Involuntary Rotations of a Steering Device Induced by Voluntary Rotations of the Head and Maintained Eccentric Head Positions

In a series of 4 experiments, the authors examined involuntary rotations of a steering device (handlebar or wheel) that were associated with periodic head rotations and eccentric head positions. Periodic head rotations resulted in isodirectional involuntary rotations of a horizontally arranged steering device of very small amplitude. When the orientation of a steering wheel was changed to vertical and to a backward tilt, the involuntary rotations were in the opposite direction. That pattern of results is consistent with the assumption that small movements of the shoulder girdle, which are associated with head turns and which cannot be prevented by mechanical immobilization of the shoulder, are propagated to the wheel, but is not consistent with previous suggestions that involuntary rotations of a steering device can result from the action of the tonic neck reflex. Effects that correspond to the pattern of the tonic neck reflex were found only when a spring-centered handlebar was held in an eccentric position; maintenance of the eccentric position was facilitated when the participant's head was turned in the opposite direction. The findings strongly suggest that head movements can result in involuntary movements of a steering device via different mechanisms.     

The effects of eccentric head positions on leftward and rightward turns of a handle-bar

We explored the structural constraints on concurrent movements and/or positions of the head and a steering device by means of a reaction-time task. In the first experiment, subjects had to respond rapidly to an imperative stimulus by way of rotating a handle-bar to the left or to the right and back to the central position while they maintained a left or right eccentric position of the head. Latency of the handle-bar responses did not depend on whether their initial directions were toward the eccentric head position or in the opposite direction, but kinematic characteristics did: iso-directional movements were of larger amplitude and longer duration until peak excursion. In the second experiment, the imperative stimuli for handle-bar rotations were presented at variable intervals after the head had been moved from the central to one of the eccentric positions and before its predictable return movement. Kinematic characteristics of the handle-bar rotations depended on the left and right eccentric head positions in the same way as in Experiment 1, but now iso-directional movements had a longer reaction time than movements in the direction of the forthcoming return movement of the head. These findings suggest that specifications of head-movement directions facilitate concurrent specifications of handle-bar rotations in the same direction and inhibit specifications of handle-bar rotations in the opposite direction, consistent with the notion of cross-talk during motor programming.     

Eccentric head positions bias random generation of leftward and rightward handle-bar rotations

We explored the effects of eccentric head positions on rapid rotations of a handle-bar in a modified randomization task. Subjects had to generate a random sequence of leftward and rightward handle-bar rotations; each pre-selected rotation was produced in response to a visual signal as rapidly as possible. Eccentric head positions induced a bias in that handle-bar rotations in the direction of the eccentric head position were chosen more frequently than handle-bar rotations in the opposite direction. This is consistent with previous evidence on a spatial coupling. In contrast to response selection, response initiation was not affected by eccentric head positions. The kinematic characteristics, however, differed: rotations in the direction of the eccentric head position were of larger amplitude and longer duration than rotations in the opposite direction. This difference may have been secondary to a difference in the start positions of the handle-bar, which were shifted in the direction opposite to the eccentric head position.     

The Lateral Coding of Rotations

A number of experimental studies have consistently shown the locus of spatial S-R compatibility effects to be the selection of the response within an abstract memory code. The purpose of the present study was to test, in the particular case of wheel rotations, the general proposition that any response that a subject internally codes in terms of left and right may be interfered with by the lateral location of the stimuli in a Simon paradigm. Experiment 1 showed that the auditory Simon effect occurred in a task where the subjects had to rotate a steering wheel bimanually either clockwise or counterclockwise according to sound pitch, despite the fact that responses of this kind are undefined with respect to laterality. Experiment 2 confirmed this result in a unimanual rotation condition and suggested that the ear-rotation compatibility effect may be added to the effect of a biomechanical factor, pronation versus supination, supporting the idea of an abstract motor code. In Experiment 3, subjects rotated the steering wheel with their hands on the lowest part of the wheel. When the response movement made the spot of a C.R.T. move laterally in accordance with the performed rotation, the subjects coded their response directly in terms of its effect on the visual display. For subjects not receiving visual feedback, no compatibility effect occurred. However, the individual data were compatible with the notion that some subjects in this group coded their responses in terms of wheel rotations, and others in terms of hand movements.     

