scholarly journals Role of Eye, Head, and Shoulder Geometry in the Planning of Accurate Arm Movements

2002 ◽  
Vol 87 (4) ◽  
pp. 1677-1685 ◽  
Author(s):  
D.Y.P. Henriques ◽  
J. D. Crawford
Keyword(s):  
Visual Information ◽  
Arm Movements ◽  
Head Rotation ◽  
Head Position ◽  
Open Loop ◽  
Target Line ◽  
Head Orientation ◽  
Complex Process ◽  
Hand Coordination ◽  
Shoulder Geometry

Eye-hand coordination requires the brain to integrate visual information with the continuous changes in eye, head, and arm positions. This is a geometrically complex process because the eyes, head, and shoulder have different centers of rotation. As a result, head rotation causes the eye to translate with respect to the shoulder. The present study examines the consequences of this geometry for planning accurate arm movements in a pointing task with the head at different orientations. When asked to point at an object, subjects oriented their arm to position the fingertip on the line running from the target to the viewing eye. But this eye-target line shifts when the eyes translate with each new head orientation, thereby requiring a new arm pointing direction. We confirmed that subjects do realign their fingertip with the eye-target line during closed-loop pointing across various horizontal head orientations when gaze is on target. More importantly, subjects also showed this head-position–dependent pattern of pointing responses for the same paradigm performed in complete darkness. However, when gaze was not on target, compensation for these translations in the rotational centers partially broke down. As a result, subjects tended to overshoot the target direction relative to current gaze; perhaps explaining previously reported errors in aiming the arm to retinally peripheral targets. These results suggest that knowledge of head position signals and the resulting relative displacements in the centers of rotation of the eye and shoulder are incorporated using open-loop mechanisms for eye-hand coordination, but these translations are best calibrated for foveated, gaze-on-target movements.

Vertical nystagmus in normal subjects: Effects of head position, nicotine and scopolamine

2000 ◽  
Vol 10 (6) ◽  
pp. 291-300
Author(s):  
J.I. Kim ◽  
J.T. Somers ◽  
J.S. Stahl ◽  
R. Bhidayasiri ◽  
R.J. Leigh
Keyword(s):  
Nicotine Patch ◽  
Head Rotation ◽  
Normal Subjects ◽  
Head Position ◽  
Slow Phase ◽  
Head Orientation ◽  
Slow Phase Velocity ◽  
Gaze Stability ◽  
Normal Humans ◽  
Vertical Nystagmus

We measured gaze stability in darkness of four normal humans using the search coil technique. Subjects were tested first with their heads erect, and then with their heads positioned 180 degrees upside-down. In each position, subjects held their head stationary for one minute, and then actively performed pitch rotations for 20 sec. All subjects showed sustained chin-beating nystagmus in the upside-down position. Each subject showed a significant increase of slow-phase velocity directed towards their brow after 40 sec in the inverted versus erect position. Pitch head rotation had little effect on subsequent nystagmus, except for transient reversal in one subject. The sustained changes of vertical eye drifts induced by 180 deg change of head position suggest that otolithic factors may contribute to vertical nystagmus in normals. The subjects were retested after wearing a nicotine patch for 2 hours. In three subjects, nicotine induced brow-beating nystagmus; adopting a head-hanging position increased this nystagmus in two subjects. In a third session, subjects were tested after wearing a scopolamine patch for 2 hours; results were generally similar to the control condition. We conclude that normal subjects may show chin-beating (“downbeating”) nystagmus in a head-hanging position in darkness, reflecting a normal, physiological change in otolithic inputs brought about by the head orientation.

scholarly journals Does Head Orientation Influence 3D Facial Imaging? A Study on Accuracy and Precision of Stereophotogrammetric Acquisition

2021 ◽  
Vol 18 (8) ◽  
pp. 4276
Author(s):  
Giuditta Battistoni ◽  
Diana Cassi ◽  
Marisabel Magnifico ◽  
Giuseppe Pedrazzi ◽  
Marco Di Blasio ◽  
...  
Keyword(s):  
Head Rotation ◽  
Anthropometric Measurements ◽  
Head Orientation ◽  
3D Images ◽  
Face Shape ◽  
Operator Error ◽  
Accuracy And Precision ◽  
Error Magnitude ◽  
Repeatability And Reproducibility ◽  
Head Positions

