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PubMed1990

Monocular stereopsis with and without head movement.

Random dots moving with various velocity gradients were presented to observers; the motion was yoked to head movement in one condition and to no head movement in another. In Experiment 1, 12 observers were shown motion gradients with sine, triangle, sawtooth, and square waveforms with amplitudes (equivalent disparities) of 12' and 1 degrees 53'. In Experiment 2, 48 observers were shown only the sinewave or square-wave gradient of 1 degrees 53' disparity either with or without head movement so that the observers' expectation to see depth in one condition did not transfer to another. The main findings were: (1) with 12' disparity, the head-movement condition produced perceived depth but almost no perceived motion, whereas the no-head-movement condition produced both perceived depth and perceived motion; (2) with 1 degrees 53' disparity, both conditions produced perceived depth and perceived motion; and (3) when the expectation to see depth was removed, the no-head-movement condition with the square-wave gradient produced no perceived depth, only motion. We suggest that monocular stereopsis with head movement can be achieved without perception of motion but monocular stereopsis without head movement requires perception of motion.

Attention↗
PubMed2003

The effect of transcranial magnetic stimulation over the cerebellum on the synkinesis of coordinated eye and head movements.

We made a study of coordinated saccadic eye and head movements following random and predictable horizontal visual targets by applying transcranial magnetic stimulation (TMS) over the cerebellum before the start of the gaze movement. We have found three effects of TMS on eye/head movements under these conditions. SACCADIC LATENCY-EFFECT: When stimulation took place shortly before movements commenced, significantly shorter latencies were found between target presentation and commencement of saccades: For predictable, to a lesser extent for random targets and TMS up to 75 ms before start of the saccade, latencies were significantly decreased when compared with no application of TMS. Without stimulation, latencies to random targets were within a range of 120-200 ms. EYE-HEAD INTERACTION-EFFECT: Without TMS, for amplitudes greater than 25 degrees, head movements usually preceded eye movements, as expected, especially for predictive responses. With the application of TMS shortly after the target display, the number of eye movements which preceded head movements, was significantly increased (p<0.001), and the delay between eye and head movements was reduced or reversed (p<0.001), compared with gaze movements without the use of TMS. SACCADIC PEAK VELOCITY-EFFECT: Applying transcranial magnetic stimulation at 5-25 ms after the position change of the 60 degrees target, and 50-5 s before the start of eye movement, mean peak velocity of synkinetic saccades increased up to 600 degrees/s, compared with 350-400 degrees/s without the use of TMS. We conclude that transient functional cerebellar deficits caused by the application of TMS can change the central synkinesis of eye-head coordination.

Adult↗
PubMed2003

On the feedback control of orienting gaze shifts made with eye and head movements.

Combined eye-head movements are routinely used to orient the visual axis (gaze) rapidly in space. The gaze control system can be modeled using a feedback system in which an internally created instantaneous gaze position error signal equivalent to the distance between the target and the current gaze position is used to drive brainstem eye and head motor circuits. The visual axis is driven until this gaze position error (GPE) is zero. The neural structure of the feedback system is discussed here. The midbrain's superior colliculus (SC) is implicated in gaze control but its 'location' in the feedback circuitry is debated. Our moving hill hypothesis proposed that the SC is within the feedback loop and that GPE is encoded topographically by a moving locus of activity on the motor map. In cat, fixation neurons of the superior colliculus encode GPE, which supports this model. Our preliminary evidence in both monkey and cat shows that neurons on the motor map respond to and encode, at very short latency, gaze shift perturbations. This further supports the hypothesis that the SC is within the gaze feedback loop.

Animals↗
PubMed2000

Head movements and neck muscle activities associated with the jaw movement during mastication in the rabbit authors.

