Combining Place and Rate of Stimulation Improves Frequency Discrimination in Cochlear Implant Users

How Switching Musical Instruments Affects Pitch Discrimination for Cochlear Implant Users

OBJECTIVES

Cochlear implant (CI) users struggle with music perception. Generally, they have poorer pitch discrimination and timbre identification than peers with normal hearing, which reduces their overall music appreciation and quality of life. This study's primary aim was to characterize how the increased difficulty of comparing pitch changes across musical instruments affects CI users and their peers with no known hearing loss. The motivation is to better understand the challenges that CI users face with polyphonic music listening. The primary hypothesis was that CI users would be more affected by instrument switching than those with no known hearing loss. The rationale was that poorer pitch and timbre perception through a CI hinders the disassociation between pitch and timbre changes needed for this demanding task.

DESIGN

Pitch discrimination was measured for piano and tenor saxophone including conditions with pitch comparisons across instruments. Adult participants included 15 CI users and 15 peers with no known hearing loss. Pitch discrimination was measured for 4 note ranges centered on A2 (110 Hz), A3 (220 Hz), A4 (440 Hz), and A5 (880 Hz). The effect of instrument switching was quantified as the change in discrimination thresholds with and without instrument switching. Analysis of variance and Spearman's rank correlation were used to test group differences and relational outcomes, respectively.

RESULTS

Although CI users had worse pitch discrimination, the additional difficulty of instrument switching did not significantly differ between groups. Discrimination thresholds in both groups were about two times worse with instrument switching than without. Further analyses, however, revealed that CI users were biased toward ranking tenor saxophone higher in pitch compared with piano, whereas those with no known hearing loss were not so biased. In addition, CI users were significantly more affected by instrument switching for the A5 note range.

CONCLUSIONS

The magnitude of the effect of instrument switching on pitch resolution was similar for CI users and their peers with no known hearing loss. However, CI users were biased toward ranking tenor saxophone as higher in pitch and were significantly more affected by instrument switching for pitches near A5. These findings might reflect poorer temporal coding of fundamental frequency by CIs.

Clinical challenges and opportunities related to the biological responses experienced by indwelling and implantable bioelectronic medical devices

Implantable electrodes have been utilized for decades to stimulate, sense, or monitor a broad range of biological processes, with examples ranging from glucose monitoring devices to cochlear implants. While the underlying science related to the application of electrodes is a mature field, preclinical and clinical studies have demonstrated that there are still significant challenges in vivo associated with a lack of control over tissue-material interfacial interactions, especially over longer time frames. Herein we discuss the current challenges and opportunities for implantable electrodes and the associated bioelectronic interfaces across the clinical landscape with a focus on emerging technologies and the obstacles of biofouling, microbial colonization, and the foreign body response. Overcoming these challenges is predicted to open the door for a new generation of implantable medical devices and significant associated clinical impact. STATEMENT OF SIGNIFICANCE: Implantable electrodes have been utilised for decades to stimulate, sense, or monitor a broad range of biological processes, with examples ranging from glucose monitoring devices to cochlear implants. Next-generation bioelectronic implantable medical devices promise an explosion of new applications that have until this point in time been impossible to achieve. However, there are several persistent biological challenges hindering the realisation of these new applications. We present a clinical perspective on how these biological challenges have shaped the device market and clinical trial landscape. Specifically, we present statistical breakdowns of current device applications and discuss biofouling, the foreign body response, and microbial colonisation as the main factors that need to be addressed before a new generation of devices can be explored.

Limitations on Temporal Processing by Cochlear Implant Users: A Compilation of Viewpoints

Cochlear implant (CI) users are usually poor at using timing information to detect changes in either pitch or sound location. This deficit occurs even for listeners with good speech perception and even when the speech processor is bypassed to present simple, idealized stimuli to one or more electrodes. The present article presents seven expert opinion pieces on the likely neural bases for these limitations, the extent to which they are modifiable by sensory experience and training, and the most promising ways to overcome them in future. The article combines insights from physiology and psychophysics in cochlear-implanted humans and animals, highlights areas of agreement and controversy, and proposes new experiments that could resolve areas of disagreement.

Tonotopic and Default Frequency Fitting for Music Perception in Cochlear Implant Recipients: A Randomized Clinical Trial

Importance

Cochlear implants are an effective technique for enhancing speech perception abilities in quiet environments for people with severe to profound deafness. Nevertheless, complex sound signals perception, such as music perception, remains challenging for cochlear implant users.

Objective

To assess the benefit of a tonotopic map on music perception in new cochlear implant users.

Design, Setting, and Participants

A prospective, randomized, double-blind, 2-period crossover study including 26 new cochlear implant users was performed over a 6-month period (June 2021 to November 2021). An anatomical tonotopic map was created using postoperative flat-panel computed tomography and a reconstruction software based on Greenwood function. New cochlear implant users older than 18 years with bilateral severe to profound sensorineural hearing loss or complete hearing loss for less than 5 years were selected in the University Hospital Centre of Rennes in France. The trial was conducted from June to November 2021 (inclusion) and to February 2022 (end of the assessment procedure at 12 weeks postactivation), and the analysis itself was completed in December 2022.