Mechanisms Controlling Head Stabilization in the Elderly During Random Rotations in the Vertical Plane

Frequency-related response characteristics of the mechanisms controlling stabilization of the head in 10 elderly subjects were compared with response characteristics in 8 young adults. Angular velocity of the head with respect to the trunk and EMG responses of 2 neck muscles were recorded in 10 seated subjects during pseudorandom rotations of the trunk in the sagittal plane at frequencies of 0.35 to 3.05 Hz. Subjects were required to actively stabilize their heads with (VS) and without (NV) visual feedback so that voluntary mechanisms and the influence of vision could be tested. Reflex mechanisms were examined when subjects were distracted by a mental calculation task during rotations in the dark (MA). Age emerged as an influential factor in the performance of head stabilization mechanisms, and decrements in performance were even more pronounced in the older as compared with younger elderly subjects. Age effects could be seen in the (a) diminished ability to voluntarily stabilize the head, particularly with the absence of vision, (b) impaired ability to stabilize the head when cognitively distracted, and (c) appearance of a resonant response of the head. Control of head stabilization shifted from reflex mechanisms to system mechanics, probably as a result of age-related changes in the integrity of the sensory systems. The elderly's system mechanics could not effectively compensate for the disturbances, however, and instability was the result.     

Effect of strength and direction of haptic cueing on steering control during near lane departure

The present study compared two distinct approaches to designing driving assistance devices. These devices aim to facilitate steering responses by delivering directional pulses on the steering wheel when lane departure is imminent. In one case, the aim is to prime the corrective gesture through a haptic cue in the direction of the lane centre (motor priming). The other approach consists of eliciting a compensatory reflex reaction by means of a jerk of the steering wheel in the opposite direction. Central to this investigation are the safety benefits of the devices and the ability of drivers to remain in full control of their steering responses. The steering behaviour of 18 participants during near lane departure in bends and in straight lines was analysed. The strength and direction of haptic cueing was manipulated. The results show that drivers were always able to control the direction of the steering response when the haptic cue was delivered. No reflex counteraction was observed, whatever the strength or the direction of the stimulus. The fastest responses were observed when the cue was directed toward lane departure, especially when cueing was strong. However, these did not necessarily lead to the fastest returns to a safe position in the lane when compared with motor priming toward the lane centre. The latter yielded improved manoeuvre execution as soon as the steering movement was initiated. These results are discussed in relation to the sensorimotor and cognitive processes involved in steering behaviour. Their implications for the design of haptic-based lane departure warning systems are considered.     

Head movements while steering around bends

In this study, the determinants of head motions (rotations) when driving around bends were investigated when drivers viewed the scene through a head-mounted display. The scene camera was either fixed or coupled to head motions along 2 or 3 axes of rotation. Eight participants drove around a triangular circuit and the range and speed of head rotations, the correlations between head rotations and lateral acceleration, and the coupling between the different axes of head rotation were calculated. Results showed that substantial head rotations were made even when head rotations had no influence on the direction of the camera, suggesting a strong motor coupling between steering actions and head motion. Head roll was determined, at least in part, by the gravito-inertial force, contradicting earlier results reported in the literature.     

Stimulus-response compatibility with wheel-rotation responses: Will an incompatible response coding be used when a compatible coding is possible?

Three experiments were conducted in which subjects responded to left-right tones with clockwise-counterclockwise rotations of a steering wheel using one of two stimulus-response assignments. When the hands were at the bottom of the wheel, where hand movement is opposite to wheel movement, subjects coded responses according to the frame that yielded a compatible mapping when the instructions did not emphasize either hand or wheel movements (Experiment 1). When instructions emphasized hand movements, responses were coded relative to the hand-referenced frame (Experiment 2), and when the wheel controlled a visual cursor, responses were coded relative to a cursor-referenced frame (Experiment 3). Coding with respect to these frames occurred even when the resulting mapping was incompatible.     

