°, masker at 15°, 37.5°, or 90° to the right ear).ResultsThe results were analyzed using a three-way repeated measure analysis of variance (ANOVA). The effect of interaural insertion depth difference (F (2,8) = 3.145, p = 0.098, ɳ2 = 0.007) and spatial separation between target and masker (F (3,12) = 1.239, p = 0.339, ɳ2 = 0.004) on speech recognition in noise was not significant.ConclusionsSpeech recognition in noise and SRM were not affected by IEDD ≤ 3 mm. Bilateral ‘n-of-m’ processing resulted in reduced speech recognition in noise and SRM.

The 100 Most-Cited Manuscripts in Hearing Implants: A Bibliometrics Analysis.

The aim of the study was to characterise the most frequently cited articles on the topic of hearing implants.A systematic search was carried out using the Thomson Reuters Web of Science Core Collection database. Eligibility criteria restricted the results to primary studies and reviews published from 1970 to 2022 in English dealing primarily with hearing implants. Data including the authors, year of publication, journal, country of origin, number of citations and average number of citations per year were extracted, as well as the impact factors and five-year impact factor of journals publishing the articles. The top 100 papers were published across 23 journals and were cited 23,139 times. The most-cited and influential articledescribes the first use of the continuous interleaved sampling (CIS)strategy utilised in all modern cochlear implants.More than half of the studies on the list were produced by authors from the United States, and the Ear and Hearing journal had both the greatest number of articlesand the greatest number of total citations. To conclude, this research serves as a guide to the most influential articles on the topic of hearing implants, although bibliometric analyses mainly focus on citations. The most-cited article was an influential description of CIS.

Music appreciation on cochlear implant simulation with contour and temporal cues

The musical appreciation of the cochlear implant simulation user on the contour and temporal cues and the effect of the coding strategy are determined. Cochlear implant simulations were processed using continuous interleaved sampling (CIS) and spectral peak (SPEAK) coding strategies with varying numbers of channels. The experiments consist of contour identification, temporal cue discrimination, and familiar melody identification. The results show cochlear implant simulation users are poor at recognizing contour cues compared with normal hearing, but good at discriminating temporal cues from tempo and rhythm varied with contour, achieving scores close to normal hearing. A poor score was observed in familiar melody identification with pitch contour, compared to normal hearing scores, which correlated (r = 0.99) with the recognition of contour cues. Temporal cue information from rhythm helped cochlear implant simulation users recognize familiar melodies with an almost 40% increase in score compared to melodies without rhythm (p 0.05). Music appreciation was poor on the variation of coding strategy with the number of channels 2 to 6 CIS and good on the SPEAK coding strategy (compared with 22 channels condition). The studies emphasize the need for advances in coding strategies to deliver pitch contour cues to cochlear implant processing.

Effect of electric-acoustic cochlear implant stimulation and coding strategies on spatial cues of speech signals in reverberant room

The comparison of spatial cues changes in different setups and coding strategies used in cochlear implants (CI) is investigated. In this experiment, we implement three voice coder setups, such as bilateral CI, bimodal CI, and electro-acoustic stimulation (EAS). Two well-known coding strategies are used, which are continuous interleaved sampling (CIS) and spectral peak (SPEAK). Speech signals are convoluted with appropriate binaural room impulse response (BRIR), creating reverberant spatial stimuli. Five different reverberant conditions (including anechoic) were applied to the stimuli. Interaural level and time differences (ILD and ITD) are evaluated objectively and subjectively, and their relationship with the intelligibility of speech is observed. Prior objective evaluation with CIS reveals that clarity (C50) becomes a more important factor in spatial cue change than reverberation time. Vocoded conditions (bilateral CI) show an increment in ILD value (compression has not been implemented yet on the vocoder processing), when the value of ITD gets more different (decreased) from the middle point. Reverberation degrades the intelligibility rate at various rates depending on the C50 value, both in unvocoded and vocoded conditions. In the vocoded condition, decrement on spatial cues was also followed by the decreement on the intelligibility of spatial stimuli.

Speech recognition as a function of the number of channels for pediatric cochlear implant recipients.

