Showing papers on "Foveal published in 1994"

The Anatomy and Physiology of Primate Neurons that Control Rapid Eye Movements

Abstract: Primates are frontal eyed animals possessing a sophisticated retina endowed with a highly differentiated foveal region with which the visual scene can be examined in detail. Vision is very important to these animals and is probably the predominant sensory modality with which they orient themselves and interact with the world. The relationship between the visual system and the motor system that moves the eyes (oculomotor) is intimate. Motion of the visual scene across the retina, particularly the fovea, can degrade visual acuity. Hence there is a necessity for accurate oculomotor control. Not surprisingly, a considerable portion of the brain� including the superior colliculus (sq, the frontal eye field (FEF), the thalamus, and the cerebellum as well as several brainstem nuclei, is entrusted with the control of eye movements (Hepp et al 1989). The most ubiquitous movements of the eyes are the rapid ones (also called saccadic) that reorient the eyes quickly toward interesting features of the surrounding world. During a saccade, two or more of six extraocular muscles

The role of the anterior attention system in semantic processing of both foveal and parafoveal words

Abstract: This research takes advantage of combined cognitive and anatomical studies to ask whether attention is necessary for high-level word processing to occur. In Experiment 1 we used a lexical decision task in which two prime words, one in the fovea and the other in the parafovea, appeared simultaneously for 150 msec, followed by a foveal target (word/nonword). Target words were semantically related either to the foveal or to the parafoveal word, or unrelated to them. In one block of trials subjects were also required to perform an auditory shadowing task. From PET studies we know that shadowing activates the anterior cingulate cortex, involved in selective attention. If the anterior attention system is always involved in semantic processing, shadowing should reduce semantic priming obtained from both foveal and parafoveal words. In contrast, if semantic priming by parafoveal words is independent of activation in that attention area, priming will not be affected by shadowing. Our results supported the latter hypothesis. A large priming effect arose from foveal primes, which was reduced by shadowing. For parafoveal primes a smaller priming effect arose, which was not affected by shadowing. In Experiment 2 prime words were masked. Semantic priming was reliable for both foveal and parafoveal words but there were then no differences between them. Most important, the size of priming was similar to that obtained from parafoveal words in Experiment 1. We conclude that the anterior attention system increases the potency of processing of consciously perceived stimuli, but there is a component of semantic priming that occurs without both focusing of attention and awareness, involving different cerebral areas to those involved in attention to language.

Dependence of visual stabilization of postural sway on the cortical magnification factor of restricted visual fields.

Abstract: Monocular visual stabilization of fore-aft and lateral body sway was tested posturographically in normal subjects (wearing visual field blinds) as a function of visual field size and location of the visual field on the central or peripheral retina. Body sway applied to a force- measuring platform is less with central (foveal) vision when central and peripheral visual fields have the same area. If, however, the peripheral field size is corrected by the cortical magnification factor of the retina in the primary cortex, body sway is stabilized by the peripheral retina to the same extent. Thus, there is no functional specialization of central and peripheral retina with respect to balance control. Visual stabilization of upright stance is a function of field size and cortical representation of the retina. The central and the peripheral retina have different thresholds to detect motion; this was surprisingly not reflected in measurements of normal fore-aft and lateral body sway.

Optimal contributions of head and eye positions to spatial accuracy in man tested by visually directed pointing.

Abstract: Encoding of visual target location in extrapersonal space requires convergence of at least three types of information: retinal signals, information about orbital eye positions, and the position of the head on the body. Since the position of gaze is the sum of the head position and the eye position, inaccuracy of spatial localization of the target may result from the sum of the corresponding three levels of errors: retina, ocular and head. In order to evaluate the possible errors evoked at each level, accuracy of target encoding was assessed through a motor response requiring subjects to point with the hand towards a target seen under foveal vision, eliminating the retinal source of error. Subjects had first to orient their head to one of three positions to the right (0, 40, 80°) and maintain this head position while orienting gaze and pointing to one of five target positions (0, 20, 40, 60, 80°). This resulted in 11 combinations of static head and eye positions, and corresponded to five different gaze eccentricities. The accuracy of target pointing was tested without vision of the moving hand. Six subjects were tested. No systematic bias in finger pointing was observed for eye positions ranging from 0 to 40° to the right or left within the orbit. However, the variability (as measured by a surface error) given by the scatter of hand pointing increased quadratically with eye eccentricity. A similar observation was made with the eye centreed and the head position ranging from 0 to 80°, although the surface error increased less steeply with eccentricity. Some interaction between eye and head eccentricity also contributed to the pointing error. These results suggest that pointing should be most accurate with a head displacement corresponding to 90% of the gaze eccentricity. These results explain the systematic hypometry of head orienting towards targets observed under natural conditions: thus the respective contribution of head and eye to gaze orientation might be determined in order to optimize accuracy of target encoding.

