Psychometrics of inertial heading perception.

BACKGROUND: Inertial self-motion perception is thought to depend primarily on otolith cues. Recent evidence demonstrated that vestibular perceptual thresholds (including inertial heading) are adaptable, suggesting novel clinical approaches for treating perceptual impairments resulting from vestibular disease. OBJECTIVE: Little is known about the psychometric properties of perceptual estimates of inertial heading like test-retest reliability. Here we investigate the psychometric properties of a passive inertial heading perceptual test. METHODS: Forty-seven healthy subjects participated across two visits, performing in an inertial heading discrimination task. The point of subjective equality (PSE) and thresholds for heading discrimination were identified for the same day and across day tests. Paired t-tests determined if the PSE or thresholds significantly changed and a mixed interclass correlation coefficient (ICC) model examined test-retest reliability. Minimum detectable change (MDC) was calculated for PSE and threshold for heading discrimination. RESULTS: Within a testing session, the heading discrimination PSE score test-retest reliability was good (ICC = 0. 80) and did not change (t(1,36) = -1.23, p = 0.23). Heading discrimination thresholds were moderately reliable (ICC = 0.67) and also stable (t(1,36) = 0.10, p = 0.92). Across testing sessions, heading direction PSE scores were moderately correlated (ICC = 0.59) and stable (t(1,46) = -0.44, p = 0.66). Heading direction thresholds had poor reliability (ICC = 0.03) and were significantly smaller at the second visit (t(1,46) = 2.8, p = 0.008). MDC for heading direction PSE ranged from 6-9 degrees across tests. CONCLUSION: The current results indicate moderate reliability for heading perception PSE and provide clinical context for interpreting change in inertial vestibular self-motion perception over time or after an intervention.

Effect of timing delay between visual and vestibular stimuli on heading perception.

Heading direction is perceived based on visual and inertial cues. The current study examined the effect of their relative timing on the ability of offset visual headings to influence inertial perception. Seven healthy human subjects experienced 2 s of translation along a heading of 0°, ±35°, ±70°, ±105°, or ±140°. These inertial headings were paired with 2-s duration visual headings that were presented at relative offsets of 0°, ±30°, ±60°, ±90°, or ±120°. The visual stimuli were also presented at 17 temporal delays ranging from -500 ms (visual lead) to 2,000 ms (visual delay) relative to the inertial stimulus. After each stimulus, subjects reported the direction of the inertial stimulus using a dial. The bias of the inertial heading toward the visual heading was robust at ±250 ms when examined across subjects during this period: 8.0° ± 0.5° with a 30° offset, 12.2° ± 0.5° with a 60° offset, 11.7° ± 0.6° with a 90° offset, and 9.8° ± 0.7° with a 120° offset (mean bias toward visual ± SE). The mean bias was much diminished with temporal misalignments of ±500 ms, and there was no longer any visual influence on the inertial heading when the visual stimulus was delayed by 1,000 ms or more. Although the amount of bias varied between subjects, the effect of delay was similar.NEW & NOTEWORTHY The effect of timing on visual-inertial integration on heading perception has not been previously examined. This study finds that visual direction influence inertial heading perception when timing differences are within 250 ms. This suggests visual-inertial stimuli can be integrated over a wider range than reported for visual-auditory integration and may be due to the unique nature of inertial sensation, which can only sense acceleration while the visual system senses position but encodes velocity.

A Protocol for Imaging of Cochlear Implantation.

