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Biomedical subjects

G R Barnes

Publications and source records attributed to G R Barnes.

At least 91 records · Page 5Linked to original sources
PubMed1979

Vestibulo-ocular function during co-ordinated head and eye movements to acquire visual targets.

1. Experiments have been conducted on human subjects in an attempt to establish the role of the vestibulo-ocular reflex in the co-ordination of head and eye movements during visual target acquisition. 2. When the subject moved head and eyes to acquire visual targets in the horizontal plane, the eye movement consisted of an initial saccade in the direction of head movement followed by a slower return towards orbital centre which compensated for remaining head movement. 3. When the head was moved either voluntarily or passively in the dark the pattern of eye movement was very similar to that seen during target acquisition. 4. The mean latency between the start of head acceleration and the onset of the saccadic eye movement was greater in the dark (108 msec, S.D. 85 msec) than for the visually induced responses (14 msec, S.D. 59 msec), in which eye movement often preceded head movement when moving to small ( less than 45 degrees) target offset angles. 5. In all experimental conditions gaze displacement at the end of the initial saccade was normally related in a predictive manner to final head position, but when fixating visual targets offset by more than 60 degrees from the central position there were often large errors, 22% of responses undershooting the target by more than 15 degrees. 6. A highly significant (P less than 0.001) linear relationship was found between gaze displacement and head velocity under all experimental conditions. During target acquisition head velocity was normally positively correlated with amplitude of target offset. The large errors in gaze displacement in response to the larger target offsets occurred at levels of head velocity lower than normally associated with such target offsets. 7. The results have led to the suggestion of a dual mode of control for head-eye co-ordination. In one mode, normally associated with small target offsets (less than 45 degrees), control is mediated by retinal error information. In the other mode, associated with larger target offsets, gaze displacement is generated as an automatic response to head turning. 8. The observation of similar relationships between head and eye movement during passive head turning implicates the vestibulo-ocular reflex in the secondary mode of control, and provides support for the hypothesis that the role of the vestibular saccade is to induce a rapid offset of the eyes in the direction of head movement, thus facilitating rapid search and target location.

Eye Movements↗
PubMed1979

Head-eye coordination in normals and in patients with vestibular disorders.

Oculomotor response in the absence of vision was examined in 8 normal subjects, 11 unilaterally labyrinthectomised patients and 2 patients with suspected bilateral canal paresis. The experiments involved (a) voluntary oscillation of the head, (b) whole body oscillation on a turntable and (c) stimulation of neck afferents by oscillation of the body with the head fixed. In the patients with unilateral lesions there was a directional preponderance of the slow phase eye velocity towards the side of the lesion which differed significantly from that of the normal population. In the patients with bilateral paresis the oculomotor response to whole body oscillation was negligible, whereas the response to voluntary head movement had a mean gain of 0.45 and at high frequency could not be suppressed when viewing a head-fixed image. The saccadic activity during voluntary head movement was similar in all subjects and was correlated with slow phase velocity.

Eye Movements↗
PubMed1979

Cervical and vestibular afferent control of oculomotor response in man.

Oculomotor response in the absence of vision has been compared in a group of 12 normal humans in two experimental conditions testing (a) the vestibulocular reflex by whole-body oscillation on a turntable, and (b) the cervico-ocular reflex by oscillation of the body with the head held stationary. The stimulus was a sinusoidal oscillation (peak angular velocity +/- 50 degrees/sec) at frequencies between 0.2 and 1.3 Hz. The slow-phase eye movements of the vestibulo-ocular response were compensatory for head movement and showed a mean gain of 0.54--0.90, increasing with frequency. The cervicoocular response was found to be very variable. The slow-phase eye movements were of low velocity (mean gain 0.05) and did not generally compensate for body movement. During neck torsion, some subjects exhibited large overall eye deviations composed of both slow and fast phase eye movements.

Eye Movements↗
PubMed1978

Vision during angular oscillation: the dynamic interaction of visual and vestibular mechanisms.

A review is presented of the dynamic behaviour of two oculomotor control systems--the vestibulo-ocular and pursuit reflexes--responsible for the spatial and temporal stabilization of the image of an observed object on the fovea of the retina, and mathematical models adduced in which the contribution of physiological components of the systems can be identified. With angular oscillation of the head below 1-2 Hz, retinal information is used to maintain unity gain of the head/eye system, but at higher frequencies stabilization is determined primarily by vestibular inputs. When the observed target moves with the head, as in a head-mounted display, the suppression of inappropriate vestibulo-ocular responses is dependent upon the dynamic performance of the pursuit system. With such a display, impairment of visual acuity may be detected at frequencies of oscillation as low as 0.5 Hz.

Humans↗
PubMed1978

Visual-vestibular interaction in the control of eye movement.

Three experimental conditions have been used to investigate the extent to which inappropriate reflex eye movements of vestibular origin can be suppressed by visual feedback. First, the ability to read digits in a display which moved with the head was assessed during angular oscillation about the yaw and pitch axes of the body. Performance decrement was observed at frequencies above 0.2 Hz in pitch and 1.0 Hz in yaw, being greater at higher stimulus velocity levels. A second experiment revealed that the performance decrement was associated with eye movements relative to the head, which increased with the frequency of stimulation. Finally, the response of the pursuit reflex was investigated under similar experimental conditions. The results indicated that the breakdown in the pursuit reflex and in the suppression of the vestibulo-ocular reflex occurred over the same frequency band, implying the similarity of the mechanisms responsible for suppression and pursuit.

Aerospace Medicine↗
PubMed1978

Visual target acquisition and tracking performance using a helmet-mounted sight.

Experiments have been conducted on human subjects to assess the efficiency with which a helmet-mounted sighting system can be used to locate and track target sources in the horizontal plane. In the first experimental condition, in which the sight was aligned with discrete stationary target sources, the latency between target presentation and final target location was in the 2-4 s range, dependent upon the amplitude of target offset and the rate of head movement. In the second condition, subjects were instructed to track a sinusoidally oscillating visual image with the sight. Tracking performance was found to be impaired when the frequency of oscillation was increased beyond 0.8-1.0 Hz. Recording of eye movement during both experimental conditions indicated that the impairment of performance could, in part, be attributed to involuntary eye movements consequent upon stimulation of the vestibulo-ocular reflex by the head turning movements.

Acceleration↗
PubMed1976

Rostral displacement of the palatopharyngeal arch: a case report.

A horse with rostral displacement of the palatopharyngeal arch was found to have a bilaterally symmetrical deformity of the laryngeal area. Both left and right cricopharyngeal muscles were absent. The shape of the thyroid cartilage was grossly abnormal and vestiges of the cricothyroid muscles were attached only to the cricoid cartilage. It was suggested that such an anomaly could have resulted from aberrant development of the fourth branchial arch.

Animals↗
PubMed1975

Head movement induced by angular oscillation of the body in the pitch and roll axes.

The transmission of angular acceleration to the head of the human subject has been investigated during sinusoidal angular oscillation of the body in either pitch or roll about an axis through the upper lumbar vertebrae. The results indicated that angular acceleration of the skull was induced in all three axes of the head by both pitch and by roll motion. At frequencies below 1-2 Hz the head moved with the body, but in the frequency range 2-8 Hz the amplitude of head acceleration was augmented indicating that oscillation about a centre of rotation low in the body may induce large angular movements in this frequency range because of the linear component of acceleration delivered at the cervical vertebrae. At higher frequencies, the acceleration at the head was attenuated with an associated increase in phase lag, probably due to the absorption of input acceleration by the upper torso.

Acceleration↗