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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 selfmotion 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 selfrotation 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 selfmotion 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. [ABSTRACT FROM AUTHOR]

Maintaining balance relies on integration of inputs from the visual, vestibular, and proprioceptive systems. The auditory system has not been credited with a similar contributory role, despite its ability to provide spatial orienting cues with extreme speed and accuracy. Here, we determined the ability of external auditory signals to reduce postural sway, measured as the root-mean-square velocity of center of pressure of a standing subject, in a series of subjects with varying levels of imbalance standing in the dark. The maximum root-mean-square center of pressure among our subjects decreased from 7.0 cm/sec in silence to 4.7 cm/sec.with the addition of external sound. The addition of sound allowed subjects to decrease sway by 41 percent. The amount of improvement due to sound was 54% of the amount of improvement observed in postural sway when visual cues only were provided to subjects standing in silence. These data support the significant effect of the auditory system in providing balance-related cues and suggest that interventions such as hearing aids or cochlear implants may be useful in improving postural stability and reducing falls. [ABSTRACT FROM AUTHOR]

Objective: Hearing loss is known to occur in some pregnant women, but improvement in sensorineural thresholds has not been audiometrically characterized. Here, we describe a patient with a history of Ménière’s disease and vestibular migraine who experienced temporary recovery of her hearing during pregnancy. Methods: Audiograms were obtained from a 31-year-old female over the course of 2 successive pregnancies. Results: Audiograms revealed a substantial improvement in hearing by the third trimester during each pregnancy, with a rapid return to baseline thresholds after delivery. Conclusion: This case is unique in documenting improvements in hearing thresholds during pregnancy and substantiates the effects of hormonal changes on hearing thresholds in humans. It raises the intriguing possibility of hormonal therapy as a treatment for sensorineural hearing loss in specific clinical situations. [ABSTRACT FROM AUTHOR]

Animal locomotion causes head rotations, which are detected by the semicircular canals of the inner ear. Morphologic features of the canals influence rotational sensitivity, and so it is hypothesized that locomotion and canal morphology are functionally related. Most prior research has compared subjective assessments of animal “agility” with a single determinant of rotational sensitivity: the mean canal radius of curvature (R). In fact, the paired variables of R and body mass are correlated with agility and have been used to infer locomotion in extinct species. To refine models of canal functional morphology and to improve locomotor inferences for extinct species, we compare 3D vector measurements of head rotation during locomotion with 3D vector measures of canal sensitivity. Contrary to the predictions of conventional models that are based upon R, we find that axes of rapid head rotation are not aligned with axes of either high or low sensitivity. Instead, animals with fast head rotations have similar sensitivities in all directions, which they achieve by orienting the three canals of each ear orthogonally (i.e., along planes at 90° angles to one another). The extent to which the canal configuration approaches orthogonality is correlated with rotational head speed independent of body mass and phylogeny, whereas R is not. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: Integration of balance-related cues from the vestibular and other sensory systems requires that they be perceived simultaneously despite arriving asynchronously at the central nervous system. Failure to perform temporal integration of multiple sensory signals represents a novel mechanism to explain symptoms in patients with imbalance. This study tested the ability of normal observers to compensate for sensory asynchronies between vestibular and auditory inputs. Study Design: Double-blinded experimental design. Methods: We performed whole-body rotations about the earth-vertical axis following a raised-cosine trajectory at 0.5 and 1.0 Hz to several peak velocities up to a maximum of 180°/s in five normal subjects. Headphones were used to present a diotic auditory stimulus at various times relative to the onset of the rotation. Subjects were required to indicate which cue occurred first. Results: The vestibular stimulus needed to be presented 61 milliseconds (at a stimulus frequency of 0.5 Hz) and 19 milliseconds (at 1.0 Hz) before the auditory stimulus. Stimuli presented within a window of 300 milliseconds (at 0.5 Hz) to 200 milliseconds (at 1.0 Hz) were judged to be simultaneous. Conclusions: The central nervous system must accommodate for delays in perception of vestibular and other sensory cues. Inaccurate temporal integration of these inputs represents a novel explanation for symptoms of imbalance. [ABSTRACT FROM AUTHOR]