The role of head position and prior contraction in manual aiming

We sought to determine if the asymmetrical tonic neck reflex influences the accuracy of self-selected arm positioning without vision and to ascertain if such accuracy is influenced by a pre-contraction of the prime movers. Participants reproduced an arm position using their abductors with the head in midline, rotated towards and away from the arm. Arm movements were made with and without a pre-contraction of the abductors. Twenty participants performed eight trials in each of the six different conditions. Compared to the midline position, participants undershot the reference position with the head turned away and overshot the position with the head rotated towards the arm. A pre-contraction caused undershooting regardless of head position. Results suggest that head position and pre-contraction may have significant and independent effects on arm positioning.     

Lane change manoeuvres and safety margins

The relation between perceptual information and the motor response during lane-change manoeuvres was studied in a fixed-based driving simulator. Eight subjects performed 48 lane changes with varying vehicle speed, lane width and direction of movement. Three sequential phases of the lane change manoeuvre are distinguished. During the first phase the steering wheel is turned to a maximum angle. After this the steering wheel is turned to the opposite direction. The second phase ends when the vehicle heading approaches a maximum that generally occurs at the moment the steering wheel angle passes through zero. During the third phase the steering wheel is turned to a second maximum steering wheel angle in opposite direction to stabilize the vehicle in the new lane. Duration of the separate phases were analysed together with steering amplitudes and Time-to-Line Crossing in order to test whether and how drivers use the outcome of each phase during the lane change manoeuvre to adjust the way the subsequent phase is executed. During the first phase the time margin to the outer lane boundary was controlled by the driver such that a higher speed was compensated for by a smaller steering wheel amplitude. Due to this mechanism the time margin to the lane boundary was not affected by vehicle speed. During the second phase the speed with which the steering wheel was turned to the opposite direction was affected by the time margins to the lane boundary at the start of the second phase. Thereafter, smaller minimum time margins were compensated for by a larger steering wheel amplitude to the opposite direction. The results suggest that steering actions are controlled by the outcome of previous actions in such a way that safety margins are maintained. The results also suggest that visual feedback is used by the driver during lane change manoeuvres to control steering actions, resulting in flexible and adaptive steering behaviour. Evidence is presented in support of the idea that temporal information on the relation between the vehicle and lane boundaries is used by the driver in order to control the motor response.     

Self-motion perception and vestibulo-ocular reflex during whole body yaw rotation in standing subjects: the role of head position and neck proprioception

Self-motion perception and vestibulo-ocular reflex (VOR) were studied during whole body yaw rotation in the dark at different static head positions. Rotations consisted of four cycles of symmetric sinusoidal and asymmetric oscillations. Self-motion perception was evaluated by measuring the ability of subjects to manually track a static remembered target. VOR was recorded separately and the slow phase eye position (SPEP) was computed. Three different head static yaw deviations (active and passive) relative to the trunk (0°, 45° to right and 45° to left) were examined. Active head deviations had a significant effect during asymmetric oscillation: the movement perception was enhanced when the head was kept turned toward the side of body rotation and decreased in the opposite direction. Conversely, passive head deviations had no effect on movement perception. Further, vibration (100 Hz) of the neck muscles splenius capitis and sternocleidomastoideus remarkably influenced perceived rotation during asymmetric oscillation. On the other hand, SPEP of VOR was modulated by active head deviation, but was not influenced by neck muscle vibration. Through its effects on motion perception and reflex gain, head position improved gaze stability and enhanced self-motion perception in the direction of the head deviation.     

Coding controlled and triggered cursor movements as action effects: influences on the auditory Simon effect for wheel-rotation responses

Four experiments investigated influences of irrelevant action effects on response selection in Simon tasks for which tone pitch was relevant and location irrelevant, and responses were clockwise- counterclockwise wheel rotations. When the wheel controlled left-right movement of a cursor in a direction opposite an instructed left-right hand-movement goal, the Simon effect was reduced. When the wheel was held at the bottom, this reduction was due to some participants coding responses relative to the cursor and others relative to the hands. However, when the wheel was held at the top, it was due to participants integrating cursor movements with hand movements as a single action concept. In contrast, a cursor triggered by the wheel movement showed little influence on the Simon effect, even when contiguity and contingency with the wheel movements were high. Experience with the controlled cursor in a prior trial block or between trials established a causal relation that enabled participants to code the triggered cursor as belonging to the action concept and thus reduce the Simon effect. Multiple factors determine the influence of an irrelevant action effect on performance.     

