Static Tilt Research Articles

Studies of the Linear Vestibuloocular Reflex to Clarify Otolith Function

The vestibular organs consist of three semicircular canals, which sense angular acceleration, and two otolith organs, which sense linear acceleration. Although we are now exposed to various degrees of linear acceleration with the development of advanced methods of transportation, less is known about the function of the otolith organs relative to the function of the semicircular canals. There are several reasons for this: the morphological and functional characteristics of the otolith organs are complex; the otolith organs respond not only to dynamic head translation but also static head tilt with respect to gravity, and it is difficult to generate sufficient linear acceleration using a compact apparatus. To clarify otolith function, this article introduces recent progress in studies of the linear vestibuloocular reflexes, which are eye movements that compensate for linear translation or tilt.

Parabrachial nucleus neuronal responses to off-vertical axis rotation in macaques

The caudal aspect of the parabrachial nucleus (PBN) contains neurons responsive to whole body, periodic rotational stimulation in alert monkeys (Balaban et al. in J Neurophysiol 88:3175-3193, 2002). This study characterizes the angular and linear motion-sensitive response properties of PBN unit responses during off-vertical axis rotation (OVAR) and position trapezoid stimulation. The OVAR responses displayed a constant firing component which varied from the firing rate at rest. Nearly two-thirds of the units also modulated their discharges with respect to head orientation (re: gravity) during constant velocity OVAR stimulation. The modulated response magnitudes were equal during ipsilateral and contralateral OVARs, indicative of a one-dimensional accelerometer. These response orientations during OVAR divided the units into three spatially tuned populations, with peak modulation responses centered in the ipsilateral ear down, contralateral anterior semicircular canal down, and occiput down orientations. Because the orientation of the OVAR modulation response was opposite in polarity to the orientation of the static tilt component of responses to position trapezoids for the majority of units, the linear acceleration responses were divided into colinear dynamic linear and static tilt components. The orientations of these unit responses formed two distinct population response axes: (1) units with an interaural linear response axis and (2) units with an ipsilateral anterior semicircular canal-contralateral posterior semicircular canal plane linear response axis. The angular rotation sensitivity of these units is in a head-vertical plane that either contains the linear acceleration response axis or is perpendicular to the linear acceleration axis. Hence, these units behave like head-based ('strapdown') inertial guidance sensors. Because the PBN contributes to sensory and interoceptive processing, it is suggested that vestibulo-recipient caudal PBN units may detect potentially dangerous anomalies in control of postural stability during locomotion. In particular, these signals may contribute to the range of affective and emotional responses that include panic associated with falling, malaise associated with motion sickness and mal-de-debarquement, and comorbid balance and anxiety disorders.

A Micropower Tilt-Processing Circuit

This paper describes a novel analog circuit for extracting the tilt angle from the output of a linear microelectromechanical-system accelerometer. The circuit uses the accelerometer signal, together with the gravitational acceleration vector, to generate the tilt signal. Using a current-mode representation with metal-oxide semiconductor devices operating in weak inversion, the appropriate trigonometric function has been realized to compute tilt. Furthermore, implementing a long-time constant filter to extract the mean tilt level provides adaptation to the static tilt level. Specifically, this circuit has been designed as part of an implantable vestibular prosthesis to provide inclination signals for bypassing dysfunctional otolith end organs. The circuit has been fabricated in AustriaMicroSystems 0.35-mum 2P4M complementary metal-oxide semiconductor technology, and this paper presents the theory, implementation, and measured results.

Influence of perceived egocentric coordinates on the subjective visual vertical

The majority of previous studies which have explored the mechanisms underlying perception of the direction of gravity in static roll tilt have proposed that the tendency to estimate the subjective visual vertical (SVV) as tilted towards body tilt (‘Aubert effect’) arises from an underestimation of perceived body tilt. The present study has evaluated an alternative assumption that erroneous estimates of verticality may be related to the ability to estimate the orientation of external objects with respect to the observer's perceived body Z-axis. Experiments showed that Aubert effects and the overestimations of 30–90° angles from the body Z-axis in the roll plane were both related to errors made in adjusting a visual rod parallel to the body Z-axis. The results suggest that errors in providing visual estimates of the observer's own body Z-axis reference are implicated in Aubert effect.

