Showing papers on "Foveal published in 2010"

Learning to combine foveal glimpses with a third-order Boltzmann machine

Abstract: We describe a model based on a Boltzmann machine with third-order connections that can learn how to accumulate information about a shape over several fixations. The model uses a retina that only has enough high resolution pixels to cover a small area of the image, so it must decide on a sequence of fixations and it must combine the "glimpse" at each fixation with the location of the fixation before integrating the information with information from other glimpses of the same object. We evaluate this model on a synthetic dataset and two image classification datasets, showing that it can perform at least as well as a model trained on whole images.

The relationship between visual resolution and cone spacing in the human fovea

Abstract: Visual resolution decreases rapidly outside the foveal center. The anatomical and physiological basis for this reduction is unclear. We used simultaneous adaptive optics imaging and psychophysical testing to measure cone spacing and resolution across the fovea, and show resolution is limited by cone spacing only at the foveal center. Immediately outside the center, resolution is worse than cone spacing predicts and better matches the sampling limit of midget retinal ganglion cells.

Correlation between visual acuity and foveal microstructural changes in diabetic macular edema.

Abstract: Purpose:The purpose of this study was to investigate the correlation between best-corrected visual acuity and foveal microstructural changes of the external limiting membrane and the junction between the inner and outer segments of the photoreceptors in diabetic macular edema.Methods:The authors per

Intersubject Variability of Foveal Cone Photoreceptor Density in Relation to Eye Length

Abstract: PURPOSE. Adaptive optics scanning laser ophthalmoscopy (AOSLO) under optimized wavefront correction allows for routine imaging of foveal cone photoreceptors. The intersubject variability of foveal cone density was measured and its relation to eye length evaluated. METHODS. AOSLO was used to image 18 healthy eyes with axial lengths from 22.86 to 28.31 mm. Ocular biometry and an eye model were used to estimate the retinal magnification factor. Individual cones in the AOSLO images were labeled, and the locations were used to generate topographic maps representing the spatial distribution of density. Representative retinal (cones/mm 2 ) and angular (cones/deg 2 ) cone densities at specific eccentricities were calculated from these maps. RESULTS. The entire foveal cone mosaic was resolved in four eyes, whereas the cones within 0.03 mm eccentricity remained unresolved in most eyes. The preferred retinal locus deviated significantly (P 0.001) from the point of peak cone density for all except one individual. A significant decrease in retinal density (P 0.05) with increasing axial length was observed at 0.30 mm eccentricity but not closer. Longer, more myopic eyes generally had higher angular density near the foveal center than the shorter eyes, but by 1°, this difference was nullified by retinal expansion, and so angular densities across all eyes were similar. CONCLUSIONS. The AOSLO can resolve the smallest foveal cones in certain eyes. Although myopia causes retinal stretching in the fovea, its effect within the foveola is confounded by factors other than cone density that have high levels of intersubject variability. (Invest Ophthalmol Vis Sci. 2010;51:6858‐6867)

Semantic preview benefit in eye movements during reading: A parafoveal fast-priming study.

Abstract: Eye movements in reading are sensitive to foveal and parafoveal word features. Whereas the influence of orthographic or phonological parafoveal information on gaze control is undisputed, there has been no reliable evidence for early parafoveal extraction of semantic information in alphabetic script. Using a novel combination of the gaze-contingent fast-priming and boundary paradigms, we demonstrate semantic preview benefit when a semantically related parafoveal word was available during the initial 125 ms of a fixation on the pretarget word (Experiments 1 and 2). When the target location was made more salient, significant parafoveal semantic priming occurred only at 80 ms (Experiment 3). Finally, with short primes only (20, 40, 60 ms), effects were not significant but were numerically in the expected direction for 40 and 60 ms (Experiment 4). In all experiments, fixation durations on the target word increased with prime durations under all conditions. The evidence for extraction of semantic information from the parafoveal word favors an explanation in terms of parallel word processing in reading.

