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Showing papers on "Foveal published in 1999"


Journal ArticleDOI
TL;DR: Although the actions of tea-making are ‘automated’ and proceed with little conscious involvement, the eyes closely monitor every step of the process, suggesting that this type of unconscious attention must be a common phenomenon in everyday life.
Abstract: The aim of this study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform. We used a head-mounted eye-movement video camera, which provided a continuous view of the scene ahead, with a dot indicating foveal direction with an accuracy of about 1 deg. A second video camera recorded the subject's activities from across the room. The videos were linked and analysed frame by frame. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. The first object-related fixation typically led the first indication of manipulation by 0.56 s, and vision moved to the next object about 0.61 s before manipulation of the previous object was complete. Each object-related act that did not involve a waiting period lasted an average of 3.3 s and involved about 7 fixations. Roughly a third of all fixations on objects could be definitely identified with one of four monitoring functions: locating objects used later in the process, directing the hand or object in the hand to a new location, guiding the approach of one object to another (e.g. kettle and lid), and checking the state of some variable (e.g. water level). We conclude that although the actions of tea-making are 'automated' and proceed with little conscious involvement, the eyes closely monitor every step of the process. This type of unconscious attention must be a common phenomenon in everyday life.

997 citations


Journal ArticleDOI
TL;DR: Detailed analyses showed that the eye movement programming deadline hypothesis could not account for the finding that the parafoveal preview benefit is smaller with a low-frequency word in foveal vision, and results are more in line with parallel processing limited by the extent to which the parfoveal word processing on fixation n can be combined with the foveAL word processingon fixation n+1.
Abstract: We tested theories of eye movement control in reading by looking at parafoveal processing. According to attention-processing theories, attention shifts towards word n+1 only when processing of the fixated word n is finished, so that attended parafoveal processing does not start until the programming of the saccade programming to word n+1 is initiated (Henderson & Ferreira, 1990; Morrison, 1984), or even later when the processing of word n takes too long (Henderson & Ferreira, 1990). Parafoveal preview benefit should be constant whatever the foveal processing load (Morrison, 1984), or should decrease when processing word n outlasts an eye movement programming deadline (Henderson & Ferreira, 1990). By manipulating the frequency and length of the foveal word n and the visibility of the parafoveal word n+1, we replicated the finding that the parafoveal preview benefit is smaller with a low-frequency word in foveal vision. Detailed analyses, however, showed that the eye movement programming deadline hypothesis...

147 citations


Journal ArticleDOI
TL;DR: The results of the present experiment suggest that, besides the difficulty of the peripheral selection task, fixation duration is an important factor determining the selection of potential targets for eye movements.

143 citations


Journal ArticleDOI
TL;DR: In these two trichromatic primates, S‐cone distribution and the developmental mechanisms determining S‐ cone topography are markedly different from the time that S cones are first detected.
Abstract: Macaca monkey and humans have three cone types containing either long-wavelength (L), medium-wavelength (M), or short-wavelength (S)-specific opsin. The highest cone density is found in the fovea, which mediates high visual acuity. Most studies agree that the adult human fovea has a small S cone-free area, but data are conflicting concerning S-cone numbers in the adult Macaca monkey fovea, and little evidence exists for how either primate fovea develops its characteristic cone pattern. Single- and double-label in situ hybridization and immunocytochemistry have been used to determine the pattern of foveal S cones in both the fetal and adult Macaca and human. Both labels find a clear difference at all ages between monkey and human. Adult humans have a distinct but variable central zone about 100 microm wide that lacks S cones and is surrounded by a ring in which the S-cone density is 8%. This S cone-free zone is detectable at fetal week 15.5 (Fwk15.5), shortly after S opsin is expressed, and is similar to the adult by Fwk20.5. Adult monkey foveas have an overall S-cone foveal density of 10%, with several areas lacking a few S cones that are not coincident with the area of highest cone density. A surrounding zone at 200-microm eccentricity has an S-cone density averaging 25%, but, by 800 microm, this has decreased to 11%. Fetal day 77-135 monkeys all have a distribution and density of foveal S cones similar to adults, although the high-density ring is not obvious in fetal retinas. Estimates of the numbers of S cones missing in the fetal human fovea range from 234 to 328, whereas no more than 40 are missing in the fetal monkey. These results show that, in these two trichromatic primates, S-cone distribution and the developmental mechanisms determining S-cone topography are markedly different from the time that S cones are first detected.

