Ability Of Eye Research Articles

Emerson's Nonlinear Nature

In this provocative study, Christopher Windolph analyzes Emersonian naturalism from the standpoint of nonlinearity, offering new ways of reading and thinking about stance toward naturalism and the influence of science on his thought. Drawing on ideas in perspective theory, architecture, and nonlinear dynamics to argue that natural philosophy follows from his analysis of the development of organic forms, Windolph breaks new ground in Emerson studies by exploring how considerations of shape and the act of seeing underpin all of theories about nature. Bringing to his study a focused attention to the history of Western science and philosophy, Windolph reexamines understanding of how the act of seeing occurs and of the eye's ability to see through appearances to organizing principles, showing how naturalism extends beyond the narrow confines of traditional linear science. Through extensive readings of journals, essays, and lectures, Windolph shows that Emerson was an empirical idealist who integrated a scientific approach to nature with an exploration of nonlinear principles, revealing him to be more prescient in his writings about certain recent developments in scientific thought than has been realized. This work makes a major contribution to the ongoing study of Emerson and science, expanding role as a major American philosopher while rebutting those who see him primarily as a rhetorician or poetic propagandist. Emerson's Nonlinear Nature opens new ways of thinking about work in its nineteenth-century contexts, reassesses his reception in twentieth-century criticism, and makes a strong case for his continuing relevance in the century ahead.

Incremental retinal-defocus theory of myopia development—Schematic analysis and computer simulation

Previous theories of myopia development involved subtle and complex processes such as the sensing and analyzing of chromatic aberration, spherical aberration, spatial gradient of blur, or spatial frequency content of the retinal image, but they have not been able to explain satisfactorily the diverse experimental results reported in the literature. On the other hand, our newly proposed incremental retinal-defocus theory (IRDT) has been able to explain all of these results. This theory is based on a relatively simple and direct mechanism for the regulation of ocular growth. It states that a time-averaged decrease in retinal-image defocus area decreases the rate of release of retinal neuromodulators, which decreases the rate of retinal proteoglycan synthesis with an associated decrease in scleral structural integrity. This increases the rate of scleral growth, and in turn the eye's axial length, which leads to myopia. Our schematic analysis has provided a clear explanation for the eye's ability to grow in the appropriate direction under a wide range of experimental conditions. In addition, the theory has been able to explain how repeated cycles of nearwork-induced transient myopia leads to repeated periods of decreased retinal-image defocus, whose cumulative effect over an extended period of time results in an increase in axial growth that leads to permanent myopia. Thus, this unifying theory forms the basis for understanding the underlying retinal and scleral mechanisms of myopia development.

Quantifying the aesthetic benefits of urban forestry

All the usual methods for valuing non-market benefits and costs may be applied to the aesthetic values of urban trees. However, evaluation has most usually been undertaken by one of two apparently dissimilar methods. The expert approach uses a mixture of measurement and judgement. Different versions of the approach have different quantitative input, produce divergent results, and theoretical justifications of their cash value are lacking. The hedonic approach attempts to derive cash values from house prices. Here too problems of quantification arise, in choice of appropriate variables, in the form of relationships and in interaction of variables. An approach using the human eye's ability to synthesise disparate variables may overcome these problems, but there remain problems of collinearity between environmental and demographic variables. At least explicit recognition of judgement in the process allows open discussion of these problems.

The arrangement of the three cone classes in the living human eye.

Human colour vision depends on three classes of receptor, the short- (S), medium- (M), and long- (L) wavelength-sensitive cones. These cone classes are interleaved in a single mosaic so that, at each point in the retina, only a single class of cone samples the retinal image. As a consequence, observers with normal trichromatic colour vision are necessarily colour blind on a local spatial scale. The limits this places on vision depend on the relative numbers and arrangement of cones. Although the topography of human S cones is known, the human L- and M-cone submosaics have resisted analysis. Adaptive optics, a technique used to overcome blur in ground-based telescopes, can also overcome blur in the eye, allowing the sharpest images ever taken of the living retina. Here we combine adaptive optics and retinal densitometry to obtain what are, to our knowledge, the first images of the arrangement of S, M and L cones in the living human eye. The proportion of L to M cones is strikingly different in two male subjects, each of whom has normal colour vision. The mosaics of both subjects have large patches in which either M or L cones are missing. This arrangement reduces the eye's ability to recover colour variations of high spatial frequency in the environment but may improve the recovery of luminance variations of high spatial frequency.

Documents mean more than just paper!

