Showing papers on "Foveal published in 1996"
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TL;DR: The result supports the hypothesis that novices need foveal vision at first for lane keeping but, with increasing practice, learn to manage with more peripheral vision.
Abstract: Much research on driver attention, including evaluations of in-car equipment, at least implicitly assumes that attention is where the gaze is. Research on the dynamics of visual attention, however, suggests that drivers may use peripheral vision and that they learn its use over time, depending on the task demands and eccentricity. To investigate effects of task load and position on lane keeping, 11 novices and 16 experienced drivers were asked to drive along a straight road using only peripheral vision for lane keeping while doing another task foveally. The task varied in position and in mental load, with two difficulty levels in each of two different tasks. In the visual attention tasks, position had a clearly different effect on lane-keeping performance among novices and the experienced, as measured by the distance covered before crossing a lane boundary. Novices' performance deteriorated with the foveal task at near periphery at the speedometer level, whereas the performance of experienced drivers drop...
274 citations
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TL;DR: A preprogramming model of the control of fixation duration during visual search appears to be indirect in a simple search task and is supported by the results of an experiment carried out under two conditions.
Abstract: Toobtain insight into the control of fixation duration during visual search, we had 4 subjects perform simple search tasks in which we systematically varied the discriminability of the target. The experiment was carried out under two conditions. Under the first condition (blocked), the discriminability of the target was kept constant during a session. Under the second condition (mixed), the discriminability of the target varied per trial. Under the blocked condition, fixation duration increased with decreasing dis criminability. For 2 subjects, we found much shorter fixation durations in difficult trials with the mixed condition than in difficult trials with the blocked condition. Overall, the subjects fixated the target, continued to search, and then went back to the target in M6-55% of the correct trials. In these trials, the result of the analysis of the foveal target was not used for preparing the next saccade. The results sup port a preprogramming model of the control of fixation duration. In a simple search task, control of fix ation duration appears to be indirect. In daily life, the oculomotor system and the visual sys tem work in close cooperation. On the one hand, eye po sition determines the part of the environment that is ac cessible to visual perception. On the other hand, visually perceived information is essential for making goal-directed eye movements. Extensive visual search and reading are good examples of this cooperation. In both tasks, a se quence of eye movements is required to gather visual in formation from a display that exceeds the area covered by a single glance. During periods of fixation (intersac cadic intervals), at least three processes relating to vision may occur. These processes are samplings of the visual field, analysis of the foveal part of the visual field, and planning ofthe next eye movement (Viviani, 1990). These three processes take time. Analysis of the foveal target takes at least 100 to 150 msec (Eriksen & Eriksen, 1971) and eye-movement programming takes about 150 to 200 msec (Becker & Jurgens, 1979). These two processes are assumed to act in parallel, but not much is known about the amount ofoverlap (Viviani, 1990). In this visual search study, we were interested in the relationship be tween the analysis of the foveal target and the control of fixation duration. In other words: Is the result ofthe analy sis ofthe foveal target used in the planning ofthe next eye movement? Two models have been proposed. The first is the process-monitoring model (Rayner, 1978), in which the analysis of the foveal target is monitored by the mecha nism that controls the fixation duration. The planning of the saccade starts after the analysis of the foveal target has been completed. Analysis ofthe foveal target and plan
194 citations
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TL;DR: The results suggest that current models of eccentricity scaling of contrast sensitivity be re-evaluated to take account of the extensive aliasing zone of spatial frequencies which becomes functional in peripheral vision when the retinal image is well focused.
152 citations
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TL;DR: The topography and spatial density of cone photoreceptors and ganglion cells was similar to that reported for macaque retina, and the found no obvious difference between dichromatic and trichromatic marmoset retinas.
