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Showing papers on "Foveal published in 1986"


Journal ArticleDOI
01 Jan 1986-Nature
TL;DR: The results, presented here, show that peripheral vision and central vision of strabismic amblyopes differ qualitatively in their sampling characteristics from those of the normal fovea.
Abstract: The human visual system is capable of making spatial discriminations with extraordinary accuracy. In normal foveal vision, relative position, width or size can be judged with an accuracy much finer than the size or spacing of even the smallest foveal cones. This remarkable accuracy of spatial vision has been termed ‘hyper-acuity’1. Almost a century ago Ewald Hering proposed that the accuracy of Vernier acuity could be accounted for by averaging of discrete samples along the length of the lines comprising the targets2; however, the discovery that Vernier acuity of a few arc seconds could be achieved with dots has rendered the nature and role of sampling in spatial discrimination unclear3. We have been investigating the sampling of spatial information in central and peripheral vision (the perifovea) of normal human observers and in observers with strabismic amblyopia. Our results, presented here, show that peripheral vision and central vision of strabismic amblyopes differ qualitatively in their sampling characteristics from those of the normal fovea. Both the periphery and the central visual field of strabismic amblyopes demonstrate marked positional uncertainty which can be reduced by averaging of spatial information from discrete samples.

148 citations


Journal ArticleDOI
TL;DR: Three phases of the disease through which the eyes progressively evolved were identified and a confluent, usually circular, area of atrophy that involved the entire central macula was identified.

121 citations


Journal ArticleDOI
TL;DR: This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue.

98 citations


Journal ArticleDOI
TL;DR: Using fundus reflectometry, a decrease in the density difference of the foveal cone visual pigments with age in human subjects is measured, consistent with a loss of visual pigment in the retina with age.

87 citations


Journal ArticleDOI
TL;DR: In this paper, the directionality of the foveal receptors of four subjects was assessed with a technique based on lightscattering and a psychophysical technique, and the width and orientation of the absorbance diagram (difference between the scattering diagram in a bleached and unbleached state of the visual pigment) were compared with the Stiles-Crawford function.

80 citations


Journal ArticleDOI
TL;DR: The cone array in the peripheral retina, unlike the fovea, is sparse and irregular, and it feeds an even sparser ganglion cell array, which provides a new challenge to establish the link between the organization of the retina and the psychophysical limits of visual resolution.

74 citations


Book ChapterDOI
TL;DR: Foveal pursuit during purely visual and combined visual-vestibular stimulus paradigms is discussed, presumably of pure vestibular origin and can be estimated as the vestibulo-ocular reflex in the dark.
Abstract: Publisher Summary Smooth pursuit eye movements incorporate at least three well-known types of eye movements: (1) Foveal pursuit, with the goal of keeping the visual projection of a small moving target continuously on the center of the fovea, as first described by Dodge (1903). (2) Schau-nystagmus (look nystagmus), in this case the subject deliberately “fixates” an object as a part of the visual world that is moving relative to the unaccelerated head. (3) Compensatory eye movements, which are known as vestibulo-ocular reflex (VOR) in the light, they manifest the attempt to “fixate” a stationary target while the head performs rotatory or translatory movements. The largest contribution to the neural control of these compensatory eye movements is presumably of pure vestibular origin and can be estimated as the vestibulo-ocular reflex in the dark. Various types of special pursuit eye movement can only be induced under certain laboratory conditions. This chapter discusses on foveal pursuit during purely visual and combined visual-vestibular stimulus paradigms.

63 citations


Journal ArticleDOI
TL;DR: The effects of cue eccentricity and cue-target distance on reaction time are discussed in terms of their effects on the component processes that comprise the act of a shift of attention.

63 citations


Journal ArticleDOI
TL;DR: The results indicate the need for more sensitive measures of visual resolution to monitor foveal integrity in patients undergoing PRP.
Abstract: • Snellen visual acuity and spatial contrast sensitivity measurements were used to monitor changes in foveal vision in two patients undergoing argon laser panretinal photocoagulation (PRP) in both eyes for proliferative diabetic retinopathy. Foveal edema developed in one of the four eyes. The remaining three eyes showed no signs of foveal edema, but developed temporary losses in high spatial frequency contrast sensitivity during the closely spaced PRP treatments. Since Snellen visual acuity remained stable at the prelaser level, these results indicate the need for more sensitive measures of visual resolution to monitor foveal integrity in patients undergoing PRP.

