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PubMedDate not supplied

Gravity and perceptual stability during translational head movement on earth and in microgravity.

We measured the amount of visual movement judged consistent with translational head movement under normal and microgravity conditions. Subjects wore a virtual reality helmet in which the ratio of the movement of the world to the movement of the head (visual gain) was variable. Using the method of adjustment under normal gravity 10 subjects adjusted the visual gain until the visual world appeared stable during head movements that were either parallel or orthogonal to gravity. Using the method of constant stimuli under normal gravity, seven subjects moved their heads and judged whether the virtual world appeared to move "with" or "against" their movement for several visual gains. One subject repeated the constant stimuli judgements in microgravity during parabolic flight. The accuracy of judgements appeared unaffected by the direction or absence of gravity. Only the variability appeared affected by the absence of gravity. These results are discussed in relation to discomfort during head movements in microgravity.

Gravitation↗
PubMed2006

Head movements evoked by electrical stimulation in the frontal eye field of the monkey: evidence for independent eye and head control.

When the head is free to move, electrical stimulation in the frontal eye field (FEF) evokes eye and head movements. However, it is unclear whether FEF stimulation-evoked head movements contribute to shifting the line of sight, like visually guided coordinated eye-head gaze shifts. Here we investigated this issue by systematically varying initial eye (IEP) and head (IHP) positions at stimulation onset. Despite the large variability of IEP and IHP and the extent of stimulation-evoked gaze amplitudes, gaze displacement was entirely accounted for by eye (re head) displacement. Overall, the majority (3/4) of stimulation-evoked gaze shifts consisted of eye-alone movements, in which head movements were below the detection threshold. When head movements did occur, they often started late (re gaze shift onset) and coincided with rapid eye deceleration, resulting in little change in the ensuing gaze amplitudes. These head movements often reached their peak velocities over 100 ms after the end of gaze shifts, indicating that the head velocity profile was temporally dissociated from the gaze drive. Interestingly, head movements were sometimes evoked by FEF stimulation in the absence of gaze shifts, particularly when IEP was deviated contralaterally (re the stimulated side) at stimulation onset. Furthermore, head movements evoked by FEF stimulation resembled a subset of head movements occurring during visually guided gaze shifts. These unique head movements minimized the eye deviation from the center of the orbit and contributed little to gaze shifts. The results suggest that head motor control may be independent from eye control in the FEF.

Animals↗
PubMed1987

Head movements during optokinetic stimulation in the alert rabbit.

Pigmented rabbits with their heads free to move about the vertical axis were seated inside a rotating optokinetic drum in order to evoke the optocollic reflex (OCR). At drum velocities below 5 degrees/s, head movements were inconsequential, and eye velocity generally matched drum velocity. At velocities between 5-15 degrees/s head movements were irregular and slight; head velocity was less than 20% of drum velocity, and gaze was undercompensatory by 1-3 degrees/s (retinal image motion of 1-3 degrees/s). At drum velocities above 15 degrees/s, and especially above 30 degrees/s, head movements were substantial (more than 20% of the drum velocity), but gaze was undercompensatory by 60-70% of the stimulus velocity. In the same rabbits in the same test periods and conditions, the vestibulo-collic reflex (VCR) was evoked with vision with minimal gaze undercompensation relative to a stationary surround; however, when deprived of vision the VCR gain dropped. The present results support the notion that with vision, the OCR does not contribute significantly to the improvement of the VCR response, since massive undercompensation of the gaze relative to the rotating drum was required in OCR testing to evoke head movements similar to those seen in VCR tests. Due to many differences in operating characteristics of the vestibular and optokinetic systems, and due to the nature of OCR testing, there were several unexpected results: in some cases head movements did not result in summation of vestibular and optokinetic reflexes, and with sinusoidal drum rotations of about 2 degrees/s2 peak acceleration there was overcompensation (gaze moves faster than the drum) for intervals up to 20 s. Thus, optokinetically generated active head movements could produce behavior strongly contrasting with passively induced head movements in visual-vestibular tests. It is tentatively concluded that in mammals there is a vestigial and specific optokinetic control of gaze and that the optokinetic control of the head is weak (relative to the eyes). However, other non-reflex mechanisms controlling head movements-such as stimulus entrainment and temporal asymmetries in the vestibular and optokinetic reflexes-must also be considered to explain all facets of the data.

Animals↗
PubMed2001

Adaptive plasticity of head movement propensity.