Suprathreshold temporal-frequency discrimination in the fovea and the periphery

Abstract: To address the question of whether temporal-frequency information in the fovea and the periphery is processed in fundamentally different ways we measured temporal-frequency-discrimination thresholds for spatiotemporally narrow-band stimuli presented at suprathreshold contrast. Temporal-frequency-discrimination thresholds are similar (within a factor of 2) at the fovea and at 30° in the periphery. We use a line-element approach and three spatiotemporally separable temporal mechanisms to model foveal and peripheral data with the same degree of fidelity. These findings suggest that not only are the front-end temporal mechanisms in the fovea and periphery likely to be similar but also the way in which their outputs are combined at more central sites is the same.

Foveal scale-space and the linear increase of receptive field size as a function of eccentricity

Abstract: This paper addresses the formulation of a foveal scale-space and its relation to the scaling property of receptive field sizes with eccentricity. It is shown how the notion of a fovea can be incorporated into conventional scale-space theory leading to a foveal log-polar scale-space. Natural assumptions about uniform treatment of structures over scales and finite processing capacity imply a linear increase of minimum receptive field size as a function of eccentricity. These assumptions are similar to the ones used for deriving linear scale-space theory and the Gaussian receptive field model for an idealized visual front-end.

How many ganglion cells are there to a foveal cone? A stereologic analysis of the quantitative relationship between cone and ganglion cells in one normal human fovea

Abstract: Published studies on humans and monkeys show discrepancies in the reported quantitative relationship between cones (C) and ganglion cells (G) Data on human foveal retina suggest that it cannot accommodate the midget on-off system in addition to other functional channels Foveal cell densities along the vertical meridian (0–18 mm eccentricity) were estimated in one normal human retina using the disector method Cell ratios were calculated from cumulative total numbers G density peaked at 065 mm eccentricity and C density at the foveola Cumulative cell numbers showed a more rapid increase in G than in C with increasing eccentricity G/C ratios of 27–34 were found using lateral displacement data modified from macaque Using one estimate of displacement from the sections, the G/C ratio was 30 This study shows that there are on average three ganglion cells per foveal cone in humans, as in monkeys

Peripheral and foveal segmentation of angle textures

Abstract: Studies of the effects of retinal eccentricity on the visual segmentation of textures are pre­ sented. The textures used in these studies were composed of angle elements. These were pre­ sented tachistoscopically to college students in three different experiments. Results showed that there were different relationships between segmentation performance and eccentricity, depending on the width of the angles used in the background and target texture. One major difference was that peak performance was found in the fovea in some conditions, and in pe­ ripheral areas in other conditions. Performance in the fovea and the periphery seemed to be determined by qualitatively different features. It was assumed that an appropriate explana­ tion is that the system-internal representation of a specific stimulus within the early visual system differs as a function of the retinal location at which it is projected. Thus, the critical features discriminating between target and background texture have to be sought in the sys­ tem-internal representation of the stimulus instead of in the stimulus itself. The data show that a relatively exact system-internal representation of the stimulus is present in the fovea, where performance is determined by angle width. In the periphery, in contrast, angles seem to be represented as "blobs," and performance is determined by the orientation of the blobs' main axes.

