Sinusoidal Rotation Research Articles

Flash induced afterimage versus single spot visual object influence on visual–vestibular interaction in detection threshold for self-motion perception

In seven healthy subjects we studied the effect of flash induced afterimage on perceptual threshold for self-motion during sinusoidal vertical axis rotation compared to rotation in darkness, and rotation with subject’s gaze fixed on a ‘real’ visual object rotated with him. For a real object we used light-emitting diode (LED) aligned with subject’s head.A MOOG motion platform was used to generate motion. Single cycles of sinusoidal acceleration at four frequencies: 0.1, 0.2, 0.5, and 1Hz were used as motion stimuli.The results show that the threshold when subjects stare at an afterimage during rotation is consistently lower compared to rotation in darkness. However, compared to the threshold during rotation with a ‘real’ object visual fixation it is higher, significantly at frequencies 0.5 and 0.2Hz (p<0.05). The threshold is frequency dependent – it decreases with increase of the frequency (p<0.01).The probable mechanism of afterimage influence on perceptual threshold for self-motion is discussed.

Neural Representation of Orientation Relative to Gravity in the Macaque Cerebellum

A fundamental challenge for maintaining spatial orientation and interacting with the world is knowledge of our orientation relative to gravity, i.e., head tilt. Sensing gravity is complicated because of Einstein's equivalence principle, in which gravitational and translational accelerations are physically indistinguishable. Theory has proposed that this ambiguity is solved by tracking head tilt through multisensory integration. Here we identify a group of Purkinje cells in the caudal cerebellar vermis with responses that reflect an estimate of head tilt. These tilt-selective cells are complementary to translation-selective Purkinje cells, such that their population activities sum to the net gravitoinertial acceleration encoded by the otolith organs, as predicted by theory. These findings reflect the remarkable ability of the cerebellum for neural computation and provide quantitative evidence for a neural representation of gravity, whose calculation relies on long-postulated theoretical concepts such as internal models and Bayesian priors.

Design and experiment of spectrometer based on scanning micro-grating integrating with angle sensor

A compact, low cost, high speed, non-destructive testing NIR (near infrared) spectrometer optical system based on MOEMS grating device is developed. The MOEMS grating works as the prismatic element and wavelength scanning element in our optical system. The MOEMS grating enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. This MOEMS grating is driven by electromagnetic force and integrated with angle sensor which used to monitored deflection angle while the grating working. Comparing with the traditional spectral system, there is a new structure with a single detector and worked at high frequency. With the characteristics of MOEMS grating, the structure of the spectrometer system is proposed. After calculating the parameters of the optical path, ZEMAX optical software is used to simulate the system. According the ZEMAX output file of the 3D model, the prototype is designed by SolidWorks rapidly, fabricated. Designed for a wavelength range between 800nm and 1500nm, the spectrometer optical system features a spectral resolution of 16nm with the volume of 97mm×81.7mm×81mm. For the purpose of reduce modulated effect of sinusoidal rotation, spectral intensity of the different wavelength should be compensated by software method in the further. The system satisfies the demand of NIR micro-spectrometer with a single detector.

Spontaneous Blink Rates in Children During Different Types of Eye Movements

The spontaneous blink rate (SBR) is variable in humans. It increases rapidly during childhood before reaching a plateau in adulthood at 10-20 blinks/minute. Our aim was to compare the SBR during different visual tasks in children. Thirty-nine healthy participants (mean age(SD):13.6(3.5)years, M=21), made horizontal and vertical visually-guided saccades, tracked a horizontal and vertical target, performed horizontal and vertical active sinusoidal head rotations in light and darkness while looking straight ahead (VOR task) or fixated straight ahead and in four directions of gaze. The eyes of each participant were videotaped and reviewed twice to determine the SBR. Parametric and non-parametric tests were used to analyze the data. The median SBR during fixation straight ahead was seven blinks/minute, which was similar to the SBR during horizontal saccades and horizontal smooth pursuit tasks. The median SBR during vertical smooth pursuit and vertical saccades were significantly lower than during fixation (p≤0.042). The median SBR during the VOR task in light and horizontal VOR in darkness were significantly higher than during fixation (p=0.019-0.024). The median SBR during visual fixation was lower than that reported previously in 5-14 years-old children during rest or 11-20 years-old subjects during quiet conversation. The median SBR was even lower during vertical smooth pursuit and saccades tasks. This may be due to differences in concentration required for visual fixation in general and vertical visual tasks more specifically. The higher SBR during the VOR may be due to drying of the eyes during head shaking.

