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Head-mounted display (HMD)-based virtual reality (VR) is ideally suited for presence and generating compelling visual experiences of self-motion, but users can suffer from side effects associated with head-to-display lag. We used the Oculus Rift HMD (consumer release – CV1) to simulate forward self-motion in depth. Observers made continuous yaw head movements at approximately 0.5 Hz or 1.0 Hz while viewing these self-motion simulations. We examined the perceptual effects of increasing the display lag, by adding lag to the baseline lag of the system (estimated to be approximately 5.3 ms or 0.5 frames per second). We found that increasing the head-to-display lag up to 212 ms reduced the presence and the strength of vection. In addition, faster (1.0 Hz) head oscillations were found to generate weaker presence and vection in the virtual environment than the slower (0.5 Hz) head oscillations. We also found that a positive correlation between vection and presence (found previously) persists across a wide range of head-to-display lags, and, increasing lag from a very low baseline level still impaired both experiences. Both vection and presence in virtual environments can therefore be impaired by either increasing head-display lag or making more rapid angular head movements.

Solute dispersion and mixing in beach aquifers is strongly influenced by highly transient flow induced from wave forcing. While transport at the groundwater-ocean interface has been modelled, little is known about the quantitative effect of wave forcing on solute dispersion and mixing in beach aquifers. We use a prototype-scale laboratory flume experiment to conduct tracer transport experiments at two locations within a wave-forced beach aquifer. For the first time we demonstrate by systematic laboratory experimentation that transient conditions in the re-circulation zone due to run-up and beach face infiltration as well as head oscillations caused by wave forcing strongly disperse and mix subsurface solute plumes. Wave forcing can increase the apparent dispersion by an order of magnitude depending on conditions, compared to solute transport without waves. Our findings illustrate that beach aquifer transport models need to consider the additional dispersion to correctly quantify mixing and biogeochemical processes in this highly dynamic zone.

We measured presence and perceived scene stability in a virtual environment viewed with different head-to-display lag (i.e., system lag) on the Oculus Rift (CV1). System lag was added on top of the measured benchmark system latency (22.3 ms) for our visual scene rendered in OpenGL Shading Language (GLSL). Participants made active head oscillations in pitch at 1.0Hz while viewing displays. We found that perceived scene instability increased and presence decreased when increasing system lag, which we attribute to the effect of multisensory visual-vestibular interactions on the interpretation of the visual information presented.

Optic flow has been found to be a significant cue for static observers’ perception of distance travelled. In previous research conducted in a large-scale immersive display (CAVE), adding viewpoint oscillations to a radial optic flow simulating forward self-motion was found to modulate this perception. In the present two experiments, we investigated (1) whether the improved distance travelled perceptions observed with an oscillating viewpoint in a CAVE were also obtained when the subjects were wearing a head mounted display (HMD, an Oculus Rift) and (2) whether the absence of viewpoint oscillations during treadmill walking was liable to affect the subjects’ perception of self-motion. In Experiment 1, static observers performed a distance travelled estimation task while facing either a purely linear visual simulation of self-motion (in depth) or the same flow in addition to viewpoint oscillations based on the subjects’ own head oscillations previously recorded during treadmill walking. Results show that the benefits of viewpoint oscillations observed in a CAVE persisted when the participants were wearing an HMD. In Experiment 2, participants had to carry out the same task while walking on a treadmill under two different visual conditions simulating self-motion in depth: the one with and the other without the visual consequences of their head translations. Results showed that viewpoint oscillations did not improve the accuracy of subjects’ distance travelled estimations. A comparison between the two experiments showed that adding internal dynamic information about actual self-motion to visual information did not allow participants better estimates.

Fall injuries in people with Parkinson's disease (PD) are a major health problem. Increased sway while walking is a risk factor and further understanding of this destabilizing gait change may assist with rehabilitation and help prevent falls.Here, stride-to-stride head oscillations are used to help characterise different aspects of gait impairment in 10 people with PD on medication (67 years, SD 4), 10 healthy age-matched (HAM) participants (66 years, SD 7), and 10 young (30 years, SD 7). A wearable accelerometer was used to analyse head oscillations during five repeat 17 m walks by each participant.People with PD had significantly faster transverse plane head oscillations than the HAM or young groups; both along mediolateral (PD 47.2 cm s(-1), HAM 32.5 cm s(-1), and young 32.7 cm s(-1)) and anterioposterior axes (PD 33.3 cm s(-1), HAM 24.5 cm s(-1), and young 20.6 cm s(-1)). These differences were uncorrelated with reduced vertical oscillation velocity (PD 15.5 cm s(-1), HAM 18.8 cm s(-1), and young 20.1 cm s(-1)) and reduced walking speed (PD 1.2 m s(-1), HAM 1.4 m s(-1), and young 1.4 m s(-1)).Increased transverse plane head oscillations in people with PD may reflect motor impairment and the inability to respond sufficiently to perturbations while walking, which appears to be distinct from gait hyperkinesia, reduced vertical oscillations, step length, and walking speed.