This study investigates the reliability and precision of anthropometric measurements collected from 3D images and acquired under different conditions of head rotation. Various sources of error were examined, and the equivalence between craniofacial data generated from alternative head positions was assessed. 3D captures of a mannequin head were obtained with a stereophotogrammetric system (Face Shape 3D MaxiLine). Image acquisition was performed with no rotations and with various pitch, roll, and yaw angulations. On 3D images, 14 linear distances were measured. Various indices were used to quantify error magnitude, among them the acquisition error, the mean and the maximum intra- and inter-operator measurement error, repeatability and reproducibility error, the standard deviation, and the standard error of errors. Two one-sided tests (TOST) were performed to assess the equivalence between measurements recorded in different head angulations. The maximum intra-operator error was very low (0.336 mm), closely followed by the acquisition error (0.496 mm). The maximum inter-operator error was 0.532 mm, and the highest degree of error was found in reproducibility (0.890 mm). Anthropometric measurements from alternative acquisition conditions resulted in significantly equivalent TOST, with the exception of Zygion (l)–Tragion (l) and Cheek (l)–Tragion (l) distances measured with pitch angulation compared to no rotation position. Face Shape 3D Maxiline has sufficient accuracy for orthodontic and surgical use. Precision was not altered by head orientation, making the acquisition simpler and not constrained to a critical precision as in 2D photographs.

Interstitial Nucleus of Cajal Encodes Three-Dimensional Head Orientations in Fick-Like Coordinates

2007 ◽  
Vol 97 (1) ◽  
pp. 604-617 ◽  
Author(s):  
Eliana M. Klier ◽  
Hongying Wang ◽  
J. Douglas Crawford
Keyword(s):  
Coordinate System ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Semicircular Canals ◽  
Head Rotation ◽  
Head Orientation ◽  
Interstitial Nucleus Of Cajal ◽  
The Gaze ◽  
Behavioral Constraints ◽  
The Right

Two central, related questions in motor control are 1) how the brain represents movement directions of various effectors like the eyes and head and 2) how it constrains their redundant degrees of freedom. The interstitial nucleus of Cajal (INC) integrates velocity commands from the gaze control system into position signals for three-dimensional eye and head posture. It has been shown that the right INC encodes clockwise (CW)-up and CW-down eye and head components, whereas the left INC encodes counterclockwise (CCW)-up and CCW-down components, similar to the sensitivity directions of the vertical semicircular canals. For the eyes, these canal-like coordinates align with Listing’s plane (a behavioral strategy limiting torsion about the gaze axis). By analogy, we predicted that the INC also encodes head orientation in canal-like coordinates, but instead, aligned with the coordinate axes for the Fick strategy (which constrains head torsion). Unilateral stimulation (50 μA, 300 Hz, 200 ms) evoked CW head rotations from the right INC and CCW rotations from the left INC, with variable vertical components. The observed axes of head rotation were consistent with a canal-like coordinate system. Moreover, as predicted, these axes remained fixed in the head, rotating with initial head orientation like the horizontal and torsional axes of a Fick coordinate system. This suggests that the head is ordinarily constrained to zero torsion in Fick coordinates by equally activating CW/CCW populations of neurons in the right/left INC. These data support a simple mechanism for controlling head orientation through the alignment of brain stem neural coordinates with natural behavioral constraints.

Transcranial Magnetic Stimulation Disrupts Eye-Hand Interactions in the Posterior Parietal Cortex

2000 ◽  
Vol 84 (3) ◽  
pp. 1677-1680 ◽  
Author(s):  
Paul Van Donkelaar ◽  
Ji-Hang Lee ◽  
Anthony S. Drew
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Parietal Cortex ◽  
Magnetic Stimulation ◽  
Posterior Parietal Cortex ◽  
Hand Movement ◽  
Open Loop ◽  
Neurophysiological Studies ◽  
Posterior Parietal ◽  
Hand Coordination

Recent neurophysiological studies have started to shed some light on the cortical areas that contribute to eye-hand coordination. In the present study we investigated the role of the posterior parietal cortex (PPC) in this process in normal, healthy subjects. This was accomplished by delivering single pulses of transcranial magnetic stimulation (TMS) over the PPC to transiently disrupt the putative contribution of this area to the processing of information related to eye-hand coordination. Subjects made open-loop pointing movements accompanied by saccades of the same required amplitude or by saccades that were substantially larger. Without TMS the hand movement amplitude was influenced by the amplitude of the corresponding saccade; hand movements accompanied by larger saccades were larger than those accompanied by smaller saccades. When TMS was applied over the left PPC just prior to the onset of the saccade, a marked reduction in the saccadic influence on manual motor output was observed. TMS delivered at earlier or later periods during the response had no effect. Taken together, these data suggest that the PPC integrates signals related to saccade amplitude with limb movement information just prior to the onset of the saccade.

scholarly journals Cartesian Control of Sit-to-Stand Motion Using Head Position Feedback

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Samina Rafique ◽  
M. Najam-ul-Islam ◽  
M. Shafique ◽  
A. Mahmood
Keyword(s):  
Well Being ◽  
Human Motion ◽  
Head Position ◽  
Head Orientation ◽  
Motor Execution ◽  
Modeling Framework ◽  
Task Control ◽  
Low Level ◽  
Sit To Stand ◽  
High Level

