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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Visual-Accommodation Trainer/Tester

Ophthalmic instrument tests and helps develop focusing ability. Movable stage on a fixed base permits adjustment of effective target position as perceived by subject. Various apertures used to perform tests and training procedures. Ophthalmic instrument provides four functions: it measures visual near and far points; provides focus stimulus in vision research; measures visual-accommodation resting position; can be used to train for volitional control of person's focus response.

Randle, Robert J., Jr.↗
NASA NTRS1990

Investigating motion sickness using the conditioned taste aversion paradigm

The avoidance of foods which are associated with uncomfortable or aversive internal states has long been recognized. Many people are aware, either directly or via anecdotal reports, of individuals who avoid foods which were eaten just before the onset of sickness. Awareness of this phenomenon can be traced to the writings of John Locke. The disruption of diet during cancer therapy is sometimes ascribed to the attribution of an unpleasant quality to foods eaten preceding the sickness induced by therapy itself. In addition, it has long been recognized by the manufacturers of rodent poisons that animals avoid the injection of food treated with nonlethal doses of poison. An important part of the laboratory study of this phenomenon was directed toward studying the role learning plays in this type of avoidance behavior. Following the lead of Garcia and his associates, this avoidance has come to be interpreted as arising from a form of classical conditioning. In typical laboratory studies of this behavior, a novel food is ingested just prior to exposure to some stimulus, commonly poisoning or irradiation, which produces illness. Following the terminology of classical conditioning, it is common to describe this procedure as one of 'pairing' a conditioned stimulus (CS), the novel food, with an unconditioned stimulus (US), the illness induced by toxicosis or irradiation. Avoidance of the food in succeeding feeding opportunities is viewed as a learned response or a conditioned taste aversion (CTA). Garcia et al. asserted that motion sickness could produce 'gustatory' aversions, but passive motion was first reported as an US to establish CTA by Green and Rachlin. The purpose is to review the manner in which CTA has been used to study motion sickness. Numerous reviews concentrating on other aspects of CTA are available in the existing literature. Readers are encouraged to consult the various papers and edited books for extensive information on other aspects of this literature.

Robert A Fox↗
NASA NTRS1992

The effect of space flight on spatial orientation

Both during and following early space missions, little neurosensory change in the astronauts was noted as a result of their exposure to microgravity. It is believed that this lack of in-flight adaptation in the spatial orientation and perceptual-motor system resulted from short exposure times and limited interaction with the new environment. Parker and Parker (1990) have suggested that while spatial orientation and motion information can be detected by a passive observer, adaptation to stimulus rearrangement is greatly enhanced when the observer moves through or acts on the environment. Experience with the actual consequences of action can be compared with those consequences expected on the basis of prior experience. Space flight today is of longer duration, and space craft volume has increased. These changes have forced the astronauts to interact with the new environment of microgravity, and as a result substantial changes occur in the perceptual and sensory-motor repsonses reflecting adaptation to the stimulus rearrangement of space flight. We are currently evaluating spatial orientation and the perceptual-motor systems' adaptation to microgravity by examining responses of postural control, head and gaze stability during locomotion, goal oriented vestibulo-ocular reflex (VOR), and structured quantitative perceptual reports. Evidence suggests that humans can successfully replace the gravitational reference available on Earth with cues available within the spacecraft or within themselves, but that adaptation to microgravity is not appropriate for a return to Earth. Countermeasures for optimal performance on-orbit and a successful return to earth will require development of preflight and in-flight training to help the astronauts acquire and maintain a dual adaptive state. An understanding of spatial orientation and motion perception, postural control, locomotion, and the VOR will aid in this process.

Reschke, Millard F.↗
NASA NTRS1999

Exercise Training During +Gz Acceleration

The overall purpose is to study the effect of passive (without exercise) and active (with exercise) +Gz (head-to-foot) acceleration training, using a short-arm (1.9m radius) centrifuge, on post- training maximal oxygen uptake (VO2 max, work capacity) and 70 deg head-up tilt (orthostatic) tolerance in ambulatory subjects to test the hypothesis that (a) both passive and active acceleration training will improve post-training tilt-tolerance, and (b) there will be no difference in tilt-tolerance between passive and active exercise acceleration training because increased hydrostatic and blood pressures, rather than increased muscular metabolism, will provide the major adaptive stimulus. The purpose of the pilot study was to test the hypothesis that there would be no significant difference in the metabolic responses (oxygen uptake, heart rate, pulmonary ventilation, or respiratory exchange ratio) during supine exercise with moderate +Gz acceleration.