With the advent of electronic documents, information is available in more than just its visual form—electronic information is display-independent. Though the principal mode of display is still visual, we can now produce alternative renderings of this information—we have designed a computing system, A ST ER, that produces an audio view. The visuasl mode of communication is characterized by the spatial nature of the display and the eye's ability to actively access parts of this display. The reader is active, while the rendering itself is passive. This active-passive role is reversed by the temporal nature of oral communication: the information flows actively past a passive listener. The passive nature of listening prohibits multiple views—it is impossible to first obtain a high-level view and then “look” at portions of the information in detail. These shortcomings become particularly severe when presenting complex mathematics orally. We overcome these problems of oral communication by developing the notion of audio formatting—a process that renders information structure in a manner attuned to an auditory display. The audio layout present in the output conveys information structure. A ST ER is an interactive system—the ability to browse information structure and obtain multiple views makes the listener an active participant in oral communication. The resulting audio documents achieve effective oral communication of structured information from a wide range of sources, including literary texts and highly technical documents containing complex mathematics.

A Strategy and Architecture for the Visualization of Complex Geographical Datasets

The use of computer visualization as a means to analyze complex geographic datasets is discussed. Visualization is a valuable tool for conducting exploratory data analysis on geographical data; making good use of the human eye's unparalleled ability to recognize structure and relationships that may be inherent within the data. Traditional GIS are extremely poor at visualization, being limited to a very restricted set of visual attributes with which to convey information (position, size, color). The use of a more sophisticated approach is discussed in detail. Specifically, a system to visualise complex environmental datasets is described, which makes use of knowledge concerning the problem domain as well as knowledge concerning human cognition. In the realizations produced, the most salient attributes in the data, for a particular task, are assigned to the most striking visual attributes. Assignments are controlled by heuristics that may be changed to alter system behavior. Results are presented showing the application of this approach on datasets involving several multi-dimensional thematic layers of environmental data, used in mineral exploration.

Visually controlled spatial stabilisation of the human head: Compensation for the eye's limited ability to roll

During movements of the head in pitch (yes-yes) or in yaw (no-no) the visual scene appears stable whereas rolling the head (ear down to shoulder) induces an apparent swinging of the world in the opposite direction. This visual instability is due to the inadequacy, in the roll plane, of the reflex eye movements which are effective in stabilising the eyes in space during pitch and yaw. We investigated whether head is stabilised in roll to protect against visual instability. Human subjects were fixed in a gimbal with their heads free and were exposed to unpredictable oscillatory movement in pitch and, for comparison roll, about axes aligned with the head. With vision, during roll motion, the head was displaced from upright by approximately half the amplitude of the gimbal motion. In comparison, with eyes closed relying on vestibular and proprioceptive cues and during pitch stimuli with or without vision, the magnitude of head displacement from upright was approximately equal to that to the gimbal. The superior head stability in roll, dependent on a visual frame of reference, compensates for poverty of eye movement in this plane.

Effects of synaptic drugs on turtle optokinetic nystagmus and the spike responses of the basal optic nucleus

Behavioral and electrophysiological measures were used to elucidate the retinal modulation of oculomotor control in the turtle. Eye movements were recorded following intravitreal applications of 2-amino-4-phosphonobutyrate (APB) and the GABA antagonists picrotoxin and bicuculline. Visual responses of single basal optic nucleus (BON) neurons of the accessory optic system were studied in parallel experiments. The effectiveness of APB, a glutamate analog thought to act selectively on the retinal ON pathway, was assessed independently by recording electroretinograms or ganglion cell activity. Injections of APB into the turtle's eye reduced or blocked the injected eye's ability to drive horizontal optokinetic nystagmus, as also observed in rabbit and cat (Knapp et al., 1988; Yucel et al., 1989). Single-unit recordings from the BON during APB superfusion (50-200 microM APB) of the contralateral retina demonstrated that these cells, which are direction-sensitive and respond to the offset of light flashes, have their responses to moving stimuli blocked by APB. During the APB effect, GABA antagonists were applied to the same eye. Although moderate doses of APB were sufficient to block optokinetic or BON light responses, the addition of GABA blockers still elicited a spontaneous temporal-to-nasal nystagmus (Ariel, 1989) or visually responsive yet direction-insensitive responses from BON cells (Schuerger et al., 1990). These results are discussed in terms of the retinal output to pathways involved in oculomotor control of optokinetic nystagmus.

Retinal direction-sensitive input to the accessory optic system: an in vitro approach with behavioral relevance

Retinal application of γ-aminobutyric acid (GABA) antagonists block direction-sensitive (DS) responses in turtle in two ways: (1) the selectivity of DS retinal ganglion cells in vitro, and (2) the eye's ability to track the direction of full field image motion. The experiments described below demonstrate that an important locus for retinal slip computation by the accessory optic system (AOS) occurs in the retina. Visual responses were measured physiologically and behaviorally from turtles which had their telencephalon removed. Physiological responses to visual field movement were recorded in the AOS using an in vitro brain preparation. DS responses of single cells were blocked by intravitreal application of bicuculline. The behavioral approach was to measure optokinetic nystagmus (OKN) in lesioned animals. OKN occured in the absence of the telencephalon, yet was disrupted following an intravitreal injection of bicuculline. Thus, both experimental approachesm showed that DS processing exists without the telencephalon, yet is disrupted by GABA antagonists applied to the retina.