47 citations


Journal ArticleDOI
TL;DR: Differences between foveal and peripheral vision in a number of psychophysical tasks are described and whether the fovea and the periphery are specialized for different functions is considered.

45 citations


Journal ArticleDOI
TL;DR: Compared with similar-aged normal subjects, most patients with dominantly inherited RP had normal or minimally reduced cone pigment density difference within the central fovea, relatively lower than normal density difference at the foveal margin, and increased foveAL reflectance.
Abstract: • Cone pigment density difference refers to a change in light absorption by cones before and after bleaching of their visual pigments. With a television ophthalmoscope image processor, we measured the foveal cone pigment density difference in patients with retinitis pigmentosa (RP), good central vision, and no clinically apparent foveal lesion. Foveal reflectance was obtained at 12 different wavelengths of illumination. Compared with similar-aged normal subjects, most patients with dominantly inherited RP had normal or minimally reduced cone pigment density difference within the central fovea, relatively lower than normal density difference at the foveal margin, and increased foveal reflectance. Compared with these normal subjects, patients with recessively inherited RP had significantly reduced cone pigment density difference within the central fovea, relatively more normal density difference at the foveal margin, and normal foveal reflectance.

Journal ArticleDOI
TL;DR: The effects of stimulus-response (S-R) spatial compatibility on reaction time (RT) and P300 component latency were studied, in order to determine whether spatial conflict effects can occur within a single cerebral hemisphere, and whether there are differences between hemispheres regarding such effects.
Abstract: The effects of stimulus-response (S-R) spatial compatibility on reaction time (RT) and P300 component latency were studied, in order to determine whether spatial conflict effects can occur within a single cerebral hemisphere, and whether there are differences between hemispheres regarding such effects. Two choice RT experimental conditions were employed: I) an extrafoveal condition, in which stimuli (small arrows pointing either to the right or to the left) appeared laterally in one visual hemifield, the responses being given with the hand situated on the same side; likewise with the opposite hemifield and hand (cond. I); and II) a foveal condition, in which the same type of stimuli appeared centrally on the fovea, the response being given successively with both hands (cond. II). In either case, the color of the stimuli (cue information) determined which finger (forefinger or ring finger) of the same hand would deliver the response. Thus, the cue was either compatible, or not, with the stimulus orientation (arrows). In each condition, the four possible stimulus combinations, according to direction and color of the arrows, were presented at random. Results showed that: 1) in the extrafoveal condition, S-R compatibility effects were observed in each single hemisphere, and were reflected both by RT and by P300 latency; 2) both hemispheres reacted in the same way to the spatial conflict; and 3) foveal vision increased the overall effect of the conflict on both P300 latency and RT.

Journal Article
TL;DR: The results suggested that monocular OKN deficits and peripheral acuity profiles are determined before the age of 5 yr, and the effects of early developmental conditions on cortical and subcortical binocularity, responsible for the deficits of stereopsis and OKN, show very close functional parallels.
Abstract: Human observers with deficient foveal stereopsis often show characteristic abnormalities of monocular optokinetic nystagmus (OKN). The present study examined the effect of binocular interactions in the peripheral visual field on these OKN deficits. A variety of binocular functions (binocular acuity summation, interocular suppression, motion-in-depth) were assessed at various positions throughout the visual field in subjects with deficient or no foveal stereopsis and related to monocular OKN deficits seen with different stimulus field sizes. Extent and location of peripheral binocular interactions accurately predicted the changes in monocular OKN observed with different field sizes. This indicates that the effects of early developmental conditions on cortical and subcortical binocularity, responsible for the deficits of stereopsis and OKN, show very close functional parallels. The results further suggested that monocular OKN deficits and peripheral acuity profiles are determined before the age of 5 yr.

