The addition of a spatial auditory cue improves spatial updating in a virtual reality navigation task.

Auditory cues are integrated with vision and body-based self-motion cues for motion perception, balance, and gait, though limited research has evaluated their effectiveness for navigation. Here, we tested whether an auditory cue co-localized with a visual target could improve spatial updating in a virtual reality homing task. Participants navigated a triangular homing task with and without an easily localizable spatial audio signal co-located with the home location. The main outcome was unsigned angular error, defined as the absolute value of the difference between the participant's turning response and the correct response towards the home location. Angular error was significantly reduced in the presence of spatial sound compared to a head-fixed identical auditory signal. Participants' angular error was 22.79° in the presence of spatial audio and 30.09° in its absence. Those with the worst performance in the absence of spatial sound demonstrated the greatest improvement with the added sound cue. These results suggest that auditory cues may benefit navigation, particularly for those who demonstrated the highest level of spatial updating error in the absence of spatial sound.

Effects of older age on visual and self-motion sensory cue integration in navigation.

Older adults demonstrate impairments in navigation that cannot be explained by general cognitive and motor declines. Previous work has shown that older adults may combine sensory cues during navigation differently than younger adults, though this work has largely been done in dark environments where sensory integration may differ from full-cue environments. Here, we test whether aging adults optimally combine cues from two sensory systems critical for navigation: vision (landmarks) and body-based self-motion cues. Participants completed a homing (triangle completion) task using immersive virtual reality to offer the ability to navigate in a well-lit environment including visibility of the ground plane. An optimal model, based on principles of maximum-likelihood estimation, predicts that precision in homing should increase with multisensory information in a manner consistent with each individual sensory cue's perceived reliability (measured by variability). We found that well-aging adults (with normal or corrected-to-normal sensory acuity and active lifestyles) were more variable and less accurate than younger adults during navigation. Both older and younger adults relied more on their visual systems than a maximum likelihood estimation model would suggest. Overall, younger adults' visual weighting matched the model's predictions whereas older adults showed sub-optimal sensory weighting. In addition, high inter-individual differences were seen in both younger and older adults. These results suggest that older adults do not optimally weight each sensory system when combined during navigation, and that older adults may benefit from interventions that help them recalibrate the combination of visual and self-motion cues for navigation.

Subcostal versus right lateral ultrasound measurements of inferior vena cava: Measurements obtained from these two views are not equivalent in non-ICU patients.

Objective: The objective of this study is to assess concordance between the subcostal and right lateral view for ultrasonographic inferior vena cava measurements including the end-inspiratory diameter, end-expiratory diameter and respiratory variation represented by the caval index in spontaneously breathing healthy adults. Methods: We recruited a convenience sample of 33 healthy adults. A phased array ultrasound probe was used to obtain inferior vena cava measurements from a subcostal view in the sagittal plane and from a right lateral view in the coronal plane with B-mode ultrasound. End-inspiratory diameter, end-expiratory diameter and caval index were obtained for each view. A two-tailed t-test was performed to compare the caval indices obtained by the two views. Bland-Altman analysis was used to obtain the limits of agreement for the inferior vena cava diameter and caval index across the two views. Results: Subcostal and right lateral caval indices across all participants were significantly different according to a paired t-test (p < 0.0001). The Bland-Altman analysis showed wide limits of agreement in end-inspiratory diameter (-0.97 and 0.50 cm) and in end-expiratory diameter (-0.94 and 0.90 cm). The right lateral view underestimated the inferior vena cava caval index relative to the subcostal view. Conclusions: The subcostal and right lateral views are not equivalent in obtaining inferior vena cava measurements in spontaneously breathing healthy adults. Current cut-off values for measurement-based applications of inferior vena cava ultrasound, including fluid responsiveness using caval indices, may not be accurate when values are obtained from the right lateral view in the coronal plane of the inferior vena cava in patients.

Reliability of Vestibular Perceptual Threshold Testing About the Yaw Axis.