Abstract: We studied the anatomical substrates of spatial vision in a New World monkey, the marmoset Callithrix jacchus. This species has good visual acuity and a foveal specialization which is qualitatively similar to that of humans and other Old World primates. We measured the spatial density of retinal ganglion cells and photoreceptors, and calculated the relative numbers of these cell populations. We find that ganglion cells outnumber photoreceptors by between 2.4 :1 and 4.2 :1 in the fovea. The peak sampling density of ganglion cells is close to 550,000 cells/mm 2 . This value falls by almost 1000-fold between the fovea and peripheral retina ; a value which approaches recent estimates of the centroperipheral ganglion cell gradient for human and macaque monkey retina and primary visual cortex. The marmoset shows a sex-linked polymorphism of color vision : all male and some female marmosets are dichromats. Six of the retinas used in the present study came from animals whose chromatic phenotype was identified in electrophysiological experiments and confirmed by polymerase chain reaction (PCR) amplification of cone opsin encoding genes. One animal was a trichromat and the others were dichromats. Antibodies against short wavelength-sensitive (SWS) cones labeled close to 8% of all cones near the fovea of one dichromat animal, consistent with electrophysiological evidence that the SWS system is present in all marmosets. The topography and spatial density of cone photoreceptors and ganglion cells was similar to that reported for macaque retina, and we found no obvious difference between dichromatic and trichromatic marmoset retinas. These results reinforce the view that the main determinate of primate foveal topography is the requirement for maximal spatial resolution.
135 citations
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TL;DR: In this paper, it was shown that both the OVP effect and the right visual field advantage for word recognition are part of a larger extended OVP curve that has the shape of a Gaussian distribution with the mode shifted to the left of the center of the stimulus word.
Abstract: Recent developments on the optimal viewing position (OVP) effect suggest that it may be caused by the same factors that underlie the right visual field advantage in word recognition. This raises the question of the relationship between foveal and parafoveal word recognition. Three experiments are reported in which participants identified tachistoscopically presented words that were presented randomly in foveal and parafoveal vision. The results show that both the OVP effect and the right visual field advantage for word recognition are part of a larger extended OVP curve that has the shape of a Gaussian distribution with the mode shifted to the left of the center of the stimulus word. The shift of the distribution is a function of word length, but not of presentation duration; it is also slightly moderated by the information value of word beginning and word end. Tachistoscopic visual half field (VHF) studies are frequently used to assess the laterality of cognitive functions. They are based on the fact that stimuli presented in the left half of the visual field (LVF) are initially projected to the right cerebral hemisphere, and stimuli shown in the right half (RVF) are sent to the left cerebral hemisphere. This anatomical feature has been taken as support for the argument that LVF-RVF differences are an index of asymmetric functioning of the two cerebral hemispheres (for reviews see Bradshaw & Nettleton, 1983; Bryden, 1982; Hellige, 1993). Thus, the repeated finding that words are recognized more easily in the RVF than in the LVF is considered a consequence of left-hemisphere dominance for language processing. Further evidence for this position is obtained by finding that individuals with left hand preference show a reduced RVF superiority for word recognition relative to persons with right hand preference (Kim, 1994; but see Brysbaert, 1994c, for a more cautious account). The interpretation of LVF-RVF differences in word processing as an indication of laterality has not remained unchallenged, however. At least three alternative explanations of the RVF superiority have been proposed. The first considers the
127 citations
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TL;DR: In this paper, word recognition thresholds and rapid serial visual presentation (RSVP) reading rates for both unrelated words and meaningful sentences were examined across the visual field, with the fovea demonstrating a qualitative superiority over the periphery, irrespective of scale.
108 citations
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TL;DR: From the results, the magnitude and extent of spatial interference across the visual field can be described quantitatively and serve as an example of how observed variations in peripheral threshold gradients might be achieved as a combination of underlying factors with different E2 values.
67 citations
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TL;DR: Northern analysis of specific fovea ESTs defined in this study suggests that there are significant quantitative differences in gene expression that distinguish the foveA from the rest of the retina.
56 citations
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TL;DR: In this article, subjects were required to detect the presence of a small region of disparate texture embedded in a larger background at a range of eccentricities, and the results showed that detection performance always peaked several degrees from fixation.
Abstract: In 3 experiments, subjects were required to detect the presence of a small region of disparate texture embedded in a larger background at a range of eccentricities. Detection performance always peaked several degrees from fixation. Experiment 1 showed that the location of the peak was not retinally specific; scaling the display changed the location of the performance peak. Experiment 2 showed that poor foveal performance could not be explained by cross-frequency interference; filtering out high spatial frequencies did not lead to improved foveal performance. Experiment 3 showed that the effect is not unique to textures comprising left and right oblique line segments. A parsimonious account of these data is that, at the fovea, there is a mismatch between the scale of the texture and the scale of the mechanisms responsible for encoding texture differences. This mismatch diminishes as the textures are moved further into the periphery. Language: en
53 citations
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TL;DR: It is shown that a physically stationary target presented during smooth tracking is perceived to have considerably less smear than a target that moves comparably across the retina, but when the eye is stationary, which implies that extraretinal signals for pursuit eye movements also contribute to the alleviation of perceived smear for non-tracked, background targets.