Effects of priority assignment of attentional resources, order of testing, and response sequence on tunnel vision '

Abstract: The effects of relative priority of attentional resources allocated to simultaneous peripheral and foveal tasks, response sequence to the tasks, and order of testing with two levels of foveal cognitive loading on tunnel vision were studied with 32 Chinese undergraduates. Two levels of foveal condition were used for the foveal task while the peripheral task required a single-target detection. Performance decrement value and a significant interaction of levels x eccentricities indicated that tunnel vision was most prominent when the foveal task was primary. Greater magnitude of tunnel vision was obtained when the more difficult foveal task was tested prior to the no-foveal-load condition. Responding sequence to the tasks was nonsignificant.

Size scaling and its effect on letter detection

Abstract: Two ways of scaling letter size across eccentricity were investigated in a choice reaction time (CRT) task. Experiments 1 and 2 tested cortical magnification theory (M-scaling), while Experiment 3 used scaled sizes drawn from Anstis’s regression formula (A-scaling). Experiment 4 compared both scaling techniques, together with the effect of exposure duration and the absolute size of the foveal letter. Results showed that scaling effectiveness improved when large rather than small foveal letters were used. A-scaling with a large foveal letter provided a good fit for the data at parafoveal locations, but underestimated the letter sizes needed at large eccentricities. M-scaling with a large foveal letter size produced CRTs that were independent of eccentricity. Exposure duration did not substantially affect performance.

Evaluation of visual acuity with Gen 3 night vision goggles

Abstract: Using laboratory simulations, visual performance was measured at luminance and night vision imaging system (NVIS) radiance levels typically encountered in the natural nocturnal environment. Comparisons were made between visual performance with unaided vision and that observed with subjects using image intensification. An Amplified Night Vision Imaging System (ANVIS6) binocular image intensifier was used. Light levels available in the experiments (using video display technology and filters) were matched to those of reflecting objects illuminated by representative night-sky conditions (e.g., full moon, starlight). Results show that as expected, the precipitous decline in foveal acuity experienced with decreasing mesopic luminance levels is effectively shifted to much lower light levels by use of an image intensification system. The benefits of intensification are most pronounced foveally, but still observable at 20 deg eccentricity. Binocularity provides a small improvement in visual acuity under both intensified and unintensified conditions.

Foveal machine vision for robots using agent based gaze control

Abstract: These SBIR data are furnished with SBIR rights under Contract No. NAS 9-19335 and subcontract E3439. For a period of not less than 4 years after acceptance of all items to be delivered under this contract, the Government agrees to use these data for Government purposes only, and they shall not be disclosed outside the Government (including disclosure for procurement purposes) during such period without permission of the Contractor, except that, subject to the foregoing use and disclosure prohibitions, such data may be disclosed for use by support Contractors. After the aforesaid period the Government has a royalty-free license to use, and to authorize others to use on its behalf, these data for Government purposes, but is relieved of all disclosure prohibitions and assumes no liability for unauthorized use of these data by third parties. This notice shall be affixed to any reproductions of these data, in whole or in part.

Morphological and functional effects of induced laser retinal fibrosis

Abstract: Human laser accident exposure cases may involve severe macula retinal injury resulting in long term visual acuity and spatial vision deficit. In order to investigate this problem, we have chosen to model the effects of such long term exposure in the monkey retina for parafoveal Q- switched exposure produced at two parafoveal exposure sites. Our results suggest significant loss of retinal function in and adjacent to the scar region. Recovery occurs in regions with less scar formation, the foveal region, although long term changes in foveal receptor mechanisms are apparent even after 1 year post-exposure, they do not correlate completely with recent human investigations of severe accidental exposure nor with brain enzyme analysis in our monkey model.

Multiscale filter bank approach to camera-movement control in active vision systems

Abstract: Active vision systems faced with the problem of searching for targets in natural scenes are finding space variant sensors increasingly important. A popular class of space variant sensors are those based on the structure of the primate retina: they have a small area near the optical axis of greatly increased resolution (the fovea) coupled with a gradual falloff in resolution as one moves towards the periphery. In such systems, a primary requirement is an efficient mechanism for targeting the optical axis to different points of interest in the visual world. In this paper, we describe a robust and efficient paradigm for achieving foveal targeting by making use of iconic scene descriptions comprised of the responses of a bank of steerable filters at multiple scales and orientations. The filter bank description is rotation and scale invariant, occlusion tolerant, and view-insensitive to a considerable extent. We describe procedures for robustly matching vectors of a previously foveated point to instances of the point in other possibly transformed images obtained after camera motion. In such situations, the multiscale structure of the filter bank lends itself naturally to an efficient targeting mechanism for the space variant sensor.

