Optic Flow Dominates Visual Scene Polarity in Causing Adaptive Modification of Locomotor Trajectory

Locomotion and posture are influenced and controlled by vestibular, visual and somatosensory information. Optic flow and scene polarity are two characteristics of a visual scene that have been identified as being critical in how they affect perceived body orientation and self-motion. The goal of this study was to determine the role of optic flow and visual scene polarity on adaptive modification in locomotor trajectory. Two computer-generated virtual reality scenes were shown to subjects during 20 minutes of treadmill walking. One scene was a highly polarized scene while the other was composed of objects displayed in a non-polarized fashion. Both virtual scenes depicted constant rate self-motion equivalent to walking counterclockwise around the perimeter of a room. Subjects performed Stepping Tests blindfolded before and after scene exposure to assess adaptive changes in locomotor trajectory. Subjects showed a significant difference in heading direction, between pre and post adaptation stepping tests, when exposed to either scene during treadmill walking. However, there was no significant difference in the subjects heading direction between the two visual scene polarity conditions. Therefore, it was inferred from these data that optic flow has a greater role than visual polarity in influencing adaptive locomotor function

Exposure to a Rotating Virtual Environment During Treadmill Locomotion Causes Adaptation in Heading Direction

The goal of the present study was to investigate the adaptive effects of variation in the direction of optic flow, experienced during linear treadmill walking, on modifying locomotor trajectory. Subjects (n = 30) walked on a motorized linear treadmill at 4.0 kilometers per hour for 24 minutes while viewing the interior of a 3D virtual scene projected onto a screen 1.5 in in front of them. The virtual scene depicted constant self-motion equivalent to either 1) walking around the perimeter of a room to one s left (Rotating Room group) 2) walking down the center of a hallway (Infinite Hallway group). The scene was static for the first 4 minutes, and then constant rate self-motion was simulated for the remaining 20 minutes. Before and after the treadmill locomotion adaptation period, subjects performed five stepping trials where in each trial they marched in place to the beat of a metronome at 90 steps/min while blindfolded in a quiet room. The subject's final heading direction (deg), final X (for-aft, cm) and final Y (medio-lateral, cm) positions were measured for each trial. During the treadmill locomotion adaptation period subject's 3D torso position was measured. We found that subjects in the Rotating Room group as compared to the Infinite Hallway group: 1) showed significantly greater deviation during post exposure testing in the heading direction and Y position opposite to the direction of optic flow experienced during treadmill walking 2) showed a significant monotonically increasing torso yaw angular rotation bias in the direction of optic flow during the treadmill adaptation exposure period. Subjects in both groups showed greater forward translation (in the +X direction) during the post treadmill stepping task that differed significantly from their pre exposure performance. Subjects in both groups reported no perceptual deviation in position during the stepping tasks. We infer that viewing simulated rotary self-motion during treadmill locomotion causes adaptive modification of sensory-motor integration in the control of position and trajectory during locomotion which functionally reflects adaptive changes in the integration of visual, vestibular, and proprioceptive cues. Such an adaptation in the control of position and heading direction during locomotion due to the congruence of sensory information demonstrates the potential for adaptive transfer between sensorimotor systems and suggests a common neural site for the processing and self-motion perception and concurrent adaptation in motor output. This will result in lack of subjects perception of deviation of position and trajectory during the post treadmill step test while blind folded

MECHANISMS OF GAZE STABILITY DURING WALKING: BEHAVIORAL AND PHYSIOLOGICAL MEASURES RELATING GAZE STABILITY TO OSCILLOPSIA

