Head Pitch Angle Research Articles

Augmented Reality Assessments to Support Human Spaceflight Performance Evaluation

INTRODUCTION: As next-generation space exploration missions require increased autonomy from crews, real-time diagnostics of astronaut health and performance are essential for mission operations, especially for determining extravehicular activity readiness. An augmented reality (AR) system may be a viable tool allowing holographic visual cueing to replace physical objects used in traditional assessments. METHODS: In this study, 20 healthy adults were compared in an Ingress and Egress Task and Obstacle Weave Task with holographic and physical objects to determine the effect of AR on performance. Subjects performed each task three times within each modality. RESULTS: AR exhibited increased task completion times with greater head pitch angles across the two tasks. The head and torso angular velocity showed a reduction in magnitude in both tasks within AR, while decreased magnitudes of head and torso acceleration were observed for the Obstacle Weave Task. The subjects were more deliberate and careful in their task completion during the Ingress and Egress Task within AR, stepping higher and lowering their heads further. DISCUSSION: Subjects successfully completed both tasks using AR and meaningful assessments of their performance were obtained. The increased head pitch observed supported the hologram visualization with the reduced AR field of view. The increased task time and reduced torso angular velocity were compared to strategies used by astronauts postflight while experiencing sensorimotor impairments. AR may be a useful instrumentation solution for assessing in-flight performance, providing embedded sensors and onboard computations; however, thresholds for assessing extravehicular activity readiness must be developed. Weiss H, Stirling L. Augmented reality assessments to support human spaceflight performance evaluation. Aerosp Med Hum Perform. 2024; 95(11):831–840.

Driver fatigue detection based on convolutional neural network and face alignment for edge computing device

Most current vision-based fatigue detection methods don’t have high-performance and robust face detector. They detect driver fatigue using single detection feature and cannot achieve real-time efficiency on edge computing devices. Aimed at solving these problems, this paper proposes a driver fatigue detection system based on convolutional neural network that can run in real-time on edge computing devices. The system firstly uses the proposed face detection network LittleFace to locate the face and classify the face into two states: small yaw angle state “normal” and large yaw angle state “distract.” Secondly, the speed-optimized SDM algorithm is conducted only in the face region of the “normal” state to deal with the problem that the face alignment accuracy decreases at large angle profile, and the “distract” state is used to detect driver distraction. Finally, feature parameters EAR, MAR and head pitch angle are calculated from the obtained landmarks and used to detect driver fatigue respectively. Comprehensive experiments are conducted to evaluate the proposed system and the results show its practicality and superiority. Our face detection network LittleFace can achieve 88.53% mAP on AFLW test set at 58 FPS on the edge computing device Nvidia Jetson Nano. Evaluation results on YawDD, 300 W, and DriverEyes show the average detection accuracy of the proposed system can reach 89.55%.

Keep your head down: Maintaining gait stability in challenging conditions.

Peripheral vision often deteriorates with age, disrupting our ability to maintain normal locomotion. Laboratory based studies have shown that lower visual field loss, in particular, is associated with changes in gaze and gait behaviour whilst walking and this, in turn, increases the risk of falling in the elderly. Separately, gaze and gait behaviours change and fall risk increases when walking over complex surfaces. It seems probable, but has not yet been established, that these challenges to stability interact. How does loss of the lower visual field affect gaze and gait behaviour whilst walking on a variety of complex surfaces outside of the laboratory? Specifically, is there a synergistic interaction between the effects on behaviour of blocking the lower visual field and increased surface complexity? We compared how full vision versus simulated lower visual field loss affected a diverse range of behavioural measures (head pitch angle, eye angle, muscle coactivation, gait speed and walking smoothness as measured by harmonic ratios) in young participants. Participants walked over a range of surfaces of different complexity, including pavements, grass, steps and pebbles. In both full vision and blocked lower visual field conditions, surface complexity influenced gaze and gait behaviour. For example, more complex surfaces were shown to be associated with lowered head pitch angles, increased leg muscle coactivation, reduced gait speed and decreased walking smoothness. Relative to full vision, blocking the lower visual field caused a lowering of head pitch, especially for more complex surfaces. However, crucially, muscle coactivation, gait speed and walking smoothness did not show a significant change between full vision and blocked lower visual field conditions. Finally, head pitch angle, muscle coactivation, gait speed and walking smoothness were all correlated highly with each other. Our study showed that blocking the lower visual field did not significantly change muscle coactivation, gait speed or walking smoothness. This suggests that young people cope well when walking with a blocked lower visual field, making minimal behavioural changes. Surface complexity had a greater effect on gaze and gait behaviour than blocking the lower visual field. Finally, head pitch angle was the only measure that showed a significant synergistic interaction between surface complexity and blocking the lower visual field. Together our results indicate that, first, a range of changes occur across the body when people walk over more complex surfaces and, second, that a relatively simple behavioural change (to gaze) suffices to maintain normal gait when the lower visual field is blocked, even in more challenging environments. Future research should assess whether young people cope as effectively when several impairments are simulated, representative of the comorbidities found with age.