This study investigated the number of channels required for asymptotic speech recognition for ten pediatric cochlear implant (CI) recipients with precurved electrode arrays. Programs with 4-22 active electrodes were used to assess word and sentence recognition in noise. Children demonstrated significant performance gains up to 12 electrodes for continuous interleaved sampling (CIS) and up to 22 channels with 16 maxima. These data are consistent with the latest adult CI studies demonstrating that modern CI recipients have access to more than 8 independent channels and that both adults and children exhibit performance gains up to 22 channels.

Speech recognition as a function of the number of channels for Mid-Scala electrode array recipients.

This study investigated the number of channels needed for maximum speech understanding and sound quality in 15 adult cochlear implant (CI) recipients with Advanced Bionics (AB) Mid-Scala electrode arrays completely within scala tympani. In experiment I, CI programs used a continuous interleaved sampling (CIS)-based strategy and 4-16 active electrodes. In experiment II, CI programs used an n-of-m strategy featuring 16 active electrodes with either 8- or 12-maxima. Speech understanding and sound quality measures were assessed. For CIS programs, participants demonstrated performance gains using up to 4-10 electrodes on speech measures and sound quality ratings. For n-of-m programs, there was no significant effect of maxima, suggesting 8-maxima is sufficient for this sample's maximum performance and sound quality. These results are largely consistent with previous studies using straight electrode arrays [e.g., Fishman, Shannon, and Slattery (1997). J. Speech Lang. Hear. Res. 40, 1201-1215; Friesen, Shannon, Baskent, and Wang (2001). J. Acoust. Soc. Am. 110, 1150-1163; Shannon, Cruz, and Galvin (2011). Audiol. Neurotol. 16, 113-123; Berg, Noble, Dawant, Dwyer, Labadie, and Gifford (2020). J. Acoust. Soc. Am. 147, 3646-3656] and in contrast with recent studies looking at cochlear precurved electrode arrays [e.g., Croghan, Duran, and Smith (2017). J. Acoust. Soc. Am. 142, EL537-EL543; Berg, Noble, Dawant, Dwuer, Labadie, and Gifford (2019b). J. Acoust. Soc. Am. 145, 1556-1564], which found continuous improvements up to 16 independent channels. These findings suggest that Mid-Scala electrode array recipients demonstrate similar channel independence to straight electrode arrays rather than other manufacturer's precurved electrode arrays.

Computational Modeling of Synchrony in the Auditory Nerve in Response to Acoustic and Electric Stimulation.

Cochlear implants are medical devices that provide hearing to nearly one million people around the world. Outcomes are impressive with most recipients learning to understand speech through this new way of hearing. Music perception and speech reception in noise, however, are notably poor. These aspects of hearing critically depend on sensitivity to pitch, whether the musical pitch of an instrument or the vocal pitch of speech. The present article examines cues for pitch perception in the auditory nerve based on computational models. Modeled neural synchrony for pure and complex tones is examined for three different electric stimulation strategies including Continuous Interleaved Sampling (CIS), High-Fidelity CIS (HDCIS), and Peak-Derived Timing (PDT). Computational modeling of current spread and neuronal response are used to predict neural activity to electric and acoustic stimulation. It is shown that CIS does not provide neural synchrony to the frequency of pure tones nor to the fundamental component of complex tones. The newer HDCIS and PDT strategies restore synchrony to both the frequency of pure tones and to the fundamental component of complex tones. Current spread reduces spatial specificity of excitation as well as the temporal fidelity of neural synchrony, but modeled neural excitation restores precision of these cues. Overall, modeled neural excitation to electric stimulation that incorporates temporal fine structure (e.g., HDCIS and PDT) indicates neural synchrony comparable to that provided by acoustic stimulation. Discussion considers the importance of stimulation rate and long-term rehabilitation to provide temporal cues for pitch perception.

Signal processing & audio processors

Signal processing algorithms are the hidden components in the audio processor that converts the received acoustic signal into electrical impulses while maintaining as much relevant information as possible. Signal processing algorithms should be smart enough to mimic the functionality of external, middle and the inner-ear to provide the cochlear implant (CI) user with a hearing experience as natural as possible. Modern sound processing strategies are based on the continuous interleaved sampling (CIS) strategy proposed by B. Wilson in 1991, which provided envelope information over several intracochlear electrodes. The CIS strategy brought significant gains in speech perception. Translational research activities of MED-EL resulted in further improvements in speech understanding in noisy environments as well as enjoyment of music by not only coding CIS-based envelope information, but by also representing temporal fine structure information in the stimulation patterns of the apical channels. Further developments include “complete cochlear coverage” made possible by deep insertion of the intracochlear electrode, elaborate front end processing, anatomy based fitting (ABF), triphasic pulse stimulation instrumental in the suppression of facial nerve stimulation, and bimodal delay compensation allowing unilateral CI users to experience hearing with hearing aids on the contralateral ear. The large number of hardware developments might be exemplified by the RONDO, the world's first single unit audio processor in 2013. This article covers the milestones of translational research around the signal processing and audio processor topic that took place in association with MED-EL.