118 citations


Journal ArticleDOI
TL;DR: Cell densities and retinal ganglion cell:cone ratio (RGC:C) from the foveal border to the peripheral retina (34 degrees eccentricity) are reported and models for neural circuitry involved in central and peripheral spatial vision can be discussed.

83 citations


Journal ArticleDOI
TL;DR: Results suggest that both FEF and IPS may constitute the main cortical regions subserving bilaterally the foveal fixation system in humans, supporting a role for the right frontal lobe in the allocation of the attentional mechanisms.
Abstract: Positron emission tomography (PET) was used to investigate the functional anatomy of the foveal fixation system in 10 subjects scanned under three different conditions: at rest (REST), during the fixation of a central point (FIX), and while fixating the same foveal target during the presentation of peripheral visual distracters (DIS) Compared with the REST condition, both FIX and DIS tasks activated a common set of cortical areas First, in addition to the involvement of the occipital visual cortex, both the frontal eye field (FEF) and the intraparietal sulcus (IPS) were bilaterally activated Right frontal activation was also found in the dorsolateral prefrontal cortex, the inferior part of the precentral gyrus, and the inferior frontal gyrus These results suggest that both FEF and IFS may constitute the main cortical regions subserving bilaterally the foveal fixation system in humans The remaining right frontal activations may be considered as part of the anterior attentional network, supporting a role for the right frontal lobe in the allocation of the attentional mechanisms Compared with the FD: condition, the DIS task also revealed the perceptual and cognitive processes related to the presence of peripheral visual distracters during foveal fixation In addition to a bilateral activation of the V5/MT motion-sensitive area, a right FEF-IPS network was activated which may correspond to the engagement of the visuospatial attention Finally, normalized regional cerebral blood flow (NrCBF) decreases were also observed during both DIS and FD:condition performance Such NrCBF decreases were centered in the superior and middle temporal gyri, the prefrontal cortex, and the precuneus and the posterior retrosplenial part of the cingulate gyrus (C) 1999 Wiley-Liss, Inc

75 citations


Journal ArticleDOI
TL;DR: Foveal fixation was monitored in normal subjects remotely and continuously by use of a noninvasive retinal scan and the detected signal was predominantly 88 Hz during central fixation and 44 Hz during paracentral fixation.
Abstract: Foveal fixation was monitored in normal subjects remotely and continuously by use of a noninvasive retinal scan. Polarized infrared light was imaged onto the retina and scanned in a 3° annulus at 44 Hz. Reflections were analyzed by differential polarization detection. In all 32 eyes studied, the detected signal was predominantly 88 Hz during central fixation (within ±1°) and 44 Hz during paracentral fixation. Phase shift at 44 Hz correlated with the direction of eye displacement. Potential applications of this technique include screening for eye disease, eye position monitoring during clinical procedures, and use of eye fixation to operate devices.

69 citations


Journal ArticleDOI
TL;DR: The proposed methodology is based on Bayesian statistical methods that allow to incorporate the previous knowledge about the eye fundus in the model, and is applied to diAerent cases of diabetic retinopathy and vein occlusions.

57 citations


Journal ArticleDOI
TL;DR: The results and modeling of the jitter experiments suggest that pattern identification is highly robust to positional jitter, and the increased number of features required in peripheral vision and strabismic amblyopia suggests that in these visual systems the stimulus is underrepresented at the stage of feature integration.

55 citations


Journal ArticleDOI
TL;DR: These simulations suggest that a pit is required for both the centripetal displacement of cone cells toward the center of the fovea, and for the elongated foveal cone morphology.
Abstract: In humans, an increasing density of foveal cone photoreceptors occurs slowly over several years after birth, and accounts for a region that subserves high visual acuity. Concurrently, inner retinal cells move centrifugally away from the foveal center. Such developmental rearrangements reflect complex cellular remodeling after the retinal neuronal cells have differentiated and have formed synapses. Explaining foveal morphogenesis is difficult, because differentiated neuronal cells seem incapable of moving actively. Presented here is a biomechanical explanation of how the above events occur. This hypothesis assumes that the cellular movements throughout the retinal layers occur passively as the eye grows and the retina is stretched. Retinal stretch was simulated using virtual engineering models that were analyzed with finite element analysis. A pit combined with retinal stretch causes the retinal layers to deform in a way that accounts for both the centrifugal and centripetal movement of various retinal cell types. Axially directed, tensile forces associated with stretching the retinal tissue surrounding the pit also accounts for the elongated morphology of foveal cone photoreceptors. These simulations suggest that a pit is required for both the centripetal displacement of cone cells toward the center of the fovea, and for the elongated foveal cone morphology. Since the primate fovea may have minimal impact on acuity, its primary role may be to initiate foveal morphogenesis in slowly developing eyes.