Formation of object representation for invariant image recognition using specific trajectories of viewing

Abstract: A model of the foveal system for Multiresolutional Attentional Representation and Recognition (MARR) of grey-level images has been developed. The system performs the following procedures: analysis of an image at several resolution levels; parallel information processing in central (basic) and context (peripheral) regions of an attention window; estimation of similarity of both object fragments at each fixation point and viewing trajectories (object scanpaths) at the stages of memorizing (learning) and recognition.

Foveal-view stereopsis using symmetric phase-only matched filtering

Abstract: This paper presents a new stereo matching method. The stereo disparity is estimated using a symmetric phase-onlymatched filter applied to fovea! views of binocular stereo images. The fovea! view at an image point is a simulation of thehuman retina image with a non-uniform spatial resolution, where the spatial resolution is the highest at the fovea! centreand decreases monotonically towards the periphery. Since spectral phase preserves the location of the image structure whileit ignores spatial intensity correlation, the symmetric phase-only matched filtering applied to nearly identical images yields avery sharp correlation peak, which makes the detection of the image shift reliable and easy. Determining stereo disparityusing the foveal view symmetric phase-only matched filtering is quite robust and accurate. The good performance of ourstereo matching algorithm has been demonstrated for determining the disparity of remote sensing stereo images. 1. INTRODUCTION Stereo image analysis is a useful technique to obtain 3-D structure of a scene from 2-D stereo images. The

Origin of the foveal granular pattern in entoptic viewing.

Abstract: PURPOSE To investigate the controversial origin of the foveal granular pattern at the center of the entoptic Purkinje vessel shadows. Both phenomena may be vividly elicited by oscillating a focused spot of light across the scleral surface of the eye in a circumferential direction. METHODS The site and pattern of oscillation of the light spot were varied and were correlated with the appearance of the foveal granular pattern. Movement of the granular pattern relative to a foveal afterimage was also observed. RESULTS Oscillation of the light in a meridional direction abolishes the granular pattern. Oscillating illumination through the central pupil can elicit Purkinje vessel shadows but not the characteristic foveal granular pattern. With transscleral illumination, the granular pattern oscillates with an "against" motion with respect to the motion of the Purkinje vessel shadows and with a "with" motion with respect to apparent motion of an afterimage serving as a fixed anatomic reference, and it is displaced from the center of the foveal avascular zone in the visual direction away from the source of illumination. CONCLUSIONS These observations strongly suggest that the foveal granular pattern is a random moire pattern produced by spatial aliasing as the striated light pattern cast by the parafoveal nerve fiber elements sweeps over the photoreceptors in the form of a faint, high-spatial-frequency, irregular grating. An anatomic section of the fovea reveals the necessary geometry for production of such striated patterns, and the Nyquist frequency for the foveal photoreceptor mosaic supports the spatial aliasing effect. Also, a grating moving over a stationary random dot background demonstrates the origin of the "against" motion that is characteristic of the foveal granular pattern.

The eye as a velocity transducer: an independent information channel?

Abstract: Aircraft instrumentation presentations are based on the recognition of static patterns. Evidence is produced to show that the visual system can respond to velocity input alone and that when it does so this constitutes an independent channel of information which does not conflict with foveal processing and that this response extends out to the limits of the periphery of vision. The experimental work described tests the ability of this aspect of vision to reduce clutter and obscuration in screen projected instrument displays. Experienced aircrew subjects are required to carry out a simulated low level lob-bomb attack followed by the rapid acquisition of an escape vector while simultaneously tracking the target presented in a space stabilized view. There are four experimental conditions, the tracking task being common to all four. Two conditions use the standard RAF fast jet head-up flight control display and two use a velocity based display which is presented in the annulus between 20 and 40 degrees visual angle. This display does not require foveal attention so the central area can be left clear. Each display is tested in two conditions. In one the tasks are presented side by side forcing subjects to switch gaze between the two. In the other the two are combined. With the peripheral display the tracking task occupies the clear central area but with the NATO version it has to share this with the flight information.