Greenleaf, J. E.↗
NASA NTRS1975

Head-eye tracking in two-dimensional pursuit tasks

The neurological control systems for the eye and head are studied by investigating dynamic eye and head rotations in two degrees of freedom using bandlimited, white noise stimuli, nominally wide field of view stimulus presentations of + or - 10 deg and power spectral analysis of the data to produce input/output transfer and coherence functions. Determined were frequency response characteristics of these systems, the linearity of the transfer functions in both coupled and decoupled vertical and horizontal stimulus/response reference axes and the amount of cross axis coupling present in system responses. A comparative study was also conducted to assess the differences in response characteristics between single axis and dual axis visual stimulation for the same subject.

Shirachi, D. K.↗
NASA NTRS1995

Temporal MTF of Motion Perception

Although human motion sensing mechanisms can be stimulated by rapid changes in the visual input the response of the motion mechanisms themselves is rather sluggish, i.e. they cannot track rapid changes in the speed or direction of a moving stimulus when there are no positional cues to the variation. We tested the ability of human observers to detect sinusoidal perturbations in the velocity of a moving stimulus at a variety of temporal frequencies and drift velocities; the results show a low-pass temporal characteristic, and performance is degraded at high velocities.

Mulligan, Jeffrey B.↗
NASA NTRS1995

Inertial acceleration as a measure of linear vection: An alternative to magnitude estimation

The present study focused on the development of a procedure to assess perceived self-motion induced by visual surround motion - vection. Using an apparatus that permitted independent control of visual and inertial stimuli, prone observers were translated along their head x-axis (fore/aft). The observers' task was to report the direction of self-motion during passive forward and backward translations of their bodies coupled with exposure to various visual surround conditions. The proportion of 'forward' responses was used to calculate each observer's point of subjective equality (PSE) for each surround condition. The results showed that the moving visual stimulus produced a significant shift in the PSE when data from the moving surround condition were compared with the stationary surround and no-vision condition. Further, the results indicated that vection increased monotonically with surround velocities between 4 and 40/s. It was concluded that linear vection can be measured in terms of changes in the amplitude of whole-body inertial acceleration required to elicit equivalent numbers of 'forward' and 'backward' self-motion reports.

Carpenter-Smith, Theodore R.↗
NASA NTRS1996

Perceptual Classification Images from Vernier Acuity Masked by Noise

Letting external noise rather than internal noise limit discrimination performance allows information to be extracted about the observer's stimulus classification rule. A perceptual classification image is the correlation over trials between the noise amplitude at a spatial location and the observer's responses. If, for example, the observer followed the rule of the ideal observer, the perceptual classification image would be an estimate of the ideal observer filter, the difference between the two unmasked images being discriminated. Perceptual classification images were estimated for a vernier discrimination task. The display screen had 48 pixels per degree horizontally and vertically. The no-offset image had a dark horizontal line of 4 pixels, a 1 pixel space, and 4 more dark pixels. Classification images were based on 1600 discrimination trials with the line contrast adjusted to keep the error rate near 25 percent. In the offset image, the second line was one pixel higher. Unlike the ideal observer filter (a horizontal dipole), the observer perceptual classification images are strongly oriented. Fourier transforms of the classification images had a peak amplitude near one cycle per degree and an orientation near 25 degrees. The spatial spread is much more than image blur predicts, and probably indicates the spatial position uncertainty in the task.