53 citations


Journal ArticleDOI
TL;DR: Commercial laser pointers, commonly used for teaching and entertainment purposes, may cause notable macular damage if abused, and this may manifest as foveal retinal pigment epithelial disturbance.

Patent
10 Sep 1999
TL;DR: In this paper, a multi-resolution rectilinear foveal image sensor chip using a novel access scheme to reduce the number of analog RAM cells needed is presented, where the pixels in the central fovea region have a smaller size than the pixels arranged in peripheral rings about the central region.
Abstract: A foveal image sensor integrated circuit comprising a plurality of CMOS active pixel sensors arranged both within and about a central fovea region of the chip. The pixels in the central fovea region have a smaller size than the pixels arranged in peripheral rings about the central region. A new photocharge normalization scheme and associated circuitry normalizes the output signals from the different size pixels in the array. The pixels are assembled into a multi-resolution rectilinear foveal image sensor chip using a novel access scheme to reduce the number of analog RAM cells needed. Localized spatial resolution declines monotonically with offset from the imager's optical axis, analogous to biological foveal vision.

Journal ArticleDOI
TL;DR: The pipefish possesses a deep, pit fovea which, although lacking the displacement of the inner retinal layers as described in other vertebrate foveae, is characterised by the exclusion of rods, a marked increase in the density of photoreceptors and a regular square mosaic of four double cones surrounding a central single cone.
Abstract: The foveal and non-foveal retinal regions of the pipefish, Corythoichthyes paxtoni (Syngnathidae, Teleostei) are examined at the level of the light and electron microscopes The pipefish possesses a deep, pit (convexiclivate) fovea which, although lacking the displacement of the inner retinal layers as described in other vertebrate foveae, is characterised by the exclusion of rods, a marked increase in the density of photoreceptors and a regular square mosaic of four double cones surrounding a central single cone In the perifoveal and peripheral retinal regions, the photoreceptor mosaic is disrupted by the insertion of large numbers of rods, which reduce spatial resolving power but may uniformly increase sensitivity for off-axis rays In addition to a temporal fovea subtending the frontal binocular field, there is also a central area centralis subtending the monocular visual field Based on morphological comparisons with other foveate teleosts, four foveal types are characterised and foveal function discussed with respect to the theoretical advantage of a regular square mosaic

Journal ArticleDOI
TL;DR: To examine the effect of reducing luminance contrast in human foveal vision, discrimination thresholds were measured in four tasks and also a numerical measure of two visual illusions were obtained by a nulling technique.

Journal ArticleDOI
01 Aug 1999-Brain
TL;DR: The results indicate that the lack of adequate pursuit eye movements is indeed deleterious for the visual analysis of moving objects.
Abstract: It is usually assumed that the raison d'etre for smooth pursuit eye movements is an advantage in the visual analysis of moving objects due to the stabilization of the retinal image on the fovea. Although such benefits resulting from foveal pursuit are plausible, there have been few attempts to demonstrate them rigorously. Moreover, it is unknown whether and to what extent pursuit deficits due to neurological disease impair vision. In this study, therefore, we measured psychophysical thresholds for two different discrimination tasks assessing the visual analysis of moving objects as a function of smooth pursuit performance. Results from a group of healthy subjects were compared with those obtained from patients exhibiting catch-up saccades ( n = 9) or saccadic intrusions in the form of square-wave jerks ( n = 2). In a first set of experiments we measured acuity thresholds for Landolt optotypes moving horizontally at velocities of up to 14°/s (dynamic visual acuity, DVA). In the control group ( n = 20), DVA thresholds were indistinguishable from thresholds observed under stationary fixation due to efficient pursuit eye movements allowing continuous foveal stabilization of the retinal Landolt image. In contrast, all patients with catch-up saccades showed pursuit gains that decreased with increasing velocity, paralleled by a dramatic rise in DVA thresholds. Patients with square-wave jerks in turn revealed sufficient pursuit velocity but impaired foveation due to the involuntary saccades that occurred at similar frequencies independent of target velocity. In these patients, thresholds were more or less independent of the Landolt velocity but significantly raised compared with controls. Similar results were obtained in a test determining the sensitivity for vertical position steps of a given pursuit target. In summary, our results indicate that the lack of adequate pursuit eye movements is indeed deleterious for the visual analysis of moving objects.