52 citations
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TL;DR: It is found that the internal representations of direct and eccentric viewing are intrinsically incommensurable, in the sense that extrafoveal pattern representations are characterized by a lower perceptual dimension in feature space relative to the corresponding physical input signals, whereas foveal representations are not.
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TL;DR: The modularity of the system and its potential as a testbed for active vision is demonstrated by incorporating two different attentional mechanisms and quantitatively evaluating their performance on artificial and natural images.
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TL;DR: The authors studied the variation of contrast sensitivity across the visual field during development in infant monkeys in order to investigate the behavioral consequences of this immaturity and found that the sensitivity of the infant foveal region is similar to that of the near periphery.
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01 Jan 1996
TL;DR: It is demonstrated that reinforcement learning (RL) significantly improves the performance of foveal visual attention, and of the overall vision system, for the task of model based target recognition.
Abstract: Foveal vision features imagers with graded acuity coupled with context sensitive sensor gaze control, analogous to that prevalent throughout vertebrate vision. Foveal vision operates more efficiently than uniform acuity vision because resolution is treated as a dynamically allocatable resource, but requires a more refined visual attention mechanism. We demonstrate that reinforcement learning (RL) significantly improves the performance of foveal visual attention, and of the overall vision system, for the task of model based target recognition. A simulated foveal vision system is shown to classify targets with fewer fixations by learning strategies for the acquisition of visual information relevant to the task, and learning how to generalize these strategies in ambiguous and unexpected scenario conditions.
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TL;DR: It is shown that simple considerations about the spatiotemporal filtering processed by the retinal neural network can account for colour processing at the level of early vision and it is established that the Red, Green, Blue signal can be considered as a low-pass luminance signal plus a colour-modulated signal.
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TL;DR: The results suggest that spatial selection in spatial cuing tasks operates on a representation that does not include depth information.
Abstract: This experiment explored whether attentional selection observed in a spatial cuing task is based on a representation that includes depth information or not. Targets were presented inside placeholders appearing at the samex,y location on a stereoscopic display, but on different depth planes, or at differentx,y locations on the same depth plane. A peripheral precue produced significant cuing effects in the latter but not in the former condition. In a control experiment, significant cuing effects were found for targets appearing at differentx,y coordinates within the fovea, confirming that the lack of cuing effects in the depth condition was not due to foveal presentation. Together, the results suggest that spatial selection in spatial cuing tasks operates on a representation that does not include depth information.
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TL;DR: After sequential bilateral ablation of the pursuit area in the frontal lobe three monkeys displayed degraded pursuit of a small foveal target but performed normally on identical measures of optokinetic pursuit.
Abstract: 1. Neural pathology which impairs foveal smooth pursuit eye movements typically also degrades optokinetic pursuit of large textures, suggesting that the two kinds of pursuit share a common circuit. This study reports an exception. After sequential bilateral ablation of the pursuit area in the frontal lobe three monkeys displayed degraded pursuit of a small foveal target but performed normally on identical measures of optokinetic pursuit. 2. A related experiment in one subject demonstrated a pursuit deficit when the foveal target moved relative to the background, but not when background and target moved together. The frontal pursuit area may specifically control pursuit of relative motion, and do so by receiving signals primarily from motion detectors in the macular part of the visual field.
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TL;DR: Some of the more important results from 30 years of research on foveal and peripheral acuity, visual search performance and the relationships between them are summarised in this paper.
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TL;DR: Perisaccadic visual localization was measured by presenting brief (250 microseconds), bright (6000 cd/m2), binocular, gaze-point (foveal) probe flashes in an otherwise dark field to normal human subjects instructed to point to them with an unseen hand, finding stable post-saccadic localization was not achieved until about 100-300 msec after completion of a saccade.