OBJECTIVES: Correct electrode placement is a challenge of cochlear implant surgery, which occurs because electrode position cannot be directly visualized. This work aims to 1) develop a protocol for a practical, consistent, single view plain radiograph able to be used to confirm cochlear implantation, 2) confirm its usefulness on patients, and 3) confirm its usefulness for identifying misplaced electrodes in cadaveric ears. STUDY DESIGN: Imaging procedure and quality improvement initiative. SETTING: Tertiary academic hospital. PATIENTS: Cadaveric ears, and patients undergoing cochlear implantation. INTERVENTIONS: An intraoperative imaging protocol was developed specifying patient head position, machine position, and exposure setting. This was tested to confirm proper cochlear implantation in patients, including one revision case. This technique allowed the electrode placement to be reliably identified in patients of all ages. Its usefulness for identifying maligned electrodes (partial insertion, and insertion into the vestibule or hypotympanum) was confirmed using four cadaveric hemi-heads. MAIN OUTCOME MEASURES: Ability to accurately identify correct or incorrect electrode insertion based on radiographic images. RESULTS: After adjusting radiographic exposure to account for the embalming process of the cadaveric heads, this new protocol was confirmed to be able to identify incorrect placement. This was also successfully used to confirm proper placement of cochlear implants in patients. CONCLUSIONS: Following a standardized radiographic protocol for cochlear implantation is a quick and easy method for checking electrode position.Supplemental Digital Content, http://links.lww.com/MAO/B253.

Common causation and offset effects in human visual-inertial heading direction integration.

Movement direction can be determined from a combination of visual and inertial cues. Visual motion (optic flow) can represent self-motion through a fixed environment or environmental motion relative to an observer. Simultaneous visual and inertial heading cues present the question of whether the cues have a common cause (i.e., should be integrated) or whether they should be considered independent. This was studied in eight healthy human subjects who experienced 12 visual and inertial headings in the horizontal plane divided in 30° increments. The headings were estimated in two unisensory and six multisensory trial blocks. Each unisensory block included 72 stimulus presentations, while each multisensory block included 144 stimulus presentations, including every possible combination of visual and inertial headings in random order. After each multisensory stimulus, subjects reported their perception of visual and inertial headings as congruous (i.e., having common causation) or not. In the multisensory trial blocks, subjects also reported visual or inertial heading direction (3 trial blocks for each). For aligned visual-inertial headings, the rate of common causation was higher during alignment in cardinal than noncardinal directions. When visual and inertial stimuli were separated by 30°, the rate of reported common causation remained >50%, but it decreased to 15% or less for separation of ≥90°. The inertial heading was biased toward the visual heading by 11-20° for separations of 30-120°. Thus there was sensory integration even in conditions without reported common causation. The visual heading was minimally influenced by inertial direction. When trials with common causation perception were compared with those without, inertial heading perception had a stronger bias toward visual stimulus direction.NEW & NOTEWORTHY Optic flow ambiguously represents self-motion or environmental motion. When these are in different directions, it is uncertain whether these are integrated into a common perception or not. This study looks at that issue by determining whether the two modalities are consistent and by measuring their perceived directions to get a degree of influence. The visual stimulus can have significant influence on the inertial stimulus even when they are perceived as inconsistent.

Superior Semicircular Canal Dehiscence Syndrome.

Superior canal dehiscence syndrome (SCDS) is a vestibular disorder caused by a pathologic third window into the labyrinth that can present with autophony, sound- or pressure-induced vertigo, and chronic disequilibrium among other vestibulocochlear symptoms. Careful history taking and examination in conjunction with appropriate diagnostic testing can accurately diagnose the syndrome. Key examination techniques include fixation-suppressed ocular motor examination investigating for sound- or pressure-induced eye movements in the plane of the semicircular canal. Audiometry, vestibular evoked myogenic potentials, and computed tomography confirm the diagnosis. Corrective surgical techniques can be curative, but many patients find their symptoms are not severe enough to undergo surgery. Although a primarily peripheral vestibular disorder, as first-line consultants for most dizziness complaints, neurologists will serve their patients well by understanding SCDS and its role in the differential diagnosis of vestibular disorders.

Effect of range of heading differences on human visual-inertial heading estimation.