Journal ArticleDOI
TL;DR: The study of visual representation in the parietal cortex by recording whole-scalp neuromagnetic responses to luminance stimuli of varying eccentricities strengthens the previous suggestion that the medial parieto–occipital sulcus is the human homologue of the monkey V6 complex.
Abstract: We studied visual representation in the parietal cortex by recording whole-scalp neuromagnetic responses to luminance stimuli of varying eccentricities. The stimuli were semicircles (5.5 degrees in radius) presented at horizontal eccentricities from 0 degrees to 16 degrees, separately in the right and left hemifields. All stimuli evoked responses in the contralateral occipital and medial parietal areas. The waveforms and distributions of the occipital responses varied with stimulus side (left, right) and eccentricity, whereas the parietal responses were remarkably similar to all stimuli. The equivalent sources of the parietal signals clustered within 1 cm 3 in the medial parieto–occipital sulcus and did not differ significantly between the stimuli. The strength of the parietal activation remained practically constant with increasing stimulus eccentricity, suggesting that the visual areas in the parieto–occipital sulcus lack the enhanced foveal representation typical of most other visual areas. This result strengthens our previous suggestion that the medial parieto–occipital sulcus is the human homologue of the monkey V6 complex, characterized by, for example, lack of retinotopy and the absence of relative foveal magnification.

Journal ArticleDOI
TL;DR: Sentence context increases reading speed regardless of the position of the text on the retina, and reading rates in peripheral retina are not decreased because of an inability to use sentence context.
Abstract: Background: Sentence context increases reading speed relative to reading unrelated words, Previous studies of normal peripheral retina and in patients with central field loss (CFL) have come to different conclusions regarding the benefits of sentence context for reading in peripheral retina. Studies of normal peripheral vision presented the text to inferior visual field; it Is presumed that most of the patients fixated using retina lateral to their scotoma. The goal of the current study was to determine whether the location of the text on the retina interacts with the usefulness of sentence context, Methods: Normally sighted subjects read sentences and random lists of words presented at the fovea and at 5 degrees to the left of and 5 degrees inferior to fixation in visual field space. Texts were presented using rapid serial visual presentation (RSVP). Results: The ratio of reading rates for sentences to random words (context gain) was the same in the inferior field (2.7 +/- 0.20) and at the fovea (2.6 +/- 0.26); context gain was greater in the left field (7.2 +/- 1.22). Conclusions: Sentence context increases reading speed regardless of the position of the text on the retina. Reading rates in peripheral retina are not decreased because of an inability to use sentence context.

Journal Article
TL;DR: Changes in temporal tuning (both psychophysical and electroretinographic) were found only within visual field scotomas, whereas changes of the log sensitivity parameter were found also in the relatively preserved foveas of this group of patients with early stage RP.
Abstract: PURPOSE. The relation between early changes in the photopic flicker electroretinogram (ERG) and photopic psychophysical changes in retinitis pigmentosa (RP) is poorly understood. Here, abnormalities in foveal and extrafoveal temporal contrast sensitivity functions (TCSFs) were studied in a group of carefully selected patients with RP who had relatively preserved macular function. The psychophysical results were compared with changes in the timing of the multifocal ERG. METHODS. Subjects were patients with RP who had acuity $20/32 and no visual field defects within 6° from the fovea. Maxwellian-view and direct-view optical systems were used to obtain foveal and extrafoveal TCSFs under a range of test conditions, including high retinal illuminances that yielded temporal contrast sensitivity independent of mean retinal illuminance. TCSFs were described using log sensitivity and corner frequency parameters. RESULTS. Foveal TCSFs in these patients showed overall reductions in sensitivity but no frequencydependent defects. Also, no macular defects were found in the timing of the multifocal ERG. TCSFs from extrafoveal locations in moderate field defects, obtained at retinal illuminances that were sufficient to render flicker sensitivity independent of effective mean luminance, showed reductions in overall sensitivity as well as changes in temporal tuning. The multifocal ERGs from these extrafoveal locations showed signs of temporal slowing. CONCLUSIONS. Changes in temporal tuning (both psychophysical and electroretinographic) were found only within visual field scotomas, whereas changes of the log sensitivity parameter were found also in the relatively preserved foveas of this group of patients with early stage RP. (Invest Ophthalmol Vis Sci. 1999;40:2932‐2944)