Effects of age, viewing distance and target complexity on static ocular counterroll

The ocular counterroll (OCR) reflex generates partially compensatory torsional eye movements during static head roll tilt. We assessed the influence of age, viewing distance and target complexity on the OCR across the age span (13–63 years; n = 47), by recording eye movements during head-on-body roll tilt (0 ± 40° in 5° steps) while subjects viewed simple vs. complex targets at 0.33 and 1 m. We found that subjects ⩾31 years had lower gains than those ⩽30 years, but only for far targets. Consistent with prior reports, far targets elicited higher OCR gains than near targets, and target complexity had no effect on gains, suggesting that visual input is primarily used to maintain vergence during OCR.

Free-space optical links for board-to-board interconnects

We describe two free-space optical links for multichannel optical interconnects. The targeted aggregate data rate is 240 Gb/s. In one implementation we use a unique implementation of telecentric optics and achieved an optical link that is simple, robust, and modular. We describe a simple, inexpensive telecentric lens that can accommodate all optical channels within a 1-mm-diameter sweet zone. We also describe the performance of an optical link with a 4×4 array of VCSELs and matching detectors. The integrity of the optical link is not significantly degraded with a>±2 mm translational misalignment between the VCSEL and detector arrays. With the telecentric optical link, we need only two low-bandwidth, single-axis active servomechanisms to compensate for static tilt and possibly low-frequency thermally-driven shift between the transmitter and receiver arrays. In the other implementaion we use two matching arrays of 1×12 optical fibers. Data are coupled optically through an air gap of 2 mm by means of a pair of collimating microlens arrays that are aligned to one another via precision mechanical subassemblies. We describe a simple, inexpensive, and robust mechanical coupling for the optical link achieved by using miniature high-flux magnets.

Change of Pelvic Tilt before and after Gait in Patients with Lumbar Degenerative Kyphosis

- Abstract - Study Design: This is a retrospective study. Objectives: We wanted to verify the value of radiography and gait analysis to analyze the changes of the pelvic tilt before and after gait in the patients with LDK. Summary of Literature Review: Patients with lumbar degenerative kyphosis show dynamic changes that are closely associated with the motion of pelvis. Materials and Methods: We analyzed 18 lumbar degenerative kyphosis patients who didn't have multiple vertebral compressio fractures, a past history of spinal surgery or surgery for degenerative arthritis of the knee or hip, and obesity which causes marker errors on the gait analysis. Pelvic tilt was statistically evaluated by utilizing radiographs and dynamically utilizing the gait analysis. The linear parameters of the gait cycle and the kinematic data were obtained from the gait analysis. Results: The LDK patients' mean walking velocity was 80.7 cm/s, and it was largely decreased to 65% of the normal value. The cause of the decreased walking velocity was a decrease of stride length, and not a decrease of cadence. The mean static pelvic tilt in the gait analysis was -1.3±8.0。 , and there were 8 cases of anterior tilt and 10 cases of posterior tilt. The mean pelvic tilt during gait was 12.5±8.2。 , and there were 17 cases of anterior tilt and 1 case of posterior tilt. It was statistically significant dif- ference (p<0.05) between the mean static pelvic tilt in gait analysis and the mean pelvic tilt during gait and the Pearson's corre- lation coefficient was -0.88. Conclusions: Though there was no statistical significance, we observed anterior pelvic rotation after gait on the radiographs. As fatigue of the pelvic extensor muscles increases during gait, anterior pelvis tilt increases with statistical significance on the gait analysis. Therefore, we feel gait analysis is useful for evaluating the dynamic change of the pelvic tilt in patients with LDK.

ELECTROSPRAYING/ELECTROSPINNING OF POLY(γ-STEARYL-L-GLUTAMATE): FORMATION OF SURFACES WITH SUPERHYDROPHOBICITY

Electrospraying/electrospinning of poly(γ-stearyl-L-glutamate) (PSLG) was investigated on a series solutions with different concentrations in chloroform. Field emission scanning electron microscopy (FESEM) and attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR/ATR) were used to characterize the morphology and structure of the electrosprayed/electrospun polypeptide mats. It was found that electrospraying of PSLG with concentrations lower than 16 wt% afforded beads, while microfibers could be electrospun at the concentration of 22 wt%. The hydrophobicity of the electrosprayed/electrospun PSLG mats was investigated with static water contact angle (WCA) and tilt angle measurements. It was demonstrated that the superhydrophobic surfaces of PSLG with WCAs and tilt angles in the ranges of 150°–170° and 16.5°–4.2°, respectively, were obtained through electrospraying/electrospinning process.