Individual humans exhibit differing propensity to move the head in association with saccadic shifts in gaze. We assessed whether this tendency can be modified in normal subjects by either reducing neck mobility with a cervical collar or restricting the field of view using aperture spectacles. We quantified head movement propensity in terms of the range of orbital eccentricity within which the eyes are customarily maintained (customary ocular motor range), and the range of final eye-in-head eccentricity for which a planned saccade is likely to be executed without a concomitant head movement (eye-only range). Three subjects wore rigid collars during waking hours for periods of up to 9 days. We measured customary and eye-only ranges with the collar removed, at various times during the adaptation and recovery periods. Collar adaptation reduced head movement propensity in all three subjects, increasing the average customary ocular range from 27.6 +/- 8.9 degrees (mean +/- SD) to 66.1 +/- 4.5 degrees and the eye-only range from 24.6 +/- 17.0 degrees to 67.6 +/- 7.4 degrees. In two subjects the modifications persisted for weeks following final collar removal. In parallel with the reduction in head movement propensity, all subjects improved in their ability to maintain eccentric gaze, suggesting that neck restriction led to effects at the level of the brainstem. Three subjects were adapted to spectacles, masked to restrict the field of view to approximately 20 degrees. The aperture spectacles were worn for periods of up to 9 days. When tested without the apertures, one subject exhibited a definite increase in head movement propensity; in the other two, the data were equivocal, indicating either a small increase in head movement propensity or no effect. Averaged across subjects, customary ocular motor range decreased from 35.1 +/- 12.8 degrees to 25.4 +/- 13.4 degrees and eye-only range decreased from 35.1 +/- 7.5 degrees to 23.0 +/- 4.0 degrees. The marked difference in the magnitudes of collar- and spectacle-induced changes suggests that the responses to the two restrictive appliances are mediated by different mechanisms. Collar adaptation may involve parametric modulation of circuits mediating reflex recruitment of head movements, while aperture adaptation may primarily reflect substitution of an alternative mode of head control triggered by the presence of the restricted field of view, with only minor parametric modulation of the underlying head recruitment circuit. The enduring effects of restricting neck mobility upon head movement tendencies may relate to the common clinical association between neck injury and persistent dysequilibrium.

Adaptation, Physiological↗
PubMed1988

Postural adjustments to head movements in the cat.

Head movements induced by motor cortex stimulation in the cat are accompanied by variations in the vertical force exerted by each limb. These postural responses were found to show stereotyped patterns: with head dorsiflexions an increase was observed in the force exerted by the anterior limbs and a decrease at the posterior limb level. From comparison between the latencies of the force variations, the beginning of head acceleration, and EMG activity in the limb extensor muscles, it was concluded that triggering of these postural responses is not reflex, but depends on the same command as the movement itself. This early response might be a means of avoiding the downward movement of the trunk which would otherwise result from the reaction force corresponding to the upward head movement.

Animals↗
PubMed1997

Cognitive difficulty of a peripherally presented visual task affects head movements during gaze displacement.

The maintenance and adjustment of visual gaze are functions both of eye and of head movement. Compared to the factors that affect eye movement during gaze displacement, the factors that affect head movement have received relatively little attention. Most experimenters have restricted head movements to determine how the eye acquires information. Information is commonly acquired without head movements (e.g., it is likely you are moving your eyes without moving your head as you read the words on this page). However, when visual information beyond the written page is acquired head movements in addition to eye movements are likely to occur. The purpose of this experiment was to study gaze displacement under more natural conditions in which the eyes and head were both free to move. Specifically, the purpose of this experiment was to identify the pattern of gaze displacement as a function of cognitive task difficulty. Visual information was presented at an eccentricity of 40 degrees of visual angle either to the left or to the right of a center fixation point (0 degree eccentricity) to 24 undergraduate subjects (12 male). On each trial, five integers were presented in rapid succession; subjects were asked to count the number of odd integers or to arithmetically manipulate the integers. When subjects expected to perform the more difficult task of arithmetic manipulation, they were more likely to make head movements in the direction of the stimuli, F1,16 = 9.34, P < 0.05. Those subjects who made head movements to acquire the peripherally presented visual information made significantly more errors than the 'non-movers', F1,24 = 6.03, P < 0.05. These results suggest subjects who moved their head to acquire peripheral information may have found the task to be more difficult than subjects who did not make head movements. The results confirm that head movements play a critical role in the intake of information even in structured laboratory tasks and suggest the common method of restricting head movements to study eye movements may not be a natural method of information intake.

Adolescent↗
PubMed1988

Head movement co-ordination in the African chameleon.

