Journal of Vestibular Research - Volume 8, issue 5

Authors: Berger, Meinhard | Lechner-Steinleitner, Silvia | Kozlovskaya, Inessa | Holzmüller, Gerhard | Mescheriakov, Sergei | Sokolov, Alexej | Gerstenbrand, Franz

Article Type: Research Article

Abstract: This contribution deals with the examination of the consequences of different head-to-trunk positions on arm movements under normal gravity and during prolonged space flight. One of the objectives of this study was to investigate the influence of weightlessness on the condition of the spatial analysis system. Aimed arm movements in the horizontal plane (pointings towards two visual targets) were recorded, first with eyes open, head straight (learning part), then with eyes closed, head straight and during yaw or roll position of the head (performance part). Measurements related to these different head-to-trunk-positions were taken in one short-term and nine long-term cosmonauts …preflight, inflight, and postflight. Terrestrial control experiments were carried out with an extended experimental design in 14 healthy volunteers. The analysis of these experiments revealed that, with eyes closed and the head in yaw position, cosmonauts before flight and control subjects exhibit significant slants of the movement plane of the arm. Contrary to terrestrial measurements, in space experiments roll tilt of the head to the right is correlated with considerable counterclockwise slant of the movement plane. This slant of the movement plane of the arm was interpreted as tilt of the internal representation of the horizontal coordinate. The effect is larger with greater distortion induced by the changed head position and with larger muscular involvement to keep this position. This effect is also increased by the reduction of information (for example, in microgravity). The amount and the direction of the horizontal offset of the arm movements are shown to be dependent on the head-to-trunk position, too. Additionally, we have found changes in the amplitude and in the duration of the arm movement, in the vertical offset, and in the curvature of the movement paths, depending on the experimental conditions. Show more

Keywords: arm movements, weightlessness, head-to-trunk position, subjective horizontal

DOI: 10.3233/VES-1998-8501

Citation: Journal of Vestibular Research, vol. 8, no. 5, pp. 341-354, 1998

Authors: Furman, Joseph M. | Durrant, John D.

Article Type: Research Article

Abstract: Head-only rotational testing (HORT) is a noninvasive technique to assess the vestibulo-ocular reflex (VOR) that can be performed in a nonlaboratory environment with inexpensive, portable equipment. Little data are available regarding the applicability of this technique to the elderly in whom limitations of cervical range of motion might reduce the usefulness of the technique. This study was designed to apply HORT to a small group of normal elderly subjects to determine whether the technique could be used successfully in this population. Also, the VOR parameters derived from HORT were compared with the results obtained from a group of healthy young …control subjects. HORT was performed both with and without visual fixation of an earth-fixed target, using both active head movement and passive head movement. Results indicated that the responses of the elderly were indistinguishable from those of the young except for a slightly higher gain at 1 Hz in the young subjects. Other findings, consistent across young and elderly, were that visual fixation increased gain and decreased phase lead at lower frequencies and that VOR parameters were unaffected by volition, that is, active and passive head rotation produced similar responses. These findings suggest that HORT can be applied to the elderly without difficulty. Future studies will assess the usefulness of HORT in elderly patients with VOR disorders. Show more

Keywords: vestibulo-ocular reflex, human, aging, vision

DOI: 10.3233/VES-1998-8502

Citation: Journal of Vestibular Research, vol. 8, no. 5, pp. 355-361, 1998

Authors: Kramer, Phillip D. | Roberts, Dale C. | Shelhamer, Mark | Zee, David S.