A method of characteristics-based computational model of a straight reservoir/pipe/valve system was created as a very simple rep- resentation of a small residential water distribution system. The model was used to assess transient modelling and analysis errors which occur due to demand aggregation and uncertainty. The effect of aggregating demand from the small network of residences was investigated and found to be most significant when the number and distribution of the demands was randomly varied. The inclusion of service connection pipes was also investigated; in this case leading to a higher peak head and a phase-shift in the head oscillations, which increased over time; this demonstrates the importance of modelling complete systems with high levels of accuracy.

Purpose To quantitatively characterize eye and head oscillations in patients with infantile nystagmus syndrome (INS). Methods Vertical and horizontal eye and head position in INS patients were measured simultaneously at a sampling frequency of 500 Hz. Eye and head movements were measured continuously for 180 seconds. The data was calibrated and converted to angular vectors, which were further analyzed with custom software. Results A total of 10 patients with INS were included: 3 with pseudo-jerk, 3 with pure-jerk, 2 with pseudo-pendular with foveating saccade form of jerk, 1 with bidirectional jerk, and 1 with asymmetric pendular nystagmus waveforms. None of the patients had periodic, aperiodic, or a superimposed latent nystagmus component. Two types of head oscillations were observed: one with a frequency of 1–3 Hz, present in all patients; and another with a frequency range of 5–8 Hz, present in only 7 patients. High-frequency oscillations were episodic, whereas low-frequency oscillations were constantly present. Peak velocity of the high-frequency head oscillations and eye velocity of nystagmus were not correlated, suggesting that these oscillations did not influence foveation. Conclusions Two types of head oscillations were found in INS patients: a constant, low-frequency and an episodic, high–frequency. Lack of correlation between the foveation period of nystagmus and peak head velocity during high-frequency oscillations suggests a coexisting pathological phenomenon rather than a compensatory mechanism used to improve the visual acuity.

The effect of behavioural context on the properties of slow and fast phases of the horizontal optocollic reflex (OCR) were investigated in head free pigeons for two situations, i.e.: (i) animals were hung in a harness (‘resting condition'); (ii) animals were additionally submitted to a frontal airflow that provoked a flight posture (‘flying condition') [Bilo & Bilo (1983) J. Comp. Physiol., 153, 111]. A ‘transient flight' was also provoked in the ‘resting condition' by tapping the breastbone region. Stimuli consisted either of velocity steps (30–300 °/s) or of an increasing velocity stimulus (0–300 °/s). The amplitude of nystagmic beats and the OCR gain increased in the ‘flying condition' and during ‘transient flight' as compared to the ‘resting condition'. The OCR working range was considerably extended toward high velocities by the flying behaviour. In the ‘resting condition', spontaneous head oscillations generally triggered a high-gain OCR, close to that obtained in the ‘flying condition'. One-third of the animals showed a higher gain in response to an increasing velocity stimulus than with step stimuli, in the high velocity range. The linear relation between amplitude and peak velocity of OCR fast phases was independent of the stimulation velocity in the ‘resting condition', whereas the amplitude and peak velocity increased with the stimulation velocity in the ‘flying condition'. In this condition, the fast phase velocity was correlated with the slow phase velocity, but not with the retinal slip velocity. Thus, both the slow and fast phases of the OCR are dependent on the behavioural context.

This study measured the rate of acquisition of head and trunk postural control during the two early developmental periods of independent walking, as defined by global gait parameters. Gait parameters were observed longitudinally in four children. The maximum angular deviations of the trunk and head oscillations were computed in the frontal and sagittal planes. These decreased most dramatically during the first 10-15 weeks of independent walking, during the same period when global gait parameters changed rapidly. This head and trunk stabilization may be a fundamental process that help to maintain equilibrium during walking, and may be a necessary step prior to the development of fine posturo-motor control. Language: en

The apparent motion of a fixated spot stimulus during head oscillations (apparent concomitant motion, ACM) was measured before and after an adaptation period during which the fixation stimulus moved in synchrony with the head. During the adaptation period, the fixation stimulus moved either in the same (with) or the opposite (against) direction as did head movement. With adaptation increased ACM in the direction opposite head motion, whereas against adaptation increased ACM in the same direction as head motion. Pre- and postadaptation measures were obtained for .25-, .5-, 1.0-, and 2.0-Hz active head movements. Each of these frequencies was used in separate sessions as the adaptation frequency. ACM changes were greatest when the test and adaptation frequencies were the same, demonstrating frequency specificity of ACM adaptation. This frequency specificity, which is similar to that of the vestibulo-ocular reflex, indicates that ACM adaptation may reflect plasticity in oculomotor systems.