Comparison of “Polarization Inversion with Spin Exchange at Magic Angle” and “Geometric Analysis of Labeled Alanines” Methods for Transmembrane Helix Alignment

Using the model alpha-helical peptide acetyl-GGALW5LALALALALALALW19LAGA-ethanolamide ("GWALP23"), we have compared the polarization inversion with spin exchange at magic angle method and geometric analysis of labeled alanines method for estimating the transmembrane helix orientation. For GWALP23 in bilayers of a short lipid, dilauroylphosphatidylcholine, we find general agreement between the two methods, with a static helix tilt of about 11degrees-13degrees with respect to the bilayer normal.

Biomimetic hierarchical structure for self-cleaning

Hierarchical roughness is beneficial for superhydrophobicity. Surfaces with microstructure, nanostructure, and hierarchical structure were fabricated by replication of micropattern and self- assembly of hydrophobic alkanes. The fabrication technique used is a low cost two step process, which provides flexibility in the fabrication of a variety of hierarchical structures. Fabricated structures and surface chemistry mimic the hierarchical surfaces of superhydrophobic and self-cleaning plant surfaces. The influence of structure on superhydrophobicity at different length scales is demonstrated by the investigation of static contact angle, hysteresis and tilt angles, and propensity of air pocket formation as well as adhesive forces.

Human ocular counter-rolling and roll tilt perception during off-vertical axis rotation after spaceflight

Ocular counter-rolling (OCR) induced by whole body tilt in roll has been explored after spaceflight as an indicator of the adaptation of the otolith function to microgravity. It has been claimed that the overall pattern of OCR responses during static body tilt after spaceflight is indicative of a decreased role of the otolith function, but the results of these studies have not been consistent, mostly due to large variations in the OCR within and across individuals. By contrast with static head tilt, off-vertical axis rotation (OVAR) presents the advantage of generating a sinusoidal modulation of OCR, allowing averaged measurements over several cycles, thus improving measurement accuracy. Accordingly, OCR and the sense of roll tilt were evaluated in seven astronauts before and after spaceflight during OVAR at 45 degrees/s in darkness at two angles of tilt (10 degrees and 20 degrees). There was no significant difference in OCR during OVAR immediately after landing compared to preflight. However, the amplitude of the perceived roll tilt during OVAR was significantly larger immediately postflight, and then returned to control values in the following days. Since the OCR response is predominantly attributed to the shearing force exerted on the utricular macula, the absence of change in OCR postflight suggests that the peripheral otolith organs function normally after short-term spaceflight. However, the increased sense of roll tilt indicates an adaptation in the central processing of gravitational input, presumably related to a re-weighting of the internal representation of gravitational vertical as a result of adaptation to microgravity.

Effect of field of view on the Levitation Illusion

Supine subjects inside a furnished room in which both they and the room are pitched 90 degrees backwards may experience themselves and the room as upright relative to gravity. This effect is known as the levitation illusion because observers report that their arms feel weightless when extended, and objects hanging in the room seem to "levitate". This illusion is an extreme example of a visually induced illusion of static tilt. Visually induced tilt illusions are commonly experienced in wide-screen movie theatres, flight simulators, and immersive virtual reality systems. For technical reasons an observer's field of view is often constrained in these environments. No studies have documented the effect of field-of-view (FOV) restriction on the incidence of the levitation illusion. Preliminary findings suggest that when concurrently manipulating the FOV and observer position within an environment, the incidence of levitation illusions depends not only on the field of view but also on the visible scene content.