Sit-to-stand (STS) motion is an indicator of an individual’s physical independence and well-being. Determination of various variables that contribute to the execution and control of STS motion is an active area of research. In this study, we evaluate the clinical hypothesis that besides numerous other factors, the central nervous system (CNS) controls STS motion by tracking a prelearned head position trajectory. Motivated by the evidence for a task-oriented encoding of motion by the CNS, we adopt a robotic approach for the synthesis of STS motion and propose this scheme as a solution to this hypothesis. We propose an analytical biomechanical human CNS modeling framework where the head position trajectory defines the high-level task control variable. The motion control is divided into low-level task generation and motor execution phases. We model CNS as STS controller and its Estimator subsystem plans joint trajectories to perform the low-level task. The motor execution is done through the Cartesian controller subsystem that generates torque commands to the joints. We do extensive motion and force capture experiments on human subjects to validate our analytical modeling scheme. We first scale our biomechanical model to match the anthropometry of the subjects. We do dynamic motion reconstruction through the control of simulated custom human CNS models to follow the captured head position trajectories in real time. We perform kinematic and kinetic analyses and comparison of experimental and simulated motions. For head position trajectories, root mean square (RMS) errors are 0.0118 m in horizontal and 0.0315 m in vertical directions. Errors in angle estimates are 0.55 rad, 0.93 rad, 0.59 rad, and 0.0442 rad for ankle, knee, hip, and head orientation, respectively. RMS error of ground reaction force (GRF) is 50.26 N, and the correlation between ground reaction torque and the support moment is 0.72. Low errors in our results validate (1) the reliability of motion/force capture methods and anthropometric technique for customization of human models and (2) high-level task control framework and human CNS modeling as a solution to the hypothesis. Accurate modeling and detailed understanding of human motion can have significant scope in the fields of rehabilitation, humanoid robotics, and virtual characters’ motion planning based on high-level task control schemes.

Influence of head orientation on visually and memory-guided arm movements

2011 ◽  
Vol 136 (3) ◽  
pp. 390-398 ◽  
Author(s):  
Michel Guerraz ◽  
Sébastien Caudron ◽  
Noémylle Thomassin ◽  
Jean Blouin
Keyword(s):  
Arm Movements ◽  
Head Orientation

Fusion of Visual and Proprioceptive Information about Hand Position Prior to Movement

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 127-127
Author(s):  
M Desmurget ◽  
Y Rossetti ◽  
C Prablanc
Keyword(s):  
Visual Information ◽  
Human Subjects ◽  
Visual Presentation ◽  
Accurate Estimate ◽  
Open Loop ◽  
The Body ◽  
Hand Position ◽  
Proprioceptive Information ◽  
Movement Onset ◽  
Loop Condition

The problem whether movement accuracy is better in the full open-loop condition (FOL, hand never visible) than in the static closed-loop condition (SCL, hand only visible prior to movement onset) remains widely debated. To investigate this controversial question, we studied conditions for which visual information available to the subject prior to movement onset was strictly controlled. The results of our investigation showed that the accuracy improvement observed when human subjects were allowed to see their hand, in the peripheral visual field, prior to movement: (1) concerned only the variable errors; (2) did not depend on the simultaneous vision of the hand and target (hand and target viewed simultaneously vs sequentially); (3) remained significant when pointing to proprioceptive targets; and (4) was not suppressed when the visual information was temporally (visual presentation for less than 300 ms) or spatially (vision of only the index fingertip) restricted. In addition, dissociating vision and proprioception with wedge prisms showed that a weighed hand position was used to program hand trajectory. When considered together, these results suggest that: (i) knowledge of the initial upper limb configuration or position is necessary to plan accurately goal-directed movements; (ii) static proprioceptive receptors are partially ineffective in providing an accurate estimate of the limb posture, and/or hand location relative to the body, and (iii) visual and proprioceptive information is not used in an exclusive way, but combined to furnish an accurate representation of the state of the effector prior to movement.

Reaching During Virtual Rotation: Context Specific Compensations for Expected Coriolis Forces

2000 ◽  
Vol 83 (6) ◽  
pp. 3230-3240 ◽  
Author(s):  
Joseph V. Cohn ◽  
Paul DiZio ◽  
James R. Lackner
Keyword(s):  
Target Location ◽  
Arm Movements ◽  
Open Loop ◽  
Tactile Feedback ◽  
Body Motion ◽  
Reaching Movements ◽  
Coriolis Forces ◽  
Enclosed Chamber ◽  
Path Curvature ◽  
Context Specific