Rhythmical head movements and neck muscle activities associated with the masticatory jaw movement were investigated in rabbits. In natural mastication, head movements and neck muscle activities showed a rhythmical feature synchronized with jaw movement. During cortically induced rhythmical jaw movements, some neck muscle showed rhythmical activity induced by biting a wooden stick. Neck muscles may contribute to the rhythmical head movement after loading the tooth with food.

Animals↗
PubMed1998

Off-centric rotation axes in natural head movements: implications for vestibular reafference and kinematic redundancy.

Until now, most studies concerning active head movements in three dimensions have used the classical rotation vector description. Although this description yields both the orientation of the head rotation axis and the amount of rotation, it is incomplete because it cannot specify the location of this rotation axis in space. The latter is of importance for a proper picture of the vestibular consequences of active head movements and has relevance for the problem of how the brain deals with the inherent kinematic redundancy of the multijoint head-neck system. With this in mind, we have extended the rotation vector description by applying the helical axes approach, which yields both the classical rotation vector as well as the location of the rotation axis in space. Subjects (n = 7), whose head movements were recorded optically, were instructed to shift gaze naturally to targets in 12 different directions at an eccentricity of 40 degrees. The results demonstrate that the axes for these head movements occupy consistently different spatial locations. For purely horizontal movements, the rotation axis is located near a point midway between the two ear canals. For gaze shifts in other directions, the rotation axes are located below the ear canals along two circles, one for movements with an upward component (up circle), the other (typically larger in size) for movements with a downward component (down circle). Purely vertical movement (up and down) axes were located on the lower pole of the up and down circles, respectively. It was found that both circles, the upper poles of which coincided, became larger in size as movement amplitude increased, which means that the axis location shifts to lower and more eccentric locations with respect to the skull for larger flexion and extension movements. Although this pattern could be recognized in most subjects, there were consistent intersubject differences in the absolute size of the circles, their increase with movement amplitude, and in the relative sizes of the up and down circles. Because multiple vertebrae are involved in head movements, there are theoretically many possibilities to execute a certain head movement. The differences in circle patterns among subjects indicate different strategies in resolving this kinematic redundancy problem, a fact that was not apparent from the classical rotation vector part of our description, which yielded a rather uniform picture. A simple model suggests that the downward shift of the location of the rotation axis requires a modulation in vestibulo-ocular reflex gain of </=10% to maintain fixation of a near target during vertical head movement. The involvement of the otolith system in this process remains to be determined.

Adult↗
PubMed1999

Firing behavior of vestibular neurons during active and passive head movements: vestibulo-spinal and other non-eye-movement related neurons.

The firing behavior of 51 non-eye movement related central vestibular neurons that were sensitive to passive head rotation in the plane of the horizontal semicircular canal was studied in three squirrel monkeys whose heads were free to move in the horizontal plane. Unit sensitivity to active head movements during spontaneous gaze saccades was compared with sensitivity to passive head rotation. Most units (29/35 tested) were activated at monosynaptic latencies following electrical stimulation of the ipsilateral vestibular nerve. Nine were vestibulo-spinal units that were antidromically activated following electrical stimulation of the ventromedial funiculi of the spinal cord at C1. All of the units were less sensitive to active head movements than to passive whole body rotation. In the majority of cells (37/51, 73%), including all nine identified vestibulo-spinal units, the vestibular signals related to active head movements were canceled. The remaining units (n = 14, 27%) were sensitive to active head movements, but their responses were attenuated by 20-75%. Most units were nearly as sensitive to passive head-on-trunk rotation as they were to whole body rotation; this suggests that vestibular signals related to active head movements were cancelled primarily by subtraction of a head movement efference copy signal. The sensitivity of most units to passive whole body rotation was unchanged during gaze saccades. A fundamental feature of sensory processing is the ability to distinguish between self-generated and externally induced sensory events. Our observations suggest that the distinction is made at an early stage of processing in the vestibular system.

Animals↗
PubMed2000

Role of the cerebellar flocculus region in the coordination of eye and head movements during gaze pursuit.