Are the Orientations of the Head and Arm Related During Pointing Movements?

The head, eye, and shoulder are each free to rotate around three mutually orthogonal axes. These three degrees of freedom allow a given gaze or pointing direction of the eye, head, or arm to be obtained in many different possible orientations. Unlike translations in three dimensions, three-dimensional (3-D) rotations are noncommutative. Therefore, the orientation of a rigid body following sequential rotations about two different axes depends on the order of the rotations. In this article, we demonstrate that only two degrees of freedom are used during orienting movements of the head and pointing movements of the arm. This provides a unique orientation of head and arm for each gaze or pointing direction despite the noncommutativity of three-dimensional rotations. This observation is in itself not new. We found, however, that (a) the two-dimensional lquot;rotation surface,rquot; which describes the orientation of the head for all gaze directions, is curved, unlike the analogous flat plane for the eye. (b) The rotation surface for the head is curved differently than that for the arm. This result argues against the hypothesis that the orientations of head and arm are directly coupled during pointing. It also implies that the orientation of the eye in space during gaze shifts of the eye and head is not uniquely determined for a given direction of gaze. This finding argues against a perceptual basis for the reduction of rotational degrees of freedom.     

Contribution of ankle, knee, and hip joints to the perception threshold for support surface rotation.

The purpose of the present experiment was to investigate the extent to which subjects can perceive, at very slow velocities, an angular rotation of the support surface about the medio-lateral axis of the ankle, knee, hip, or neck joint when visual cues are not available. Subjects were passively displaced on a slowly rotating platform at .01, .03, and .05 deg/sec. The subjects' task was to detect movements of the platform in four different postural conditions allowing body oscillations about the ankle, knee, hip, or neck joint. In Experiment 1, subjects had to detect backward and forward rotation (pitching). In Experiment 2, they had to detect left and right rotations of the platform (rolling). In Experiment 3, subjects had to detect both backward/forward and left/right rotations of the platform, with the body fixed and the head either fixed or free to move. Overall, when the body was free to oscillate about the ankle, knee, or hip joints, a similar threshold for movement perception was observed. This threshold was lower for rolling than for pitching. Interestingly, in these postural conditions, an unconscious compensation in the direction opposite to the platform rotation was observed on most trials. The threshold for movement perception was much higher when the head was the only segment free to oscillate about the neck joint. These results suggest that, in static conditions, the otoliths are poor detectors of the direction of gravity forces. They also suggest that accurate perception of body orientation is improved when proprioceptive information can be dynamically integrated.     

Contribution of ankle, knee, and hip joints to the perception threshold for support surface rotation

The purpose of the present experiment was to investigate the extent to which subjects can perceive, at very slow velocities, an angular rotation of the support surface about the medio-lateral axis of the ankle, knee, hip, or neck joint when visual cues are not available. Subjects were passively displaced on a slowly rotating platform at .01, .03, and .05 deg/sec. The subjects’ task was to detect movements of the platform in four different postural conditions allowing body oscillations about the ankle, knee, hip, or neck joint. In Experiment 1, subjects had to detect backward and forward rotation (pitching). In Experiment 2, they had to detect left and right rotations of the platform (rolling). In Experiment 3, subjects had to detect both backward/forward and left/right rotations of the platform, with the body fixed and the head either fixed or free to move. Overall, when the body was free to oscillate about the ankle, knee, or hip joints, a similar threshold for movement perception was observed. This threshold was lower for rolling than for pitching. Interestingly, in these postural conditions, an unconscious compensation in the direction opposite to the platform rotation was observed on most trials. The threshold for movement perception was much higher when the head was the only segment free to oscillate about the neck joint. These results suggest that, in static conditions, the otoliths are poor detectors of the direction of gravity forces. They also suggest that accurate perception of body orientation is improved when proprioceptive information can be dynamically integrated.     