Body-Tilt and Visual Verticality Perception During Multiple Cycles of Roll Rotation

To assess the effects of degrading canal cues for dynamic spatial orientation in human observers, we tested how judgments about visual-line orientation in space (subjective visual vertical task, SVV) and estimates of instantaneous body tilt (subjective body-tilt task, SBT) develop in the course of three cycles of constant-velocity roll rotation. These abilities were tested across the entire tilt range in separate experiments. For comparison, we also obtained SVV data during static roll tilt. We found that as tilt increased, dynamic SVV responses became strongly biased toward the head pole of the body axis (A-effect), as if body tilt was underestimated. However, on entering the range of near-inverse tilts, SVV responses adopted a bimodal pattern, alternating between A-effects (biased toward head-pole) and E-effects (biased toward feet-pole). Apart from an onset effect, this tilt-dependent pattern of systematic SVV errors repeated itself in subsequent rotation cycles with little sign of worsening performance. Static SVV responses were qualitatively similar and consistent with previous reports but showed smaller A-effects. By contrast, dynamic SBT errors were small and unimodal, indicating that errors in visual-verticality estimates were not caused by errors in body-tilt estimation. We discuss these results in terms of predictions from a canal-otolith interaction model extended with a leaky integrator and an egocentric bias mechanism. We conclude that the egocentric-bias mechanism becomes more manifest during constant velocity roll-rotation and that perceptual errors due to incorrect disambiguation of the otolith signal are small despite the decay of canal signals.

Inducing non-adiabatic effects through coadsorption: CO + NO on iridium

We compare the response of the intramolecular C–O stretch of carbon monoxide alone and coadsorbed with nitric oxide on Ir{1 1 1} following femtosecond laser heating with the help of time-resolved vibrational sum frequency (SF) spectroscopy. The C–O stretch of a pure CO layer couples anharmonically to the CO frustrated translation and its frequency adiabatically follows the temperature of the iridium surface. In a mixed CO/NO layer, the C–O frequency exhibits non-adiabatic coupling to the hot iridium electrons with a friction coefficient that depends on the electron temperature and the CO:NO ratio. Two possible scenarios emerge: NO causes a static tilt of the CO with a tilt angle depending on the relative coverage. This increases the degree of bonding of the CO 2 π ∗ orbital to the iridium surface, which in turn increases the degree of non-adiabatic coupling. Alternatively, the C–O frequency reflects transient changes in the bonding configuration of the neighboring NO. The latter interaction could be the primary step in the direct reduction of NO by CO to form CO 2.

Eye orientation during static tilts and its relationship to spontaneous head pitch in the laboratory mouse

Both eye position and head orientation are influenced by the macular (otolith) organs, via the tilt maculo-ocular reflex (tiltMOR) and the vestibulo-collic reflexes, respectively. The mechanisms that control head position also influence the rest position of the eye because head orientation influences eye position through the tiltMOR. Despite the increasing popularity of mice for studies of vestibular and ocular motor functions, relatively little is known in this species about tiltMOR, spontaneous orientation of the head, and their interrelationship. We used 2D video oculography to determine in C57BL/6 mice the absolute horizontal and vertical positions of the eyes over body orientations spanning 360° about the pitch and roll axes. We also determined head pitch during ambulation in the same animals. Eye elevation varied approximately sinusoidally as functions of pitch or roll angle. Over the central ± 30° of pitch, sensitivity and gain in the light were 31.7°/ g and 0.53, respectively. The corresponding values for roll were 31.5°/ g and 0.52. Absolute positions adopted in light and darkness differed only slightly. During ambulation, mice carried the lambda–bregma plane at a downward pitch of 29°, corresponding to a horizontal eye position of 64° and a vertical eye position of 22°. The vertical position is near the center of the range of eye movements produced by the pitch tiltMOR. The results indicate that the tiltMOR is robust in this species and favor standardizing pitch orientation across laboratories. The robust tiltMOR also has significant methodological implications for the practice of pupil-tracking video oculography in this species.

