Showing papers on "Foveal published in 1972"

A method for the investigation of those transformations under which the visual recognition of a given object is invariant. I. The theory.

Abstract: An experiment is described which shows in operation the program set out in Foster (1972a) for the investigation of the invariance transformations of visual recognition. The concern in the present study is with the Lie group of rotations SO(2), and a certain centrally located foveal Landolt ring. By presenting to the visual system this Landolt ring and a rotated image in rapid succession, one attempted to induce a specified rotation-type phi-motion. Two subjects were employed. Both reported the existence of the required type of phi-motion for rotations ϱ0 of the Landolt ring about the visual axis with -2π/7≦θ≦2π/7. By appealing to the basic Proposition 2 of Foster (1972 a), the conclusion is reached that the visual system appears capable of effecting upon a certain centrally located foveal annulus the local 1-parameter group of rotations about the visual axis ϱ0, θ∈[−2π/7,2π/7].

An electro-ophthalmological study of affections of the optic pathway.

Abstract: To establish the diagnosis in cases of an acute affection of the optic nerve, the investigator must rely on functional examinations such as determination of visual acuity and of the visual field. Only when the process is localized at the optic disc abnormalities become apparent with the aid of the ophthalmoscope. Affections of longer standing may lead to atrophy of nerve fibres, and this may become visible in the fundus in that the disc is pale of appearance. However, not in all cases is the so-called disc atrophy associated with poor visual acuity: in these cases the functional findings seem to contradict the fundoscopic findings. Another example is the choked disc, which produces highly pathological fundoscopic features even though visual acuity and visual field are quite intact. The opposite situation is that of the acute stage of retrobulbar neuritis, in which the optic disc may present an entirely normal appearance whereas visual acuity and visual field are severely disturbed. Findings such as the above mentioned evoke the wish for an extended examination which includes methods supplying some information on the manner in which, under pathological circumstances, the optic nerve does or does not conduct. Recording visually evoked responses provides a possibility in this respect. Visually evoked responses are known to be largely determined by photic stimulation of the central retina (Vav Hof1960; Copenhaver & Perry 1964). However, stimulation of the peripheral retina likewise makes a contribution be it much smaller - in illiciting the VER. This means that intactness of the central fovea, the maculopapillary fibre bundle in the optic nerve, and the projection of the fovea in the optic cortex, is a prerequisite for recording VERs. On the other hand, the development of sophisticated recording techniques (e.g. with the aid of the computer) which make it possible to identify the VER amidst the ever-present background activity (the EEG), has enabled the investigator to record an ERG from a very small retinal area, e.g. the local photopic ERG of the central fovea (FERG). Simultaneous recording of FERG and VER makes it possible to examine the function of, exclusively, that part of the optic system that encompasses the fovea, the maculopapillary fibre bundle and the projection of the fovea in the optic cortex. Visual acuity is determined by this part of the optic system. It is the diminished visual acuity (and a central scotoma in the visual field) that, in many cases, characterizes an affection of the optic nerve. If, under these pathological conditions, one can nevertheless record VERs after local (foveal) stimulation, and recognize pathological changes in the recordings, then it should be ascertained that these VERs have indeed been obtained by stimulation of the fovea. This can be achieved by recording the FERG, for which normal values are given in chapter VI. Chapters II and III discuss the development of methods to record VER and FERG. The method used in our study is described in detail in chapter IV. Chapter V presents a description of the protocol of examination to which our patients were submitted, and lists the number of patients examined. Chapter VII describes the electro-ophthalmological findings obtained in patients with optic neuritis. In the acute stage of optic neuritis (diminished visual acuity and a central scotoma in the visual field), no VER can be recorded after local (foveal) stimulation of the retina. The impairment of conduction, thus objectively demonstrated, may result from the development of an inflammatory-like oedema which impairs the capillary blood circulation in the optic nerve; one of the consequences of this situation is a pathological metabolism of the nerve tissue and release of toxins (e.g. Bonamour 1968). If in such cases it is possible to identify a VER in the recordings after full field stimulation