Subjects who are in an enclosed chamber rotating at constant velocity feel physically stationary but make errors when pointing to targets. Reaching paths and endpoints are deviated in the direction of the transient inertial Coriolis forces generated by their arm movements. By contrast, reaching movements made during natural, voluntary torso rotation seem to be accurate, and subjects are unaware of the Coriolis forces generated by their movements. This pattern suggests that the motor plan for reaching movements uses a representation of body motion to prepare compensations for impending self-generated accelerative loads on the arm. If so, stationary subjects who are experiencing illusory self-rotation should make reaching errors when pointing to a target. These errors should be in the direction opposite the Coriolis accelerations their arm movements would generate if they were actually rotating. To determine whether such compensations exist, we had subjects in four experiments make visually open-loop reaches to targets while they were experiencing compelling illusory self-rotation and displacement induced by rotation of a complex, natural visual scene. The paths and endpoints of their initial reaching movements were significantly displaced leftward during counterclockwise illusory rotary displacement and rightward during clockwise illusory self-displacement. Subjects reached in a curvilinear path to the wrong place. These reaching errors were opposite in direction to the Coriolis forces that would have been generated by their arm movements during actual torso rotation. The magnitude of path curvature and endpoint errors increased as the speed of illusory self-rotation increased. In successive reaches, movement paths became straighter and endpoints more accurate despite the absence of visual error feedback or tactile feedback about target location. When subjects were again presented a stationary scene, their initial reaches were indistinguishable from pre-exposure baseline, indicating a total absence of aftereffects. These experiments demonstrate that the nervous system automatically compensates in a context-specific fashion for the Coriolis forces associated with reaching movements.

Effect of Head Orientation on the Diagnostic Sensitivity of Posturography in Patients with Compensated Unilateral Lesions

1992 ◽  
Vol 106 (4) ◽  
pp. 355-362 ◽  
Author(s):  
Kamran Barin ◽  
Curtis M. Seitz ◽  
D. Bradley Welling
Keyword(s):  
Postural Sway ◽  
Head Position ◽  
Diagnostic Sensitivity ◽  
Test Sequence ◽  
Order Effects ◽  
Head Orientation ◽  
Additional Information ◽  
Head Extension ◽  
The Difference ◽  
Unilateral Vestibulopathy

Patients with compensated unilateral vestibular lesions often have no detectable abnormality on conventional posturography. The purpose of this study was to determine whether a change in head orientation could improve the diagnostic sensitivity of the test for these patients. Twenty-four patients with known unilateral vestibulopathy and twenty-four normal controls were tested on the EqulTest apparatus in four head positions: head centered, head tilted right, head tilted left, and head extended. The sensory organization test was performed for each head position, using a single trial for each sensory condition. The test sequence was randomized to account for simple order effects. The subject's equilibrium was quantified by a performance index and a composite score of all sensory conditions was calculated for each head position. Patients with unilateral vestibulopathy had more postural sway with the head tilted contralateral to the side of lesion. The difference between the mean composite scores for ipsilateral and contralateral head tilts was statistically significant ( p < 0.05). When individual trials were compared, equilibrium scores were significantly different only for sensory conditions that required vestibular input. Head extension increased postural sway in both patients and controls. Equilibrium scores were significantly different for all sensory conditions in which the support was sway-referenced. We suggest that the results of head extension in patients are similar to those found in normal individuals. However, equilibrium scores for right-left head flits are sensitive to the side of lesion and can provide additional information for patients with unilateral vestibulopathy.

scholarly journals Visualization of the Process of Processing Welds by a Deformation Wave

2020 ◽  
pp. short39-1-short39-7
Author(s):  
Andrey Kirichek ◽  
Sergey Barinov ◽  
Alexandr Yashin
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Visual Information ◽  
Calculated Data ◽  
Welding Process ◽  
Element Model ◽  
Temperature Fields ◽  
Subsequent Stage ◽  
Deformation Wave ◽  
Complex Process

The aim of the paper is to obtain a unified finite element model of a complex process, which makes it possible to obtain visual information related to the influence of the welding process parameters on the results of the process of wave strain hardening of the weld material. Modeling of sequentially executed technological processes of different physical nature - welding and hardening, makes it possible to obtain more general and objective visual information about the process as a whole. Modeling in the Ansys software package is performed in stages, with the output of an earlier stage of modeling acting as the input data of the subsequent stage. At the first stage, the problem of visualizing the process of forming a weld is solved with the possibility of calculating temperature fields, stress and strain fields during heating and cooling of the welded workpiece. At the second stage, the calculated data is imported into the finite element model of processing welds with a deformation wave. A finite element model makes it possible to build microhardness maps for selected (dangerous) sections and visually monitor the change in stresses and strains in welded workpieces, depending on the technological modes of hardening by a deformation wave. The obtained visual information allows for a qualitative and quantitative assessment of the result of a complex process, which contributes to an increase in the bearing capacity and performance of the product as a whole.

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