Efferent control of temporal response properties of the Limulus lateral eye.

The sensitivity of the Limulus lateral eye exhibits a pronounced circadian rhythm. At night a circadian oscillator in the brain activates efferent fibers in the optic nerve, inducing multiple changes in the physiological and anatomical characteristics of retinal cells. These changes increase the sensitivity of the retina by about five orders of magnitude. We investigated whether this increase in retinal sensitivity is accompanied by changes in the ability of the retina to process temporal information. We measured the frequency transfer characteristic (FTC) of single receptors (ommatidia) by recording the response of their optic nerve fibers to sinusoidally modulated light. We first measured the FTC in the less sensitive daytime state and then after converting the retina to the more sensitive nighttime state by electrical stimulation of the efferent fibers. The activation of these fibers shifted the peak of the FTC to lower frequencies and reduced the slope of the low-frequency limb. These changes reduce the eye's ability to detect rapid changes in light intensity but enhance its ability to detect dim flashes of light. Apparently Limulus sacrifices temporal resolution for increased visual sensitivity at night.

Form from motion parallax and form from luminance contrast: vernier discrimination.

Some objects are perfectly camouflaged when stationary, but are clearly visible when moving; the boundaries of such an object are defined entirely by motion parallax. Little is known about the eye's ability to make spatial discriminations between motion-defined objects. In this study, subjects viewed a pseudo-random pattern of dots within which a camouflaged bar was made visible by relative motion of dots. Vernier acuity for the motion-defined bar was 27-45 sec arc for three subjects, much less than the interdot separation of 360 sec arc, much less than the 2 deg receptive field size for motion, and comparable with the foveal intercone separation of 30 sec arc. It is proposed that an opponent-orientation process and an opponent-position process can both contribute to vernier judgements for motion-defined objects. Real-world motion contrast commonly confounds the following cues for figure-ground segregation: (1) different texture velocities on either side of the figure's boundary; (2) in any given time interval, texture in figure and ground moves different distances; and (3) texture continually appears and disappears along the figure's boundary. When cues (2) and (3) were eliminated, thus ensuring figure-ground segregation was achieved entirely by motion-sensitive neural elements, vernier acuity was 44 +/- 5 sec arc compared with 36 +/- 8 sec arc for a dotted bar defined by luminance contrast. Vernier acuity for a dotted bar whose boundary was defined entirely by motion-sensitive neural elements was similar to vernier acuity for a dotted bar whose boundary was defined by luminance contrast.

THE AGEING EYE

ABSTRACTMost of the changes of vision due to ageing are attributable to changes in the crystalline lens. Hardening of the crystalline lens decreases the eye's ability to focus for near vision and so “reading” or “intermediate” glasses become necessary. Flattening of the crystalline lens causes a hyperopic shift in refractive error in the over 40 age group.Pathological conditions such as cataract, glaucoma and retinal degeneration can impair visual performance. Older persons need stronger and more carefully arranged lighting.

Simple Method of Measuring Brightness Threshold of Dark Adapted Eye at All Ages

The relation between the vitamin A status of the body and the eye's ability to adapt to the dark is now well established. The chemical mechanism underlying this relation has been studied by Wald. While several instruments for measuring dark adaptation are available, none is applicable to infants and very young children. In the course of an investigation of the vitamin A requirements of infants, necessity impelled us to devise a method for measuring their ability to adapt to the dark. Fortunately, our task was simplified by a number of recent studies of this function in adults. It has been demonstrated that whereas the dark adaptation of persons with certain diseases is more or less delayed,, alterations in the vitamin A status of clinically normal individuals are accompanied by a simple rise or fall of the visual threshold, the speed of adaptation remaining constant.,, Hence, where it is not possible or convenient to measure the complete time course of dark adaptation, it is sufficient for purposes of dietary studies of normal subjects to determine the final or equilibrium threshold alone. The present apparatus and procedure accomplishes this in a satisfactory and simple manner. In measurements of the precise course of dark adaptation, fixation of the eye in relation to the direction of the stimulus is essential to insure that the portion of the retina measured is the same throughout the test. If only the final or equilibrium threshold of the most sensitive portion of the retinal periphery after complete dark adaptation is to be determined, fixation is unnecessary.