Journal ArticleDOI
TL;DR: In the fovea, the phase configuration had no effect on detection threshold, suggesting a full-wave rectification operation mediating foveal spatial summation, and at 5 deg in the periphery, detection thresholds for the in-phase configuration were lower than those for the alternating-phase Configuration.
Abstract: We measured the effect of phase coherence on the detectability of a chain of Gabor patches. The stimuli were elongated patterns consisting of 1-8 vertical Gabor patches, aligned vertically and either in phase or 180 deg out of phase from their immediate neighbors. In the fovea, the phase configuration had no effect on detection threshold, suggesting a full-wave rectification operation mediating foveal spatial summation. At 5 deg in the periphery, detection thresholds for the in-phase configuration were lower than those for the alternating-phase configuration, to an extent compatible with a half-wave rectification operation mediating peripheral spatial summation.

Journal ArticleDOI
TL;DR: It was found that scene exploration was hampered especially when foveal masking occurred early during fixations, and fixation durations were shown to increase linearly as the mask delay decreased, which validates the fixation duration as a measure of perceptual processing speed.

Journal ArticleDOI
W. Burke1
TL;DR: Some distortions of image experienced when I view objects with my right eye which has a macular hole are described, suggesting that the perceptual changes are due to physiological changes in the visual cortex.

Journal ArticleDOI
TL;DR: The ability to discriminate perfect from imperfect mirror symmetry was examined at the fovea and at eccentricities out to 10 degrees in the nasal visual field and given sufficient size scaling, perfectly symmetric stimuli can be discriminated from degraded symmetric stimulus in extra-foveal vision.

Journal ArticleDOI
TL;DR: Turning off a fixation point prior to or coincident with the appearance of a visual target reduces the latency of saccades to that target, and saccadic reaction time was reduced in the Gap relative to 0-Gap condition irrespective of the type of fixation anchor.

Journal ArticleDOI
TL;DR: The notion that pursuit is not exclusively a foveal function is strengthened, as the initial eye acceleration during smooth pursuit initiation eliciting by an imaginary target decreased in comparison to the acceleration elicited by a real target.

Journal ArticleDOI
TL;DR: Although automated visual fields in amblyopic eyes typically appear normal, all four types of amblyopia are associated with a generalized depression of light sensitivity, which is proportionately greatest at the fovea and highly correlated with visual acuity loss.

Journal ArticleDOI
TL;DR: Foveal, vertical separations were consistently overestimated relative to horizontal separations, a result which is consistent with the well-documented horizontal-vertical illusion (HVI).
Abstract: The visual mechanism by which human observers determine the separation between objects has long been of interest. This study examines the extent to which separation in visual space can be misperceived in foveal and extrafoveal vision. Foveally, vertical separations were consistently overestimated relative to horizontal separations, a result which is consistent with the well-documented horizontal-vertical illusion (HVI). Extrafoveally, much larger misrepresentations of visual space were perceived. In addition, separations tangential to fixation were consistently perceived as being greater than separations in a radial direction. These marked misperceptions of visual space which occur in extrafoveal vision take the form of a radial/tangential anisotropy combined with an overestimation of vertical distance. The results have important implications for meridional anisotropies which have previously been documented in a number of visual performance tasks.

Journal ArticleDOI
TL;DR: In this paper, the authors measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30 degrees in the periphery to determine if peripheral resolution is sampling limited for this stimulus.

01 Jan 1999
TL;DR: In this paper, the authors measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30° in the periphery to determine if peripheral resolution is sampling limited for this stimulus.
Abstract: We measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30° in the periphery to determine if peripheral resolution is sampling limited for this stimulus. In the fovea, where acuity is optically limited, detection and resolution were the same. At 30°, however, detection was markedly better than resolution indicating that peripheral resolution is sampling limited for this stimulus. Detection acuity was higher when contrast was 90% rather than 40%, but resolution did not change with contrast. The vanishing optotype is a legitimate perimetric stimulus to measure retinal ganglion cell density provided the task is resolution and not detection. © 1999 Elsevier Science Ltd. All rights reserved.


Journal ArticleDOI
TL;DR: It is found that the strabismic amblyopes misperceived the orientation of the grating at spatial frequencies that are a factor of two to six lower than the sampling frequency of the foveal cones.