Journal of Vestibular Research - Volume 12, issue 5-6

Authors: Oman, Charles M.

Article Type: Research Article

DOI: 10.3233/VES-2003-125-601

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 201-203, 2003

Authors: Dornhoffer, John L. | Mamiya, N. | Bray, P. | Skinner, Robert D. | Garcia-Rill, Edgar

Article Type: Research Article

Abstract: Sopite syndrome, characterized by loss of initiative, sensitivity to normally innocuous sensory stimuli, and impaired concentration amounting to a sensory gating deficit, is commonly associated with Space Motion Sickness (SMS). The amplitude of the P50 potential is a measure of level of arousal, and a paired-stimulus paradigm can be used to measure sensory gating. We used the rotary chair to elicit the sensory mismatch that occurs with SMS by overstimulating the vestibular apparatus. The effects of rotation on the manifestation of the P50 midlatency auditory evoked response were then assessed as a measure of arousal and distractibility. Results showed that …rotation-induced motion sickness produced no change in the level of arousal but did produce a significant deficit in sensory gating, indicating that some of the attentional and cognitive deficits observed with SMS may be due to distractibility induced by decreased habituation to repetitive stimuli. Show more

Keywords: arousal, rotary chair, sleep, Sopite syndrome, space motion sickness

DOI: 10.3233/VES-2003-125-602

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 205-209, 2003

Authors: Shelhamer, Mark | Clendaniel, Richard A. | Roberts, Dale C.

Article Type: Research Article

Abstract: Previous studies established that vestibular reflexes can have two adapted states (e.g., gains) simultaneously, and that a context cue (e.g., vertical eye position) can switch between the two states. Our earlier work demonstrated this phenomenon of context-specific adaptation for saccadic eye movements: we asked for gain decrease in one context state and gain increase in another context state, and then determined if a change in the context state would invoke switching between the adapted states. Horizontal and vertical eye position and head orientation could serve, to varying degrees, as cues for switching between two different saccade gains. In the present …study, we asked whether gravity magnitude could serve as a context cue: saccade adaptation was performed during parabolic flight, which provides alternating levels of gravitoinertial force (0 g and 1.8 g). Results were less robust than those from ground experiments, but established that different saccade magnitudes could be associated with different gravity levels. Show more

Keywords: saccades, physiological adaptation, context, learning, gravity, human

DOI: 10.3233/VES-2003-125-603

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 211-221, 2003

Authors: Richards, Jason T. | Oman, Charles M. | Shebilske, Wayne L. | Beall, Andrew C. | Liu, Andrew | Natapoff, Alan

Article Type: Research Article

Abstract: Human orientation requires one to remember and visualize spatial arrangements of landmarks from different perspectives. Astronauts have reported difficulties remembering relationships between environmental landmarks when imagined in arbitrary 3D orientations. The present study investigated the effects of strategy training on humans' 1) ability to infer their orientation from landmarks presented ahead and below, 2) performance when subsequently learning a different array, and 3) retention of configurational knowledge over time. On the first experiment day, 24 subjects were tested in a virtual cubic chamber in which a picture of an animal was drawn on each wall. Through trial-by-trial exposures, they had …to memorize the spatial relationships among the six pictures around them and learn to predict the direction to a specific picture when facing any view direction, and in any roll orientation. Half of the subjects ("strategy group") were taught methods for remembering picture groupings, while the remainder received no such training ("control group"). After learning one picture array, the procedure was repeated in a second. Accuracy (% correct) and response time learning curves were measured. Performance for the second array and configurational memory of both arrays were also retested 1, 7, and 30 days later. Results showed that subjects "learned how to learn" this generic 3D spatial memory task regardless of their relative orientation to the environment, that ability and configurational knowledge was retained for at least a month, that figure rotation ability and field independence correlate with performance, and that teaching subjects specific strategies in advance significantly improves performance. Training astronauts to perform a similar generic 3D spatial memory task, and suggesting strategies in advance, may help them orient in three dimensions. Show more

Keywords: vision, vestibular, spatial orientation, spatial memory, mental imagery, mental rotation, training

DOI: 10.3233/VES-2003-125-604

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 223-238, 2003

Authors: Wall III, C. | Oddsson, L.I. | Patronik, N. | Sienko, K. | Kentala, E.