Responses of central vestibular neurons to sinusoidal yaw rotation in compensated macaques after unilateral labyrinthectomy

After vestibular labyrinth injury, behavioral measures of vestibular function partially recover through the process of vestibular compensation. The present study was performed to improve our understanding of the physiology of macaque vestibular nucleus neurons in the compensated state (>6 wk) after unilateral labyrinthectomy (UL). The responses of neurons to sinusoidal yaw rotation at a series of frequencies (0.1-2.0 Hz) and peak velocities (7.5-210°/s) were examined to determine how the behavior of these cells differed from those in animals with intact labyrinths. The sensitivity of neurons responding to ipsilateral rotation (type I) did not differ between the intact and injured sides after UL, although this sensitivity was lower bilaterally after lesion than before lesion. The sensitivity of neurons that increase firing with contralateral rotation (type II) was higher ipsilateral to the UL than before lesion or in the nucleus contralateral to the UL. UL did not increase asymmetry in the responses of individual type I or II neurons to ipsilateral vs. contralateral rotation, nor does it change the power law relationship between neuronal firing and level of stimulation. Increased sensitivities of contralesional type I neurons to the remaining vestibular nerve input and increased efficacy of inhibitory vestibular commissures projecting to the ipsilesional vestibular nucleus appear to be responsible for recovery of dynamic function of central vestibular neurons in compensated animals. The portion of type I neurons on the ipsilesional side is reduced in compensated animals, which likely accounts for the asymmetries in vestibular reflexes and perception that characterize vestibular function after UL.

Vestibular Role of KCNQ4 and KCNQ5 K+ Channels Revealed by Mouse Models

The function of sensory hair cells of the cochlea and vestibular organs depends on an influx of K(+) through apical mechanosensitive ion channels and its subsequent removal over their basolateral membrane. The KCNQ4 (Kv7.4) K(+) channel, which is mutated in DFNA2 human hearing loss, is expressed in the basal membrane of cochlear outer hair cells where it may mediate K(+) efflux. Like the related K(+) channel KCNQ5 (Kv7.5), KCNQ4 is also found at calyx terminals ensheathing type I vestibular hair cells where it may be localized pre- or postsynaptically. Making use of Kcnq4(-/-) mice lacking KCNQ4, as well as Kcnq4(dn/dn) and Kcnq5(dn/dn) mice expressing dominant negative channel mutants, we now show unambiguously that in adult mice both channels reside in postsynaptic calyx-forming neurons, but cannot be detected in the innervated hair cells. Accordingly, whole cell currents of vestibular hair cells did not differ between genotypes. Neither Kcnq4(-/-), Kcnq5(dn/dn) nor Kcnq4(-/-)/Kcnq5(dn/dn) double mutant mice displayed circling behavior found with severe vestibular impairment. However, a milder form of vestibular dysfunction was apparent from altered vestibulo-ocular reflexes in Kcnq4(-/-)/Kcnq5(dn/dn) and Kcnq4(-/-) mice. The larger impact of KCNQ4 may result from its preferential expression in central zones of maculae and cristae, which are innervated by phasic neurons that are more sensitive than the tonic neurons present predominantly in the surrounding peripheral zones where KCNQ5 is found. The impact of postsynaptic KCNQ4 on vestibular function may be related to K(+) removal and modulation of synaptic transmission.

Tests of linearity in the responses of eye-movement-sensitive vestibular neurons to sinusoidal yaw rotation.