Physical and perceptual measures of walking surface complexity strongly predict gait and gaze behaviour.

Walking surfaces vary in complexity and are known to affect stability and fall risk whilst walking. However, existing studies define surfaces through descriptions only. This study used a multimethod approach to measure surface complexity in order to try to characterise surfaces with respect to locomotor stability. We assessed how physical measurements of walking surface complexity compared to participant's perceptual ratings of the effect of complexity on stability. Physical measurements included local slope measures from the surfaces themselves and shape complexity measured using generated surface models. Perceptual measurements assessed participants' perceived stability and surface roughness using Likert scales. We then determined whether these measurements were indicative of changes to stability as assessed by behavioural changes including eye angle, head pitch angle, muscle coactivation, walking speed and walking smoothness. Physical and perceptual measures were highly correlated, with more complex surfaces being perceived as more challenging to stability. Furthermore, complex surfaces, as defined from both these measurements, were associated with lowered head pitch, increased muscle coactivation and reduced walking smoothness. Our findings show that walking surfaces defined as complex, based on physical measurements, are perceived as more challenging to our stability. Furthermore, certain behavioural measures relate better to these perceptual and physical measures than others. Crucially, for the first time this study defined walking surfaces objectively rather than just based on subjective descriptions. This approach could enable future researchers to compare results across walking surface studies. Moreover, perceptual measurements, which can be collected easily and efficiently, could be used as a proxy for estimating behavioural responses to different surfaces. This could be particularly valuable when determining risk of instability when walking for individuals with compromised stability.

Human Face Tilt Is a Dynamic Social Signal That Affects Perceptions of Dimorphism, Attractiveness, and Dominance.

Previous research has shown that manipulating the pitch of a face (tilting the face upward or downward) affects the perceived femininity, masculinity, attractiveness, and dominance of the given face. However, previous research has not considered the influence of direct eye gaze on dominance perceptions or the ambiguity surrounding the proposed social signals sent from a static face. The current research used 94 participants across two studies (women = 63%, age: M = 31). Stimuli varied in head pitch angle, eye gaze, and motion/static appearance. Participants rated the stimuli for levels of masculinity, femininity, attractiveness, and dominance. Both studies confirmed that pitching the face upward at incrementally increasing angles resulted in a linear increase in ratings of masculinity, physical dominance, and social dominance and a linear decrease in ratings of femininity, physical attractiveness, and behavioral allure. Study 2 showed that these effects can be dependent on either the perceived structural change of the face or the actual movement of the face, and these are different for each rating category. The perceived dimorphism, attractiveness, and dominance of a face will change dependent on the angle of pitch it is presented but also whether it is moving or not, where it is moving in space, and what direction it is moving.