The contribution of the flocculus region of the cerebellum to horizontal gaze pursuit was studied in squirrel monkeys. When the head was free to move, the monkeys pursued targets with a combination of smooth eye and head movements; with the majority of the gaze velocity produced by smooth tracking head movements. In the accompanying study we reported that the flocculus region was necessary for cancellation of the vestibuloocular reflex (VOR) evoked by passive whole body rotation. The question addressed in this study was whether the flocculus region of the cerebellum also plays a role in canceling the VOR produced by active head movements during gaze pursuit. The firing behavior of 121 Purkinje (Pk) cells that were sensitive to horizontal smooth pursuit eye movements was studied. The sample included 66 eye velocity Pk cells and 55 gaze velocity Pk cells. All of the cells remained sensitive to smooth pursuit eye movements during combined eye and head tracking. Eye velocity Pk cells were insensitive to smooth pursuit head movements. Gaze velocity Pk cells were nearly as sensitive to active smooth pursuit head movements as they were passive whole body rotation; but they were less than half as sensitive ( approximately 43%) to smooth pursuit head movements as they were to smooth pursuit eye movements. Considered as a whole, the Pk cells in the flocculus region of the cerebellar cortex were <20% as sensitive to smooth pursuit head movements as they were to smooth pursuit eye movements, which suggests that this region does not produce signals sufficient to cancel the VOR during smooth head tracking. The comparative effect of injections of muscimol into the flocculus region on smooth pursuit eye and head movements was studied in two monkeys. Muscimol inactivation of the flocculus region profoundly affected smooth pursuit eye movements but had little effect on smooth pursuit head movements or on smooth tracking of visual targets when the head was free to move. We conclude that the signals produced by flocculus region Pk cells are neither necessary nor sufficient to cancel the VOR during gaze pursuit.

Animals↗
PubMed1998

Timing of secondary vestibular neuron responses to a range of rotational head movements.

Secondary vestibular neurons exhibit a wide variety of responses to a head movement, with the response of each secondary neuron depending upon the particular primary afferents converging onto it. A single head movement is thereby registered in a distributed manner. This paper focuses on implications of afferent convergence to the relative timing of secondary neuron response modulation during rotational movements about a combination of horizontal axes. In particular, the neurons of interest are those that receive input from afferents innervating the vertical semicircular canals, and the movements of interest are those that have a sinusoidal component about one vertical canal axis and a sinusoidal component about another, approximately orthogonal, vertical canal axis. Under these conditions, the present research shows that it is possible for two or more secondary neurons to have a different relative timing of response (i.e., different relative phase of the periodic modulation in firing rate) for different head movements, and for the neurons to switch their order of response for different movements. For particular head movements, those same neurons will respond in phase. From the point of view of the nervous system, the relative timing of neuron responses may tell which movement is taking place, but with certain restrictions as discussed in the present paper. Shown here is that, among those head movements for which the two components of rotation may be at any phase relative to one another and have any relative amplitude, an in-phase response of just two neurons cannot identify a single motion. Two neurons that respond in phase for one motion must respond in phase for an entire range of motions; all motions in that range are thus response-equivalent, in the sense that the pair of neurons cannot distinguish between the two motions. On the other hand, an in-phase response of three neurons can identify a single motion, for certain patterns of primary afferent convergence.

Afferent Pathways↗
PubMed2000

Sensory processing in the vestibular nuclei during active head movements.