OBJECTIVES: Vestibular reflexes have traditionally formed the cornerstone of vestibular evaluation, but perceptual tests have recently gained attention for use in research studies and potential clinical applications. However, the unknown reliability of perceptual thresholds limits their current importance. This is addressed here by establishing the test-retest reliability of vestibular perceptual testing. DESIGN: Perceptual detection thresholds to earth-vertical, yaw-axis rotations were collected in 15 young healthy people. Participants were tested at two time intervals (baseline, 5 to 14 days later) using an adaptive psychophysical procedure. RESULTS: Thresholds to 1 Hz rotations ranged from 0.69 to 2.99°/s (mean: 1.49°/s; SD: 0.63). They demonstrated an excellent intraclass correlation (0.92; 95% confidence interval: 0.77 to 0.97) with a minimum detectable difference of 0.45°/s. CONCLUSIONS: The excellent test-retest reliability of perceptual vestibular testing supports its use as a research tool and motivates further exploration for its use as a novel clinical technique.

Frequency-dependent integration of auditory and vestibular cues for self-motion perception.

Recent evidence has shown that auditory information may be used to improve postural stability, spatial orientation, navigation, and gait, suggesting an auditory component of self-motion perception. To determine how auditory and other sensory cues integrate for self-motion perception, we measured motion perception during yaw rotations of the body and the auditory environment. Psychophysical thresholds in humans were measured over a range of frequencies (0.1-1.0 Hz) during self-rotation without spatial auditory stimuli, rotation of a sound source around a stationary listener, and self-rotation in the presence of an earth-fixed sound source. Unisensory perceptual thresholds and the combined multisensory thresholds were found to be frequency dependent. Auditory thresholds were better at lower frequencies, and vestibular thresholds were better at higher frequencies. Expressed in terms of peak angular velocity, multisensory vestibular and auditory thresholds ranged from 0.39°/s at 0.1 Hz to 0.95°/s at 1.0 Hz and were significantly better over low frequencies than either the auditory-only (0.54°/s to 2.42°/s at 0.1 and 1.0 Hz, respectively) or vestibular-only (2.00°/s to 0.75°/s at 0.1 and 1.0 Hz, respectively) unisensory conditions. Monaurally presented auditory cues were less effective than binaural cues in lowering multisensory thresholds. Frequency-independent thresholds were derived, assuming that vestibular thresholds depended on a weighted combination of velocity and acceleration cues, whereas auditory thresholds depended on displacement and velocity cues. These results elucidate fundamental mechanisms for the contribution of audition to balance and help explain previous findings, indicating its significance in tasks requiring self-orientation.NEW & NOTEWORTHY Auditory information can be integrated with visual, proprioceptive, and vestibular signals to improve balance, orientation, and gait, but this process is poorly understood. Here, we show that auditory cues significantly improve sensitivity to self-motion perception below 0.5 Hz, whereas vestibular cues contribute more at higher frequencies. Motion thresholds are determined by a weighted combination of displacement, velocity, and acceleration information. These findings may help understand and treat imbalance, particularly in people with sensory deficits.

Geographic Disparities in US Veterans' Access to Cochlear Implant Care Within the Veterans Health Administration System.

IMPORTANCE: Veterans are at high risk for developing sensorineural hearing loss leading to cochlear implant (CI) candidacy; however, the ability to care for these patients is limited by the number and location of Veterans Health Administration (VHA) facilities that provide specialized CI services. OBJECTIVE: To investigate geographic disparities in access to CI care within the VHA system for US veterans. DESIGN, SETTING, AND PARTICIPANTS: An analysis of census tract-level data including US veterans was conducted using the nationwide American Community Survey data collected by the US Census Bureau from January to December 2016, which were accessed in 2017. MAIN OUTCOMES AND MEASURES: Maps showing the geographic variability in need for specialized CI services, estimated as a function of the number of veterans and the distance to the nearest established VHA-based CI surgical or audiologic facilities. RESULTS: A total of 19.9 million veterans within the continental United States resided at a median distance of 80 miles (interquartile range [IQR], 30.1-140.9 miles; mean [SD], 1002 [465.8] miles) from the nearest VHA facility offering CI care; of these, 3.98 million (20.0%) resided more than 160.7 miles from the nearest VHA facility. When considering only comprehensive facilities offering both surgical and audiologic care, the median distance was 101.3 miles (IQR, 39.4-178.7 miles; mean [SD], 126.0 [448.4] miles), but 20.0% of veterans had to travel more than 201.0 miles to a VHA facility. Veterans residing in urban areas (74.0%) lived a median distance of 61.2 miles (IQR, 23.7-121.3 miles; mean [SD], 83.8 [477.1] miles) from the nearest VHA facility, with 2.9 million (20.0%) living the farthest at 140.7 miles. Veterans residing in rural areas (26.0%) lived a median distance of 119.8 miles (IQR, 79.0-182.4 miles; mean [SD], 146.9 [431.0] miles) from their nearest VHA facility, with 1.04 million (20.0%) living more than 206.2 miles from the nearest VHA facility. CONCLUSIONS AND RELEVANCE: This study's findings suggest that large disparities exist in the distance to the nearest VHA-based CI facilities. Veterans face considerable geographic barriers to obtaining VHA-based CI care in many parts of the country, including some large metropolitan areas. Those requiring only audiologic services face similar geographic barriers as those requiring surgery. Thoughtful placement of new facilities, along with upcoming advances in remote programming of implants, may help ensure appropriate care for this high-risk population.

