Journal of Vestibular Research

Vestibular information is an important factor in maintaining accurate spatial awareness. Yet, each of the cortical areas involved in processing vestibular information has unique functionality. Further, the anatomical pathways that provide vestibular input for cognitive processes are also distinct. This review outlines some of the current understanding of vestibular pathways contributing to the perception of self-motion in the cortex. The vestibulo-thalamic pathway is associated with self-motion cues for updating motor behaviors, spatial representations, and self versus object motion distinctions. The mammillo-tegmental pathway supplies vestibular input to create a cognitive representation of head direction. Self-motion and head direction information then converge to define self-location. By outlining the functional anatomy of the vestibular cortical pathways, a multi-sensory and multi-faceted view of vestibular related spatial awareness emerges.

Chuck Oman has been a guide and mentor for research in human perception and performance during space exploration for over 25 years. His research has provided a solid foundation for our understanding of how humans cope with the challenges and ambiguities of sensation and perception in space. In many of the environments associated with work in space the human visual system must operate with unusual combinations of visual and other perceptual cues. On Earth physical acceleration cues are normally available to assist the visual system in interpreting static and dynamic visual features. Here we consider two cases where the visual system is not assisted by such cues. Our first experiment examines perceptual stability when the normally available physical cues to linear acceleration are absent. Our second experiment examines perceived orientation when there is no assistance from the physically sensed direction of gravity. In both cases the effectiveness of vision is paradoxically reduced in the absence of physical acceleration cues. The reluctance to rely heavily on vision represents an important human factors challenge to efficient performance in the space environment.

Commercial sub-orbital operators will soon offer the excitement of traveling to space to thousands of people. Based on previous experience in space flight and parabolic flight, sensorimotor disruptions in eye movements, postural stability, and motor coordination are likely in these travelers. Here we propose a framework for developing strategies to overcome these sensorimotor disruptions. We delineate how approaches should differ from those applied to orbital flight and between sub-orbital passengers and pilots based on differing frequency of flights and mission objectives. Sensorimotor adaptation is one strategy for overcoming disruptions; an important question is whether it occurs quickly enough to be of use during periods of reduced and enhanced gravity lasting less than five minutes. Data are presented showing that sensorimotor adaptation of the pitch vestibulo-ocular reflex during parabolic flight takes a few consecutive days of flying to overcome an initial disruption. We conclude with recommendations for operators and researchers to improve safety and comfort during sub-orbital o perations. We recommend using parabolic flight as a tool for pre-adapting sub-orbital passengers, along with further research into the required quantity and timing of these pre-adaptation flights and the tasks conducted during these flights. Likewise, for sub-orbital pilots, we recommend emphasizing recency of experience.

Subjective body position, as influenced by 21-day 6Âř-head-down bed rest and intermittent supine centrifugation, was investigated in two experimental groups. Treatment subjects were exposed to a daily dose of 1-hour of horizontal centrifugation, whereas control subjects were also put on the centrifuge, but were not spun. During the centrifuge runs subjects were exposed to a constant gradient with 1-G z at the heart and 2.5-G z at the feet. Subjects reported their subjective postural position (SPP) before, during and after each 1-hour centrifuge exposure.

We find that subjects shift their frame of reference over the first week of bed rest and perceive the 6Âř-head-down position as horizontal. Spinning shifts the SPP by about 30Âř towards an upright position, consistent with the angle of the gravito-inertial vector positioned close to the vestibular system. The SPP estimates for the upper and lower body failed to reflect the massive gravity gradient between head and feet, and subjects generally reported a single tilt for the whole body.

Human cognitive performance is an important factor for the successful and safe outcome of commercial and non-commercial manned space missions. This article aims to provide a systematic review of studies investigating the effects of microgravity on the cognitive abilities of parabolic or space flight participants due to the absence of the gravito-inertial force. We will focus on mental imagery: one of the best studied cognitive functions. Mental imagery is closely connected to perception and motor behavior. It aids important processes such as perceptual anticipation, problem solving and motor simulation, all of which are critical for space travel. Thirteen studies were identified and classified into the following topics: spatial representations, mental image transformations and motor imagery. While research on spatial representation and mental image transformation continues to grow and specific differences in cognitive functioning between 1 g and 0 g have been observed, motor imagery has thus far received little attention.

Vibrotactile tilt feedback was used to help vestibulopathic subjects control their anterioposterior (AP) sway during sensory organization tests 5 and 6 of Equitest computerized dynamic posturography. We used four kinds of signals to activate the feedback. The first signal was proportional (P) to the measured tilt of the subject, while the second used the first derivative (D) of the tilt. The third signal was the sum of the proportional and one half of the first derivative signals (PD). The final signal used a prediction of the subject's sway projected 100 msec in advance. The signals were used to activate vibrators mounted on the front of the torso to signal forward motion, and on the back of the torso for backward motion. Subject responses varied significantly with the kind of feedback signal. Proportional and derivative feedback resulted in similar root mean squared tilt, but the PD signal significantly reduced the tilt compared to either P or D feedback. The predicted motion signal also reduced the response compared to the PD signal. These preliminary results are somewhat consistent with an inverted pendulum model of postural control, but need to be confirmed with a larger study that also considers mediolateral tilt and feedback. The improvement by using a predictor is consistent with compensating for a neural processing delay.

Among other problems, patients with vestibular problems suffer imbalance, spatial disorientation, and blurred vision. These problems lead to varying degrees of disability and can be debilitating. Unfortunately, a large number of patients with vestibular complaints cannot be diagnosed with the clinical tests available today. Nor do we have treatments for all patients that we can diagnose. These clinical problems provide challenges to and opportunities for the field of vestibular research. In this paper, we discuss some new diagnostic and treatment options that could become available for tomorrow's patients. As a new diagnostic, we have begun measuring patient's perceptual direction-detection thresholds. Preliminary results appear encouraging; patients diagnosed with bilateral loss have yaw rotation thresholds almost ten times greater than normals, while patients diagnosed with migraine associated vertigo have roll tilt thresholds well below normal at 0.1 Hz. As a new treatment, we have performed animal studies looking at responses evoked by electrical stimulation provided by a vestibular prosthesis. Results measuring the VOR demonstrate promise and preliminary studies of balance and perception are also encouraging. While electrical stimulation is a standard means of stimulation, optical stimulation is also being investigated as a way to improve prosthetic stimulation specificity.