Many secondary vestibular neurons are sensitive to head on trunk rotation during reflex-induced and voluntary head movements. During passive whole body rotation the interaction of head on trunk signals related to the vestibulo-collic reflex with vestibular signals increases the rotational gain of many secondary vestibular neurons, including many that project to the spinal cord. In some units, the sensitivity to head on trunk and vestibular input is matched and the resulting interaction produces an output that is related to the trunk velocity in space. In other units the head on trunk inputs are stronger and the resulting interaction produces an output that is larger during the reflex. During voluntary head movements, inputs related to head on trunk movement combine destructively with vestibular signals, and often cancel the sensory reafferent consequences of self-generated movements. Cancellation of sensory vestibular signals was observed in all of the antidromically identified secondary vestibulospinal units, even though many of these units were not significantly affected by reflexive head on trunk movements. The results imply that the inputs to vestibular neurons related to head on trunk rotation during reflexive and voluntary movements arise from different sources. We suggest that the relative strength of reflexive head on trunk input to different vestibular neurons might reflect the different functional roles they have in controlling the posture of the neck and body.

Animals↗
PubMed2000

Coordination of the eyes and head: movement kinematics.

When the head is restrained, saccades are characterized by lawful relationships between movement amplitude, peak velocity, and duration. In addition, the spatiotemporal progression of saccades (i.e., movement kinematics) is predictable if saccade amplitude and direction are known. However, when the head is free to move, changes in the direction of the line of sight (gaze shifts) often involve saccades associated with simultaneous head movements. The metrics (duration, amplitude, peak velocity) and kinematics of saccades occurring in conjunction with head movements cannot be predicted on the basis of saccade amplitude and direction alone. For example, when the head is unrestrained, velocity profiles of 35 degree eye movements can be symmetrical and might have peaks approximately 600 degrees/s. But, 35 degrees eye movements can also have peak velocities of approximately 300 degrees/s and have velocity profiles with two pronounced peaks: an initial peak followed by a reduction and subsequent increase in velocity. Saccade amplitude and direction are insufficient to predict the shape of the velocity profile. However, as illustrated in this report, if the amplitude of the concurrent head movement is taken into account, saccade kinematics are predictable even during gaze shifts with large head components. The data presented here are indicative of an interaction between eye and head motor systems in which head movement commands alter the execution of concurrent saccades.

Animals↗
PubMed2006

On the barn owl's visual pre-attack behavior: I. Structure of head movements and motion patterns.

Barn owls exhibit a rich repertoire of head movements before taking off for prey capture. These movements occur mainly at light levels that allow for the visual detection of prey. To investigate these movements and their functional relevance, we filmed the pre-attack behavior of barn owls. Off-line image analysis enabled reconstruction of all six degrees of freedom of head movements. Three categories of head movements were observed: fixations, head translations and head rotations. The observed rotations contained a translational component. Head rotations did not follow Listing's law, but could be well described by a second-order surface, which indicated that they are in close agreement with Donder's law. Head translations did not contain any significant rotational components. Translations were further segmented into straight-line and curved paths. Translations along an axis perpendicular to the line of sight were similar to peering movements observed in other animals. We suggest that these basic motion elements (fixations, head rotations, translations along a straight line, and translation along a curved trajectory) may be combined to form longer and more complex behavior. We speculate that these head movements mainly underlie estimation of distance during prey capture.

Animals↗
PubMed2003

Effect of putting grip on eye and head movements during the golf putting stroke.