Relationship between vestibular sensitivity and multisensory temporal integration.

A single event can generate asynchronous sensory cues due to variable encoding, transmission, and processing delays. To be interpreted as being associated in time, these cues must occur within a limited time window, referred to as a "temporal binding window" (TBW). We investigated the hypothesis that vestibular deficits could disrupt temporal visual-vestibular integration by determining the relationships between vestibular threshold and TBW in participants with normal vestibular function and with vestibular hypofunction. Vestibular perceptual thresholds to yaw rotation were characterized and compared with the TBWs obtained from participants who judged whether a suprathreshold rotation occurred before or after a brief visual stimulus. Vestibular thresholds ranged from 0.7 to 16.5 deg/s and TBWs ranged from 13.8 to 395 ms. Among all participants, TBW and vestibular thresholds were well correlated ( R2 = 0.674, P < 0.001), with vestibular-deficient patients having higher thresholds and wider TBWs. Participants reported that the rotation onset needed to lead the light flash by an average of 80 ms for the visual and vestibular cues to be perceived as occurring simultaneously. The wide TBWs in vestibular-deficient participants compared with normal functioning participants indicate that peripheral sensory loss can lead to abnormal multisensory integration. A reduced ability to temporally combine sensory cues appropriately may provide a novel explanation for some symptoms reported by patients with vestibular deficits. Even among normal functioning participants, a high correlation between TBW and vestibular thresholds was observed, suggesting that these perceptual measurements are sensitive to small differences in vestibular function. NEW & NOTEWORTHY While spatial visual-vestibular integration has been well characterized, the temporal integration of these cues is not well understood. The relationship between sensitivity to whole body rotation and duration of the temporal window of visual-vestibular integration was examined using psychophysical techniques. These parameters were highly correlated for those with normal vestibular function and for patients with vestibular hypofunction. Reduced temporal integration performance in patients with vestibular hypofunction may explain some symptoms associated with vestibular loss.

The contribution of cochlear implants to postural stability.

OBJECTIVES: To determine whether spatial auditory cues provided by cochlear implants can improve postural balance in adults with severe deafness. METHODS: In the presence of spatial white noise, 13 adult cochlear implantees wore head and lumbar-mounted inertial sensors while standing in the dark for 30 seconds in two auditory conditions: hearing assistive devices on and off. RESULTS: Stability was improved with implants on (aided condition) compared to off (unaided condition) with respect to differences in mean head velocity (Cohen's d = 0.912, P = 0.006) as well as to root mean square (RMS) acceleration (Cohen's d = 0.456, P = 0.048). This was particularly evident in measures of anteroposterior accelerations (mean difference = 0.034 m/s2 ; Cohen's d = 0.612; P = 0.011). CONCLUSION: The decrease in RMS head acceleration and velocity while wearing cochlear implants suggests that they could be recognized as balance implants in addition to auditory implants. The clinical importance of this finding in various patient populations remains to be determined. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:1676-1680, 2018.

Localization performance correlates with binaural fusion for interaurally mismatched vocoded speech.

Bilateral cochlear implant users often have difficulty fusing sounds from the two ears into a single percept. However, measuring fusion can be difficult, particularly with cochlear implant users who may have no reference for a fully fused percept. As a first step to address this, this study examined how localization performance of normal hearing subjects relates to binaural fusion. The stimuli were vocoded speech tokens with various interaural mismatches. The results reveal that the percentage of stimuli perceived as fused was correlated with localization performance, suggesting that changes in localization performance can serve as an indicator for binaural fusion changes.

The Effect of Hearing Aids and Cochlear Implants on Balance During Gait.