Ahumada, A. J.↗
NASA NTRS2002

Skeletal Adaptation to Daily Activity: A Biochemical Perspective

Musculoskeletal forces generated by normal daily activity on Earth maintain the functional and structural properties of muscle and bone throughout most of one's adult life. A reduction in the level of cumulative daily loading caused by space flight, bed rest or spinal cord injury induces rapid muscle atrophy, functional changes in muscle, and bone resorption in regions subjected to the reduced loading. Bone cells in culture and bone tissue reportedly respond to a wide variety of non-mechanical and mechanical stimuli ranging, from electromagnetic fields, and hormones to small amplitude, high frequency vibrations, fluid flow, strain rate, and stress/strain magnitude. However, neither the transduction mechanism that transforms the mechanical input into a muscle or bone metabolic response nor the characteristics, of the loading history that directly or indirectly stimulates the cell is known. Identifying the factors contributing to the input stimulus will have a major impact on the design of effective countermeasures for long duration space flight. This talk will present a brief overview of current theories of bone remodeling and functional adaptation to mechanical loading. Work from our lab will be presented from the perspective of daily cumulative loading on Earth and its relationship to bone density and structure. Our objective is to use the tibia and calcaneus as model bone sites of cortical and cancellous bone adaptation, loaded daily by musculoskeletal forces in equilibrium with the ground reaction force. All materials that will be discussed are in the open scientific literature.

Whalen, Robert T.↗
NASA NTRS1992

Springback and diagravitropism in Merit corn roots

Dark-treated Merit corn (Zea mays L.) roots are diagravitropic and lose curvature upon withdrawal of the gravity stimulus (springback). Springback was not detected in a variety of corn that is orthogravitropic in the dark, nor in Merit roots in which tropistic response was enhanced either with red light or with abscisic acid. A possible interpretation is that springback may be associated with a weak growth response of diagravitropic roots.

Non-NASA Center↗
NASA NTRS2014

Improving Sensorimotor Adaptation Following Long Duration Space Flight by Enhancing Vestibular Information Transfer

Crewmember adapted to the microgravity state may need to egress the vehicle within a few minutes for safety and operational reasons after gravitational transitions. The transition from one sensorimotor state to another consists of two main mechanisms: strategic and plastic-adaptive and have been demonstrated in astronauts returning after long duration space flight. Strategic modifications represent "early adaptation" - immediate and transitory changes in control that are employed to deal with short-term changes in the environment. If these modifications are prolonged then plastic-adaptive changes are evoked that modify central nervous system function, automating new behavioral responses. More importantly, this longer term adaptive recovery mechanism was significantly associated with their strategic ability to recover on the first day after return to Earth G. We are developing a method based on stochastic resonance to enhance information transfer by improving the brain's ability to detect vestibular signals (Vestibular Stochastic Resonance, VSR) especially when combined with balance training exercises such as sensorimotor adaptability (SA) training for rapid improvement in functional skill, for standing and mobility. This countermeasure to improve detection of vestibular signals is a stimulus delivery system that is wearable/portable providing low imperceptible levels of white noise based binaural bipolar electrical stimulation of the vestibular system (stochastic vestibular stimulation). To determine efficacy of vestibular stimulation on physiological and perceptual responses during otolith-canal conflicts and dynamic perturbations we have conducted a series of studies: We have shown that imperceptible binaural bipolar electrical stimulation of the vestibular system across the mastoids enhances balance performance in the mediolateral (ML) plane while standing on an unstable surface. We have followed up on the previous study showing VSR stimulation improved balance performance in both ML and anteroposterior planes while stimulating in the ML axis only. We have shown the efficacy of VSR stimulations on enhancing physiological and perceptual responses of whole-body orientation during low frequency perturbations (0.1 Hz) on the ocular motor system using a variable radius centrifuge on both physiological (using eye movements) and perceptual responses (using a joystick) to track imposed oscillations. The variable radius centrifuge provides a selective tilting sensation that is detectable only by the otolith organs providing conflicting information from the canal organs of the vestibular system (intra-vestibular conflict). These results indicate that VSR can improve performance in sensory conflict scenarios like that experienced during space flight. We have showed the efficacy of VSR stimulation to improve balance and locomotor control on subjects exposed to continuous, sinusoidal lateral motion of the support surface while walking on a treadmill while viewing perceptually matched linear optic flow. We have shown the safety of short term continuous use of up to 4 hours of VSR stimulation and its efficacy in improving balance and locomotor function in Parkinson's Disease patients. This technique for improving vestibular signal detection may thus provide additional information to improve strategic abilities. We hypothesize that VSR stimulation will act synergistically with SA training to improve adaptability by increased utilization of vestibular information and therefore serve to optimize and personalize the SA countermeasure prescription. This forms the basis of its usefulness both as a training modality and further help in significantly reducing the number of days required to recover functional performance to preflight levels after long duration space flight.