Foveal vision function before and after fluorescein angiography.

Abstract: PURPOSE Fluorescein angiography is routinely used in ophthalmologic practice with minimal changes in vision reported by the patient after the procedure. Recent animal work has suggested that fluorescein may be cytotoxic in the presence of light and may cause retinal damage. The authors examined whether any changes occur in foveal vision function after fluorescein angiography. METHODS A battery of tests of vision function--including visual acuity, contrast sensitivity, color vision, and two-color increment thresholds designed to isolate individual cone pathways--was administered before and 48 hours after fluorescein angiography to a group of 10 patients with good visual acuity. RESULTS Most of the patients showed significant abnormalities with the nonstandard tests; however, no significant changes in central vision function were found 48 hours after fluorescein angiography. CONCLUSION Even sensitive vision tests show no measurable effect of fluorescein angiography on foveal vision function in eyes with significant disease.

Simulating the foveal cone receptive field

Abstract: The foveal midget ganglion cell has a receptive field center fed by one cone. The surround might also be fed by the same center cone since a cone terminal laterally connects to neighboring cones through electrical coupling and horizontal cells. To explore the contributions of the cone lateral connections to the receptive field, we constructed a compartmental model of the primate foveal outer plexiform layer based on the known anatomy and physiology. The similarity between the computed cone receptive field and the measured midget cell receptive field suggest that much of the retina’s spatial filtering occurs at the very first synapse.

Depth perception using crossed-looking stereo vision system

Abstract: It has been well known that the human vision system is a multi-resolution and spatially shift- variant system. The size of the edge filters on each retina are small and roughly constant within the foveal area, and are increased linearly with eccentricity outside the fovea. This mechanism allows the human visual system to perceive detailed description about the target surface within the fovea vision area, and to obtain a global description about the scene in the peripheral vision area. This paper describes a stereo vision system which simulates this mechanism of human vision. The system uses a pair of crossed-looking cameras as sensors. The fixation point is used as the geometric center of the 3D space. With this perception geometry, the vision system perceives depth variation of the target surface, rather than the absolute distance from the target surface to the sensors. This property allows the stereo correspondence to be achieved through a fusion process, which is similar to the optical fusion of two diffraction patterns. The fusion process obtains disparity information of the entire image in one convolution operation. The volume of calculation, and therefore the processing time needs for depth perception, is largely reduced. The mechanism of spatially shift-variant processing is implemented by applying logarithm conformal mapping to the images. As a result, the sensitivity in depth perception decreases exponentially from the center to the peripheral area of the image. This allows the vision system to obtain depth information about the scene within a broad field of view.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three-dimensional reconstruction based on a foveal sensing technique

Abstract: This paper introduces a new biologically inspired technique that retrieves scene surface information. The human eye provides the inspiration for this technique. Human vision essentially comprises peripheral and foveal vision. Information processing under peripheral vision is very fast since fewer features are sensed. Peripheral vision provides guiding information for the subsequent foveal analysis. Foveal vision involves a high resolution examination of a particular region of the scene. The biologically inspired technique involves a pyramid hierarchy that provides the platform for three-dimensional reconstruction at different resolution levels. Three-dimensional reconstruction is based on a cue combination process that involves feature-based stereo, occlusion, and visible surface reconstruction. The technique enables fine resolution surface information to be obtained for a specified region of interest which is surrounded by coarse resolution surface information. Experimental results are presented to illustrate the performance of this technique.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A foveal vision based approach to ATR

Abstract: Unlike traditional automatic target recognition (ATR) approaches, the foveal vision based approach uses a foveated sensor to dynamically allocate visual resolution spatially and temporally to objects relevant to the task. It mimics human eye movements to find "attractive" regions quickly and accurately. A software demonstration system has been built based on the foveal vision approach and tested on a variety of sensor data including TV, infrared (IR), and laser radar (LADAR). Test results indicated that the foveal vision based approach not only supports a decrease of several orders of magnitude in the amount of data processing but also provides an increased ability to discriminate targets. >