Active 3D scene segmentation and detection of unknown objects

Abstract: We present an active vision system for segmentation of visual scenes based on integration of several cues. The system serves as a visual front end for generation of object hypotheses for new, previously unseen objects in natural scenes. The system combines a set of foveal and peripheral cameras where, through a stereo based fixation process, object hypotheses are generated. In addition to considering the segmentation process in 3D, the main contribution of the paper is integration of different cues in a temporal framework and improvement of initial hypotheses over time.

Modeling Magnification and Anisotropy in the Primate Foveal Confluence

Abstract: A basic organizational principle of the primate visual system is that it maps the visual environment repeatedly and retinotopically onto cortex. Simple algebraic models can be used to describe the projection from visual space to cortical space not only for V1, but also for the complex of areas V1, V2 and V3. Typically a conformal (angle-preserving) projection ensuring local isotropy is regarded as ideal and primate visual cortex is often regarded as an approximation of this ideal. However, empirical data show systematic deviations from this ideal that are especially relevant in the foveal projection. The aims of this study were to map the nature of anisotropy predicted by existing models, to investigate the optimization targets faced by different types of retino-cortical maps, and finally to propose a novel map that better models empirical data than other candidates. The retino-cortical map can be optimized towards a space-conserving homogenous representation or a quasi-conformal mapping. The latter would require a significantly enlarged representation of specific parts of the cortical maps. In particular it would require significant enlargement of parafoveal V2 and V3 which is not supported by empirical data. Further, the recently published principal layout of the foveal singularity cannot be explained by existing models. We suggest a new model that accurately describes foveal data, minimizing cortical surface area in the periphery but suggesting that local isotropy dominates the most foveal part at the expense of additional cortical surface. The foveal confluence is an important example of the detailed trade-offs between the compromises required for the mapping of environmental space to a complex of neighboring cortical areas. Our models demonstrate that the organization follows clear morphogenetic principles that are essential for our understanding of foveal vision in daily life.

Transitions between Central and Peripheral Vision Create Spatial/Temporal Distortions: A Hypothesis Concerning the Perceived Break of the Curveball

Abstract: Background The human visual system does not treat all parts of an image equally: the central segments of an image, which fall on the fovea, are processed with a higher resolution than the segments that fall in the visual periphery. Even though the differences between foveal and peripheral resolution are large, these differences do not usually disrupt our perception of seamless visual space. Here we examine a motion stimulus in which the shift from foveal to peripheral viewing creates a dramatic spatial/temporal discontinuity. Methodology/Principal Findings The stimulus consists of a descending disk (global motion) with an internal moving grating (local motion). When observers view the disk centrally, they perceive both global and local motion (i.e., observers see the disk's vertical descent and the internal spinning). When observers view the disk peripherally, the internal portion appears stationary, and the disk appears to descend at an angle. The angle of perceived descent increases as the observer views the stimulus from further in the periphery. We examine the first- and second-order information content in the display with the use of a three-dimensional Fourier analysis and show how our results can be used to describe perceived spatial/temporal discontinuities in real-world situations. Conclusions/Significance The perceived shift of the disk's direction in the periphery is consistent with a model in which foveal processing separates first- and second-order motion information while peripheral processing integrates first- and second-order motion information. We argue that the perceived distortion may influence real-world visual observations. To this end, we present a hypothesis and analysis of the perception of the curveball and rising fastball in the sport of baseball. The curveball is a physically measurable phenomenon: the imbalance of forces created by the ball's spin causes the ball to deviate from a straight line and to follow a smooth parabolic path. However, the curveball is also a perceptual puzzle because batters often report that the flight of the ball undergoes a dramatic and nearly discontinuous shift in position as the ball nears home plate. We suggest that the perception of a discontinuous shift in position results from differences between foveal and peripheral processing.

The what and why of perceptual asymmetries in the visual domain.