Article Type: Research Article

Abstract: We compared the mediolateral (M/L) responses to perturbations during locomotion of vestibulopathic (VP) subjects to those of controls. Eight subjects with unilateral vestibular loss (100% Reduced Vestibular Response from the caloric test) resulting from surgery for vestibular schwannoma and 11 controls were selected for this study. Despite their known vestibulopathy, all VP subjects scored within the normal range on computerized dynamic posturography Sensory Organization Tests. During gait, subjects were given surface perturbations of the right support-phase foot in two possible directions (forward-right and backward-left) at two possible magnitudes (5 and 10 cm) that were randomly mixed with trials having no …perturbations. M/L stability was quantified by estimating the length of the M/L moment arm between the support foot and the trunk, and the M/L accelerations of the sternum and the head. The VP group had greater changes (p < 0.05) in their moment arm responses compared to controls. The number of steps that it took for the moment arm oscillations to return to normal and the variability in the moment arms were greater for the VP group. Differences in the sternum and head accelerations between VP and control groups were not as consistent, but there was a trend toward greater response deviations in the VP group for all 4 perturbation types. Increased response magnitude and variability of the VP group is consistent with an increase in their sensory noise of vestibular inputs due to the surgical lesion. Another possibility is a reduced sensitivity to motion inputs. This perturbation approach may prove useful for characterizing subtle vestibulopathies and similar changes in the human orientation mechanism after exposure to microgravity. Show more

Keywords: balance, postural stability, vestibular, microgravity, vestibular testing, locomotor perturbations, impulse response

DOI: 10.3233/VES-2003-125-605

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 239-253, 2003

Authors: Mulavara, Ajitkumar P. | Bloomberg, Jacob J.

Article Type: Research Article

Abstract: The goal of the present study was to determine how the multiple, interdependent full-body sensorimotor subsystems respond to a change in gaze stabilization task constraints during locomotion. Nine subjects performed two gaze stabilization tasks while walking at 6.4 km/hr on a motorized treadmill: 1) focusing on a central point target; 2) reading numeral characters; both presented at 2 m in front at the level of their eyes. While subjects performed the tasks we measured: temporal parameters of gait, full body sagittal plane segmental kinematics of the head, trunk, thigh, tibia and foot, accelerations along the vertical axis at the head …and the tibia, and the vertical forces acting on the support surface. We tested the hypothesis that with the increased demands placed on visual acuity during the number recognition task, subjects would modify full-body segmental kinematics in order to reduce perturbations to the head in order to successfully perform the task. We found that while reading numeral characters as compared to the central point target: 1) compensatory head pitch movement was on average 22% greater despite the fact that the trunk pitch and trunk vertical translation movement control were not significantly changed; 2) coordination patterns between head and trunk as reflected by the peak cross correlation between the head pitch and trunk pitch motion as well as the peak cross correlation between the head pitch and vertical trunk translation motion were not significantly changed; 3) knee joint total movement was on average 11% greater during the period from the heel strike event to the peak knee flexion event in stance phase of the gait cycle; 4) peak acceleration measured at the head was significantly reduced by an average of 13% in four of the six subjects. This was so even when the peak acceleration at the tibia and the transmission of the shock wave at heel strike (measured by the peak acceleration ratio of the head/tibia and the time lag between the tibial and head peak accelerations) remained unchanged. Taken together these results provide further evidence that the full body contributes to gaze stabilization during locomotion, and that its different functional elements can be modified online to contribute to gaze stabilization for different visual task constraints. Show more

DOI: 10.3233/VES-2003-125-606

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 255-269, 2003

Authors: Brown, Erika L. | Hecht, Heiko | Young, Laurence R.