Intervention

Each participant was randomized to receive a conventional map followed by a tonotopic map or vice versa.

Main Outcomes and Measures

Participants performed pitch-scaling tasks (multidimensional qualitative assessment, melodic contour identification, melodic recognition test) after 6 weeks of each setting.

Results

Thirteen participants were randomized to each sequence. Two of the 26 participants recruited (1 in each sequence) had to be excluded due to the COVID-19 pandemic. The multidimensional qualitative assessment (Gabrielsson test), melodic contour identification, and melodic recognition scores were significantly higher with the tonotopic setting than the conventional one (mean effect [ME], 7.8; 95% CI, 5.0-10.5; ME, 12.1%; 95% CI, 5.7%-18.4%; ME, 14.4%, 95% CI, 8.5%-20.2%; and ME, 2.1, 95% CI, 1.7-2.5, respectively). Among the different dimensions evaluated by the Gabrielsson test, the mean scores for clarity, spaciousness, fullness, nearness, and total impression were significantly higher with tonotopic fitting. Ninety-two percent of the participants kept the tonotopy-based map after the study period.

Conclusions

In this randomized clinical trial of patients with new cochlear implants, a tonotopic-based fitting was associated with better results in perception of complex sound signals such as music listening experience.

Trial Registration

ClinicalTrials.gov Identifier: NCT04922619.

Temporal pitch matching with bilateral cochlear implants

Interaural pitch matching is a common task used with bilateral cochlear implant (CI) users, although studies measuring this have largely focused on place-based pitch matches. Temporal-based pitch also plays an important role in CI users' perception, but interaural temporal-based pitch matching has not been well characterized for CI users. To investigate this, bilateral CI users were asked to match amplitude modulation frequencies of stimulation across ears. Comparisons were made to previous place-based pitch matching data that were collected using similar procedures. The results indicate that temporal-based pitch matching is particularly sensitive to the choice of reference ear.

Estimating Pitch Information From Simulated Cochlear Implant Signals With Deep Neural Networks

Cochlear implant (CI) users, even with substantial speech comprehension, generally have poor sensitivity to pitch information (or fundamental frequency, F0). This insensitivity is often attributed to limited spectral and temporal resolution in the CI signals. However, the pitch sensitivity markedly varies among individuals, and some users exhibit fairly good sensitivity. This indicates that the CI signal contains sufficient information about F0, and users' sensitivity is predominantly limited by other physiological conditions such as neuroplasticity or neural health. We estimated the upper limit of F0 information that a CI signal can convey by decoding F0 from simulated CI signals (multi-channel pulsatile signals) with a deep neural network model (referred to as the CI model). We varied the number of electrode channels and the pulse rate, which should respectively affect spectral and temporal resolutions of stimulus representations. The F0-estimation performance generally improved with increasing number of channels and pulse rate. For the sounds presented under quiet conditions, the model performance was at best comparable to that of a control waveform model, which received raw-waveform inputs. Under conditions in which background noise was imposed, the performance of the CI model generally degraded by a greater degree than that of the waveform model. The pulse rate had a particularly large effect on predicted performance. These observations indicate that the CI signal contains some information for predicting F0, which is particularly sufficient for targets under quiet conditions. The temporal resolution (represented as pulse rate) plays a critical role in pitch representation under noisy conditions.

The Relationship of Pitch Discrimination with Segregation of Tonal and Speech Streams for Cochlear Implant Users

Cochlear implant (CI) users often complain about music appreciation and speech recognition in background noise, which depend on segregating sound sources into perceptual streams. The present study examined relationships between frequency and fundamental frequency (F0) discrimination with stream segregation of tonal and speech streams for CI users and peers with no known hearing loss. Frequency and F0 discrimination were measured for 1,000 Hz pure tones and 110 Hz complex tones, respectively. Stream segregation was measured for pure and complex tones using a lead/lag delay detection task. Spondee word identification was measured in competing speech with high levels of informational masking that required listeners to use F0 to segregate speech. The hypotheses were that frequency and F0 discrimination would explain a significant portion of the variance in outcomes for tonal segregation and speech reception. On average, CI users received a large benefit for stream segregation of tonal streams when either the frequency or F0 of the competing stream was shifted relative to the target stream. A linear relationship accounted for 42% of the covariance between measures of stream segregation and complex tone discrimination for CI users. In contrast, such benefits were absent when the F0 of the competing speech was shifted relative to the target speech. The large benefit observed for tonal streams is promising for music listening if it transfers to separating instruments within a song; however, the lack of benefit for speech suggests separate mechanisms, or special requirements, for speech processing.