Abstract: Perceptual asymmetry is one of the most important characteristics of our visual functioning. We carefully reviewed the scientific literature in order to examine such asymmetries, separating them into two major categories: within-visual field asymmetries and between-visual field asymmetries. We explain these asymmetries in terms of perceptual aspects or tasks, the what of the asymmetries; and in terms of underlying mechanisms, the why of the asymmetries. Tthe within-visual field asymmetries are fundamental to orientation, motion direction, and spatial frequency processing. between-visual field asymmetries have been reported for a wide range of perceptual phenomena. foveal dominance over the periphery, in particular, has been prominent for visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds true for object or face recognition and reading performance. upper-lower visual field asymmetries in favour of the lower have been demonstrated for temporal and contrast sensitivities, visual acuity, spatial resolution, orientation, hue and motion processing. Iin contrast, the upper field advantages have been seen in visual search, apparent size, and object recognition tasks. left-right visual field asymmetries include the left field dominance in spatial (e.g., orientation) processing and the right field dominance in non-spatial (e.g., temporal) processing. left field is also better at low spatial frequency or global and coordinate spatial processing, whereas the right field is better at high spatial frequency or local and categorical spatial processing. All these asymmetries have inborn neural/physiological origins, the primary why, but can be also susceptible to visual experience, the critical why (promotes or blocks the asymmetries by altering neural functions).

Fastigial Oculomotor Region and the Control of Foveation During Fixation

Abstract: When primates maintain their gaze directed toward a visual target (visual fixation), their eyes display a combination of miniature fast and slow movements. An involvement of the cerebellum in visual fixation is indicated by the severe gaze instabilities observed in patients suffering from cerebellar lesions. Recent studies in non-human primates have identified a cerebellar structure, the fastigial oculomotor region (FOR), as a major cerebellar output nucleus with projections toward oculomotor regions in the brain stem. Unilateral inactivation of the FOR leads to dysmetric visually guided saccades and to an offset in gaze direction when the animal fixates a visual target. However, the nature of this fixation offset is not fully understood. In the present work, we analyze the inactivation-induced effects on fixation. A novel technique is adopted to describe the generation of saccades when a target is being fixated (fixational saccades). We show that the offset is the result of a combination of impaired saccade accuracy and an altered encoding of the foveal target position. Because they are independent, we propose that these two impairments are mediated by the different projections of the FOR to the brain stem, in particular to the deep superior colliculus and the pontomedullary reticular formation. Our study demonstrates that the oculomotor cerebellum, through the activity in the FOR, regulates both the amplitude of fixational saccades and the position toward which the eyes must be directed, suggesting an involvement in the acquisition of visual information from the fovea.