Single Supply PWM Fully Implantable Cochlear Implant Interface Circuit With Active Charge Balancing

Low powered fully implantable cochlear implants (FICIs) untangle the aesthetic concerns and battery replacement problems of conventional cochlear implants. However, the reported FICIs lack proper charge balancing and require multiple external supplies to operate. In this work, a complete low power FICI interface circuit is designed that operates with a single supply and uses short-pulse-injection method for charge balancing. The system takes input from multi-channel piezoelectric transducers and stimulates the auditory neurons with pulse width modulated (PWM) output currents. By utilizing pulse width modulation technique with continuous interleaved sampling (CIS) sound processing strategy, a time gap is formed between two consecutive channels. Then, this gap is used for charge balancing operation. Overall power consumption of the low power FICI interface is decreased by clocked gated subthreshold amplifier and rectifier design. Furthermore, power efficient design of analog to digital converter (ADC) enhances the power reduction. The system is tested with an in-vitro test setup and it stimulates a single channel cochlear electrode with 50 dB input dynamic range while consuming $695~\mu \text{W}$ power from a single 1.8 V supply. The implemented FICI system can safely stimulate neurons for more than 18 days (with 16-hour daily operation) with an implantable 200 mWh battery without recharging. Furthermore, the short charge balance current pulses keep the electrode voltage difference after the stimulation within ±100 mV range, which ensures the residual charge is not hazardous for the auditory neurons.

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.

Simulated output of Continuous Interleaved Sampling and Frequency Amplitude Modulation Encoding techniques used in Cochlear Implant

Cochlear Implant (CI) is an excellent electronic device to overcome congenital or profound hearing loss in humans. It provides an alternative to the natural hearing for the hearing-impaired humans in the form of artificial electrical hearing. Several coding techniques such as Continuous interleaved sampling (CIS) and Frequency amplitude modulation encoding (FAME) is used in CI for the conversion of analog signal to the digital one. This study is intended to assess the performance level of these two techniques in music, vowels, words perception with different channels to assess the quality of hearing in hearing impaired person.

Simulated output of Continuous Interleaved Sampling and Frequency Amplitude Modulation Encoding techniques used in Cochlear Implant

Cochlear Implant (CI) is an excellent electronic device to overcome congenital or profound hearing loss in humans. It provides an alternative to the natural hearing for the hearing-impaired humans in the form of artificial electrical hearing. Several coding techniques such as Continuous interleaved sampling (CIS) and Frequency amplitude modulation encoding (FAME) is used in CI for the conversion of analog signal to the digital one. This study is intended to assess the performance level of these two techniques in music, vowels, words perception with different channels to assess the quality of hearing in hearing impaired person.

Simulated output of Continuous Interleaved Sampling and Frequency Amplitude Modulation Encoding Techniques used in Cochlear Implant

Cochlear Implant (CI) is an excellent electronic device to overcome congenital or profound hearing loss in humans. It provides an alternative to the natural hearing for the hearing-impaired humans in the form of artificial electrical hearing. Several coding techniques such as Continuous interleaved sampling (CIS) and Frequency amplitude modulation encoding (FAME) is used in CI for the conversion of analog signal to the digital one. This study is intended to assess the performance level of these two techniques in music, vowels, words perception with different channels to assess the quality of hearing in hearing impaired person.