Mulavara, A. P.↗
NASA NTRS1985

Color measurement and discrimination

The present investigation is concerned with new results which show that for test lights with slow temporal modulations, and thus little effect on the luminance system, the vector-difference hypothesis represents an adequate characterization of discrimination data. It is pointed out that for certain experimental conditions color measurements can be successfully extended to include a difference measure which predicts the discriminability of pairs of lights. When discrimination depends principally on opponent-channel responses, discrimination thresholds can be predicted from the detection contour alone. Attention is given to discriminations with a 6-Hz Gabor function, the categorization of stimulus regions, and the nature of the visual mechanisms.

Wandell, B. A.↗
NASA NTRS2001

State-space receptive fields of semicircular canal afferent neurons in the bullfrog

Receptive fields are commonly used to describe spatial characteristics of sensory neuron responses. They can be extended to characterize temporal or dynamical aspects by mapping neural responses in dynamical state spaces. The state-space receptive field of a neuron is the probability distribution of the dynamical state of the stimulus-generating system conditioned upon the occurrence of a spike. We have computed state-space receptive fields for semicircular canal afferent neurons in the bullfrog (Rana catesbeiana). We recorded spike times during broad-band Gaussian noise rotational velocity stimuli, computed the frequency distribution of head states at spike times, and normalized these to obtain conditional pdfs for the state. These state-space receptive fields quantify what the brain can deduce about the dynamical state of the head when a single spike arrives from the periphery. c2001 Elsevier Science B.V. All rights reserved.

Non-NASA Center↗
NASA NTRS2004

Stereomotion speed perception: contributions from both changing disparity and interocular velocity difference over a range of relative disparities

The role of two binocular cues to motion in depth-changing disparity (CD) and interocular velocity difference (IOVD)- was investigated by measuring stereomotion speed discrimination and static disparity discrimination performance (stereoacuity). Speed discrimination thresholds were assessed both for random dot stereograms (RDS), and for their temporally uncorrelated equivalents, dynamic random dot stereograms (DRDS), at relative disparity pedestals of -19, 0, and +19 arcmin. While RDS stimuli contain both CD and IOVD cues, DRDS stimuli carry only CD information. On average, thresholds were a factor of 1.7 higher for DRDS than for RDS stimuli with no clear effect of relative disparity pedestal. Results were similar for approaching and receding targets. Variations in stimulus duration had no significant effect on thresholds, and there was no observed correlation between stimulus displacement and perceived speed, confirming that subjects responded to stimulus speed in each condition. Stereoacuity was equally good for our RDS and DRDS stimuli, showing that the difference in stereomotion speed discrimination performance for these stimuli was not due to any difference in the precision of the disparity cue. In addition, when we altered stereomotion stimulus trajectory by independently manipulating the speeds and directions of its monocular half-images, perceived stereomotion speed remained accurate. This finding is inconsistent with response strategies based on properties of either monocular half-image motion, or any ad hoc combination of the monocular speeds. We conclude that although subjects are able to discriminate stereomotion speed reliably on the basis of CD information alone, IOVD provides a precise additional cue to stereomotion speed perception.

Depth Perception/physiology↗
NASA NTRS1996

Can Monkeys (Macaca mulatta) Represent Invisible Displacement?

Four experiments were conducted to assess whether or not rhesus macaques (Macaca mulatta) could represent the unperceived movements of a stimulus. Subjects were tested on 2 computerized tasks, HOLE (monkeys) and LASER (humans and monkeys), in which subjects needed to chase or shoot at, respectively, a moving target that either remained visible or became invisible for a portion of its path of movement. Response patterns were analyzed and compared between target-visible and target-invisible conditions. Results of Experiments 1, 2, and 3 demonstrated that the monkeys are capable of extrapolating movement. That this extrapolation involved internal representation of the target's invisible movement was suggested but not confirmed. Experiment 4, however, demonstrated that the monkeys are capable of representing the invisible displacements of a stimulus.

Filion, Christine M.↗