of the retina, then we are dealing, we believe, with the contribution of the peripheral retina to the generation of the VER. In this context it is to be noted that, in the acute stage of optic neuritis, it is often surprising to see how well the patient can fix the (small) photic stimulus in spite of the poor visual acuity and the central scotoma in the visual field. If visual acuity and visual field fail to recover after the acute stage, then the VER after local (foveal) stimulation remains absent. This is a result of demyelination and atrophy of nerve fibres, particularly those of the maculopapillary bundle. In this stage examination does become more difficult because the patient's ability to fix the stimulus diminishes as poor visual acuity is of longer standing. Upon partial recovery from optic neuritis (e.g. visual acuity 0.6–0.7 and a relative central scotoma in the visual field), we have observed that the VER after local (foveal) stimulation can nevertheless remain absent. We believe that in these cases there has been demyelination of the fibres in the maculopapillary bundle, but that yet the majority of these fibres does still conduct, even over the segment of demyelination. The mode of conduction in the demyelinated segment differs from normal and may well resemble that in naturally unmyelinated fibres in the peripheral nervous system. A consequence of this might be that the conduction velocity diminishes. As a result, the conduction time of the nerve fibres can come to show interdifferences due to which depolarization of the projection of the fovea in the optic cortex takes place only gradually so that at no time a potential occurs of sufficient amplitude to permit our apparatus to record it. In the case of complete recovery from optic neuritis, one can observe a return of the VER after local (foveal) stimulation to the extent that there is no longer a significant difference between the VER recorded after stimulation of the one (unaffected) eye and that recorded after stimulation of the other (affected) eye. We believe that electro-ophthalmological examination demonstrates in these cases that no demyelination as a result of the optic neuritis has occurred, or that, as a result of remyelination, a restitutio ad integrim has occurred. Chapter VIII presents the results of an examination of twelve patients with Leber's hereditary optic atrophy. The majority had regained fair-to-good visual acuity in at least one eye. In only one patient of this group were VERs identifiable in the responses after local (foveal) stimulation. We observed that in a few cases of Leber's optic atrophy a visual acuity of 1.0 could be attained. In these cases a central scotoma in the visual field had in its exact centre an intact sparing corresponding to ≤ 1 ° subtended visual angle. The absence of the VER after local (foveal) stimulation is ascribed to the fact that only a small number of fibres in the maculopapillary bundle is still intact; impulses conducted by these few fibres, effect depolarization of so small a part of the projection of the central fovea in the optic cortex that a potential of sufficient amplitude to be recorded, is never produced. In patients with traumatic optic atrophy, it was difficult to record ERG and VER after local (foveal) stimulation because all were examined long after the accident, so that visual acuity had long been poor. However, in one case (visual acuity 0.6 in the eye, of which the optic nerve was affected) a disturbance of conduction in the maculopapillary bundle could be demonstrated because the VER after local (foveal) stimulation of this eye was absent (chapter IX). Simple glaucoma (chapter X) was not systematically studied. Two patients are discussed. The results of their examinations do not warrant the expectation that a more comprehensive examination by the techniques we used will reveal many new points of view on the disturbance of conduction of the nerve fibres in this condition. A patient with toxic opticoneuropathy due to ethambutol medication and one with juxtapapillary retinitis (Jensen) are discussed in the same chapter. Chapter XI describes the examination of patients with intracranially localized causes of disturbed vision. With the placements chosen for the scalp electrodes (see chapter IV), it proved impossible in patients with dysfunction of one optic hemicortex to demonstrate its inactivity versus the activity of the intact hemicortex. In patients with (incomplete) bitemporal hemianopia due to a hypophyseal process, the VER after local (foveal) stimulation was disturbed if the maculopapillary fibre bundle had been affected by compression atrophy. This fact, however, was already known in these cases from examination of visual acuity and visual fields. In cases of choked disc, a normal VER after local (foveal) stimulation was found whenever visual acuity and visual fields were (still) adequate. Whenever the visual acuity was diminished as a result of secondary optic atrophy, the VER after local (foveal) stimulation was absent.