Human stance control beyond steady state response and inverted pendulum simplification

Systems theory analyses have suggested that human upright stance can be modelled in terms of continuous multi-sensory feedback control. So far, these analyses have considered mainly steady-state responses to periodic stimuli and relied on a simplifying model of the body's mechanics in the form of an inverted pendulum. Therefore, they may have ignored relevant aspects of the postural behaviour. To prove a more general validity of a stance control model that we previously derived from such analyses, we now presented subjects with static-dynamic stimulus combinations and assessed response transients, anterior-posterior (a-p) response asymmetries, and possible deviations from the 'inverted pendulum' simplification (by measuring hip and knee bending). We presented normal subjects (Ns) and vestibular loss patients (Ps) with a-p support surface tilt on a motion platform under the instruction to maintain, with eyes closed, the body upright in space. In addition, subjects were to indicate perceived platform tilt with the help of pointers. We combined a fixed-amplitude sinusoidal tilt (0.1 Hz) with static tilts that were varied in amplitude and direction. We recorded upper body (shoulder) and lower body (hip) excursions in space and centre of pressure (COP) shift, and calculated the centre of mass (COM) angular excursion. We found that: (1) Immediately prior to stimulus onset (which was highly predictable), subjects showed a small anticipatory forward lean. (2) The subsequent transient response consisted of two parts. First, the body was moved along with the platform tilt and then, in the second part, the body excursion was braked by starting tilt compensation. Upon increasing tilt amplitude, the braking point showed a pronounced saturation with for-aft asymmetry. (3) During the following prolonged tilt, the tonic body excursions saturated with increasing static tilt amplitude. This saturation also showed a for-aft asymmetry (backwards saturation more pronounced). In contrast, the dynamic body excursions did not depend on the static tilt stimulus. (4) Tilt compensation occurred mainly in the ankle joints, but also involved small synergistic bendings in hips and knees in fixed register to the ankle rotation. (5) After the end of the stimulus, the body returned towards primary position, followed by a pronounced and slowly decaying tonic overshoot which was mainly related to tilt amplitude and initial tonic body excursion. (6) The responses of Ps qualitatively resembled those of Ns, apart from larger body excursions, less pronounced saturations, and less for-aft asymmetries. (7) Perceived platform tilt of Ns and Ps was correlated with their postural tilt compensations, but unlike the postural responses the perceptual responses overestimated actual static and dynamic tilt by a factor of 3-4. Our findings suggest two, so far undescribed and highly nonlinear mechanisms in human stance control. (a) The braking during the transient response appears to reflect a 'sensory reweighting switch' by which subjects change from a control that is referenced to the support to one that is referenced to space. (b) The saturation of the tonic body excursion also reflects a sensory reweighting mechanism; by this, subjects keep their balancing within a certain excursion limit. The two mechanisms were originally not predicted by our stance control model, but do not invalidate it, because they can simply be added to it. Also the observed for-aft asymmetries can be accounted for (by making thresholds in the two mechanisms asymmetric). In its extended form, the model mimics the previous and the new findings. We also conclude that the 'inverted pendulum' simplification is a legitimate simplification. We demonstrate the utility of the model by implementing it into a humanoid robot that then mimics closely the human experimental data. Finally, we present a hypothetical concept on sensory reweighting mechanisms in human stance control, which is meant to serve as a framework for future research.

Vertical (Z-axis) acceleration alters the ocular response to linear acceleration in the rabbit

Whether ocular orientation to gravity is produced solely by linear acceleration in the horizontal plane of the head or depends on both horizontal and vertical components of the acceleration of gravity is controversial. Here, we compared orienting eye movements of rabbits during head tilt to those produced by centrifugation that generated centripetal acceleration along the naso-occipital (X-), bitemporal (Y-) and vertical (Z-) axes in a constant gravitational field. Sensitivities of ocular counter-pitch and vergence during pitch tilts were approximately 25 degrees /g and approximately 26 degrees /g, respectively, and of ocular counter-roll during roll tilts was approximately 20 degrees /g. During X-axis centripetal acceleration with 1 g of gravity along the Z-axis, pitch and vergence sensitivities were reduced to approximately 13 degrees /g and approximately 16 degrees /g. Similarly, Y-axis acceleration with 1g along the Z-axis reduced the roll sensitivity to approximately 16 degrees /g. Modulation of Z-axis centripetal acceleration caused sensitivities to drop by approximately 6 degrees /g in pitch, approximately 2 degrees /g in vergence, and approximately 5 degrees /g in roll. Thus, the constant 1g acceleration along the Z-axis reduced the sensitivity of ocular orientation to linear accelerations in the horizontal plane. Orienting responses were also modulated by varying the head Z-axis acceleration; the sensitivity of response to Z-axis acceleration was linearly related to the response to static tilt. Although the sign of the Z-axis modulation is opposite in the lateral-eyed rabbit from that in frontal-eyed species, these data provide evidence that the brain uses both the horizontal and the vertical components of acceleration from the otolith organs to determine the magnitude of ocular orientation in response to linear acceleration.