Visual sensory input plays a significant role in maintaining upright posture during walking. Visual input contributes to control of head, trunk, and leg motion during walking to facilitate interaction with and avoidance of objects and individuals in the environment. The vestibular system contributes to postural control during walking and also to stabilization of the eyes during head motion which may allow for more accurate use of visual information. This dissertation reports the findings of five experiments which explore how the nervous system uses vision to control upright posture during walking and also whether the act of walking contributes to gaze stability for individuals with severe vestibular loss. In the first experiment, continuous oscillatory visual scene motion was used to probe how the use of visual input changes from standing to walking and also to determine whether the trunk motion response to visual motion was the same in the medio-lateral (ML) and anterior-posterior (AP) directions. In the second experiment, visual feedback (VFB) regarding the approximate center of mass position in the ML and AP directions was used to demonstrate that ML path stability was enhanced by concurrent visual feedback for young and older adults. In the third experiment, adults with vestibular loss and healthy adults were both able to use VFB during treadmill walking to enhance ML path stability and also to separately modify their trunk orientation to vertical. The final two experiments investigated whether gaze stability was enhanced during treadmill walking compared to passive replication of sagittal plane walking head motion (seated walking) for individuals with severe vestibular loss. Individuals with severe bilateral vestibular hypofunction displayed appropriately timed eye movements which compensated for head motion during active walking compared to seated walking. Timing information from the task of active walking may have contributed to enhancement of gaze stability that was better than predictions from passive head motion. This dissertation demonstrates: 1) the importance of visual sensory input for postural control during walking; 2) that visual information can be leveraged to modify trunk and whole body walking behavior; and 3) that the nervous system may leverage intrinsic timing information during active walking to enhance gaze stability in the presence of severe vestibular disease

Effects of fear and attention on human balance control

A fall is one of the main causes of injury-related hospitalisation and injury-related deaths. Besides physical degeneration, fear of falling and attentional focus strategies are related to fall risk and decline of balance performance. The aim of this research was to expose the mechanisms by which fear of falling and attentional focus affect human balance control. We used galvanic vestibular stimulation (GVS) to induce vestibular balance reflexes while participants stood at ground level and on a narrow walkway at 3.85 m height to induce fear of falling. Using questionnaires and skin conductance measurements, a fear of falling at height was confirmed. Full-body kinematics was collected to measure the vestibular balance response. We concluded that fear modifies vestibular balance control and proposed a mechanism in which both the short- and medium-latency reflexes functionally contribute to whole body balance. Furthermore, the literature suggests that fear of falling could impair balance mechanisms in elderly through changes in attentional focus. Therefore, we also investigated the effect of attentional focus (internal vs. external focus and reinvestment) and fall history on walking stability in healthy older adults. Participants’ gait was perturbed through randomly occurring unilateral treadmill decelerations to evoke balance recovery movements. Using full body kinematics, coefficients of variation of spatiotemporal gait parameters and local divergence exponents were calculated to assess gait performance of balance recovery responses and unperturbed gait. Fallers showed increased gait variability and decreased gait stability, however no effects of attentional focus were found. The benefits of an external focus of attention on motor performance do not seem to apply to gait in elderly. Continued investigation into attentional focus effects and fear of falling on gait including holistic and partial internal focus and continuous gait perturbations, might further clarify the relations between fear of falling and attentional focus and how they could affect fall risk. Follow-up studies with clinical subgroups could further clarify the relation between fear of falling, attentional focus and balance performance

Multimodal Perception and Multicriterion Control of Nested Systems

This report reviews the operational demands made of a Shuttle pilot or commander within the context of a proven empirical methodology for describing human sensorimotor performance and whole-body coordination in mechanically and perceptually complex environments. The conclusions of this review pertain to a) methods for improving our understanding of the psychophysics and biomechanics of visual/manual control and whole-body coordination in space vehicle cockpits; b) the application of scientific knowledge about human perception and performance in dynamic inertial conditions to the development of technology, procedures, and training for personnel in space vehicle cockpits; c) recommendations for mitigation of safety and reliability concerns about human performance in space vehicle cockpits; and d) in-flight evaluation of flight crew performance during nominal and off-nominal launch and reentry scenarios

Life Sciences Program Tasks and Bibliography

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1995. Additionally, this inaugural edition of the Task Book includes information for FY 1994 programs. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web pag

Life Sciences Program Tasks and Bibliography for FY 1996

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1996. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web page