Simulation Studies of Descending and Reflex Control of Fast Movements

Several neurological control strategies for fast head movements are considered using computer simulations of a stretch reflex model. Each control strategy incorporates a different amount of proprioceptive feedback contributing to braking and/or clamping the movement. The model behavior for each control strategy is qualitatively compared to experimental data that includes the agonist and antagonist EMGs, and the head position, velocity, and acceleration. Significance of the study is discussed with respect to the characteristic tri-phasic EMG pattern for fast voluntary movements and the possible roles that the stretch reflex may have in contributing to this pattern of activation.     

Joint position error after neck protraction-retraction movements in healthy office workers: a cross-sectional study

Since the upper cervical spine (UCS) has been regarded to be distinct from the lower cervical spine (LCS), joint position error (JPE) needs to be tested separately for both regions. The purpose of this study was to investigate the JPE after cervical protraction/retraction movements, involving opposite movements of extension and flexion for the UCS and LCS. These movements are frequently performed during office work.Cervical JPEs were tracked in thirty healthy office workers while performing four tests of cervical pro-retraction movements with variations in vision and movement direction, and assessed using the Kinect head tracker (Microsoft Corp), placed in front of each participant. The JPE was expressed in constant (CE), absolute (AE) and variable errors (VE). Multilevel linear models evaluated main and interaction effects of vision, movement direction, cervical region and sex.Slightly larger JPEs have been found in the UCS. Vision showed no effect on any outcome variable. No effect exceeded typical measurement errors reported for the Kinect head tracker.This study showed, that JPEs after pro-retraction movements of the head and neck may differ for UCS and LCS. The differences were small and not beyond measurement error reported for the Kinect.     

Coupling of Eye,Finger, Elbow,and Shoulder Movements During Manual Aiming

Temporal and spatial coupling of point of gaze (PG) and movements of the finger, elbow, and shoulder during a speeded aiming task were examined. Ten participants completed 40-cm aiming movements with the right arm, in a situation that allowed free movement of the eyes, head, arm, and trunk. On the majority of trials, a large initial saccade undershot the target slightly, and 1 or more smaller corrective saccades brought the eyes to the target position. The finger, elbow, and shoulder exhibited a similar pattern of undershooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at the target well in advance of the finger. There was a clear temporal coupling between primary saccade completion and peak acceleration of the finger, elbow, and shoulder. The initiation of limb-segment movement usually occurred in a proximal-to-distal pattern. Increased variability in elbow and shoulder position as the movement progressed may have served to reduce variability in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the position of the finger and the target late in the movement.     

Head rotations in the play of Hanuman langurs (Semnopithecus entellus): description and analysis of function

Although head rotations are frequent patterns in play behavior in many mammalian species and differ from head movements used in other contexts, they have not been quantitatively described and their function remains unclear. The head rotations occurring in the play behavior of free-ranging Hanuman langurs (Semnopithecus entellus) were described from videotaped sequences. The authors tested 2 possible hypotheses about their function. Either the head rotations serve to create unexpected situations and should therefore occur in both solitary and social play and also be very variable, or they serve as play signals and should therefore occur only in social play and be ritualized. If head rotations have both functions, they should be less variable in social play. The data revealed that head rotations were very variable and were present both in solitary and social play. Furthermore, there was no difference in the variability between the head rotations present in the 2 types of play. The results do not support the function of head rotations as play signals but, rather, suggest that head rotations may serve to create unexpected situations in play.     

Coupling of eye, finger, elbow, and shoulder movements during manual aiming

Temporal and spatial coupling of point of gaze (PG) and movements of the finger, elbow, and shoulder during a speeded aiming task were examined. Ten participants completed 40-cm aiming movements with the right arm, in a situation that allowed free movement of the eyes, head, arm, and trunk. On the majority of trials, a large initial saccade undershot the target slightly, and 1 or more smaller corrective saccades brought the eyes to the target position. The finger, elbow, and shoulder exhibited a similar pattern of undershooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at the target well in advance of the finger. There was a clear temporal coupling between primary saccade completion and peak acceleration of the finger, elbow, and shoulder. The initiation of limb-segment movement usually occurred in a proximal-to-distal pattern. Increased variability in elbow and shoulder position as the movement progressed may have served to reduce variability in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the position of the finger and the target late in the movement.