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Visual Performance Challenges To Low-Frequency Perturbations After Long-Duration Space Flight and Countermeasure Development A.P. Mulavara, 1 S. J. Wood,

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Presentation on theme: "Visual Performance Challenges To Low-Frequency Perturbations After Long-Duration Space Flight and Countermeasure Development A.P. Mulavara, 1 S. J. Wood,"— Presentation transcript:

1 Visual Performance Challenges To Low-Frequency Perturbations After Long-Duration Space Flight and Countermeasure Development A.P. Mulavara, 1 S. J. Wood, 1 M. J. Fiedler, 2 I. Kofman, 2 W. B. Kulecz, 2 C. Miller, 2 B. Peters, 2 J. M. Serrador, 3 H. Cohen, 4 M. F. Reschke, 5 and J. J. Bloomberg 5 1 Universities Space Research Association, Houston, TX, USA, 2 Wyle Integrated Science and Engineering Group, Houston, TX, USA, 3 Dept of Veterans Affairs NJ Healthcare System, East Orange, NJ, USA, 4 Baylor College of Medicine, Houston, TX, USA, and 5 NASA Johnson Space Center, Houston, TX, USA. Typical curve of output performance (e.g. discrimination index) vs noise magnitude - McDonnell MD and Abbott D., PLOS Computational Biology, May 2009, Vol 5 (5) and Harry J, Niemi JB, Priplata AA, Collins JJ, IEEE Spectrum, April Discrimination Index 4. Decreased Sensation 3. Peak Sensation 2. Some Sensation 1. No Sensation 1.Dynamic visual acuity (DVA) is reduced in the vertical plane at frequencies of 2 Hz and in the horizontal plane at frequencies of 0.8 Hz. DVA varies with target location, with acuity optimized for targets in the plane of motion. Perturbations at low frequency motions (0.1-2 Hz) may exacerbate sensorimotor deficits after space flight. 2.Low imperceptible levels of white noise based electrical stimulation of the vestibular system improves balance performance consistent with the stochastic resonance phenomenon in normal healthy control subjects. The amplitude of optimal stimulus for improving balance performance was predominantly in the range of μA. 3.An SRVS based device may be fielded, either as a training modality to enhance adaptability or skill acquisition, or as a miniature patch type stimulator that may be worn by astronauts to enhance adaptation following gravitational transitions including people with disabilities due to aging or disease, improving posture and locomotion function. This study was supported in part by a grant from the National Space Biomedical Research Institute through NASA NCC 9-58 and National Institutes of Health grant RO1-DC Conclusions Acknowledgements Trial Epochs Control TrialOptimal TrialControl TrialOptimal Trial Trial Epochs Optimal Stimulus level Optimal Stimulus level Astronauts experience disturbances in sensorimotor function following their return to Earth due to adaptive responses that occur during exposure to the microgravity conditions of space flight. Crewmembers adapted to the microgravity state may need to egress the vehicle within a few minutes after landing for safety and operational reasons. Exposure to even low frequency motions coupled with the varying environmental conditions can cause performance deficits by affecting the efficacy of motor and visual acuity dependent skills in tasks critical to emergency egress activities such as visual monitoring of displays, actuating discrete controls, operating auxiliary equipment and communicating with Mission Control and recovery teams. Thus, during exploration class missions the sensorimotor disturbances due to the crewmember's adaptation to microgravity may lead to disruption in the ability to maintain postural stability and perform functional egress tasks during the initial introduction to the Earth's gravitational environment. The first objective of this study was to document human motor and visual performance during simulated motion below 2.0 Hz. The second objective was to develop a countermeasure to mitigate sensorimotor disturbances after space flight. Central reinterpretation vestibular information Alteration in sensorimotor responses Exposure to space flight Reduction in performance of visual /motor tasks Sensorimotor Performance Profile During Inter-Planetary Missions Inter planetary transit Lunar/Mars surface opsEarth PostflightEarth Preflight g-transitions X4 Earth transit  Inter planetary missions have 4 periods requiring sensorimotor adaptation  Each transition requires adaptation to altered gravity environment  Performance decrements occur during and after g-transitions Stochastic resonance (SR) is a phenomenon whereby the response of a nonlinear system to a weak input signal is optimized by the presence of a particular non-zero level of noise (Collins et al. 1995, for reviews see Collins et al. 2003, Moss et al. 2004, McDonnell and Abott 2009 and Aihara et al. 2010). This phenomenon of SR is based on the concept of maximizing the flow of information through a system by a nonzero level of noise (Collins et al. 2003). Application of imperceptible SR noise coupled with sensory input through the proprioceptive, visual, or vestibular sensory system has been shown to improve motor function as well as cardiovascular responses (Soma et al. 2003; Yamamoto et al 2005, Priplata et al. 2006). SR phenomenon using vestibular electrical stimulation by imperceptible stochastic noise (SRVS), when applied to normal young and elderly subjects, showed significantly improved ocular stabilization reflexes in response to whole-body tilt as well as improved balance performance during postural disturbances (Geraghty et al. 2008; Mulavara et al. 2011). Visual Acuity  Visual acuity was measured in 12 healthy subjects as they moved a hand held joystick to indicate the orientation of a computer generated landholt C as quickly and as accurately as possible.  