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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 181 records · Page 10

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NASA NTRS1975

Binocular summation and peripheral visual response time

Six males were administered a peripheral visual response time test to the onset of brief small stimuli imaged in 10-deg arc separation intervals across the dark adapted horizontal retinal meridian under both binocular and monocular viewing conditions. This was done in an attempt to verify the existence of peripheral binocular summation using a response time measure. The results indicated that from 50-deg arc right to 50-deg arc left of the line of sight binocular summation is a reasonable explanation for the significantly faster binocular data. The stimulus position by viewing eye interaction was also significant. A discussion of these and other analyses is presented along with a review of related literature.

Gilliland, K.↗

NASA NTRS1975

Monte Carlo simulation of astronaut light flash observations on Apollo and Skylab missions

Monte Carlo calculations are performed to study the relation between cosmic ray nuclei and visual flashes observed by astronauts, in space. A satisfactory overall fit to all available data excluding the Skylab observations in the South Atlantic Anomaly (SAA) has been achieved by varying three visual system parameters: effective retinal thickness, minimum projected track length inside retina and minimum energy loss rate. All light flash data from space excluding the SAA observations can be understood fully upon the basis of the primary cosmic ray charge and energy spectra together with the fitted values of the three visual system parameters. Monte Carlo simulations of the SAA observations suggest the existence of a previously unobserved multiply-charged component of the inner radiation belt.

Osborne, W. Z.↗

NASA NTRS1976

Eye movements during afterimage tracking under sinusoidal and random vestibular stimulation

The smooth portion of the horizontal vestibulo-ocular reflex was analyzed in terms of the frequency response, relating slow-phase eye velocity to angular velocity of a rotating chair under four different cases: sinusoidal rotation about a vertical axis in total darkness, sinusoidal rotation during afterimage tracking, pseudorandom head rotation in total darkness, and pseudorandom head rotation during afterimage tracking. Eye movements were recorded using a photoelectric limbus tracking method. The observation that the presence of an afterimage during vestibular stimulation increases the velocity of slow-phase eye movements is in support of the theory that such slow-phase movements are generated, at least in part, by the perceived velocity of the target. Since the target is immobilized on the retina, this perceived velocity is clearly not generated by retinal slip, but rather by a mechanism related to the eye movement such as corollary discharge.

Yasui, S.↗

NASA NTRS1977

Light energy transduction by the purple membrane of halophilic bacteria; Proceedings of the Symposium, San Francisco, Calif., June 6, 1976

Several aspects of bacteriorhodopsin, the retinal protein component of the purple membranes of Halobacterium halobium, are discussed. Structural studies are presented. Photochemical properties of the protein complex and of its chromophore are described. Proton translocation of bacteriorhodopsin is compared to that of a protein from a thermophilic bacterium. Ionophore activity of bacteriorhodopsin is considered with attention to conformational changes, light dependency, and electrical potential. Amino acid transport is also examined and the light-energy budget is investigated. Bacteriorhodopsin is of interest because of its similarity to rhodopsin, which plays a major role in mammalian vision, and also because its attainability and distinctive characteristics will facilitate studies of certain bacterial physiological functions, such as ion transport and membrane organization.

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NASA NTRS1978

Illumination-dependent changes in the intrinsic fluorescence of bacteriorhodopsin

The paper describes the intrinsic UV fluorescence of bacteriorhodopsin in some detail and determines the changes during the rapid cyclic reaction following light flashes. The results suggest that several tryptophan residues are affected in the protein, among them one or more exposed to aqueous medium. The kinetics of the fluorescence changes coincide closely with events involving the retinal residue during the deprotonation and reprotonation of the Schiff base group.

Bogomolni, R. A.↗

NASA NTRS1977

Visual response time to colored stimuli in peripheral retina - Evidence for binocular summation

Simple onset response time (RT) experiments, previously shown to exhibit binocular summation effects for white stimuli along the horizontal meridian, were performed for red and green stimuli along 5 oblique meridians. Binocular RT was significantly shorter than monocular RT for a 45-min-diameter spot of red, green, or white light within eccentricities of about 50 deg from the fovea. Relatively large meridian differences were noted that appear to be due to the degree to which the images fall on corresponding retinal areas.