The rotational vestibulo-ocular reflex in primates is linear and stabilizes gaze in space over a large range of head movements. Best evidence suggests that position-vestibular-pause (PVP) and eye-head velocity (EHV) neurons in the vestibular nuclei are the primary mediators of vestibulo-ocular reflexes for rotational head movements, yet the linearity of these neurons has not been extensively tested. The current study was undertaken to understand how varying magnitudes of yaw rotation are coded in these neurons. Sixty-six PVP and 41 EHV neurons in the rostral vestibular nuclei of 7 awake rhesus macaques were recorded over a range of frequencies (0.1 to 2 Hz) and peak velocities (7.5 to 210°/s at 0.5 Hz). The sensitivity (gain) of the neurons decreased with increasing peak velocity of rotation for all PVP neurons and EHV neurons sensitive to ipsilateral rotation (type I). The sensitivity of contralateral rotation-sensitive (type II) EHV neurons did not significantly decrease with increasing peak velocity. These data show that, like non-eye-movement-related vestibular nuclear neurons that are believed to mediate nonlinear vestibular functions, PVP neurons involved in the linear vestibulo-ocular reflex also behave in a nonlinear fashion. Similar to other sensory nuclei, the magnitude of the vestibular stimulus is not linearly coded by the responses of vestibular neurons; rather, amplitude compression extends the dynamic range of PVP and type I EHV vestibular neurons.

Visual-vestibular stimulation influences spatial and non-spatial cognitive processing

This study investigated the impact of visual-vestibular stimulation on performance of an auditory information processing task in young and older adults. Performance on a spatial choice reaction time task was compared to performance on a non-spatial choice reaction time task. The tasks were performed during simultaneous rotational and moving visual stimulation. The non-spatial task was an auditory frequency discrimination task while the spatial task was a right-left lateralization task. Visual and vestibular conditions consisted of a non-movement baseline, sinusoidal earth-vertical axis rotation (EVAR) in darkness, off-vertical axis rotation (OVAR) in darkness at a constant velocity, OVAR in darkness with a sinusoidal profile, EVAR with a lighted visual surround, constant velocity optokinetic stimulation, and sinusoidal optokinetic stimulation. Baseline reaction times were subtracted from reaction times during each stimulus condition to yield "task cost", which was analyzed statistically. Subjects were healthy young (n=20; 24 ± 2.7 yrs; 10F) and older (n=29; 73 ± 6.0 yrs; 18F) adults. Results indicated that task cost was affected by the visual-vestibular condition and a task x condition interaction. There was no main effect of task or age group and no significant interaction with age. Otolithic stimulation and visual stimulation were associated with greater task cost compared to semicircular canal stimulation. Combining semicircular canal with otolithic or visual stimulation had no additional effect beyond otolithic or visual stimulation alone. This pattern of task cost being larger for otolith or visual vs. semicircular canal stimulation was found for both the spatial and non-spatial tasks. The significant interaction between condition and task type revealed that the task cost for the spatial task was larger than the task cost for the non-spatial task during visual conditions but not during non-visual conditions although the visual and non-visual conditions were not entirely comparable. This study suggests that interference of vestibular stimulation with cognitive processing is especially prominent for otolithic and visual stimulation although the strength of the various visual-vestibular stimuli may not have been uniform. Also, spatial tasks are more affected than non-spatial tasks during visual stimulation and interference between vestibular stimulation and cognitive processing is not age dependent for these relatively easy tasks.

Adaptive tuning of perceptual timing to whole body motion

In a previous work we have shown that sinusoidal whole-body rotations producing continuous vestibular stimulation, affected the timing of motor responses as assessed with a paced finger tapping (PFT) task (Binetti et al. (2010). Neuropsychologia, 48(6), 1842–1852). Here, in two new psychophysical experiments, one purely perceptual and one with both sensory and motor components, we explored the relationship between body motion/vestibular stimulation and perceived timing of acoustic events. In experiment 1, participants were required to discriminate sequences of acoustic tones endowed with different degrees of acceleration or deceleration. In this experiment we found that a tone sequence presented during acceleratory whole-body rotations required a progressive increase in rate in order to be considered temporally regular, consistent with the idea of an increase in “clock” frequency and of an overestimation of time. In experiment 2 participants produced self-paced taps, which entailed an acoustic feedback. We found that tapping frequency in this task was affected by periodic motion by means of anticipatory and congruent (in-phase) fluctuations irrespective of the self-generated sensory feedback. On the other hand, synchronizing taps to an external rhythm determined a completely opposite modulation (delayed/counter-phase). Overall this study shows that body displacements “remap” our metric of time, affecting not only motor output but also sensory input.