Journal ArticleDOI
TL;DR: There was little evidence to support the hypothesis that children have poorer peripheral vision than adults relative to their foveal vision, but there were some experimental differences: in Expt 1, 7-year-olds made fewer detections, particularly in the extreme periphery; and, in both experiments, detections tended to be slower.
Abstract: In both adults and children, peripheral vision is poorer than foveal vision, but there is evidence that detection in peripheral vision is relatively poorer in children than it is in adults. That may contribute to the particularly high pedestrian accident rates of children. Two laboratory experiments investigated peripheral vision in men and women and in boys and girls aged 7, 9 and 11. Using an array of stationary lights, Expt 1 examined reactions to apparent movement (the phi phenomenon) in mid and extreme periphery; and, using film sequences of a moving car, Expt 2 included a comparison of foveal and peripheral fields. Overall there was little evidence to support the hypothesis that children have poorer peripheral vision than adults relative to their foveal vision. Nonetheless there were some experimental differences: in Expt 1, 7-year-olds made fewer detections, particularly in the extreme periphery; and, in both experiments, detections tended to be slower. The relatively complex car movements in Expt 2 were detected faster in foveal than peripheral vision. There were no sex differences. Children detected more movements on the left. In Expt 2 these detections were faster, and children made relatively more simulated road crossings when the car approached from the left (all adults 'crossed' in all trials).

Journal ArticleDOI
TL;DR: A significant correlation between foveal cone thresholds and the midpoints of the patients' Rayleigh matches demonstrated that the threshold elevations resulted in part from a decreased cone optical density.
Abstract: • To determine the relationship of foveal absolute thresholds to visual acuity in retinitis pigmentosa, we measured thresholds in 40 patients with various forms of retinitis pigmentosa (including Usher's syndrome) whose Snellen visual acuities were 20/30 or better. At all visual acuity levels, the patients' foveal thresholds were significantly higher than those of 20 similarly aged normal observers; threshold elevations tended to be greater for a 500-nm than for a 655-nm test flash. Foveal cone spatial summation functions were normal (test flash diameter range, 7' to 1.7°), indicating that the patients'threshold elevations did not result from altered summation properties. A significant correlation between foveal cone thresholds and the midpoints of the patients' Rayleigh matches demonstrated that the threshold elevations resulted in part from a decreased cone optical density.

Book ChapterDOI
01 Jan 1986
TL;DR: For instance, the human eye darts about the scene, bringing aspects of interest into the narrow field of the fovea for the resolution of detail as discussed by the authors, which is a critical part of visual perception.
Abstract: A critical part of visual perceptions, our ability to orient to a visual environment and quickly identify its most interesting attributes, depends upon our control of eye movements. Within a few seconds of confronting a page of text or a city street our oculomotor control system organizes and executes a series of saccades. The eye darts about the scene, bringing aspects of interest into the narrow field of the fovea for the resolution of detail. In this manner, our oculomotor system paints a global perception of a visual scene or transmits a message from the printed page to the brain.

Journal ArticleDOI
01 Sep 1986
TL;DR: The results showed no losses in peripheral sensitivity under the experimental conditions employed, contrary to data from previous studies.
Abstract: The main objective of the research was to investigate the effects of load on peripheral sensitivity in the visual field. Foveal load was varied by using simple fixation of a vs. a first-order (rate) compensatory tracking task. Peripheral sensitivity was determined simultaneously for light flashes located at different eccentricities along the horizontal meridian. The effects of training on the tracking task were also examined. In general, the results showed no losses in peripheral sensitivity under the experimental conditions employed, contrary to data from previous studies.