The objective of this article is to determine the effect of three different putting grips (conventional, cross-hand, and one-handed) on variations in eye and head movements during the putting stroke. Seven volunteer novice players, ranging in age from 21 to 22 years, participated in the study. During each experimental session, the subject stood on a specially designed platform covered with artificial turf and putted golf balls towards a standard golf hole. The three different types of grips were tested at two distances: 3 and 9 ft. For each condition, 20 putts were attempted. For each putt, data were recorded over a 3-s interval at a sampling rate of 100 Hz. Eye movements were recorded using a helmet-mounted eye movement monitor. Head rotation about an imaginary axis through the top of the head and its center-of-rotation was measured by means of a potentiometer mounted on a fixed frame and coupled to the helmet. Putter-head motion was measured using a linear array of infrared phototransistors embedded in the platform. The standard deviation (STD, relative to the initial level) was calculated for eye and head movements over the duration of the putt (i.e., from the beginning of the backstroke, through the forward stroke, to impact). The averaged STD for the attempted putts was calculated for each subject. Then, the averaged STDs and other data for the seven subjects were statistically compared across the three grip conditions. The STD of eye movements were greater (p < 0.1) for conventional than cross-hand (9 ft) and one-handed (3 and 9 ft) grips. Also, the STD of head movements were greater (p < 0.1; 3 ft) for conventional than cross-hand and one-handed grips. Vestibulo-ocular responses associated with head rotations could be observed in many 9 ft and some 3 ft putts. The duration of the putt was significantly longer (p < 0.05; 3 and 9 ft) for the one-handed than conventional and cross-hand grips. Finally, performance, or percentage putts made, was significantly better (p < 0.05; 9 ft) for cross-hand than conventional grip. The smaller variations, both in eye movements during longer putts and head movements during shorter putts, using cross-hand and one-handed grips may explain why some golfers, based on their playing experience, prefer these over the conventional grip. Also, the longer duration for the one-handed grip, which improves tempo, may explain why some senior players prefer the long-shaft (effectively one-handed grip) putter.

Adult↗
PubMed1990

Horizontal and vertical components of head movement are controlled by distinct neural circuits in the barn owl.

To generate behaviour, the brain must transform sensory information into signals that are appropriate to control movement. Sensory and motor coordinate frames are fundamentally different, however: sensory coordinates are based on the spatiotemporal patterns of activity arising from the various sense organs, whereas motor coordinates are based on the pulling directions of muscles or groups of muscles. Results from psychophysical experiments suggest that in the process of transforming sensory information into motor control signals, the brain encodes movements in abstract or extrinsic coordinate frames, that is ones not closely related to the geometry of the sensory apparatus or of the skeletomusculature. Here we show that an abstract code underlies movements of the head by the barn owl. Specifically, the data show that subsequent to the retinotopic code for space in the optic tectum yet before the motor neuron code for muscle tensions there exists a code for head movement in which upward, downward, leftward and rightward components of movement are controlled by four functionally distinct neural circuits. Such independent coding of orthogonal components of movement may be a common intermediate step in the transformation of sensation into behaviour.

Animals↗
PubMed2003

Adaptation of the vestibulo-ocular reflex, subjective tilt, and motion sickness to head movements during short-radius centrifugation.

Head movements made while the whole body is rotating at unusually high angular velocities (here with supine body position about an earth-vertical axis) result in inappropriate eye movements, sensory illusions, disorientation, and frequently motion sickness. We investigated the acquisition and retention of sensory adaptation to cross-coupled components of the vestibulo-ocular reflex (VOR) by asking eight subjects to make headturns while being rotated at 23 rpm on two consecutive days, and again a week later. The dependent measures were inappropriate vertical VOR, subjective tilt, and motion sickness in response to 90 degrees yaw out-of-plane head movements. Motion sickness was evaluated during and following exposure to rotation. Significant adaptation effects were found for the slow phase velocity of vertical nystagmus, the reported magnitude of the subjective tilt experienced during head turns, and motion-sickness scores. Retention of adaptation over a six-day rest period without rotation occurred, but was not complete for all measures. Adaptation of VOR was fully maintained while subjective tilt was only partially maintained and motion-sickness scores continued to decrease. Practical implications of these findings are discussed with particular emphasis on artificial gravity, which could be produced in weightlessness by means of a short-radius (2 m) rotator.

Adaptation, Physiological↗
PubMed1988

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Adolescent↗
PubMed2005

Kinematics of head movement in simulated low velocity rear-end impacts.