A novel treatment for vestibular disorder with FGLM-NH2 plus SSSR

Topical FGLM-NH2 (Phenylalanine–Glycine–Leucine–Methionine–Amide) plus SSSR (Serine–Serine–Serine–Arginine) facilitates recovery from vestibular disorders induced by (±)-α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) in guinea pigs and might offer a treatment strategy for patients with peripheral vestibular disorders.The tetrapeptide FGLM-NH2 derived from substance P (SP) can be used to treat corneal disorders when combined with SSSR, which is a tetrapeptide derived from insulin-like growth factor-1 (IGF-1). We examined the influence of FGLM-NH2 plus SSSR when locally applied to the unilateral inner ear of guinea pigs with vestibular disorder induced by AMPA. A total of 18 Hartley white guinea pigs were assigned to groups receiving either FGLM-NH2 plus SSSR, artificial perilymph, or no treatment at all. A hole was drilled adjacent to the round window, with AMPA then infused into the hole in order to induce the vestibular disorder. Thereafter, FGLM-NH2 plus SSSR or artificial perilymph was delivered via an osmotic pump that was inserted into the hole. Sinusoidal rotation tests were used for observing spontaneous nystagmus and for measurements of the vestibulo-ocular reflexes (VOR). Two animals from each group were immunohistochemically examined at 24h after the treatment. Spontaneous nystagmus decreased immediately after FGLM-NH2 plus SSSR infusion. The recovery of the VOR gains was statistically faster than that seen in the control group at 3 and 7 days after treatment. Immunohistochemical examination revealed that many synaptic ribbons, which are markers of the synapse, were stained in the FGLM-NH2 plus SSSR group compared with the untreated group. Topical application of FGLM-NH2 plus SSSR accelerates functional recovery from AMPA-induced vestibular disorders by facilitating synaptic regeneration in guinea pigs.

Galvanic stimulation of the vestibular periphery in guinea pigs during passive whole body rotation and self-generated head movement

Irregular vestibular afferents exhibit significant phase leads with respect to angular velocity of the head in space. This characteristic and their connectivity with vestibulospinal neurons suggest a functionally important role for these afferents in producing the vestibulo-collic reflex (VCR). A goal of these experiments was to test this hypothesis with the use of weak galvanic stimulation of the vestibular periphery (GVS) to selectively activate or suppress irregular afferents during passive whole body rotation of guinea pigs that could freely move their heads. Both inhibitory and excitatory GVS had significant effects on compensatory head movements during sinusoidal and transient whole body rotations. Unexpectedly, GVS also strongly affected the vestibulo-ocular reflex (VOR) during passive whole body rotation. The effect of GVS on the VOR was comparable in light and darkness and whether the head was restrained or unrestrained. Significantly, there was no effect of GVS on compensatory eye and head movements during volitional head motion, a confirmation of our previous study that demonstrated the extravestibular nature of anticipatory eye movements that compensate for voluntary head movements.

Control System of Moving Target Simulator

To test the accuracy of image motion compensation of space camera, the moving target simulator was developed according to the principle of relative motion. As the core controller, PIC microcontroller controls DC motor to drive photoetching turntable rotating to simulate the relative linear velocity between ground target and aircraft, and the rotation motion is divided into uniform velocity rotation and sinusoidal velocity rotation. Furthermore, the simulation of drift angle of aircraft was realized by controlling stepper motor to drive the photoetching turntable deflecting, and the deflection includes uniform deflection, sinusoidal velocity deflection and specified angle positioning. The design of the hardware and software of control system has been completed and tested, and the experiment results show that the control system has high control precision and meets the design requirements.