HYPOTHESIS: Auditory input in people with hearing impairment will improve balance while walking. BACKGROUND: Auditory input is increasingly recognized as an additional input for balance. Several studies have found auditory cues to improve static balance measured on a sway platform. The effect of audition on gait, a dynamic task also linked to fall risk, has not been fully examined. If a positive effect were shown between audition and balance, it would further indicate that improving hearing could also improve balance. METHODS: Inertial sensors quantified gait parameters of 13 bilateral hearing aid users and 12 bilateral cochlear implant (CI) users with their hearing devices on and off. Outcome measures included gait velocity, stride length variability, swing time variability, and double support phase. RESULTS: Group analysis of each of the gait outcomes showed no significant differences between the aided and unaided conditions in both the hearing aid and CI groups. Gait velocity, an outcome most strongly linked to fall risk had 95% confidence interval differences of -2.16 to 1.52 and -1.45 to 4.17 cm/s in hearing aid and CI users, respectively (aided versus unaided condition). There was considerable variation among participants with some individuals improving in all four parameters. CONCLUSION: The overall findings were not statistically significant, however, a small subset of our population improved clinically across several outcomes. This demonstrates that audition may have a clinically beneficial effect on balance in some patients.

Binaural pitch fusion: Comparison of normal-hearing and hearing-impaired listeners.

Binaural pitch fusion is the fusion of dichotically presented tones that evoke different pitches between the ears. In normal-hearing (NH) listeners, the frequency range over which binaural pitch fusion occurs is usually <0.2 octaves. Recently, broad fusion ranges of 1-4 octaves were demonstrated in bimodal cochlear implant users. In the current study, it was hypothesized that hearing aid (HA) users would also exhibit broad fusion. Fusion ranges were measured in both NH and hearing-impaired (HI) listeners with hearing losses ranging from mild-moderate to severe-profound, and relationships of fusion range with demographic factors and with diplacusis were examined. Fusion ranges of NH and HI listeners averaged 0.17 ± 0.13 octaves and 1.7 ± 1.5 octaves, respectively. In HI listeners, fusion ranges were positively correlated with a principal component measure of the covarying factors of young age, early age of hearing loss onset, and long durations of hearing loss and HA use, but not with hearing threshold, amplification level, or diplacusis. In NH listeners, no correlations were observed with age, hearing threshold, or diplacusis. The association of broad fusion with early onset, long duration of hearing loss suggests a possible role of long-term experience with hearing loss and amplification in the development of broad fusion.

Improvements in Gait With Hearing Aids and Cochlear Implants.

OBJECTIVE: To evaluate whether wearing auditory assistive devices can improve gait and dynamic balance. PATIENTS: Three adult users of bilateral hearing assistive devices: one with cytomegalovirus exposure wearing cochlear implants, one with Ménière's disease wearing hearing aids, and one with presbystasis wearing hearing aids. INTERVENTION: Rehabilitative intervention involved participants performing gait and dynamic posture tasks with and without their hearing assistive devices. MAIN OUTCOME MEASURES: Gait velocity and Mini-BESTest score. RESULTS: The participant with Ménière's disease showed a clinically significant improvement in gait in the aided versus the unaided condition (20.5 cm/s higher velocity and five point better Mini-BESTest score). The other two participants also improved with augmented audition, but to a lesser degree. CONCLUSIONS: Bilateral hearing augmentation may promote clinically significant improvements in gait, although the effects are not uniform among patients. Hearing aids or cochlear implants may be important interventions for improving stability during walking in some people with hearing loss.

Taste Disturbance Due to Cochlear Implant Stimulation.

OBJECTIVE: To characterize stimulation of taste fibers in the facial nerve following cochlear implantation. PATIENT: A 34-year old presented with reversible dysgeusia following activation of a cochlear implant. INTERVENTION: Reprogramming targeted to specific offending electrodes reduced symptom intensity. Computed tomography demonstrated dehiscence of the bone separating the labyrinthine segment of the facial nerve and the basal turn of the cochlea in proximity to the electrode array. RESULTS: Dysgeusia was attributed to stimulation of taste fibers in the facial nerve by electrodes 13 to 16 of the cochlear implant array located in the superior-most portion of the basal turn. CONCLUSIONS: Dysgeusia following cochlear implant activation has not previously been reported. This likely results from stimulation of taste fibers through dehiscence of the bone separating the labyrinthine segment of the Fallopian canal and the basal turn of the cochlea. While in some cases of apparent dehiscence there may be thin bone present, recognition of this potential anatomic feature may influence the choice of which ear and which electrode design to implant.