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16 Sep 1996
TL;DR: Reconfigurable geometries for image sensors based on a concentric cartesian multiresolution lattice modified by four configuration parameters allow one, without moving the image sensor, to examine any region of the field of view with the highest available resolution, as well as to select the acuity profile for the regions surrounding the fovea.
Abstract: This paper describes reconfigurable geometries for image sensors based on a concentric cartesian multiresolution lattice modified by four configuration parameters. They allow one, without moving the image sensor, to examine any region of the field of view with the highest available resolution, as well as to select the acuity profile for the regions surrounding the fovea. The efficient processing of the multiresolution images obtained requires discrete shifts of fovea and rings whose magnitudes are calculated. Real time foveal images have been preprocessed and examples are given.
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TL;DR: By combining the results of two different types of dissection, the authors found that in the neural retina, vitamin E displayed a minimum correlated anatomically with the site at which areolar (geographic) atrophy frequently occurs in retinal pigment epithelial cells in the human disease, age-related macular degeneration.
Abstract: Purpose. To map vitamin E as a function of distance from the foveal center in the primate retina and retinal pigment epithelium (RPE)-choroid. Methods. Eyecups from rhesus monkeys were dissected with circular trephines so that the innermost disc, centered on the fovea, was in the center of a series of concentric rings. Two different types of dissection were performed. For one type, the authors used circular trephines with diameters of 1, 4, 8, and 10 mm (1,4-D), whereas for the other type the diameters were 2, 5, 8, and sometimes 10 mm (2,5-D). When possible, the neural retina was separated from the RPE-choroid. Tissues were analyzed for vitamin E, retinyl palmitate, and protein. Results. Surface area, volume, and protein were used as indexes of the amount of tissue analyzed. Distributions of vitamin E in neural retina were dependent on the tissue metric used and type of dissection performed. However, regardless of the tissue metric used, the central 1-mm disc of the 1,4-D was, on average, higher in vitamin E content than was the central 2-mm disc of the 2,5-D. This was particularly true when volume was the tissue metric. From the average values of vitamin E in a series of concentric discs, a composite plot of the vitamin E concentration in the neural retina was generated that took into consideration both types of dissection. That plot displayed a local maximum in the fovea and then precipitously declined to a minimum in the region between 0.5 and 1.0 mm eccentricity (near the foveal crest) ; at greater eccentricities, the vitamin E concentration rose to a value similar to that in the fovea, i.e., the composite plot indicated that vitamin E has a V-shaped distribution in the central neural retina. Vitamin E distribution in the RPE-choroid, with surface area as the tissue metric, also was measured. For this tissue, the foveal region displayed a local maximum. Conclusions. By combining the results of two different types of dissection, the authors found that in the neural retina, vitamin E displayed a minimum near the foveal crest. This minimum correlated anatomically with the site at which areolar (geographic) atrophy frequently occurs in retinal pigment epithelial cells in the human disease, age-related macular degeneration.
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TL;DR: Foveal synapses are present before many photoreceptor-specific proteins such as opsins can be detected, suggesting that some phenotypic information from the inner retina could influence the direction ofPhotoreceptor development.
Abstract: New and existing data are presented regarding synaptic development in primate retina with the aims to identify the sequence in which individual cell types form synapses in the inner plexiform (IPL) and outer plexiform (OPL) layers; to compare synaptic development sequences in cone-dominated fovea and rod-dominated peripheral retina; to compare synaptic formation with other aspects of cell differentiation; and to explore the possible roles for synapses in development The first synapses are formed in the foveal IPL by bipolar axons at fetal day 55, followed at fetal day 60 by cone ribbon synapses Amacrine synapses in the foveal IPL only appear in significant numbers at fetal day 88 In peripheral retina amacrine synapses are formed at fetal day 78, bipolar at 99, and photoreceptors at 105 Thus, the fovea forms the first synapses and the IPL matures before the OPL across the retina, but the fovea has a different bipolar/amacrine sequence than peripheral retina Foveal synapses are present before many photoreceptor-specific proteins such as opsins can be detected, suggesting that some phenotypic information from the inner retina could influence the direction of photoreceptor development The early synaptic development in the fovea may serve an important mechanical role during subsequent cell migrations that form the mature foveal pit and tightly packed cone foveola
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TL;DR: The precision of spatial localization is measured for a single Gaussian or Gabor patch briefly presented in the periphery when the standard deviation of the stimulus envelope is less than 1/5 the stimulus eccentricity, and localization thresholds are independent of SD and are approximately 1/50 of eccentricity.