Thermal Sensitivity of Vestibular Neuroepithelium in the Toadfish

Core body temperature is known affect the static and dynamic properties of vestibular nerve afferents, although the underlying mechanisms for the differential sensitivity of the two afferents types to temperature changes are unknown. We recorded the changes in spontaneous discharge rate, regularity, adaptation to step hair bundle displacements and responses to sinusoidal head rotations of single-units to changes in temperature of the crista ampullaris in the oyster toadfish. Similar temperature gradients were introduced with perfusion of temperature-controlled artificial perilymph and with irradiation of the crista with 980 and 1860 nm light. A broad spectrum of afferent responses to thermal perfusion was observed: some neurons were insensitive to temperature, some increased their spontaneous discharge rate, and others showed a decrease in their discharge rate with temperature. The very short focused pulses of light at the two wavelengths deliver transient pulses of thermal energy (dT/dt) without large increases in accumulated temperature of cells or tissue. The irradiation of the crista produced different responses from the same afferents for a similar change in temperature. These results suggest potential wavelength specific absorption within the vestibular neuroepithelium underlies the differences between the three forms of heat delivery. Depending upon the hair cell type irradiated, the fast temperature changes induced may modulate the intracellular Ca2+ levels differently affecting the neurotransmitter release. Regardless of the mechanisms involved, the presence of temperature compensating mechanisms in the hair cell and afferent complex may allow sensitive function over a wide range of temperatures.

Migraine, motion sensitivity, and temporal binding

Little is known about vestibular-related timing processes in patients with disequilibrium. Patients with a history of migraine headaches often complain of significant motion sensitivity and long-term vague imbalance inconsistent with a peripheral vestibular disorder. Some of these people have episodic spells of severe vertigo termed ‘vestibular migraines’. Other patients have no history of migraine but do report significant motion sensitivity. Motion sensitivity has typically been explained as a mismatch between the amplitude of vestibular and other (typically visual) sensory inputs. Another possibility is that motion sensitive patients may suffer from a mismatch in the temporal integration of vestibular and other sensory inputs. Here, we compared the temporal binding window (TBW) of vestibular + auditory stimuli in normal subjects, subjects with motion sensitivity, and those with both migraine and motion sensitivity. We asked subjects undergoing earth-vertical sinusoidal rotations at 0.5 Hz, 128°/s to identify whether a metronome-like series of tone bursts was synchronous with their cyclic motion. We calculated the TBW as the range in time encompassing the middle 68% of the area under the psychometric curve. The TBW in normal subjects was 312 ± 135 ms (mean ± SD), in subjects with motion sensitivity was 454 ± 103 ms, and in subjects with migraine and motion sensitivity was 451 ± 124 ms. The TBW of normal subjects was significantly shorter than the other groups. Temporal errors in perception, as manifested by a prolongation of the TBW, are a plausible mechanism for imbalance in patients with migraine and motion sensitivity.

Numerical simulation of the fluid dynamics in vitreous cavity due to saccadic eye movement

In this study, the flow dynamics of vitreous due to saccadic movements following vitreous liquefaction or in post-vitrectomy eyes is investigated. Using a dynamic mesh technique, the eye motion was modeled and unsteady three-dimensional forms of continuity and Navier–Stokes equations were solved numerically. Firstly, the numerical model was validated for a sphere as a model of vitreous chamber and agrees well with the results based on available analytic solutions and experimental data. Then, numerical simulation was performed based on a deformed sphere with an indentation representing the lens. This consists of a vitreous cavity filled with a liquid having the viscosity of liquefied vitreous and balanced salt solution. The wall shear stress on the retina was computed and compared for various saccade amplitudes. Also, the effect of variation in vitreous viscosity and the size of lens indentation are investigated. The results show that the secondary flow in the vertical direction in the vitreous cavity is much higher for the liquefied vitreous and balanced salt solution compared with that for silicone oil. The possible effect of shear stress on the retinal detachment for all studied cases is discussed. A semi-analytic correlation is also developed for maximum wall shear stress of the spherical domain that is subjected to sinusoidal rotations.