Both visual and inertial cues are salient in heading determination. However, optic flow can ambiguously represent self-motion or environmental motion. It is unclear how visual and inertial heading cues are determined to have common cause and integrated vs perceived independently. In four experiments visual and inertial headings were presented simultaneously with ten subjects reporting visual or inertial headings in separate trial blocks. Experiment 1 examined inertial headings within 30° of straight-ahead and visual headings that were offset by up to 60°. Perception of the inertial heading was shifted in the direction of the visual stimulus by as much as 35° by the 60° offset, while perception of the visual stimulus remained largely uninfluenced. Experiment 2 used ± 140° range of inertial headings with up to 120° visual offset. This experiment found variable behavior between subjects with most perceiving the sensory stimuli to be shifted towards an intermediate heading but a few perceiving the headings independently. The visual and inertial headings influenced each other even at the largest offsets. Experiments 3 and 4 had similar inertial headings to experiments 1 and 2, respectively, except subjects reported environmental motion direction. Experiment 4 displayed similar perceptual influences as experiment 2, but in experiment 3 percepts were independent. Results suggested that perception of visual and inertial stimuli tend to be perceived as having common causation in most subjects with offsets up to 90° although with significant variation in perception between individuals. Limiting the range of inertial headings caused the visual heading to dominate the perception.

An adaptive vestibular rehabilitation technique.

OBJECTIVES/HYPOTHESIS: There is a large variation in vestibular rehabilitation (VR) results depending on type of therapy, adherence, and the appropriateness for the patient's level of function. A novel adaptive vestibular rehabilitation (AVR) program was developed and evaluated. STUDY DESIGN: Technology and procedure development, and prospective multicenter trial. METHODS: Those with complete unilateral vestibular hypofunction and symptomatic at least 3 months with a Dizziness Handicap Inventory (DHI) >30 were eligible. Patients were given a device to use with their own computer. They were instructed to use the program daily, with each session lasting about 10 minutes. The task consisted of reporting orientation of the letter C, which appeared when their angular head velocity exceeded a threshold. The letter size and head velocity required were adjusted based on prior performance. Performance on the task was remotely collected by the investigator as well as a weekly DHI score. RESULTS: Four patients aged 31 to 74 years (mean = 51 years) were enrolled in this feasibility study to demonstrate efficacy. Two had treated vestibular schwannomas and two had vestibular neuritis. Starting DHI was 32 to 56 (mean = 42), which was reduced to 0 to 16 (mean = 11.5) after a month of therapy, a clinically and statistically significant (P < .05) improvement. The three who continued therapy an additional month improved to a DHI of 4. CONCLUSIONS: This AVR method has advantages over traditional VR in terms of cost and customization for patient ability and obtained a major improvement in symptoms. This study demonstrated a clinically and statistically significant decrease in symptoms after 4 weeks of therapy. LEVEL OF EVIDENCE: 2b. Laryngoscope, 128:713-718, 2018.

Effect of eye position during human visual-vestibular integration of heading perception.

Visual and inertial stimuli provide heading discrimination cues. Integration of these multisensory stimuli has been demonstrated to depend on their relative reliability. However, the reference frame of visual stimuli is eye centered while inertia is head centered, and it remains unclear how these are reconciled with combined stimuli. Seven human subjects completed a heading discrimination task consisting of a 2-s translation with a peak velocity of 16 cm/s. Eye position was varied between 0° and ±25° left/right. Experiments were done with inertial motion, visual motion, or a combined visual-inertial motion. Visual motion coherence varied between 35% and 100%. Subjects reported whether their perceived heading was left or right of the midline in a forced-choice task. With the inertial stimulus the eye position had an effect such that the point of subjective equality (PSE) shifted 4.6 ± 2.4° in the gaze direction. With the visual stimulus the PSE shift was 10.2 ± 2.2° opposite the gaze direction, consistent with retinotopic coordinates. Thus with eccentric eye positions the perceived inertial and visual headings were offset ~15°. During the visual-inertial conditions the PSE varied consistently with the relative reliability of these stimuli such that at low visual coherence the PSE was similar to that of the inertial stimulus and at high coherence it was closer to the visual stimulus. On average, the inertial stimulus was weighted near Bayesian ideal predictions, but there was significant deviation from ideal in individual subjects. These findings support visual and inertial cue integration occurring in independent coordinate systems.NEW & NOTEWORTHY In multiple cortical areas visual heading is represented in retinotopic coordinates while inertial heading is in body coordinates. It remains unclear whether multisensory integration occurs in a common coordinate system. The experiments address this using a multisensory integration task with eccentric gaze positions making the effect of coordinate systems clear. The results indicate that the coordinate systems remain separate to the perceptual level and that during the multisensory task the perception depends on relative stimulus reliability.