Both optical expansion and depth information are used to control 2D pedestrian following

Collective motion in human crowds emerges from local interactions between individuals, in which pedestrian follows their near neighbors (Rio, Dachner, & Warren, PRSB, 2018). In previous work, we found that a follower’s speed and heading are controlled by nulling the optical expansion and angular velocity of a leader, depending on the leader’s position. This model explains following one neighbor (Dachner & Warren, VSS 2017; Bai & Warren, VSS 2018, 2019) and following crowds (Dachner & Warren, VSS 2018), based on visual information. However, our previous experiments isolated optical expansion and angular velocity, removing distance information. Here we add depth information (vergence, binocular disparity, declination angle from the horizon), and put it in conflict with optical expansion. 10 participants walked in a virtual environment while head position and orientation were recorded at 90 Hz. They were instructed to follow a virtual target (speckled pole, 40 cm diameter) that rested on a textured ground plane. The target appeared in three initial positions relative to the participant (0°, 30°, 60° from straight ahead), two initial distances (1m, 4m), and moved forward in the walking direction at 0.8 m/s. After 5 seconds, the pole changed its expansion rate, heading direction (+/− 35°), or both. Although its position and motion on the ground plane were consistent with its trajectory, the pole’s width expanded or contracted as if it changed speed (+/− 0.2 m/s). Participants changed speed in response to this expansion; this effect was significantly reduced by the inclusion of depth information (36% less compared to control, t(9)=3.77, p< 0.01). As well, head pitch angle indicated that participants centered their field of view at the target’s base. These results imply that following is controlled by both optical expansion and declination angle of neighbors. We plan to integrate this into our visual model of crowd behavior.

A role for the lower visual field information in stair climbing

BackgroundLocomotion on stairs is challenging for balance control and relates to a significant number of injurious falls. The visual system provides relevant information to guide stair locomotion and there is evidence that peripheral vision is potentially important. Research questionThis study investigated the role of the lower visual field information for the control of stair walking. It was hypothesized that restriction in the lower visual field (LVF) would significantly impact gaze and locomotor behaviour specifically during descent and during transition phases emphasizing the importance of the LVF information during online control. MethodsHealthy young adults (n = 12) ascended and descended a 7-step staircase while wearing customized goggles that restricted the LVF. Three visual conditions were tested: full field of view (FULL); 30° (MILD), and 15° (SEVERE) of lower field of view available. Stride time, head pitch angle and handrail use were assessed during approach, transition steps (two steps at the top and bottom of the stairs) and middle step phases. ResultsTransient downward head pitch angle increased with LVF restriction, while walk speed decreased and handrail use increased. Occlusion impaired stair descent more strongly than ascent reflected by a larger downward head pitch angles and slower walk times. LVF restriction had a greater influence on stride time and head angle during the approach and first transition compared to other stair regions. SignificanceInformation from the lower visual field is important to guide stair walking and particularly when negotiating the first few steps of a staircase. Restriction in the lower visual field during stair walking results in more cautious locomotor behaviour such as walking slower and using the handrails. In daily activities, tasks or conditions that restrict or alter the lower visual field information may elevate the risk for missteps and falls.

The quality of visual information about the lower extremities influences visuomotor coordination during virtual obstacle negotiation.

Successful negotiation of obstacles during walking relies on the integration of visual information about the environment with ongoing locomotor commands. When information about the body and the environment is removed through occlusion of the lower visual field, individuals increase downward head pitch angle, reduce foot placement precision, and increase safety margins during crossing. However, whether these effects are mediated by loss of visual information about the lower extremities, the obstacle, or both remains to be seen. Here we used a fully immersive, virtual obstacle negotiation task to investigate how visual information about the lower extremities is integrated with information about the environment to facilitate skillful obstacle negotiation. Participants stepped over virtual obstacles while walking on a treadmill with one of three types of visual feedback about the lower extremities: no feedback, end-point feedback, and a link-segment model. We found that absence of visual information about the lower extremities led to an increase in the variability of leading foot placement after crossing. The presence of a visual representation of the lower extremities promoted greater downward head pitch angle during the approach to and subsequent crossing of an obstacle. In addition, having greater downward head pitch was associated with closer placement of the trailing foot to the obstacle, further placement of the leading foot after the obstacle, and higher trailing foot clearance. These results demonstrate that the fidelity of visual information about the lower extremities influences both feedforward and feedback aspects of visuomotor coordination during obstacle negotiation. NEW & NOTEWORTHY Here we demonstrate that visual information about the lower extremities is utilized for precise foot placement and control of safety margins during obstacle negotiation. We also found that when a visual representation of the lower extremities is present, this information is used in the online control of foot trajectory. Together, our results highlight how visual information about the body and the environment is integrated with motor commands for planning and online control of obstacle negotiation.