Article Type: Research Article

Abstract: Short-radius centrifugation offers a promising and affordable countermeasure to the adverse effects of prolonged weightlessness. However, head movements made in a fast rotating environment elicit Coriolis effects, which seriously compromise sensory and motor processes. We found that participants can adapt to these Coriolis effects when exposed intermittently to high rotation rates and, at the same time, can maintain their perceptual-motor coordination in stationary environments. In this paper, we explore the role of inter-sensory conflict in this adaptation process. Different measures (vertical nystagmus, illusory body tilt, motion sickness) react differently to visual-vestibular conflict and adapt differently. In particular, proprioceptive-vestibular conflict sufficed …to adapt subjective parameters and the time constant of nystagmus decay, while retinal slip was required for VOR gain adaptation. A simple correlation between the strength of intersensory conflict and the efficacy of adaptation fails to explain the data. Implications of these findings, which differ from existing data for low rotation rates, are discussed. Show more

Keywords: coriolis effects, artificial gravity, orientation illusions, motion sickness, classical conditioning, control theory, sensory conflict, space sickness, vestibulo-ocular reflex

DOI: 10.3233/VES-2003-125-607

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 271-282, 2003

Authors: Mast, Fred W. | Newby, Nathaniel J. | Young, Laurence R.

Article Type: Research Article

Abstract: The effects of cross-coupled stimuli on the semicircular canals are shown to be influenced by the position of the subject's head with respect to gravity and the axis of rotation, but not by the subject's head position relative to the trunk. Seventeen healthy subjects made head yaw movements out of the horizontal plane while lying on a horizontal platform (MIT short radius centrifuge) rotating at 23 rpm about an earth-vertical axis. The subjects reported the magnitude and duration of the illusory pitch or roll sensations elicited by the cross-coupled rotational stimuli acting on the semicircular canals. The results suggest an …influence of head position relative to gravity. The magnitude estimation is higher and the sensation decays more slowly when the head's final position is toward nose-up (gravity in the subject's head x-z-plane) compared to when the head is turned toward the side (gravity in the subject's head y-z-plane). The results are discussed with respect to artificial gravity in space and the possible role of pre-adaptation to cross-coupled angular accelerations on earth. Show more

Keywords: coriolis effects, otoliths, nystagmus, velocity storage, sensory conflict, semicircular canals, vestibular illusions

DOI: 10.3233/VES-2003-125-608

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 283-289, 2003

Authors: DiZio, Paul | Lackner, James R.

Article Type: Research Article

Abstract: As a countermeasure to the debilitating physiological effects of weightlessness, astronauts could live continuously in an artificial gravity environment created by slow rotation of an entire spacecraft or be exposed to brief daily "doses" in a short radius centrifuge housed within a non-rotating spacecraft. A potential drawback to both approaches is that head movements made during rotation may be disorienting and nauseogenic. These side effects are more severe at higher rotation rates, especially upon first exposure. Head movements during rotation generate aberrant vestibular stimulation and Coriolis force perturbations of the head-neck motor system. This article reviews our progress toward distinguishing …vestibular and motor factors in side effects of rotation, and presents new data concerning the rates of rotation up to which adaptation is possible. We have studied subjects pointing to targets during constant velocity rotation, because these movements generate Coriolis motor perturbations of the arm but do not involve unusual vestibular stimulation. Initially, reaching paths and endpoints are deviated in the direction of the transient lateral Coriolis forces generated. With practice, subjects soon move in straighter paths and land on target once more. If sight of the arm is permitted, adaptation is more rapid than in darkness. Initial arm movement trajectory and endpoint deviations are proportional to Coriolis force magnitude over a range of rotation speeds from 5 to 20 rpm, and there is rapid, complete motor adaptation at all speeds. These new results indicate that motor adaptation to high rotation rates is possible. Coriolis force perturbations of head movements also occur in a rotating environment but adaptation gradually develops over the course of many head movements. Show more

Keywords: coriolis force, artificial gravity, disorientation, motion sickness, sensorimotor, vestibular, head, arm

DOI: 10.3233/VES-2003-125-609

Citation: Journal of Vestibular Research, vol. 12, no. 5-6, pp. 291-299, 2003