Perception of combined translation and rotation in the horizontal plane in humans.

Thresholds and biases of human motion perception were determined for yaw rotation and sway (left-right) and surge (fore-aft) translation, independently and in combination. Stimuli were 1 Hz sinusoid in acceleration with a peak velocity of 14°/s or cm/s. Test stimuli were adjusted based on prior responses, whereas the distracting stimulus was constant. Seventeen human subjects between the ages of 20 and 83 completed the experiments and were divided into 2 groups: younger and older than 50. Both sway and surge translation thresholds significantly increased when combined with yaw rotation. Rotation thresholds were not significantly increased by the presence of translation. The presence of a yaw distractor significantly biased perception of sway translation, such that during 14°/s leftward rotation, the point of subjective equality (PSE) occurred with sway of 3.2 ± 0.7 (mean ± SE) cm/s to the right. Likewise, during 14°/s rightward motion, the PSE was with sway of 2.9 ± 0.7 cm/s to the left. A sway distractor did not bias rotation perception. When subjects were asked to report the direction of translation while varying the axis of yaw rotation, the PSE at which translation was equally likely to be perceived in either direction was 29 ± 11 cm anterior to the midline. These results demonstrated that rotation biased translation perception, such that it is minimized when rotating about an axis anterior to the head. Since the combination of translation and rotation during ambulation is consistent with an axis anterior to the head, this may reflect a mechanism by which movements outside the pattern that occurs during ambulation are perceived.

Frequency and Demographics of Gentamicin Use.

OBJECTIVE: To understand how aminoglycosides such as gentamicin are used in a tertiary care setting. To familiarize otologists with the demographics and risk factors associated with gentamicin use at major medical centers to allow the possibility of early intervention. STUDY DESIGN: Retrospective review of existing clinical data. SETTING: University of Rochester Medical Center (URMC), including all associated hospitals (Strong Memorial Hospital, Highland Hospital, etc.). PATIENTS: All hospital inpatients who were prescribed intravenous gentamicin over a 4-year period starting in February 2011. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Major patient populations receiving gentamicin and the associated diagnoses for which gentamicin was prescribed. RESULTS: A total of 5,257 patients were found to have received gentamicin. Three major populations of patients were found to have received gentamicin: 1) more than half the gentamicin exposures were children and 42% were under 2 years. 2) 18% of the exposures were young adults age 18 to 34 and in this population 88% were woman with most of these hospitalizations pregnancy related. 3) Patients >55 were 19% of the exposures and most of these had serious infections. Disorders associated with patients receiving gentamicin included: perinatal complications (1,564); sepsis (1,399); acute/chronic renal disease (1,287); labor, delivery, or neonatal complications (1,250); diabetes (949); and UTI/pyelonephritis (775). CONCLUSIONS: Gentamicin is still widely used, and the neonatal population and young adult women are at especially high risk for gentamicin-induced ototoxicity. Further data analysis should focus strategies to protect these populations by avoiding unnecessary exposures and by possible concurrent administration of protective medications such as metformin and aspirin.

Static and dynamic visual vertical perception in subjects with migraine and vestibular migraine.