In search of rules behind environmental framing; the case of head pitch.

BackgroundWhether, and how, animals move requires them to assess their environment to determine the most appropriate action and trajectory, although the precise way the environment is scanned has been little studied. We hypothesized that head attitude, which effectively frames the environment for the eyes, and the way it changes over time, would be modulated by the environment.MethodTo test this, we used a head-mounted device (Human-Interfaced Personal Observation platform - HIPOP) on people moving through three different environments; a botanical garden (‘green’ space), a reef (‘blue’ space), and a featureless corridor, to examine if head movement in the vertical axis differed between environments. Template matching was used to identify and quantify distinct behaviours.ConclusionsThe data on head pitch from all subjects and environments over time showed essentially continuous clear waveforms with varying amplitude and wavelength. There were three stylised behaviours consisting of smooth, regular peaks and troughs in head pitch angle and variable length fixations during which the head pitch remained constant. These three behaviours accounted for ca. 40 % of the total time, with irregular head pitch changes accounting for the rest. There were differences in rates of manifestation of behaviour according to environment as well as environmentally different head pitch values of peaks, troughs and fixations. Finally, although there was considerable variation in head pitch angles, the peak and trough values bounded most of the variation in the fixation pitch values. It is suggested that the constant waveforms in head pitch serve to inform people about their environment, providing a scanning mechanism. Particular emphasis to certain sectors is manifest within the peak and trough limits and these appear modulated by the distribution of the points where fixation, interpreted as being due to objects of interest, occurs. This behaviour explains how animals allocate processing resources to the environment and shows promise for movement studies attempting to elucidate which parts of the environment affect movement trajectories.

Vertical torque responses to vestibular stimulation in standing humans

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

Vibrotactile Balance Rehabilitation Gait Assist Device

Visual, vibrotactile, and auditory cues have proven successful in numerous applications to supplement or in some cases completely replace missing sensory information. Sensory substitution using vibrotactile stimulation has been effective in improving postural stability during stationary tasks and tasks involving perturbed stance. The challenge increases, however, when designing a wearable device that provides meaningful information during a dynamic task such as walking. Techniques that directly apply the feedback strategies effective in stance (trunk tilt) to walking have largely proven ineffective (excluding heel-to-toe walking, which is essentially a series of standing balance tasks). We have demonstrated a device for correcting vestibulopathic gait using a novel feedback methodology that was co-developed with physical therapists specializing in balance rehabilitation. The device supplies vibrotactile cues based on factors during walking that are considered important by physical therapists, including gait velocity, stride length, and gaze. The device consists of three independent units, each consisting of an inertial measurement unit (IMU), vibrotactile display, and microprocessor. Head tilt (which approximates eye gaze), trunk tilt, stride length, and velocity are estimated by the IMUs and displayed to the patient in the form of vibrotactile cues on the head, trunk, and tibia, respectively. Algorithms were developed to estimate stride length and gait velocity in real time from measured heel-strike and toe-off events. Feedback of the head pitch angle is provided continuously to the subject, while gait velocity and stride length feedback are provided during heel strike events only. Preliminary results demonstrate that healthy subjects can interpret this feedback to correct their head pitch and adjust their stride length and gait velocity.

Visual information from the lower visual field is important for walking across multi-surface terrain

Visual information concerning characteristics of the environment is critical for safe navigation. The purpose of this study was to determine the importance of vision from the lower visual field for negotiating multi-surface terrain. Ten healthy young adults and ten healthy older adults walked across a walkway where the middle portion consisted of solid, rock, slippery, compliant, tilt, and irregular surfaces (i.e. multi-surface terrain). Participants performed the walking trials with and without special glasses that blocked the lower visual field. Head pitch angle along with step parameters were measured. Young and older adults demonstrated increased mean and maximum head pitch angle downward when the lower visual field was blocked suggesting the importance of vision from this area when stepping on multi-surface terrain. In addition, young and older adults altered their gait pattern by reducing gait speed and step length when the lower visual field was blocked. These results suggest that information from the lower visual field is normally used when walking across multi-surface terrain. The results have implications for those individuals who wear multi-focal glasses and who use them while walking in complex environments, which may challenge balance.