Incomplete Cortical Reorganization in Macular Degeneration

Abstract: Macular degeneration (MD) is an eye condition that affects the fovea and perifoveal retina, resulting in a loss of central vision. Age-related macular degeneration (AMD) is the leading cause of legal blindness and low vision in the United States and one of the most common causes of legal blindness and low vision globally.1 Juvenile macular degeneration (JMD), primarily Stargardt's disease, is a different type of MD that affects children or young adults. Central vision has the highest spatial resolution and is vital for many aspects of visual function such as reading. Early visual cortex contains a retinotopic map in which the central visual field is highly magnified with respect to the peripheral field. Approximately 50% of the primary visual cortex (V1) is devoted to the central 15° of the visual field.2,3 People with advanced AMD often develop bilateral, dense central scotomas subtending 10° to 15° (see Ref. 4 for review). In the absence of any retinotopic reorganization, a 15° bilateral central scotoma would result in no visual responses in the posterior half of V1. Recent fMRI studies have claimed reorganization of visual processing in persons with loss of foveal vision from MD; however, the extent and mechanisms of the reorganization remain unclear.5–10 Further complicating the picture, it has been shown that the activity seen in the lesion projection zone (LPZ) is task dependent,7 and at least some aspects of the cortical system plasticity decrease with aging.11 In this article, reorganization of visual cortex refers to the pattern of cortical responses measured with fMRI in patients with macular degeneration that differs from the expected loss of response in the cortical projection from the retinal scotoma. We consider such changed cortical activity as evidence for functional reorganization, without necessarily implying anatomic changes in cortical structure. For instance, the changed activation patterns observable with fMRI might be due to modification of synaptic connection strength or unmasking of existing signals when bottom-up input is no longer present.12 Our experiments were designed to address three unresolved issues related to cortical reorganization in MD. First, patients with macular degeneration usually adopt a spared location in nonfoveal retina for fixation, called the preferred retinal locus (PRL).4,13 The PRL assumes the role of the former fovea as an oculomotor reference point and may adopt some of the fovea's functional characteristics. Evidence from Schumacher et al.9 supports the view that there is more extensive cortical representation of PRL compared with non-PRL locations, including extension of activation toward the LPZ. In contrast, Dilks et al.8 found similar activation for stimuli at the PRL and comparable non-PRL locations. The discrepant results might be due to differences in task design and methods of data analysis. In our study, we compared cortical responses when a small flickering checkerboard was presented either at the PRL or at another functioning retinal location with comparable eccentricity. Second is the influence on cortical reorganization of the age of onset and the etiology of MD. In previous studies, often only one type of MD was investigated. In our study, we were able to compare cortical reorganization in AMD and JMD subjects by testing groups of comparable size and similar visual function characteristics using the same protocols. Third, task demands and stimulus properties have varied across previous studies. Sometimes, the visual stimuli were meaningful objects5,6,8 and sometimes meaningless patterns.9,10 Sometimes, the subjects actively responded to the stimuli,5 and sometimes viewing was passive.10 Sometimes the stimuli were spatially localized5 and sometimes full field.7 We tested our subjects with separate tasks designed to compare cortical responses during passive and active viewing, similar to the Masuda et al.7 study of JMD subjects. A preview of our results is as follows: Cortical activation with a small stimulus at the PRL was more extensive than at a non-PRL location; full-field stimuli in both passive and active conditions left a silent zone in the posterior pole of the occipital cortex, implying a lack of complete reorganization; the extent of the silent zone was smaller in the active task than the passive task, implying an important role for feedback signals in functional reorganization in the visual system; evidence for functional reorganization was more robust in JMD than AMD subjects.

Modeling the foveal cone mosaic imaged with adaptive optics scanning laser ophthalmoscopy

Abstract: To better understand the limitations of high-resolution adaptive optics scanning laser ophthalmoscopy (AOSLO), we describe an imaging model that examines the smallest cone photoreceptors in the fovea of normal human subjects and analyze how different factors contribute to their resolution. The model includes basic optical factors such as wavelength and pupil size, and defines limits caused by source coherence which are specific to the AOSLO imaging modality as well as foveal cone structure. The details of the model, its implications for imaging, and potential techniques to circumvent the limitations are discussed in this paper.

A Functional and Statistical Bottom-Up Saliency Model to Reveal the Relative Contributions of Low-Level Visual Guiding Factors

Abstract: When looking at a scene, we frequently move our eyes to place consecutive interesting regions on the fovea, the retina centre. At each fixation, only this specific foveal region is analysed in detail by the visual system. The visual attention mechanisms control eye movements and depend on two types of factor: bottom-up and top-down factors. Bottom-up factors include different visual features such as colour, luminance, edges, and orientations. In this paper, we evaluate quantitatively the relative contribution of basic low-level features as candidate guiding factors to visual attention and hence to eye movements. We also study how these visual features can be combined in a bottom-up saliency model. Our work consists of three interactive parts: a functional saliency model, a statistical model and eye movement data recorded during free viewing of natural scenes. The functional saliency model, inspired by the primate visual system, decomposes a visual scene into different feature maps. The statistical model indicates which features best explain the recorded eye movements. We show an essential role of high frequency luminance and an important contribution of central fixation bias. The relative contribution of features, calculated by the statistical model, is then used to combine the different feature maps into a saliency map. Finally, the comparison between the saliency model and experimental data confirmed the influence of these contributions.