Mandarin tone recognition in English speakers with normal hearing and with cochlear implants

Objective: Mandarin-speaking cochlear implant users have difficulty perceiving tonal changes in speech with current signal processing strategies. The purpose of this study was to evaluate whether English-speaking cochlear implant and normal hearing listeners can be trained to recognise closed-set Mandarin tones. The validity of using native-English speakers to evaluate Mandarin tone perception in cochlear implants was tested.Design: Two groups of native-English speaking participants were evaluated. All listeners were given training rounds and evaluation rounds in which their tonal identification was tested. The normal-hearing group was also tested with acoustic simulations of the traditional Continuous Interleaved Sampling (CIS) strategy.Study sample: Ten normal-hearing English speakers and seven cochlear implant listeners participated.Results: The normal-hearing group correctly identified unprocessed tones at 87% and CIS-processed tones at 58% on average. The cochlear implant listeners achieved 56% correct identification on average.Conclusions: This level of performance for native English speaking CI users was comparable to previous studies using native Mandarin-speaking CI listeners, which showed a mean of 59% in 19 CI users.

Nonhuman primate vestibuloocular reflex responses to prosthetic vestibular stimulation are robust to pulse timing errors caused by temporal discretization.

Electrical stimulation of vestibular afferent neurons to partially restore semicircular canal sensation of head rotation and the stabilizing reflexes that sensation supports has potential to effectively treat individuals disabled by bilateral vestibular hypofunction. Ideally, a vestibular implant system using this approach would be integrated with a cochlear implant, which would provide clinicians with a means to simultaneously treat loss of both vestibular and auditory sensation. Despite obvious similarities, merging these technologies poses several challenges, including stimulus pulse timing errors that arise when a system must implement a pulse frequency modulation-encoding scheme (as is used in vestibular implants to mimic normal vestibular nerve encoding of head movement) within fixed-rate continuous interleaved sampling (CIS) strategies used in cochlear implants. Pulse timing errors caused by temporal discretization inherent to CIS create stair step discontinuities of the vestibular implant's smooth mapping of head velocity to stimulus pulse frequency. In this study, we assayed electrically evoked vestibuloocular reflex responses in two rhesus macaques using both a smooth pulse frequency modulation map and a discretized map corrupted by temporal errors typical of those arising in a combined cochlear-vestibular implant. Responses were measured using three-dimensional scleral coil oculography for prosthetic electrical stimuli representing sinusoidal head velocity waveforms that varied over 50-400°/s and 0.1-5 Hz. Pulse timing errors produced negligible effects on responses across all canals in both animals, indicating that temporal discretization inherent to implementing a pulse frequency modulation-coding scheme within a cochlear implant's CIS fixed pulse timing framework need not sacrifice performance of the combined system's vestibular implant portion. NEW & NOTEWORTHY Merging a vestibular implant system with existing cochlear implant technology can provide clinicians with a means to restore both vestibular and auditory sensation. Pulse timing errors inherent to integration of pulse frequency modulation vestibular stimulation with fixed-rate, continuous interleaved sampling cochlear implant stimulation would discretize the smooth head velocity encoding of a combined device. In this study, we show these pulse timing errors produce negligible effects on electrically evoked vestibulo-ocular reflex responses in two rhesus macaques.

Speech recognition as a function of the number of channels in perimodiolar electrode recipients

This study investigated the number of channels needed for maximum speech understanding and sound quality in 30 adult cochlear implant (CI) recipients with perimodiolar electrode arrays verified via imaging to be completely within scala tympani (ST). Performance was assessed using a continuous interleaved sampling (CIS) strategy with 4, 8, 10, and 16 channels and n-of-m with 16 maxima. Listeners were administered auditory tasks of speech understanding [monosyllables, sentences (quiet and +5 dB signal-to-noise ratio, SNR), vowels, consonants], spectral modulation detection, as well as subjective estimates of sound quality. Results were as follows: (1) significant performance gains were observed for speech in quiet (monosyllables and sentences) with 16- as compared to 8-channel CIS, (2) 16 channels in a 16-of-m strategy yielded significantly higher outcomes than 16-channel CIS for sentences in noise (percent correct and subjective sound quality) and spectral modulation detection, (3) 16 channels in a 16-of-m strategy yielded significantly higher outcomes as compared to 8- and 10-channel CIS for monosyllables, sentences (quiet and noise), consonants, spectral modulation detection, and subjective sound quality, (4) 16 versus 8 maxima yielded significantly higher speech recognition for monosyllables and sentences in noise using an n-of-m strategy, and (5) the degree of benefit afforded by 16 versus 8 maxima was inversely correlated with mean electrode-to-modiolus distance. These data demonstrate greater channel independence with perimodiolar electrode arrays as compared to previous studies with straight electrodes and warrant further investigation of the minimum number of maxima and number of channels needed for maximum auditory outcomes.