Virtual head rotation reveals a process of route reconstruction from human vestibular signals

The vestibular organs can feed perceptual processes that build a picture of our route as we move about in the world. However, raw vestibular signals do not define the path taken because, during travel, the head can undergo accelerations unrelated to the route and also be orientated in any direction to vary the signal. This study investigated the computational process by which the brain transforms raw vestibular signals for the purpose of route reconstruction. We electrically stimulated the vestibular nerves of human subjects to evoke a virtual head rotation fixed in skull co-ordinates and measure its perceptual effect. The virtual head rotation caused subjects to perceive an illusory whole-body rotation that was a cyclic function of head-pitch angle. They perceived whole-body yaw rotation in one direction with the head pitched forwards, the opposite direction with the head pitched backwards, and no rotation with the head in an intermediate position. A model based on vector operations and the anatomy and firing properties of semicircular canals precisely predicted these perceptions. In effect, a neural process computes the vector dot product between the craniocentric vestibular vector of head rotation and the gravitational unit vector. This computation yields the signal of body rotation in the horizontal plane that feeds our perception of the route travelled.

Quantification of B0 homogeneity variation with head pitch by registered three-dimensional field mapping

In this study, we quantify the extent to which B 0 homogeneity in adult humans is dependent on head pitch relative to the B 0 vector. Three-dimensional, whole-brain B 0 field maps were acquired in five normal subjects for three generalized head pitch angles. Optimal first- and second-order shimming of the experimental B 0 maps were simulated numerically. The spatial B 0 distribution within the brain was analyzed following automated volumetric co-registration of all data. Increasing head pitch improves both the resonance offset and local homogeneity in the inferior frontal lobes, but introduces inhomogeneities in other regions of the brain which cannot be compensated by first-order shimming but are further improved by second-order shimming.

Cerebellar nodulectomy impairs spatial memory of vestibular and optokinetic stimulation in rabbits.

Natural vestibular and optokinetic stimulation were used to investigate the possible role of the cerebellar nodulus in the regulation and modification of reflexive eye movements in rabbits. The nodulus and folium 9d of the uvula were destroyed by surgical aspiration. Before and after nodulectomy the vertical and horizontal vestibuloocular reflexes (VVOR, HVOR) were measured during sinusoidal vestibular stimulation about the longitudinal (roll) and vertical (yaw) axes. Although the gain of the HVOR (G(HVOR) = peak eye movement velocity/peak head velocity) was not affected by the nodulectomy, the gain of the VVOR (G(VVOR)) was reduced. The gains of the vertical and horizontal optokinetic reflexes (G(VOKR), G(HOKR)) were measured during monocular, sinusoidal optokinetic stimulation (OKS) about the longitudinal and vertical axes. Following nodulectomy, there was no reduction in G(VOKR) or G(HOKR). Long-term binocular OKS was used to generate optokinetic afternystagmus, OKAN II, that lasts for hours. After OKAN II was induced, rabbits were subjected to static pitch and roll, to determine how the plane and velocity of OKAN II is influenced by a changing vestibular environment. During static pitch, OKAN II slow phase remained aligned with earth-horizontal. This was true for normal and nodulectomized rabbits. During static roll, OKAN II remained aligned with earth-horizontal in normal rabbits. During static roll in nodulectomized rabbits, OKAN II slow phase developed a centripetal vertical drift. We examined the suppression and recovery of G(VVOR) following exposure to conflicting vertical OKS for 10-30 min. This vestibular-optokinetic conflict reduced G(VVOR) in both normal and nodulectomized rabbits. The time course of recovery of G(VVOR) after conflicting OKS was the same before and after nodulectomy. In normal rabbits, the head pitch angle, at which peak OKAN II velocity occurred, corresponded to the head pitch angle maintained during long-term OKS. If the head was maintained in a "pitched-up" or "pitched-down" orientation during long-term OKS, the subsequently measured OKAN II peak velocity occurred at the same orientation. This was not true for nodulectomized rabbits, who had OKAN II peak velocities at head pitch angles independent of those maintained during long-term OKS. We conclude that the nodulus participates in the regulation of compensatory reflexive movements. The nodulus also influences "remembered" head position in space derived from previous optokinetic and vestibular stimulation.