Role of peripheral vision and time sharing in driving

Abstract: THE ROLE OF EXTRA-FOVEAL AND FOVEAL VISION IN THE VISUAL INFORMATION ACQUISITION PROCESS OF THE DRIVER, AND THE EFFECT OF A DRIVER'S VISUAL INFORMATION ACQUISITION BEHAVIOR ON HIS DRIVING PERFORMANCE ARE INVESTIGATED. IT WAS FOUND THAT DRIVERS ACQUIRE CONSIDERABLE AMOUNTS OF INFORMATION THROUGH EXTRA-FOVEAL VISION FOR BOTH LATERAL AND LONGITUDINAL CONTROL PERFORMANCE. FOVEAL VISION, BECAUSE OF ITS FINER DISCRIMINATION CAPABILITIES, CAN PROCESS INFORMATION MORE ACCURATELY AND AT HIGHER SPEEDS, BUT IT COVERS ONLY A SMALL PORTION OF THE TOTAL VISUAL FIELD AVAILABLE TO A DRIVER. THE RESULTS OBTAINED IN THIS EXPERIMENT HAVE IMPLICATIONS IN MANY DESIGN PROBLEMS WHERE DEGRADATION IN BOTH LATERAL AND LONGITUDINAL CONTROL PERFORMANCE IS CRITICAL AND A NUMBER OF OTHER SPATIALLY SEPARATED TASKS SUCH AS READING SIDE-MOUNTED SIGNS AND JUDGING MOTION CHARACTERISTICS OF MERGING VEHICLES EXIST. /HSL/

Spectral Deficits in Visual Acuity Due to Laser Irradiation

Abstract: : The increased use of lasers and laser devices has made it essential to determine the potential kinds of visual deficits associated with accidental laser exposure. Maximal visual acuity and normal color vision are closely associated with foveal receptor function. When the fovea is destroyed by laser irradiation, severe and permanent losses in visual acuity ensue. The purpose of the study was the determination of permanent photopic or color deficits in animal subjects following foveal injury produced by ruby laser irradiation.

Backward masking: stimulus energy and positional uncertainity

Abstract: Backward masking functions were obtained for recognition of single letters off or on foveal center or of one of 12 letters in a circular display; stimulus energy was high (no-mask performance above 95% for the single letters) or low. Stimulus energy, but not foveal location, affected masking ranges for the single letters, yet the same 4:1 energy ratio did not produce differential masking ranges or no-mask performance for the 12-letter displays.

Spatial behavior and its alterations: old and new concepts

Abstract: In a normal perceptual situation, the eye not only sees but also moves. This crude evidence seems to have been largely neglected in the classical models of space perception, in which all the retinal information was thought to be gathered while the retina was stationary. There is no doubt, however, that the retina works as a system of polar coordinates, with their origin in the fovea. Each retinal locus can thus be assigned a "local sign," defined by its position on the polar diagram: distance from the origin and angular distance from one of the axes of reference (vertical or horizontal). Each local sign is assumed to represent a given portion of the physical space, and consequently the retinal image might constitute a reliable two-dimensional spatial mosaic. The point-to-point correspondence between the retinal image and a central "copy," caused by the spatial organization of the upper visual centers, is well known. Such a design certainly holds true in the foveal "pure cone system," in which each cone-bipolar-cell-ganglion-cell wiring is individual and represents a single spatial unit. But it becomes largely an ideal in the periphery of the fovea itself and in all of the extrafoveal retina, in which the cone size (and the intercone distance) increases and the cone-optic-tract wiring becomes more and more diffuse. Under these circumstances, the spatial retinal map would be better represented in three dimensions, by plotting the spatial resolving power or the spatial reliability on the Z axis; this would show a peak at the center of the fovea and a rapid exponential decrease toward the periphery (see Jones & Higgins, 1947; Polyak, 1941). As a consequence of the nonhomogeneity of the spatial retinal map and of the poor spatial discrimination outside the fovea, the eyes move so as to bring