A Sub-500 $\mu$ W Interface Electronics for Bionic Ears

This paper presents an ultra-low power current-mode circuit for a bionic ear interface. Piezoelectric (PZT) sensors at the system input transduce sound vibrations into multi-channel electrical signals, which are then processed by the proposed circuit to stimulate the auditory nerves consistently with the input amplitude level. The sensor outputs are first amplified and range-compressed through ultra-low power logarithmic amplifiers (LAs) into AC current waveforms, which are then rectified through custom current-mode circuits. The envelopes of the rectified signals are extracted, and are selectively sampled as reference for the stimulation current generator, armed with a 7-bit user-programmed DAC to enable patient fitting (calibration). Adjusted biphasic stimulation current is delivered to the nerves according to continuous inter-leaved sampling (CIS) stimulation strategy through a switch matrix. Each current pulse is optimized to have an exponentially decaying shape, which leads to reduced supply voltage, and hence ~20% lower stimulator power dissipation. The circuit has been designed and fabricated in 180nm high-voltage CMOS technology with up to 60 dB measured input dynamic range, and up to 1 mA average stimulation current. The 8-channel interface has been validated to be fully functional with 472μW power dissipation, which is the lowest value in the literature to date, when stimulated by a mimicked speech signal.

Low variable rate stimulation strategy for cochlear implants using temporal cues and electrophysiological factors.

The performance of a cochlear implant (CI), especially in conveying pitch depends on its electrical stimulation strategy. The present study proposes a variable-rate stimulation algorithm which improves speech emotion perception by using temporal fine-structure cues and electrophysiological parameters of the patient. This method is based on the coding of the phase information at the peak time intervals of the band-passed signals. The stimulation pulse is generated at the time of peak occurrence, which is able to excite the number of fibers with a discharge probability above a threshold. Calculating the discharge probability is based on the excitable fiber model and taking into account the biological characteristics of the patient, such as the fiber threshold and the distribution of remaining intact fibers. The results of the emotion detection test on selective reconstructed sentences from the Persian emotional speech database (Persian ESD) indicated that the listeners have been able to detect the emotion by an average of 83.82% using the proposed stimulation algorithm while it was 75% and 48.03% for the zero-crossing and the continuous interleaved sampling (CIS), respectively. Furthermore, the number of pulses compared to the zero-crossing and the CIS has decreased by 76.3% and 75.4%, respectively. In this paper, a stimulation method was proposed for cochlear implants by considering the patient's biological parameters. It has been successful in transmitting speech emotion despite the reduction of stimulating pulses. This has some advantages such as reducing the interaction of current fields between electrodes during stimulation and reducing battery usage.

Improved Speech Perception in Cochlear Implant Users With Interleaved High-Rate Pulse Trains.

Electrical stimulation with a cochlear implant (CI) elicits abnormally high neural synchrony, which poses significant challenges for speech perception. Previous investigations showed that constant-amplitude high-rate pulse trains (HRPs) desynchronize neural responses and improve stimulus encoding. The study objective was to investigate the effects of HRP on speech perception in adult CI users. Prospective, within-subject design. Tertiary CI center. Ten adult CI recipients. Sentence stimuli were created by modifying a basic continuous interleaved sampling (CIS) strategy (1,000 pulses per second; pps) with interleaved biphasic pulse trains (3,000 pps) on even electrodes. Institute of Electrical and Electronics Engineers sentences in quiet and in noise were tested without HRP, and with HRPs of various stimulation levels. Sentence perception in percent correct was calculated for all conditions. The highest speech perception score with HRP stimulation was defined as "max-HRP." Group analyses showed significantly improved sentence perception in background noise with HRPs (p < 0.001). There was no significant difference for sentence perception in quiet for the group. However, seven of 10 subjects experienced some benefit from HRP stimuli in quiet and the degree of HRP benefit showed significant relationships with baseline performance and age at implantation, indicating that HRP stimuli may be most beneficial for older patients or poorer performers. Significant improvement in speech perception in noise was observed with HRP stimuli. Some recipients may also benefit from HRP stimulation in quiet. Interleaved HRPs hold promise as a novel stimulation paradigm with clinical sound processing strategies to improve patient performance.