OBJECTIVES: To evaluate kinematics of head movement related to impact velocity, gender and awareness in simulated low velocity rear-end impacts. METHODS: Thirty individuals were subjected in random order to three rear-end impacts: two unexpected impacts causing chair acceleration of 4.5m/s2 (slow) and 10.0m/s2 (fast) and one 10.0m/s2 expected impact. Rearward head displacement, and linear and angular head accelerations were recorded. RESULTS: Angular head displacement was almost two times higher for the fast than the slow unexpected-impacts (P=0.04). Rearward and forward angular head accelerations increased two to three times with increased impact magnitude (P<0.05). Rearward and forward linear head accelerations were two and a half to three and a half times higher for the fast than for the slow unexpected impacts (P<0.05). Males presented two times higher upward linear head acceleration than females in the unexpected fast impact. No significant magnitude differences were identified for impact awareness in kinematics of head movement (P>0.05). Rearward angular head acceleration reached the peak between 62 and 84 ms later than the rearward linear head acceleration (P<0.05) in all impacts. No significant differences were identified for timing of kinematics of head movement (P>0.05) with increased impact magnitude; however, statistical powers were low. INTERPRETATION: Kinematics of head movement increases with increased impact magnitude. Gender differences exist for vertical linear head acceleration only. Temporal and amplitude awareness do not change the magnitude in kinematics of head movement. There are temporal differences between angular and linear head accelerations.

Acceleration↗
PubMed1990

Neural maps of head movement vector and speed in the optic tectum of the barn owl.

1. This study investigates the contribution of the optic tectum in encoding the metric and kinetic properties of saccadic head movements. We describe the dependence of head movement components (size, direction, and speed) on parameters of focal electrical stimulation of the barn owl's optic tectum. The results demonstrate that both the site and the amount of activity can influence head saccade metrics and kinetics. 2. Electrical stimulation of the owl's optic tectum elicited rapid head movements that closely resembled natural head movements made in response to auditory and visual stimuli. The kinetics of these movements were similar to those of saccadic eye movements in primates. 3. The metrics and kinetics of head movements evoked from any given site depended strongly on stimulus parameters. Movement duration increased with stimulus duration, as did movement size. Both the size and the maximum speed of the movement increased to a plateau value with current strength and pulse rate. Movement direction was independent of stimulus parameters. 4. The initial position of the head influenced the size, direction, and speed of movements evoked from any given site: when the owl initially faced away from the direction of the induced saccade, the movement was larger and faster than when the owl initially faced toward the direction of the induced movement. 5. A characteristic movement of particular size, direction, and speed could be defined for each site by the use of stimulation parameters that elicited plateau movements with normal kinetic profiles and by having the head initially centered on the body. The size, direction, and speed of these characteristic movements varied systematically with the site of stimulation across the tectum. The map of head movement vector (size and direction) was aligned with the sensory representations of visual and auditory space, such that the movement elicited from a given site when the owl initially faced straight ahead brought the owl to face that region of space represented by the sensory responses of the neurons at the site of stimulation. 6. The results imply that both the site and the amount of neural activity in the optic tectum contribute to encoding the metrics and kinetics of saccadic movements. A comparison of the present findings with previous studies on saccadic eye movements in primates and combined eye and head movements in cats suggests striking similarities in the ways in which tectal activity specifies a redirection in gaze to such dissimilar motor effectors as the eyes and head.

Animals↗
PubMed1997

Relationship between age and head movement during stepping in place by nonhandicapped children and persons with mental retardation.

We investigated developmental changes in head movement during stepping in place by nonhandicapped children and clarified the relationship between chronological or mental age and head movement of persons with mental retardation. 39 nonhandicapped children aged 3 to 6 years, 13 adults aged 19 to 22 years, and 10 persons with mental retardation (range of chronological age: 17 to 22 years, range of mental age: 3 to 8 years) participated. The total extent of head movement in the frontal plane during ordinary stepping in place for 20.48 sec. was measured to assess the magnitude of head movement. Changes in the magnitude of head movement of children are noticeable across ages, and the magnitude clearly was smaller at the age of 6 years. For subjects with mental retardation, no relationship has been found between chronological age and the magnitude of head movement but rather between mental age and the magnitude of head movement.

Adult↗