We tested the range of visual fixation during head oscillations in a group of normal subjects who were asked to fix a visual target during oscillation of the head in the horizontal and vertical directions. Head and eye movements and the sum of both movements were recorded with a polygraph and stored in a microcomputer. To detect head and eye movements, we used a specially designed photodetector and an electronystagmographic method respectively. From the stored data, transfer function was calculated with head movements as input and eye movements as output. The normal range was defined as the mean and the standard deviation of the results.Eleven healthy male and female adults were tested.(1)The normal range obtained from polygraph records was 3.6Hz in the horizontal direction and 2.2 Hz in the vertical direction.(2)The normal range obtained from transfer functions was 4-5Hz in both horizontal and vertical directions.

Tests of visual fixation during head movements were evaluated.The subjects were asked to fix a visual target while the head was oscillated. Head and eye movements and the sum of both movements were recorded with a polygraph and stored in a microcomputer. From the stored data, transfer function was calculated with head movements as input and eye movements as output. As conditions of head movements, the following three head oscillations were studied. 1) "1 Hz method" in which the head was oscillated at 1 Hz ; 2) "acceleration-deceleration method", in which oscillation of the head started at 0.3 Hz, accelerated gradually until it was as rapid as possible, then decelerated gradually ; 3) "pseudo-random method", in which oscillation of the head was as random as possible.In the "acceleration-deceleration method", visual fixation ability at 0.3 to 5 Hz was examined and the frequency at which failure of visual fixation occurred was easily noted, since the change of the frequency of head oscillation was sequential. Transfer function obtained from the "acceleration-deceleration method" was similar to that obtained from the "pseudo-random method".These results indicate that the "acceleraion-deceleration method" is the best of the tests of visual fixation during head oscillation.

Congenital anomalies of the optic disc underlie many cases of decreased vision, strabismus, and nystagmus in childhood [54, 151]. A comprehensive evaluation necessitates an understanding of the ophthalmoscopic features, associated neuro-ophthalmologic findings, pathogenesis, and appropriate ancillary studies for each anomaly [46]. The subclassification of different forms of colobomatous defects on the basis of their ocular and systemic associations has further refined our ability to predict the likelihood of associated central nervous system (CNS) anomalies solely on the basis of the appearance of the optic disc [46]. The widespread availability of modern neuroimaging has refined the ability to identify subtle associated CNS anomalies and to prognosticate neurodevelopmental and endocrinological problems [46]. Genetic analysis has now advanced the understanding of some anomalies. It has been recognized [194, 218, 333] that many of these disorders are accompanied by some degree of peripheral retinal nonperfusion.

Healthy subjects use the vestibulo-ocular reflex (VOR) to stabilize gaze. Labyrinthine-defective humans without VOR still are, to some extent, able to maintain gaze stability during active eye-head movements. Here it is investigated whether this stabilization is due to anticipatory mechanisms or proprioceptive feedback. The head inertia was increased in humans who have undergone bilateral vestibulectomy (vestibular subjects) and in healthy controls during large gaze shifts. This leads to head oscillations in both groups. Whereas controls compensate for head oscillations and maintain gaze stability, vestibular subjects display gaze oscillations along with head oscillations. This indicates that vestibular subjects mainly use learned, anticipatory mechanisms, and not proprioception, to stabilize gaze.

The main goal of the engine-gear-clutch electronic control system is to improve the performance of the vehicle even in terms of passenger's comfort. Based on trajectory generation techniques, this paper proposes a nonlinear filter for the generation of comfortable car acceleration profiles during automatic gear shift operations. The passenger's head oscillations are evaluated by means of a head-neck dynamic model validated by experimental measurements. The on-line generation of the acceleration profiles ensures the required flexibility. The paper proposes also a methodology that can easily be extended either to fit with different comfort specifications or to match driveline constraints.