Haines, R. F.↗

NASA NTRS1979

Light-driven solute transport in Halobacterium halobium

The cell membrane of Halobacterium halobium exhibits differential regions which contain crystalline arrays of a single kind of protein, termed bacteriorhodopsin. This bacterial retinal-protein complex resembles the visual pigment and, after the absorption of protons, translocates H(+) across the cell membrane, leading to an electrochemical gradient for protons between the inside and the outside of the cell. Thus, light is an alternate source of energy in these bacteria, in addition to terminal oxidation. The paper deals with work on light-driven transport in H. halobium with cell envelope vesicles. The discussion covers light-driven movements of H(+), Na(+), and K(+); light-driven amino acid transport; and apparent allosteric control of amino acid transport. The scheme of energy coupling in H. halobium vesicles appears simple, its quantitative details are quite complex and reveal regulatory phenomena. More knowledge is required of the way the coupling components are regulated by the ion gradients present.

Lanyi, J. K.↗

NASA NTRS1979

Modification of a Kowa RC-2 fundus camera for self-photography without the use of mydriatics

Research on retinal circulation during space flight required the development of a simple technique to provide self monitoring of blood vessel changes in the fundus without the use of mydriatics. A Kowa RC-2 fundus camera was modified for self-photography by the use of a bite plate for positioning and cross hairs for focusing the subject's retina relative to the film plane. Dilation of the pupils without the use of mydriatics was accomplished by dark-adaption of the subject. Pictures were obtained without pupil constriction by the use of a high speed strobe light. This method also has applications for clinical medicine.

Philpott, D. E.↗

NASA NTRS1979

Energy transduction in Halobacterium halobium

The properties and functions of the light-energy-transducing purple membrane of Halobacterium halobium are reviewed. Consideration is given to the protein structure and composition of the membrane and the photochemistry of the protein-retinal complex known as bacteriorhodopsin. The role of bacteriorhodpsin in establishing and maintaining an electrochemical (H(+)) gradient is examined, and interactions of this gradient with Na(+) and K(+) gradients, the light-induced transport of amino acids and the light-induced phosphorylation of ADP are considered. Bacteriorhodopsin and the respiratory chain are discussed as alternative sources of energy for the maintenance of the H(+) gradient. Advantages of the Halobacterium purple membrane system for studies of membrane energetics and the confirmation of the chemiosmotic hypothesis are also noted.

Lanyi, J. K.↗

NASA NTRS1980

The architecture of the avian retina following exposure to chronic 2 G

Rhode Island Red female chicks at 2 weeks posthatch were subjected, for 7 d, to either earth gravity of 1 G or a 2-G hypergravity environment by chronic whole-body centrifugation. Animals were sacrificed at 3 weeks posthatch and the eyes were enucleated, fixed in 10% BNF, doubly embedded, sectioned at 7-8 microns and routinely processed with H & E for histological examination. Compared to normogravity controls, animal exposure for 1 week to the chronic effects of 2-G resulted in a significantly decreased mean width of the photoreceptor, inner nuclear, and inner plexiform retinal layers. The outer nuclear, outer plexiform, and ganglion cell layers of the retina appeared minimally affected by the hypergravity state since the mean width of these layers showed no noticeable differences from earth gravity control animals. The present anatomic findings suggest a reduction in the detection of motion or rapid changes in illumination by the avian retina when the animal is exposed at a 2-G environment.

Orlando, R. G.↗

NASA NTRS1981

The guidance of saccadic eye movements to perceptually mislocalized visual and non-visual targets

The present experiment examined whether saccadic eye movements to visual targets are dependent on the perceived directions of the targets or on their retinally specified directions. Perceptual mislocations of visual targets were induced by having the target light attached to a subject's stationary hand while his biceps or triceps muscle was vibrated. Such vibration leads to apparent extension or flexion of the subject's restrained forearm and perceived visual motion of the stationary target light. Subjects always made accurate saccadic eye movements to a visual target, even when the target was perceptually mislocalized by as much as 20 deg. By contrast, when subjects made saccadic eye movements to a nonvisual target, the location of their hand in the dark, they always looked to the perceived direction of the target even though it did not necessarily correspond to the true direction. These findings indicate that a distinction is maintained between 'reflexive aspects' of oculomotor control related to foveation and the computation of perceived visual direction.