Chameleon head movement was studied to learn how information from more than one sensory system can be co-ordinated to produce a single motor behavior. In this study, the co-ordination of visual, vestibular, and kinesthetic senses was examined by: (1) moving a cricket back and forth in front of a hungry chamelon, (2) moving the body of an alert chameleon or the body of an anesthetized chameleon, and (3) moving both a cricket and the body of an alert chameleon. During cricket movement, the chameleon locked both eyes straight forward in their orbits and followed the cricket movement with a visually guided head movement. During movement of the body of an alert chameleon, the vestibulo-collic reflex kept the chameleon's head relatively stationary in space. During movement of the body of an anesthetized chameleon, there was no measurable movement of the head relative to the body. Thus, during the body movements used in this study, passively induced kinesthetic stimulation was negligible. It was hypothesized that during movement of both a cricket and the body of an alert chameleon, the visually guided head movement and the vestibulo-collic reflex were additive. This hypothesis was supported by demonstrating that in this situation, the vestibulo-collic reflex was not suppressed. It is suggested that the vestibulo-collic reflex compensated for the passive head movement produced by body movement without canceling active, visually guided head movement. This may have been accomplished by the use of an efference copy system associated with the motor commands that produce visually guided head movement.

Afferent Pathways↗
PubMed2001

Transcranial magnetic stimulation over the cerebellum delays predictive head movements in the coordination of gaze.

We investigated coordinated saccadic eye and head movements following predictive horizontal visual targets at +/- 30 degrees by applying transcranial magnetic stimulation (TMS) over the cerebellum before the start of the gaze movement in 10 young subjects. We found three effects of TMS on eye-head movements: 1. Saccadic latency effect. When stimulation took place shortly before movements commenced (75-25 ms before), significantly shorter latencies were found between predictive target presentation and initiation of saccades. Eye latencies were significantly decreased by 45 ms on average, but head latencies were not. 2. Gaze amplitude effect. Without TMS, for the 60 degrees target amplitudes, head movements usually preceded eye movements, as expected (predictive gaze type 3). With TMS 5-75 ms before the gaze movement, the number of eye movements preceding head movements by 20-50 ms was significantly increased (p < 0.001) and the delay between eye and head movements was reversed (p < 0.001), i.e. we found eye-predictive gaze type 1. 3. Saccadic peak velocity effect. For TMS 5-25 s before the start of head movement, mean peak velocity of synkinetic eye saccades increased by 20-30% up to 600 degrees/s, compared to 350-400 degrees/s without TMS. We conclude that transient functional cerebellar deficits exerted by means of TMS can change the central synkinesis of eye-head coordination, including the preprogramming of the saccadic pulse and step of a coordinated gaze movement.

Adult↗
PubMed1993

Dissociation of kainic acid lesion effects on the asymmetry of rotation and lateral head movements.

The present study tested the relationship between horizontal head movement asymmetry and rotation behavior after unilateral kainic acid (KA) lesions of the pontine reticular formation (PRF). In line with previous studies, the lesions decreased the rate of ipsilateral spontaneous head movements and spared contralateral spontaneous head movements. In contrast to previous studies, however, these lesions facilitated ipsilateral rather than contralateral rotation. Histological analysis revealed that the ipsilateral rotation may be accounted for by distant effects of the KA injection in the PRF on the ipsilateral substantia nigra (SN). We conclude that unilateral lesions consisting solely of the PRF lead to a preference for contralateral horizontal head movements which then channel rotated away from the lesioned side. KA injections in the PRF, however, are also associated with distant lesions within the ipsilateral extrapyramidal system which override the channeling effect of the contralateral head movements and induce instead ipsilateral rotation.

Animals↗
PubMed1997

Dynamic electron microscopy of ATP-induced myosin head movement in living muscle thick filaments.

Although muscle contraction is known to result from movement of the myosin heads on the thick filaments while attached to the thin filaments, the myosin head movement coupled with ATP hydrolysis still remains to be investigated. Using a gas environmental (hydration) chamber, in which biological specimens can be kept in wet state, we succeeded in recording images of living muscle thick filaments with gold position markers attached to the myosin heads. The position of individual myosin heads did not change appreciably with time in the absence of ATP, indicating stability of the myosin head mean position. On application of ATP, the position of individual myosin heads was found to move by approximately 20 nm along the filament axis, whereas no appreciable movement of the filaments was detected. The ATP-induced myosin head movement was not observed in filaments in which ATPase activity of the myosin heads was eliminated. Application of ADP produced no appreciable myosin head movement. These results show that the ATP-induced myosin head movement takes place in the absence of the thin filaments. Because ATP reacts rapidly with the myosin head (M) to form the complex (M. ADP.Pi) with an average lifetime of >10 s, the observed myosin head movement may be mostly associated with reaction, M + ATP --> M.ADP. Pi. This work will open a new research field to study dynamic structural changes of individual biomolecules, which are kept in a living state in an electron microscope.