Acuity thresholds were established with optotypes presented centrally on a wall-mounted LCD screen at 1.3 m distance, first without motion (static condition) and then while oscillating at 0.8 Hz (DVA, peak velocity 60 de/sec). Acuity was also measured using a standard wall chart 10’ distance. All acuity measures were made using a forced- choice strategy and determined by the smallest size in which the subjects answered correctly in 3 of 5 responses. Target Location  The effect of target location was then measured during horizontal rotation with the optotypes randomly presented in one of nine different locations on the screen (offset upto 10 degrees).  The optotype size was logMar 0, 0.2 or 0.4 corresponding to Snellen ratios of 20/20, 20/30 or 20/50.  Presentation duration was 150, 300 and 450 ms. All these conditions were counterbalanced across 5 trials each utilizing horizontal rotation at 0.8 Hz. Target Location Horizontal Plane Vertical Plane Dynamic visual acuity threshold was reduced relative to static acuity in 7 of 12 subjects by one step size. Both accuracy and reaction time varied as a function of target location, with greater performance decrements when acquiring vertical targets. These data show that this subject had an optimal response at an amplitude of 200 μA (0-30 Hz ) and 100 μA (1-2 Hz). A multivariate repeated measures ANOVA was used for analysis, using all six variables with two within subject factors: Period (2 levels – Baseline, Stimulation), Trials (2 levels – No stimulation and Optimal amplitude) and one between subject factor: Frequency (2 levels – 1-2 Hz and 0-30 Hz). The within subject factor Period was significant (Wilk’s Lambda = 0.694, p<0.0001) and the interaction Trial * Period was also significant (Wilk’s Lambda = 0.277; p<0.012). The RMS values of the parameters for the stimulation period is less than that for the baseline period showing improved balance control with SRVS. 2” x 4” electrodes (Axelgaard manufacturing Co., Fallbrook, CA) used for delivering the electrical stimulation to the vestibular system Figure shows subject performing the standardized balance task standing on an unstable compliant surface. Performance was measured using IMU’s attached to the head and trunk segments and a force plate underneath the foam surface. Portable bipolar constant current stimulator used in the stand alone mode. Baseline Window Stimulus amplitude = 0 μA Stimulus Window Stimulus amplitude = 0-± 700μA Stimulation periods Mediolateral Force (Fy, N) Mediolateral Moments (Mx, N - mm) Mediolateral Acceleration – Head (Hay, m/s 2 ) Roll Angular Velocity– Head (Hrv, deg/sec) Mediolateral Acceleration- Trunk (Tay, m/s 2 ) Roll Angular Velocity – Trunk (Trv, deg/sec) Optimization of stimulus amplitude and frequency characteristics for vestibular stochastic resonance countermeasure Introduction Visual performance during horizontal rotational motion at 0.8 Hz Average Visual AcuitySubject in rotary chair Target Location Target size: 20/30 Presentation time: 300 ms Target Size Presentation time: 300 ms Presentation Time Target size: 20/30 Chair for Dynamic Visual Acuity Test Landolt-C Visual acuity is significantly reduced during 2 Hz vertical translational motion compared to static, across all age ranges within and between control and clinical vestibular subjects.  Subjects sat in a comfortable chair, and were strapped in using a standard seat belt.  A personal computer set upon a tripod was 2 m away from the chair. The center of the computer screen was set at eye level for each subject.  In both the static and dynamic testing phases the Landolt C flashed on the computer screen for 75 ms around peak velocity of motion. The size of optotypes presented ranged from 0.4 to 1.0 logMAR (log of the Minimum Angle Resolvable) or 20/8 to 20/200 Snellen ratios, in one of 8 configurations: up, down, right, left, up-right, up-left, down-right and down-left.  Subjects were instructed to state the orientation of the C.  In the static testing phase, always performed first, the chair was stationary.  In the dynamic testing phase, the chair moved vertically, at 2 Hz,  5 cm to mimic vertical oscillations during walking.  The Best PEST (i.e. parameter estimation by sequential testing) psychophysical threshold detection algorithm was used to determine the visual acuity threshold for each condition. L D U R Visual performance during vertical linear motion at 2 Hz Display Visual Acuity threshold by decade during 2 Hz vertical motion Objective 1: Investigate performance of motor and visual tasks during varying vehicle motion (0.1-2Hz) Objective 2: Develop a countermeasure using stochastic resonance to enhance sensorimotor adaptation. Two bipolar stochastic stimulation signals were generated with frequencies in the bandwidth of 0-30 Hz and 1-2 Hz. Seven stimulation levels of 0 µA, ±100 µA, ±200 µA, ±300 µA, ±400 µA, ±500 µA, and ±700µA were tested. The fully generated signal was checked for zero mean (±1%) and RMS [(30 µA RMS/100µA) ±5%]. Stimulation signals These results show that as a group normal healthy control subjects significantly improved their balance performance at the optimal level of SRVS. Subjects younger than 50 showed no differences between control and patient groups, p=0.33, while, in subjects older than age 50 patients had significantly higher scores than controls, p=0.02 in static and dynamic conditions.


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