Ocular centration of visual axis and evaluation of retinal function

Abstract: A method and device to assess centration of a visual axis, evaluate retinal function, foveal function, and/or visual field.

Optical Coherence Tomography Imaging of the Fovea in Retinopathy of Prematurity

Abstract: Background and objective To report foveal optical coherence tomography (OCT) findings in patients with a history of retinopathy of prematurity (ROP). Patients and methods In a case-control study, OCT imaging of the fovea was performed on mostly adult patients with a history of ROP and no significant macular pathology. The same OCT imaging was performed on control subjects who were born full-term. Results Fourteen eyes of 12 patients with ROP were studied. Mean age was 39 years and mean gestational age at birth was 28 weeks. Of the 11 eyes with no cataract or pseudophakia, median best-corrected visual acuity was 20/40. Three eyes with cataracts had visual acuities of 20/50, 20/60, and 20/100. OCT imaging showed that eyes in the ROP group had a relative loss of the foveal depression, increased macular thickness, and continuation of inner retinal layers within the fovea. Conclusion OCT imaging demonstrated abnormal foveal architecture in patients with a history of ROP, but most of these patients maintained good visual acuity.

Spectral domain-optical coherence tomography study of retinas with a normal foveal contour and thickness after retinal detachment surgery.

Abstract: Purpose:The purpose was to study the disruption of the inner segment (IS) and outer segment (OS) junction associated with suboptimal visual outcome after successful retinal detachment surgery with an otherwise normal foveal contour and thickness.Materials and Methods:A comparative study of 2 groups,

Visual search in the (un)real world: how head-mounted displays affect eye movements, head movements and target detection

Abstract: Head-mounted displays (HMDs) that use a see-through display method allow for superimposing computer-generated images upon a real-world view. Such devices, however, normally restrict the user's field of view. Furthermore, low display resolution and display curvature are suspected to make foveal as well as peripheral vision more difficult and may thus affect visual processing. In order to evaluate this assumption, we compared performance and eye-movement patterns in a visual search paradigm under different viewing conditions: participants either wore an HMD, had their field of view restricted by blinders or could avail themselves of an unrestricted field of view (normal viewing). From the head and eye-movement recordings we calculated the contribution of eye rotation to lateral shifts of attention. Results show that wearing an HMD leads to less eye rotation and requires more head movements than under blinders conditions and during normal viewing.

Viewing verification systems

Abstract: A viewing verification system is disclosed that allows a user to view an image by providing a viewer for the image, determining the space bounded by the foveal-vision of the user, verifying whether substantially the entire meaningful portion of the image has been correlated to the space bounded by the foveal vision of the user.

Early Spatial Attentional Modulation of Inputs to the Fovea

Abstract: Attending to a specific spatial location modulates responsivity of neurons with receptive fields processing that part of the environment. A major outstanding question is whether attentional modulation operates differently for the foveal (central) representation of the visual field than it does for the periphery. Indeed, recent animal electrophysiological recordings suggest that attention differentially affects spatial integration for central and peripheral receptive fields in primary visual cortex. In human electroencephalographic recordings, spatial attention to peripheral locations robustly modulates activity in early visual regions, but it has been claimed that this mechanism does not operate in foveal vision. Here, however, we show clear early attentional modulation of foveal stimulation with the same timing and cortical sources as seen for peripheral stimuli, demonstrating that attentional gain control operates similarly across the entire field of view. These results imply that covertly attending away from the center of gaze, which is a common paradigm in behavioral and electrophysiological studies of attention, results in a precisely timed push-pull mechanism. While the amplitude of the initial response to stimulation at attended peripheral locations is significantly increased beginning at 80 ms, the amplitude of the response to foveal stimulation begins to be attenuated.