Influence of Gravity on the Spatial Orientation of Eye Nystagmus Induced by Unilateral Lesion of Horizontal Semicircular Canal

The influence of gravity in the orientation and slow phase eye velocity of the ocular nystagmus following unilateral damage of the cupula in the ampulla of the horizontal semicircular canal (UHCD) was investigated. The nystagmus was analysed at different sagittal head positions using the x-y infrared eye monitor technique. The nystagmus was almost horizontal at 0 degrees head pitch angle and remained partially fixed in space when the head was pitched upward or downward. The reorientation gain of the slow and quick phases was high (about 0.75) within +/- 45 degrees of head pitch angle, but beyond this range, it decreased greatly. The gain value depended on the lesion extension to otolithic receptors. The absolute value of the slow phase eye velocity of UHCD nystagmus was also modified systematically by the head pitch, showing a reduction in the upward and an increase in the downward.

Optokinetic and Vestibular Stimulation Determines the Spatial Orientation of Negative Optokinetic Afternystagmus in the Rabbit

Prolonged binocular optokinetic stimulation (OKS) in the rabbit induces a high-velocity negative optokinetic afternystagmus (OKAN II) that persists for several hours. We have taken advantage of this uniform nystagmus to study how changes in static head orientation in the pitch plane might influence the orientation of the nystagmus. After horizontal OKS, the rotation axis of the OKAN II remained almost constant in space as it was kept aligned with the gravity vector when the head was pitched by as much as 80 degrees up and 35 degrees down. Moreover, during reorientation, slow-phase eye velocity decreased according to the head pitch angle. Thereafter, we analyzed the space orientation of OKAN II after optokinetic stimulation during which the head and/or the OKS were pitched upward and downward. The rotation axis of OKAN II did not remain aligned with an earth vertical axis nor a head vertical axis, but it tended to be aligned with that of the OKS respace. The slow-phase eye velocity of OKAN II was also affected by the head pitch angle during OKS, because maximal OKAN II velocity occurred at the same head pitch angle as that during optokinetic stimulation. We suggest that OKAN II is coded in gravity-centered rather than in head-centered coordinates, but that this coordinate system may be influenced by optokinetic and vestibular stimulation. Moreover, the velocity attenuation of OKAN II seems to depend on the mismatch between the space-centered nystagmus rotation axis orientation and that of the "remembered" head-centered optokinetic pathway activated by OKS.

Otolithic and Extraocular Muscle Proprioceptive Influences on the Spatial Organization of the Vestibulo- and Cervico-Ocular Quick Phases

The cervico-ocular reflex (COR) was studied alone or in combination with the vestibulo-ocular reflex (VOR) in the rabbit. Step stimulations of the body with respect to the fixed head induced small slow compensatory responses followed by large compensatory quick phases (QP). These responses remained aligned with the horizon at different head pitch angles. The QP reorientation in space was due to the gravity influence on the otolithic receptors. The vestibular induced QPs exhibit a similar pattern. Because of this reorientation, the reduction of the amplitude of the vestibular induced QPs, due to the addition of the COR, was maintained even at different static head positions. The electrolytic lesion of the ophthalmic branch of the trigeminal nerve deeply affected the space orientation of the COR. In particular, the cervically induced compensatory QPs of the eye ipsilateral to the lesion showed a remarkable variability of their trajectories and they lost space reorientation. These findings suggest that the coordinate system controlling the QPs is influenced by signals, originating from both head position in space and eye position in the orbit.