Article Type: Research Article

Abstract: Testing of the vestibular system requires a vestibular stimulus (motion) and/or a visual stimulus. We have developed a versatile, low cost, stereoscopic visual display system, using “virtual reality” (VR) technology. The display system can produce images for each eye that correspond to targets at any virtual distance relative to the subject, and so require the appropriate ocular vergence. We elicited smooth pursuit, “stare” optokinetic nystagmus (OKN) and after-nystagmus (OKAN), vergence for targets at various distances, and short-term adaptation of the vestibulo-ocular reflex (VOR), using both conventional methods and the stereoscopic display. Pursuit, OKN, and OKAN were comparable with both methods. …When used with a vestibular stimulus, VR induced appropriate adaptive changes of the phase and gain of the angular VOR. In addition, using the VR display system and a human linear acceleration sled, we adapted the phase of the linear VOR. The VR-based stimulus system not only offers an alternative to more cumbersome means of stimulating the visual system in vestibular experiments, it also can produce visual stimuli that would otherwise be impractical or impossible. Our techniques provide images without the latencies encountered in most VR systems. Its inherent versatility allows it to be useful in several different types of experiments, and because it is software driven it can be quickly adapted to provide a new stimulus. These two factors allow VR to provide considerable savings in time and money, as well as flexibility in developing experimental paradigms. Show more

Keywords: virtual reality, head mounted display, vestibular, oculomotor

DOI: 10.3233/VES-1998-8503

Citation: Journal of Vestibular Research, vol. 8, no. 5, pp. 363-379, 1998

Authors: Szturm, Tony | Fallang, Bjorg

Article Type: Research Article

Abstract: Different movement synergies used to restore balance in response to sudden support surface displacements have been described, which include the ankle movement synergy and a number of multisegmental movement synergies. The purpose of this study was to extend the analysis of the effects of stimulus magnitude on the pattern and scaling of balance reactions to larger magnitudes of balance disturbances, and to other types of balance disturbances, in particular, forward translations (FT), backward translations (BT), and toes-up rotations (RT). In addition, we examined whether the timing and magnitude of center of body mass (CM) displacement is an invariant feature of …corrective responses to varying magnitudes of balance disturbances. Thirteen healthy adults were subjected to FT, BT, and RT of varying acceleration/velocity. The balance disturbance induced by FT and BT was fundamentally different from that induced by RT. The balance requirement during FT and BT was to rapidly translate the CM forward/backward to the new position within the displaced base of support. For RT, the requirement was to minimize the backward displacement of the CM. As evidenced from the initial phase of ankle, knee, and hip angular displacements and anterior-posterior (A-P) center of foot pressure displacement, the magnitude of the balance disturbance increased with increasing platform acceleration/velocity. For FT and BT, the present findings are consistent with the view that trajectory of CM is a control variable, as the timing, peak magnitude, and time to peak CM displacement did not vary as a function of platform acceleration/velocity. However, for RT, the peak magnitude and time to peak CM displacement did increase with increasing platform acceleration/velocity. The results demonstrate that in response to FT, BT, and RT, stability was restored by distinct multisegmental movement synergies. The corrective response to FT consisted of early knee flexion then ankle dorsiflexion and hip extension. The corrective response to BT consisted of hip flexion and ankle plantar flexion. For RT early hip flexion and knee flexion was observed. AU muscles recorded (tibialis anterior, soleus, gastrocnemius, hamstrings, and quadriceps) were activated within a range of 60 to 170 ms from onset of platform displacement. For FT, BT, and RT, the pattern and timing of angular displacements and muscle responses did not vary as a function of platform acceleration/velocity, while there was a significant effect of platform acceleration/velocity on the magnitude of the corrective response, that is, peak magnitude of corrective hip, knee, and ankle angular displacements and magnitude of muscle responses. The present findings indicate that multiple sources of spatial information are necessary for the selection and initiation of the appropriate corrective response to meet the requirements of the different balance tasks. The present results strongly endorse the concept of a postural control network for recovery of standing balance, as opposed to positive feedback through local segmental or long loop reflex circuits. Show more

Keywords: motor control, postural reactions, human, kinematics, electromyography, center of foot pressure, total body center of mass

DOI: 10.3233/VES-1998-8504

Citation: Journal of Vestibular Research, vol. 8, no. 5, pp. 381-397, 1998