OBJECTIVE: To measure the static visual vertical and the effect of visual rotation on the perception of visual vertical in migraine and vestibular migraine subjects. By so doing, we may better understand the vestibular contribution to the pathophysiology of migraine, as well as the capacity for visual compensation. METHODS: The perception of visual vertical in the presence of static and dynamic visual cues was prospectively studied in 10 subjects with migraine, 6 subjects with vestibular migraines, and 10 controls. Subjects used a dial to rotate a fluorescent green line to the vertical position. Static visual vertical (SVV) was measured with a black background, as well as with a static random-dot visual pattern. This pattern was then rotated at various velocities to measure dynamic visual vertical (DVV). RESULTS: Migraine subjects had greater deviation from true vertical than controls in SVV (P < 0.05). The DVV in migraine subjects was greater than controls when rotated in the counterclockwise at -5°/s (P < 0.01), -20°/s (P < 0.01), and -80°/s (P < 0.01), but not when the line was rotated clockwise. Vestibular migraine subjects did not deviate significantly from controls in SVV (P < 0.37, P < 0.22), but did show greater deviation in the DVV tasks at -80 and -20°/s (P < 0.05, P < 0.03). Migraine and vestibular migraine subjects demonstrated a wider range of vertical deviance when compared to controls (P < 0.02). CONCLUSIONS: This study demonstrates a significant deviation of the perceived static as well as dynamic visual vertical in migraine subjects. Moving stimuli may have a greater influence on migraine and vestibular migraine subjects, which suggests an underlying sensory integration disorder.

Human Vection Perception Using Inertial Nulling and Certainty Estimation: The Effect of Migraine History.

Vection is an illusory perception of self-motion that can occur when visual motion fills the majority of the visual field. This study examines the effect of the duration of visual field movement (VFM) on the perceived strength of self-motion using an inertial nulling (IN) and a magnitude estimation technique based on the certainty that motion occurred (certainty estimation, CE). These techniques were then used to investigate the association between migraine diagnosis and the strength of perceived vection. Visual star-field stimuli consistent with either looming or receding motion were presented for 1, 4, 8 or 16s. Subjects reported the perceived direction of self-motion during the final 1s of the stimulus. For the IN method, an inertial nulling motion was delivered during this final 1s of the visual stimulus, and subjects reported the direction of perceived self-motion during this final second. The magnitude of inertial motion was varied adaptively to determine the point of subjective equality (PSE) at which forward or backward responses were equally likely. For the CE trials the same range of VFM was used but without inertial motion and subjects rated their certainty of motion on a scale of 0-100. PSE determined with the IN technique depended on direction and duration of visual motion and the CE technique showed greater certainty of perceived vection with longer VFM duration. A strong correlation between CE and IN techniques was present for the 8s stimulus. There was appreciable between-subject variation in both CE and IN techniques and migraine was associated with significantly increased perception of self-motion by CE and IN at 8 and 16s. Together, these results suggest that vection may be measured by both CE and IN techniques with good correlation. The results also suggest that susceptibility to vection may be higher in subjects with a history of migraine.

The influence of head and body tilt on human fore-aft translation perception.

The tilt-translation ambiguity occurs because acceleration due to translation cannot be differentiated from gravitational acceleration. Head tilt can occur independent of body tilt which further complicates the problem. The tilt-translation ambiguity is examined for fore-aft (surge) translation with head and/or body orientations that are tilted in pitch 10° forward or backward. Eleven human subjects (six female), mean age 40 years participated. Conditions included no tilt (NT), head and body tilt (HBT), head only tilt (HOT), and body only tilt (BOT). The fore-aft stimulus consisted of a 2 s (0.5 Hz) sine wave in acceleration which a maximum peak velocity of 10 cm/s. After each stimulus, the subject reported the direction of motion as forward or backward. Subsequent stimuli were adjusted to determine the point at which subjects were equally likely to report motion in either direction. During the HBT, responses were biased such that upward pitch caused a neutral stimulus to be more likely to be perceived as forward and downward pitch caused the stimulus to be more likely to be perceived as backward. The difference in the point of subjective equality based on the direction of tilt was 3.3 cm/s. During the BOT condition, the bias with respect to the direction of body tilt was in a similar direction with a difference in PSE 1.6 cm/s. During HOT and NT, there was no significant bias on fore-aft perception. These findings demonstrate that body tilt shifts the PSE of fore-aft direction discrimination while head tilt has no influence.

In vitro efficacy of a consumer-marketed ear cleaning tool.