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TL;DR: A physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina could support the hypothesis that, for moderate contrasts (≤ 40%), hyperacuity is mediated by the magnocellular (MC-) pathway.
Abstract: We developed a physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina. With the predictions of this model we could support the hypothesis that, for moderate contrasts (≤ 40%), hyperacuity is mediated by the magnocellular (MC-) pathway. Despite the lower sampling density in the MC pathway, as compared to the parvocellular (PC-) pathway, the information that is transferred by the MC ganglion cells is sufficient to achieve thresholds comparable to those of human subjects in psychophysical tasks. This is a result of the much higher signal-to-noise ratio of the MC pathway cell signals. The PC pathway cells do not transfer enough information for hyperacuity thresholds.
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18 Jun 1996TL;DR: It is shown that the fovea appears as a compromise between the tightness of the tracking specifications and computational constraints, and a control strategy can indeed be defined so that this objective can be met under appropriate operating conditions.
Abstract: Foveated vision and two-mode tracking, as inspired by the human oculomotor system, are often used in active vision system. The purpose of this paper is to provide answers to the following basic questions which arise from implementations. First, is it beneficial to have foveated vision and what is the optimal size of the foveal window? Second, is there a need for two control mechanisms (smooth pursuit and saccade) for improved performance and how can one efficiently switch between them? In order to do so, a setup is proposed in which these strategies can be evaluated in a systematic manner. It is shown that the fovea appears as a compromise between the tightness of the tracking specifications and computational constraints. Introducing a model for the later and postulating some a priori knowledge of the target behavior, it is possible to compute the size of the fovea in an optimal way. As a by-product, "smooth-pursuit" can be defined in a natural way, and the use of a two-mode tracking scheme is justified. The second mode, i.e. "saccadic control", aims at re-centering the target on the fovea so that the smooth pursuit controller can continue to operate. It is shown that a control strategy can indeed be defined so that this objective can be met under appropriate operating conditions.
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25 Aug 1996TL;DR: It is demonstrated that with intelligent, fovea driven priority assignment of image data, it can reduce the negative impact of information loss over ATM networks and demonstrate the advantages of priority dithered foveal prioritization over traditional methods.
Abstract: A fundamental drawback to increasingly popular ATM-based switching is the possibility of information loss with congestion. We demonstrate that with intelligent, fovea driven priority assignment of image data, we can reduce the negative impact of information loss over ATM networks. ATM standards allow a single bit to indicate high or low packet priority. To reduce the effect of this restriction we introduce the concept of priority dithering. Network multimedia multicast scenarios over heterogeneous link capacities where foveal prioritization would be of benefit are described. Network simulation results of this method are included which demonstrate the advantages of priority dithered foveal prioritization over traditional methods.
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TL;DR: Fast disconjugate adaptation is possible in microstrabismus demonstrating that foveal fusion is not necessary to achieve it.
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TL;DR: In the present study, vernier detection and discrimination thresholds were measured at the fovea and at two retinal eccentricities, two presentation durations, and three lengths with the targets either vertical or in a variable orientation.
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TL;DR: While the two channel model of foveal color vision is generalizable to the parafovea, simple models with a unitary red/green process are not, a small contribution from a luminance mechanism might improve the ability of theTwo channel model to account for threshold discrimination and additivity data.
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TL;DR: Testing of foveal cone photoreceptor function using scanning laser densitometry may determine the location of pathological changes in certain patients with unexplained visual loss.
Abstract: AIM: To assess foveal cone photoreceptor function in patients with unexplained loss of central visual acuity. METHODS: Testing of foveal cone photoreceptor function was performed using scanning laser densitometry, colour matching (Rayleigh equation), and pattern electroretinography (ERG). Standard tests included full field ERG, electrooculography, visual evoked potentials, static perimetry, and fluorescein angiography. RESULTS: Decreased foveal cone photopigment density and abnormal pattern ERG were found in three patients. Results of colour matching were not unequivocal. CONCLUSION: Testing of foveal cone photoreceptor function using scanning laser densitometry may determine the location of pathological changes in certain patients with unexplained visual loss.