Abstract: The orientations of the semicircular canals determines the response of the canals to head rotations and, in turn, the brain’s ability to interpret those motions. The geometry of chinchillas’ semicircular canals has never been reported. Volumetric representations of three chinchilla skulls were generated using a microCT scanner. The centroids of each semicircular canal lumen were identified as they passed through the image slices and were regressed to a plane. Unit vectors normal to the plane representing canal orientations were used to calculate angles between canal pairs. Pitch and roll maneuvers required to bring any canal into the horizontal plane for physiologic investigation were calculated. The semicircular canals of the chinchilla were found to be relatively planar. The horizontal canal was found to be oriented 55.0° anteriorly upward. Pairs of ipsilateral chinchilla canals were not orthogonal and contralateral synergistic pairs were not parallel. Despite this arrangement, the canal plane unit normal vectors were organized to respond with approximately equal overall sensitivity to rotations in any direction. The non-orthogonal chinchilla labyrinth may provide an opportunity to determine whether the frame of reference used by the central vestibular and oculomotor system is based on directions of afferent maximum sensitivity or prime directions. [Copyright &y& Elsevier]

Falls are one of the leading causes of disability in the elderly. Previous research has shown that falls may be related to changes in the temporal integration of multisensory stimuli. This study compared the temporal integration and processing of a vestibular and auditory stimulus in younger and older subjects. The vestibular stimulus consisted of a continuous sinusoidal rotational velocity delivered using a rotational chair and the auditory stimulus consisted of 5 ms of white noise presented dichotically through headphones (both at 0.5 Hz). Simultaneity was defined as perceiving the chair being at its furthest rightward or leftward trajectory at the same moment as the auditory stimulus was perceived in the contralateral ear. The temporal offset of the auditory stimulus was adjusted using a method of constant stimuli so that the auditory stimulus either led or lagged true simultaneity. 15 younger (ages 21–27) and 12 older (ages 63–89) healthy subjects were tested using a two alternative forced choice task to determine at what times they perceived the two stimuli as simultaneous. Younger subjects had a mean temporal binding window of 334 ± 37 ms (mean ± SEM) and a mean point of subjective simultaneity of 83 ± 15 ms. Older subjects had a mean TBW of 556 ± 36 ms and a mean point of subjective simultaneity of 158 ± 27. Both differences were significant indicating that older subjects have a wider temporal range over which they integrate vestibular and auditory stimuli than younger subjects. These findings were consistent upon retesting and were not due to differences in vestibular perception thresholds. [ABSTRACT FROM AUTHOR]

Imbalance among patients with vestibular hypofunction has been related to inadequate compensatory eye movements in response to head movements. However, symptoms of imbalance might also occur due a temporal mismatch between vestibular and other balance-related sensory cues. This temporal mismatch could be reflected in a widened temporal binding window (TBW), or the length of time over which simultaneous sensory stimuli may be offset and still perceived as simultaneous. We hypothesized that decreased vestibular input would lead to a widening of the temporal binding window. We performed whole-body rotations about the earth-vertical axis following a sinusoidal trajectory at 0.5 Hz with a peak velocity of 60°/s in four normal subjects. Dichotic auditory clicks were presented through headphones at various phases relative to the rotations. Subjects were asked to indicate whether the cues were synchronous or asynchronous and the TBW was calculated. We then simulated decreased vestibular input by rotating at diminished peak velocities of 48, 24 and 12°/s in four normal subjects. TBW was calculated between ±1 SD away from the mean on the psychometric curve. We found that the TBW increases as amplitude of rotation decreases. Average TBW of 251 ms at 60°/s increased to 309 ms at 12°/s. This result leads to the novel conclusion that changes in temporal processing may be a mechanism for imbalance in patients with vestibular hypofunction. [ABSTRACT FROM AUTHOR]