Actin Cytoskeleton↗
PubMed2003

Coordination of eye and head movements during reading.

PURPOSE: There is little information regarding the characteristics of head movements during reading. This study was undertaken to investigate horizontal and vertical head movements during two different reading tasks. METHODS: Head and eye movements were monitored with an infrared pupil and head tracker in 15 subjects during repeated reading of text from an A4-sized card and a card 90 degrees wide. In addition, head and eye movements were recorded in 45 subjects to compare head movement propensity during an A4 text-reading task and a saccadic task of an equivalent gaze shift. RESULTS: During the A4 standard reading task, horizontal and vertical head movements accounted for 4.7% and 28.7% of the gaze shift, respectively. During the 90 degrees text reading, horizontal head movements accounted for 40.3% of the gaze amplitude, and vertical head movements accounted for 28.4%. Horizontal gaze velocities increased significantly on repeated A4 and 90 degrees text readings, as did horizontal head velocities and amplitudes. Reading head movement propensities were significantly smaller than saccadic head movement propensities (P < 0.001). CONCLUSIONS: Head movement strategies are rapidly switched between the A4 and 90 degrees text-reading paradigms. They are minimized during A4 text reading but actively assist the gaze strategy during 90 degrees text reading. Horizontal head movement is reduced during A4 reading compared to the equivalent saccadic task and may be suppressed to improve fixation stability. The results support the view that the head and eye movement system is a highly coupled but extremely flexible system.

Adult↗
PubMed2000

Reaching measures of monocular distance perception: forward versus side-to-side head movements and haptic feedback.

We investigated whether forward or side-to-side head movements yielded more accurate and precise monocular egocentric distance information, as shown by performance in a reaching task. Observers wore a head-mounted camera and display to isolate the optic flow generated by their head movements and had to reach to align a stylus directly under a target surface. Performance in the two head movement conditions was also tested with normal monocular vision. We tested performance in the two head movement conditions when the observers were given haptic feedback and compared performance when haptic feedback was removed. Performance was both more accurate and more precise in the forward head movement condition than in the side-to-side head movement condition. Performance in the side-to-side condition also deteriorated more after the removal of haptic feedback than did performance in the forward head movement condition. In the normal monocular condition, performance was comparable for the two head movement conditions. The implications for enucleated patients are discussed.

Distance Perception↗
PubMed2003

Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated computer-based environment.

PURPOSE: To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment. METHODS: Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV). RESULTS: Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition. CONCLUSIONS: Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.

Aged↗
PubMed1997

Gain adaptation of eye and head movement components of simian gaze shifts.

Gain adaptation of eye and head movement components of simian gaze shifts. J. Neurophysiol. 78: 2817-2821, 1997. To investigate the site of gaze adaptation in primates, we reduced the gain of large head-restrained gaze shifts made to 50 degrees target steps by jumping the target 40% backwards during a targeting saccade and then tested gain transfer to the eye- and head-movement components of head-unrestrained gaze shifts. After several hundred backstep trials, saccadic gain decreased by at least 10% in 8 of 13 experiments, which were then selected for further study. The minimum saccadic gain decrease in these eight experiments was 12.8% (mean = 18.4%). Head-unrestrained gaze shifts to ordinary 50 degrees target steps experienced a gain reduction of at least 9.3% (mean = 14.9%), a mean gain transfer of 81%. Both the eye and head components of the gaze shift also decreased. However, average head movement gain decreased much more (22.1%) than eye movement gain (9.2%). Also, peak head velocity generally decreased significantly (20%), but peak eye velocity either increased or remained constant (average increase of 5.6%). However, the adapted peak eye and head velocities were appropriate for the adapted, smaller gaze amplitudes. Similar dissociations in eye and head metrics occurred when head-unrestrained gaze shifts were adapted directly (n = 2). These results indicated that head-restrained saccadic gain adaptation did not produce adaptation of eye movement alone. Nor did it produce a proportional gain change in both eye and head movement. Rather, normal eye and head amplitude and velocity relations for a given gaze amplitude were preserved. Such a result could be explained most easily if head-restrained adaptation were realized before the eye and head commands had been individualized. Therefore, gaze adaptation is most likely to occur upstream of the creation of separate eye and head movement commands.