Vertical eye position responses to steady-state sinusoidal fore–aft head translation in monkeys

A major function of the otolith organ is to detect linear acceleration generated by two different head conditions, dynamic linear translation and static tilt relative to gravity. To investigate these sensory functions of the otolith organ, we analyzed vertical eye position in response to steady-state sinusoidal fore-aft translation over a range of frequencies (0.5-4 Hz) and amplitudes (0.10-0.33 g) in three monkeys. Vertical vestibuloocular reflexes elicited by linear acceleration (LVORs) during sinusoidal fore-aft translation were divided into translational LVOR component and tilt LVOR component taking vertical gaze-dependent properties into account. Based on geometrical considerations, the translational LVOR component, but not the tilt LVOR component, depended on vertical gaze eccentricity. To quantify these two components, we used a V-shaped function model, plotting vertical eye sensitivities (deg/cm) against vertical gaze eccentricities (deg). The slope (deg/cm per degree) and intercept (sensitivity at zero gaze eccentricity) of this function approximately reflected the translational and tilt LVOR components, respectively. Our data show that the tilt LVOR component is independent of the reciprocal of the fixation distance (MA), whereas the translational LVOR component is almost linearly related to MA. The gain of the tilt LVOR component, characterized by low-pass dynamics, was greatest (0.36) at 0.5 Hz. Visual information clearly reduced the gain of the tilt LVOR component, by approximately 50%. There was no difference between the effects of large-field and small-spot stimuli. These findings demonstrate that steady-state sinusoidal fore-aft translation at lower frequencies stimulates the otolith organs and produces a pseudo-pitch tilt in cooperation with the gravito-inertial force and as a result elicits an ocular response equivalent to the tilt LVOR.

GPR surveying over burial mounds: correcting for topography and the tilt of the GPR antenna

ABSTRACTA new method for static corrections of radargrams, which accounts for the tilt that the GPR antenna encounters on sites with topography, has been developed. The method uses the average electromagnetic wave velocity and assumed antenna tilt according to the first derivative of the topography profile, in order to adjust the normal ray projecting from the GPR antenna into its correct subsurface location. Static tilt corrections for radargrams with under sampled scan locations can be effectively adjusted using scan sweeping across small angles. Radargrams that are corrected for topography and antenna tilt show that changes in the imaged locations of subsurface structures can be significant, resulting in improved focusing and more accurate positioning of reflections.

Verticality Perception During Off-Vertical Axis Rotation

During prolonged rotation about a tilted yaw axis, often referred to as off-vertical axis rotation (OVAR), a percept of being translated along a conical path slowly emerges as the sense of rotation subsides. Recently, we found that these perceptual changes are consistent with a canal-otolith interaction model that attributes the illusory translation percept to improper interpretation of the ambiguous otolith signals. The model further predicts that the illusory translation percept must be accompanied by slowly worsening tilt underestimates. Here, we tested this prediction in six subjects by measuring the time course of the subjective visual vertical (SVV) during OVAR stimulation at three different tilt-rotation speed combinations, in complete darkness. Throughout the 2-min run, at each left-ear-down and right-ear-down position, the subject indicated whether a briefly flashed line deviated clockwise or counterclockwise from vertical to determine the SVV with an adaptive staircase procedure. Typically, SVV errors indicating tilt underestimation were already present at rotation onset and then increased exponentially to an asymptotic value, reached at about 60 s after rotation onset. The initial error in the SVV was highly correlated to the response error in a static tilt control experiment. The subsequent increase in error depended on both rotation speed and OVAR tilt angle, in a manner predicted by the canal-otolith interaction model. We conclude that verticality misjudgments during OVAR reflect a dynamic component linked to canal-otolith interaction, superimposed on a tilt-related component that is also expressed under stationary conditions.