Lackner, J. R.↗

NASA NTRS1981

A single-channel model does not predict visibility of asynchronous gratings

A single channel model is shown to lack the capability to predict the visibility of asynchronous compound gratings. A constant Beta was assumed, based on Monte-Carlo simulations, and used to show that an SE of 6.73 (Limb, 1981) lies outside of an acceptable confidence interval. Potential imbalances between two eyes cannot be as large as 1.5 dB, which can only affect one eye, or one region of a retina. An average unbalance of 0.53 dB (SE = 0.12) employed in experiments to measure thresholds was compensated for by estimated threshold reductions. Trial-to-trial variability was included in the single channel model, as were considerations of retinal inhomogeneity. Temporal sensitivity for 2 and 4 c/deg grating patches were measured, and the amplitude response of a single channel at the two spatial frequencies was obtained. Threshold reductions with a Beta of 3.1 are then determined to not be significant enough to warrant adoption of the single channel model predictions.

Watson, A. B.↗

NASA NTRS1983

Spectral consequences of photoreceptor sampling in the rhesus retina

Optical transforms were used to compute the power spectra of rhesus cones treated as arrays of image sampling points. Spectra were obtained for the central fovea, parafovea, periphery, and far periphery. All were consistent with a novel spatial sampling principle that introduces minimal noise for spatial frequencies below the Nyquist limits implied by local receptor densities, while frequencies above the nominal Nyquist limits are not converted into conspicuous moiree patterns, but instead are scattered into broadband noise. This sampling scheme allows the visual system to escape aliasing distortion despite a large mismatch between retinal image bandwidth and the Nyquist limits implied by extrafoveal cone densities.

Yellott, J. I., Jr.↗

NASA NTRS1984

Color film preservation system: Breadboard development

The development of an economically feasible system to prevent and/or substantially reduce the degradation of the color dyes of the retinal reflex images recorded on color slide films is discussed. Three different types of film storage systems were designed, fabricated, and tested. An extruded plastic cylindrical container was pressurized and no observable leakage occurred, indicating that long term storage is possible. An operational breadboard was fabricated. The system offers the capability to determine purging requirements to achieve various levels of oxygen concentration and precise leakage of various container configurations. The system has digitial display of oxygen content of the container, automatic control of the oxygen content as well as of the container to atmosphere pressure differential, and flow rate readout during purging.

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NASA NTRS1984

Peripheral vision displays: The future

Several areas of research relating to peripheral vision displays used by aircraft pilots are outlined: fiber optics, display color, and holography. Various capacities and specifications of gas and solid state lasers are enumerated. These lasers are potential sources of green light for the peripheral vision displays. The relative radiance required for rod and cone vision at different wavelengths is presented graphically. Calculated and measured retinal sensitivities (foveal and peripheral) are given for wavelength produced by various lasers.

Assenhein, H. M.↗

NASA NTRS1985

Generation-V dual-Purkinje-image eyetracker

Major advances characterize the Generation-V dual-Purkinje-image eyetracker compared with the Generation-III version previously described. These advances include a large reduction in size, major improvements in frequency response and noise level, automatic alignment to a subject, and automatic adjustment for different separation between the visual and optic axes, which can vary considerably from subject to subject. In a number of applications described in the paper, the eyetracker is coupled with other highly specialized optical devices. These applications include accurately stabilizing an image on a subject's retina; accurately simulating a visually dead retinal region (i.e., a scotoma) of arbitrary shape, size, and position; and, for clinical purposes, stabilizing the position of a laser coagulator beam on a patient's retina so that the point of contact is unaffected by the patient's own eye movements.

Crane, H. D.↗

NASA NTRS1985

Computational models of human vision with applications

Perceptual problems in aeronautics were studied. The mechanism by which color constancy is achieved in human vision was examined. A computable algorithm was developed to model the arrangement of retinal cones in spatial vision. The spatial frequency spectra are similar to the spectra of actual cone mosaics. The Hartley transform as a tool of image processing was evaluated and it is suggested that it could be used in signal processing applications, GR image processing.

Wandell, B. A.↗

NASA NTRS1985

Photoenergy transduction in halobacterium halobium

The structure and function of a rhodopsin-like pigment bacteriorhodopsin, discovered and isolated from the membranes of the halophile Halobacterium halobium, were studied. Intermediatesm appearing in the cyclic photoreaction that drives the proton translocation, were spectroscopically characterized. The charge translocation in membrane monolayers and mulitlayers placed between electrodes were kinetically resolved. A model was developed for the proton translocation process, in which the isomerization of the retinal Schiff base decreases its pK to drive the proton off and simultaneaouly changes the connectivity from the cytoplasmic surface to the external surface. The stoichiometry of proton pumping in intact cells and the effect of the light generated electrochemical potential on the kinetics of the photoreaction cycle and the synthesis of ATP were investigated.

Stoeckenius, W.↗