Little is known of the functionality of the vestibulo-collic reflex (VCR) and cervico-collic reflex (CCR) during head and neck movements caused by perturbations of the trunk, previously, the authors formulated mathematical expressions for these neck reflexes and incorporated them into a model of horizontal plane head movements. The formalism of this neuromechanical model allowed the authors to examine separately the main components of head movement control. In the present study, they examine selected parameters within the main components of the model, and associate variations of these parameters with disease processes affecting head and neck movements, such as loss of sensory input or modification in central or motor function. The authors' simulations led them to several conclusions. First, the probable use of the VCR and CCR in yaw plane head movements is to tune the head response. In the time domain, they diminish natural head oscillations (head wobble) related to head mechanics. Equivalently, in the frequency domain, they reduce the amplitude of head wobble (resonances) around 2 Hz. Second, the authors' simulations suggest that the VCR is about ten times stronger than the CCR in normal humans. Moreover, this disproportion is associated with only very minor contributions from the CCR in yaw. Third, head oscillations (or instability) ran be generated by mechanical or neural changes in the head and neck system. Finally, readjustments of central nervous system dynamic operations could provide mechanisms to compensate for sensory and motor dysfunction caused by disease.

Postural sway during upright stance was analyzed in 12 patients with phobic postural vertigo (PPV) and in 12 age-matched healthy volunteers. Recordings were made under different conditions (with the eyes open or closed): when standing on a foam rubber pad with the head upright, turned 30 degrees to the right or left, or during 1 Hz horizontal head oscillations. Sway analysis included calculation of sway path, of root mean square values of sway and of the power spectrum of sway in fore/aft and lateral directions. There was a significant increase in sway activity in the 3.53-8 Hz frequency band in patients with PPV. This did not impair objective postural stability. Increase in higher frequency sway activity may simply reflect a change in postural strategy rather than a sensorimotor dysfunction. The patients' conscious control of stance may augment co-activation of anti-gravity muscles, a strategy applied by normal subjects when performing demanding balancing tasks.

Perceived movement of a stationary visual stimulus during head motion was measured before and after adaptation intervals during which participants performed voluntary head oscillations while viewing a moving spot. During these intervals, participants viewed the spot stimulus moving alternately in the same direction as the head was moving during either .25- or 2.0-Hz oscillations, and then in the opposite direction as the head at the other of the two frequencies. Postadaptation measures indicated that the visual stimuli were perceived as stationary only if traveling in the same direction as that viewed during adaptation at the same frequency of head motion. Thus, opposite directions of spot motion were perceived as stationary following adaptation depending on head movement frequency. The results provide an example of the ability to establish dual (or "context-specific") adaptations to altered visual-vestibular feedback.

We have shown that the thresholds for egocentric perception of object motion are significantly raised during concurrent head oscillations of ± 20° about the vertical Z-axis and fixation of the target (Degner and Brandt 1981; Brandt 1982). Subjects were exposed to the target which randomly moved either to the right or to the left at a constant angular velocity of 24’ arc/s with a stepwise increase in exposure times from 0.25 to 10 s (20 repetitions of each stimulus condition). Conservative determination of threshold was based on 18 out of 20 possible correct perceptions of movement as well as direction. Sinusoidal active head oscillations raised the detection threshold for object motion by a factor of 2.9 at 1 Hz and 6.4 at 2 Hz oscillations (Fig. 2) despite intended stabilization of the target on the retina. This effect increases disproportionately with increasing eccentricity of the image of the moving stimulus on the retina (Fig. 3).

Gaze functions under high-frequency head oscillations with large amplitudes were investigated in 12 normal subjects. Oscillation amplitude decreased as the frequency increased (31 degrees at 2 Hz to 11 degrees at 5 Hz on average). Maximum head velocity and acceleration were 170-200 degrees/s and 2,500-5,000 degrees/s2, respectively. At frequencies higher than 2 Hz, the mean ratio of eye amplitude to head amplitude reached high large values (1.2 at 2 Hz to 1.8 at 5 Hz, on average), whereas it dropped to extremely low values (0.5-0.6 at 3-5 Hz) in the 2 referred patients with bilateral labyrinthine loss. High ratio values, different from the previous reports, may result from a failure of compensation due to abnormally high-frequency and large head oscillations. The present study indicated that the frequency range of VOR influenced by gaze should correspond to that of daily-experienced oscillations, and that once head oscillations exceed the limit, compensation quickly deteriorates.