Acclimatization↗
PubMed2006

Development of head movement propensity in 4-15 year old children in response to visual step stimuli.

Head movement frequency of children in response to horizontal step stimulus is investigated. The aim is to determine if there is a correlation between the age of the child and the frequency of head movements made to visual step stimuli presented at a fixed distance. Also of importance is whether there is a period of rapid change in the frequency of head movements, and if so, what factors could be influencing this change. Seventy-three participants, between the ages of 4 and 15 years were requested to "look at a spot of light" in response to step stimuli which varied in size from 5 to 60 degrees. Eye and head movements were recorded with a video based eye tracker (EL-Mar 2020) equipped with a Flock of Birds head tracker. Frequency of head movements was calculated for each participant and averaged across participants for each age group. Average head movement frequency was then plotted as a function of age. The frequency and variability of head movements decreases as a function of age. This decrease is linear between the ages of 4 and 15 years (y = -1.465x + 22.58; R(2) = 0.4378; F = 26.48; P < 0.0001). More head movements are made in response to larger step sizes than to smaller ones for all ages. The gradual decrease in frequency of head movements in response to step stimuli suggests that a specific environmental event, such as reading, is not the cause of the decline. Improved efficiency of eye movements could be due to pre-programmed factors related to neurological development. Alternatively, cognitive factors may be involved. Children may actually learn that utilizing their head for gaze shifts is more energy and time consuming, than merely using the eyes alone.

Adolescent↗
PubMed2006

Sleepiness and head movements.

Sleepiness in working life is critical and strongly associated to work related accidents. The relationship between sleepiness and head movements is poorly investigated. The pattern of head movements over time was investigated in a laboratory study with ten subjects either sleep-deprived or rested. Head movements were obtained by an inclinometer placed on the subject's forehead, and the recording was continuous. Results show that subjects when sleep-deprived moved their head more and had more extreme head movements compared to when rested. An increase of the velocity and the number of extreme head movements over time were noted when the subjects were sleep-deprived and when rested. The increase of head movements was more linear over time in the rested condition, whereas in sleep-deprived conditions most of the increase appeared during the first hour. No significant differences of between forward-backward movements and left-right movements could be found. When rested, the changes in head movements correlated with ratings of sleepiness, EEG activity, and heart rate variability. Head movements can be a used as an indicator of sleepiness.

Accidents, Occupational↗
PubMed1988

Active head-movement analysis of cisplatin-induced vestibulotoxicity.

The vestibulo-ocular reflex (VOR) acts to maintain a clear and stationary image of the visual world during movements of the head. Accurate measurement of the VOR is therefore an important clinical method for evaluation of the vestibular system. We applied a new method of computerized vestibular testing, the Vestibular Autorotation Test (VAT), which is based on 18 seconds of active head movements. The VAT was used to prospectively study the horizontal VOR of nine patients with cancer who were being treated with cisplatin. Patients were instructed to move their heads in the horizontal plane in synchrony with audible clicks of a linearly increasing frequency range, from 0.5 to 6.5 Hz. Electro-oculographic (EOG) eye movements and head velocity were monitored and digitized to compute horizontal VOR gain and phase from 2 to 6 Hz. Patients were tested with the VAT before the initial cisplatin treatment, and then before each subsequent cisplatin treatment. The pretreatment gains and phases were compared with those obtained after the final cisplatin treatment. Results showed decreased VOR gains at 3.1 Hz, 3.9 Hz, and 5.1 Hz, and increased phase lags at 3.1 Hz and 3.9 Hz. We conclude that VAT analysis of the horizontal VOR at frequencies 3 to 5 Hz is useful for detection and monitoring of cisplatin vestibulotoxicity.

Adult↗
PubMed2004

Neck posture and head movement in four rescue stretchers.

Neck posture and head movements were measured in four rescue stretchers: the Neil Robertson stretcher, which has been in service in the Royal Navy for almost 100 years, and three potential replacements. A repeated measures laboratory study was carried out to quantify neck posture and head movements while subjects reclined in the stretchers. Stretchers were compared on the basis of this critical aspect of their performance to complement the findings of ship-based usability trials. When the subjects were secured in each of the stretchers, wearing cervical collars and any restraints integral to that stretcher, the resting posture of the neck and the range of voluntary movement in flexion/extension, lateral flexion, and rotation were measured. In all of the stretchers, the neck was in an extended posture. The collars restricted head movements but they did not immobilize the neck. Stretcher 3, which had all of the functionality of the Neal Robertson stretcher, but with integral backboard and head blocks, limited head movements the most.

Confined Spaces↗