Journal ArticleDOI
TL;DR: Measurement of target spectral irradiance levels which are just sufficient to yield the comet effect suggests that the lengthening of the circular target reflects a rodcone interaction and therefore it may be due to unsuppressed, saturated rod responses at high retinal illuminance levels.
Abstract: A small circular target of high retinal illuminance level can have a comet-like appearance when presented moving continuously with a speed as low as 0.2 deg/s. This perceived lengthening of the circular target increases with the speed of movement and is only observed for target presentations outside the foveal region. Data on the parametric properties of the “comet effect” are presented together with related results on the time-course of recovery of retinal sensitivity following brief exposure to intense stimuli. Measurement of target spectral irradiance levels which are just sufficient to yield the comet effect suggests that the lengthening of the circular target reflects a rodcone interaction and therefore it may be due to unsuppressed, saturated rod responses at high retinal illuminance levels. The restriction of the comet effect to areas outside the foveal region is used to produce spatial maps of what appears to be the rod-free area of the retina. A model simulation by means of a computational approach shows that the predicted appearance of the moving target matches very closely the experimental observations on the comet effect. Model predictions based on psychophysical estimates of comet length for the stimulus conditions of these experiments yield an overall response time for the rod system of some 600 ms.

Proceedings ArticleDOI
05 Aug 1986
TL;DR: Preliminary data indicates that punctate retinal lesions in the fovea vary over time somewhat differently than similar size lesions placed parafoveally, which may aid in explanation of visual functional affects of such lesions.
Abstract: Small foveal retinal lesions are often difficult to detect with conventional ophthalmoscopy, as well as the visual functions effects of such damage. In order to improve conventional ophthalmoscopy of such lesions we have adapted computer image analysis techniques to quantify the spatial and temporal characteristics of such lesions. Our methodology incorporates conventional statistical tests of significance for plotting gray scale differences along common retinal landmarks. Preliminary data indicates that punctate retinal lesions in the fovea vary over time somewhat differently than similar size lesions placed parafoveally. Such temporal variations in gray scale distribution may aid in explanation of visual functional affects of such lesions.

Journal ArticleDOI
TL;DR: It is shown that the foveal vision and not peripheral vision is responsible for the suppression of fixation, and that fixation overrides the vestibular stimulus and results in suppressing both per- and postrotational nystagmus.
Abstract: The nystagmus of 20 normal subjects was compared by means of the rotatory test in the dark, in respect of visual fixation, and with stabilization of vision. Visual fixation was tested by means of a small lamp placed at a distance of 40 cm in front of the eyes of the subject. This point of fixation was attached to the rotating chair. Stabilization of vision was attained through a box placed above the head of the test person. This box - covering the whole visual field - moved synchronously with the rotating chair. Contrary to the test with fixation, the eye received no information about the real movement. The question was whether there would be any differences between the fixation test and the stabilization of vision. In both test conditions, fixation overrides the vestibular stimulus and results in suppressing both per- and postrotational nystagmus. This proves that the foveal vision and not peripheral vision is responsible for the suppression of fixation.

Journal ArticleDOI
TL;DR: A card sorting task was found to correlate significantly with visual lobe dimensions and it is suggested that this relationship may be used as the basis of a test for screening individuals for certain types of inspection and monitoring activities.
Abstract: Visual search is a very common form of inspection and monitoring activity. This paper reviews work by the author that demonstrates a relationship between visual lobe size and search performance. A card sorting task was found to correlate significantly with visual lobe dimensions and it is suggested that this relationship may be used as the basis of a test for screening individuals for certain types of inspection and monitoring activities. The test is considered to be a more useful measure of visual scanning ability than tests of foveal acuity.

Journal ArticleDOI
01 Sep 1986
TL;DR: The functional field of view appears to be sensitive to various cognitive load manipulations of foveal portions of displays and there is considerable evidence for a kind of tunnel-vision which is induced via cognitive loading.
Abstract: The functional field of view appears to be sensitive to various cognitive load manipulations of foveal portions of displays. Several studies are summarized which provide considerable evidence for a kind of tunnel-vision which is induced via cognitive loading.

Journal ArticleDOI
TL;DR: In this article, brief presentations of letter arrays were probed by bar markers within or outside the fovea after various time delays, showing that figural information in the rods and cones decays at similar rates.
Abstract: Brief presentations of letter arrays were probed by bar markers within or outside the fovea after various time delays. Figural information presented to the foveal region was retained better under a photopic condition than information in the parafoveal region, but under a scotopic condition parafoveal information demonstrated superior retention. However, decay rates over time of all functions were similar, demonstrating that figural information in the rods and cones decays at similar rates.