The behavioural activities during movement, feeding and defaecation have been recorded and measured in adult females of Caenorhabditis elegans. The postures and components of recognizable wave forms are described. Stress has been laid on the mechanism of antagonistic interaction of backward and forward movement, and the rates and characteristics of “spontaneous” and “induced” reversal periods. During feeding, rapid rates of pharyngeal activity are invariably related to low rates of somatic muscle wave propagation. Head oscillations are considered to be separate events not directly linked with feeding or foraging. The combination of certain wave forms, together with other measurements have been used to develop a hypothesis to describe a co-ordinating mechanism applicable to the nematode level of organization.

Egg deposition behaviors are analyzed from time-lapse recordings during which “spontaneous” discharges of the neuroendocrine bag cells are recorded with chronically implanted cuff electrodes. In the laboratory,Aplysia brasiliana normally deposit long egg cordons on the substrate in a characteristic “figure 8” pattern similar to the configuration of egg masses observed in the natural environment. The overt behaviors associated with egg deposition are rhythmic head movements consisting of three components that overlap with characteristic relative latencies: up-and-down “undulations”, side-to-side “weaves” and in-and-out “tamps”. The characteristics of the three behaviors and their time courses relative to the appearance of eggs on the substrate suggest that undulations prepare the substrate, weaves distribute the egg cordon and tamps attach the cordon to the substrate. The same rhythmic head movements are also elicited by injections of homogenized abdominal ganglia (HAG) containing bag cell clusters, with comparable “relative” latencies and maximum frequencies but for shorter total durations. The overt behaviors begin earlier for normal than for triggered egg laying, often before the “spontaneous” release of bag cell hormones. This suggests that the head oscillations in intact animals are not normally initiated by bag cell activity. The mean latency to the appearance of the egg cordon on the substrate is the same (about 34 min) following either HAG injections or spontaneous bag cell discharges, confirming previous suggestions that the bag cell discharge triggers ovulation. Furthermore, the head movements appear to terminate at the same time following release or injection of hormone. The accompanying paper demonstrates that the full expression of the behavioral effects of bag cell injections depend upon normal movement of eggs in the reproductive tract.

A variable proportion of albino rats 6-11 days old exhibit spontaneous and infrequent rotatory head-shaking episodes. This motor pattern is slightly anticipated and significantly increased in occurrence and duration by the administration of D-amphetamine (5 mg/Kg), with a maximal effect of the drug on the 9th day. The rate of amphetamine induced rhythmic head oscillations increases with age from below 5 cps on the 5th day to about 9 cps on the 10th day. The results are discussed in relation to maturation of both the underlying catecholaminergic pathways, activated by D-amphetamine, and the stretch reflex systems of the head and neck muscles participating in the rhythmic activity. Emphasis is placed on the difference between head-shaking and stereotyped activity.

During locomotion, maintenance of clear vision and postural stability is a common problem for many animals. As the body moves, passive head oscillations are reduced by the action of compensatory vestibulo-collic and optokinetic-collic reflexes, which cooperatively tend to stabilize the position of the head in space. The slip of retinal images is further reduced by the action of these reflexes on the extraocular motor system i.e. the vestibulo-ocular and the optokinetic-ocular reflexes. In a natural situation (head free to move in response to rotation of the whole body) all these reflexes are active conjointly and simultaneously and ‘stability’ of gaze results from their combined effects through the collico-motor and the oculo-motor systems.

The gain of the vestibulo-ocular reflex in the sagittal plane may be due to a cooperation between otoliths and the vertical semi-circular canals. The present space experiment was aimed at studying the influence of the absence of gravity stimulation on the otoliths, by comparing VOR gain and phase in space and on ground. Measurements were taken the 5th and the 7th day of flight, the subject being asked to perform, eyes closed, active head oscillations in pitch while fixating an imaginary target in front of him. No significant decrease of the VOR gain was found in space, but a change in phase was noted. A significant increase of the VOR gain was found 14 h after landing. Control experiments have been done on ground on several subjects. They indicate that pitch VOR gain during active head movements is about one, with eyes open in darkness at 1 Hz.

Objective: To assess the diagnostic value of eye-head coupling in seesaw nystagmus(SSN). Back-ground: SSN is a rare binocular disorder characterized by alternating skew deviation and conjugate ocular torsion.Methods: We examined a patient with a congenital nystagmus that switched to a pendular SSN on near viewing and was associated with involuntary torsional head oscillations.Results: The binocular torsional eye movements were in phase with the clinically visible head oscillations (i.e., head movements were not compensatory for the torsional eye movements).Conclusion: This finding suggests that torsional eye-head coupling in pendular SSN has a common pathologic origin. We suggest that alternating vertical disparity of both eyes in pendular SSN is compatible with an oscillating signal acting on an intact vestibular system. The absence of brainstem lesions on high-resolution MRI supports this assumption.