HYPOTHESIS: The WaxVac ear cleaning device may be a useful adjunct for patients requiring aural toilet. BACKGROUND: Cerumen removal and routine aural toilet is a common complaint that presents to the otolaryngology clinic. We tested this device to make an appropriate recommendation to our patients. METHODS: We conducted in vitro testing of the WaxVac device on an artificial ear canal model and cadaveric temporal bones testing the strength of the suction, noise created by the device, and the ability of the device to remove foreign bodies from the external auditory canal. These foreign bodies included a PE tube, baby powder, a q-tip head, saline, and artificial cerumen. RESULTS: The WaxVac created very little suction as compared with Frazier tip suctions used in clinic. The device produced very little noise in the canal, which was equivalent to a #3 Frazier tip suction. The WaxVac was unable to remove q-tip heads or artificial cerumen from the ear canal model or the cadaveric temporal bones. Very little of the saline could be removed by the WaxVac, and only 20% to 50% of trials demonstrated removal of a PE tube. However, a large amount of the powder was able to be removed by the device. CONCLUSION: Although the concept of this device is good, the actual product does not produce adequate suction to remove cerumen or most common foreign bodies from the external auditory canal. It is unlikely to be useful for aural toilet.

Human yaw rotation aftereffects with brief duration rotations are inconsistent with velocity storage.

In many sensory systems, perception of stimuli is influenced by previous stimulus exposure such that subsequent stimuli may be perceived as more neutral. This phenomenon is known as an aftereffect and has been studied for vision, audition, and some vestibular stimuli including roll and translation. Previous data on yaw rotation perception has focused on low-frequency stimuli on the order of a minute which may not be directly applicable to frequencies during ambulation. The aim of the current study is to look at the influence of yaw rotation on subsequent perception near 1 Hz, the predominant frequency of yaw rotation during human ambulation. Humans were rotated with 12 ° whole body adapting stimulus over 1 or 1.5 s. After an interstimulus interval (ISI) of 0.5, 1.0, 1.5, or 3 s, a test stimulus the same duration as the adapting stimulus was presented, and subjects pushed a button to identify the direction of the test stimulus as right or left. The direction and magnitude of the test stimulus was adjusted based on prior responses to find the stimulus at which no rotation was perceived. Experiments were conducted both in darkness and with a visual fixation point. The presence of a fixation point did not influence the aftereffect which was largest at 0.5 s with an average size of 0.78 ± 0.18°/s (mean ± SE). The aftereffect diminished with a time constant of ~1 s. Thresholds were elevated after the adapting stimulus and also decreased with a time constant of ~1 s. These findings demonstrate that short adapting stimuli can induce significant aftereffects in yaw rotation perception and that these aftereffects are independent from the previously described velocity storage.

Human visual and vestibular heading perception in the vertical planes.

Heading estimation has not previously been reported in the vertical planes. This is a potentially interesting issue because although distribution of neuronal direction sensitivities is near uniform for vertical headings, there is an overrepresentation of otolith organs sensitive to motion in the horizontal relative to the vertical plane. Furthermore, thresholds of horizontal motion perception are considerably lower than those of vertical motion which has the potential to bias heading perception. The current data from 14 human subjects (age 19 to 67) measured heading estimation in response to vestibular motion of 14 cm (28 cm/s) over a 360° of headings at 5° intervals. An analogous visual motion was tested in separate trials. In this study, earth and head vertical/horizontal were always aligned. Results demonstrated that the horizontal component of heading was overestimated relative to the vertical component for vestibular heading stimuli in the coronal (skew) and sagittal (elevation) planes. For visual headings, the bias was much smaller and in the opposite direction such that the vertical component of heading was overestimated. Subjects older than 50 had significantly worse precision and larger biases relative to that of younger subjects for the vestibular conditions, although visual heading estimates were similar. A vector addition model was fit to the data which explains the observed heading biases by the known distribution of otolith organs in humans. The greatly decreased precision with age is explained by the model with decreases in end organ numbers, and relatively greater loss of otoliths that are sensitive to vertical motion.