Computational model of an infant brain subjected to periodic motion simplified modelling and bayesian sensitivity analysis

Non-accidental head injury in infants, or shaken baby syndrome, is a highly controversial and disputed topic. Biomechanical studies often suggest that shaking alone cannot cause the classical symptoms, yet many medical experts believe the contrary. Researchers have turned to finite element modelling for a more detailed understanding of the interactions between the brain, skull, cerebrospinal fluid (CSF), and surrounding tissues. However, the uncertainties in such models are significant; these can arise from theoretical approximations, lack of information, and inherent variability. Consequently, this study presents an uncertainty analysis of a finite element model of a human head subject to shaking. Although the model geometry was greatly simplified, fluid-structure-interaction techniques were used to model the brain, skull, and CSF using a Eulerian mesh formulation with penalty-based coupling. Uncertainty and sensitivity measurements were obtained using Bayesian sensitivity analysis, which is a technique that is relatively new to the engineering community. Uncertainty in nine different model parameters was investigated for two different shaking excitations: sinusoidal translation only, and sinusoidal translation plus rotation about the base of the head. The level and type of sensitivity in the results was found to be highly dependent on the excitation type.

Restoration of 3D vestibular sensation in rhesus monkeys using a multichannel vestibular prosthesis

Profound bilateral loss of vestibular hair cell function can cause chronically disabling loss of balance and inability to maintain stable vision during head and body movements. We have previously shown that chinchillas rendered bilaterally vestibular-deficient via intratympanic administration of the ototoxic antibiotic gentamicin regain a more nearly normal 3-dimensional vestibulo-ocular reflex (3D VOR) when head motion information sensed by a head-mounted multichannel vestibular prosthesis (MVP) is encoded via rate-modulated pulsatile stimulation of vestibular nerve branches. Despite significant improvement versus the unaided condition, animals still exhibited some 3D VOR misalignment (i.e., the 3D axis of eye movement responses did not precisely align with the axis of head rotation), presumably due to current spread between a given ampullary nerve’s stimulating electrode(s) and afferent fibers in non-targeted branches of the vestibular nerve. Assuming that effects of current spread depend on relative orientation and separation between nerve branches, anatomic differences between chinchilla and human labyrinths may limit the extent to which results in chinchillas accurately predict MVP performance in humans. In this report, we describe the MVP-evoked 3D VOR measured in alert rhesus monkeys, which have labyrinths that are larger than chinchillas and temporal bone anatomy more similar to humans. Electrodes were implanted in five monkeys treated with intratympanic gentamicin to bilaterally ablate vestibular hair cell mechanosensitivity. Eye movements mediated by the 3D VOR were recorded during passive sinusoidal (0.2–5 Hz, peak 50°/s) and acceleration-step (1000°/s 2 to 150°/s) whole-body rotations in darkness about each semicircular canal axis. During constant 100 pulse/s stimulation (i.e., MVP powered ON but set to stimulate each ampullary nerve at a constant mean baseline rate not modulated by head motion), 3D VOR responses to head rotation exhibited profoundly low gain [(mean eye velocity amplitude)/(mean head velocity amplitude) < 0.1] and large misalignment between ideal and actual eye movements. In contrast, motion-modulated sinusoidal MVP stimuli elicited a 3D VOR with gain 0.4–0.7 and axis misalignment of 21–38°, and responses to high-acceleration transient head rotations exhibited gain and asymmetry closer to those of unilaterally gentamicin-treated animals (i.e., with one intact labyrinth) than to bilaterally gentamicin-treated animals without MVP stimulation. In comparison to responses observed under similar conditions in chinchillas, acute responses to MVP stimulation in rhesus macaque monkeys were slightly better aligned to the desired rotation axis. Responses during combined rotation and prosthetic stimulation were greater than when either stimulus was presented alone, suggesting that the central nervous system uses MVP input in the context of multisensory integration. Considering the similarity in temporal bone anatomy and VOR performance between rhesus monkeys and humans, these observations suggest that an MVP will likely restore a useful level of vestibular sensation and gaze stabilization in humans.

Absence of Spatial Updating when the Visuomotor System Is Unsure about Stimulus Motion

How does the visuomotor system decide whether a target is moving or stationary in space or whether it moves relative to the eyes or head? A visual flash during a rapid eye-head gaze shift produces a brief visual streak on the retina that could provide information about target motion, when appropriately combined with eye and head self-motion signals. Indeed, double-step experiments have demonstrated that the visuomotor system incorporates actively generated intervening gaze shifts in the final localization response. Also saccades to brief head-fixed flashes during passive whole-body rotation compensate for vestibular-induced ocular nystagmus. However, both the amount of retinal motion to invoke spatial updating and the default strategy in the absence of detectable retinal motion remain unclear. To study these questions, we determined the contribution of retinal motion and the vestibular canals to spatial updating of visual flashes during passive whole-body rotation. Head- and body-restrained humans made saccades toward very brief (0.5 and 4 ms) and long (100 ms) visual flashes during sinusoidal rotation around the vertical body axis in total darkness. Stimuli were either attached to the chair (head-fixed) or stationary in space and were always well localizable. Surprisingly, spatial updating only occurred when retinal stimulus motion provided sufficient information: long-duration stimuli were always appropriately localized, thus adequately compensating for vestibular nystagmus and the passive head movement during the saccade reaction time. For the shortest stimuli, however, the target was kept in retinocentric coordinates, thus ignoring intervening nystagmus and passive head displacement, regardless of whether the target was moving with the head or not.

Fuzzy Neural Network Control for Robot Manipulator Directly Driven by Switched Reluctance Motor

Applications of switched reluctance motor (SRM) to direct drive robot are increasingly popular because of its valuable advantages. However, the greatest potential defect is its torque ripple owing to the significant nonlinearities. In this paper, a fuzzy neural network (FNN) is applied to control the SRM torque at the goal of the torque-ripple minimization. The desired current provided by FNN model compensates the nonlinearities and uncertainties of SRM. On the basis of FNN-based current closed-loop system, the trajectory tracking controller is designed by using the dynamic model of the manipulator, where the torque control method cancels the nonlinearities and cross-coupling terms. A single link robot manipulator directly driven by a four-phase 8/6-pole SRM operates in a sinusoidal trajectory tracking rotation. The simulated results verify the proposed control method and a fast convergence that the robot manipulator follows the desired trajectory in a 0.9-s time interval.

Cross-axis adaptation improves 3D vestibulo-ocular reflex alignment during chronic stimulation via a head-mounted multichannel vestibular prosthesis

By sensing three-dimensional (3D) head rotation and electrically stimulating the three ampullary branches of a vestibular nerve to encode head angular velocity, a multichannel vestibular prosthesis (MVP) can restore vestibular sensation to individuals disabled by loss of vestibular hair cell function. However, current spread to afferent fibers innervating non-targeted canals and otolith end organs can distort the vestibular nerve activation pattern, causing misalignment between the perceived and actual axis of head rotation. We hypothesized that over time, central neural mechanisms can adapt to correct this misalignment. To test this, we rendered five chinchillas vestibular deficient via bilateral gentamicin treatment and unilaterally implanted them with a head-mounted MVP. Comparison of 3D angular vestibulo-ocular reflex (aVOR) responses during 2 Hz, 50°/s peak horizontal sinusoidal head rotations in darkness on the first, third, and seventh days of continual MVP use revealed that eye responses about the intended axis remained stable (at about 70% of the normal gain) while misalignment improved significantly by the end of 1 week of prosthetic stimulation. A comparable time course of improvement was also observed for head rotations about the other two semicircular canal axes and at every stimulus frequency examined (0.2-5 Hz). In addition, the extent of disconjugacy between the two eyes progressively improved during the same time window. These results indicate that the central nervous system rapidly adapts to multichannel prosthetic vestibular stimulation to markedly improve 3D aVOR alignment within the first week after activation. Similar adaptive improvements are likely to occur in other species, including humans.