Showing papers on "Foveal published in 2013"
TL;DR: It is suggested that the advantages of having a pit in central retina are relatively few, and minor, but together work to enhance acuity.
195 citations
TL;DR: It is shown that prior to microsaccade onset, spatial perception is altered in a very specific manner: foveal stimuli are erroneously perceived as more eccentric, whereas peripheral stimuli are rendered more fveal.
141 citations
TL;DR: It is shown that high-acuity judgments are impaired when stimuli are presented just a few arcminutes away from the preferred retinal locus of fixation, and a reduced precision in oculomotor control may be responsible for the visual acuity impairments observed in various disorders.
129 citations
TL;DR: The presence of 2 distinct phenotypes of Stargardt disease (foveal sparing and foveal atrophy) suggests that there may be more than 1 disease mechanism in ABCA4 retinopathy.
97 citations
TL;DR: At an early stage of an ERM, only the photoreceptor structures are significantly associated with the BCVA, and the appearance of the COST line was most highly associated.
Abstract: Objective To determine the relationship between the morphology of the fovea and visual acuity in patients with an untreated idiopathic epiretinal membrane (ERM). Methods We examined 52 eyes of 45 patients diagnosed with an ERM. The morphology of the foveal area was determined by spectral-domain optical coherence tomography. The relationships between the best-corrected visual acuity (BCVA) and 8 optical coherence tomography features, central retinal thickness, cone outer segment tip (COST) line, photoreceptor inner/outer segment (IS/OS) junction line, foveal bulge of the IS/OS line, external limiting membrane, inner limiting membrane, foveal pit, and ERM over the foveal center, were evaluated. Results Multiple regression analysis showed that intact COST line, IS/OS junction line, and external limiting membrane independently and significantly contributed to the BCVA. The standardized partial regression coefficient β was 0.415 for the COST line, 0.287 for the IS/OS junction line, and 0.247 for the external limiting membrane. However, the other features, eg, foveal bulge, inner limiting membrane, foveal pit, and ERM, were not significantly associated with the BCVA. The central retinal thickness was significantly correlated with the BCVA (r 2 = 0.274; P Conclusions At an early stage of an ERM, only the photoreceptor structures are significantly associated with the BCVA, and the appearance of the COST line was most highly associated. Detailed examinations of the photoreceptor structures using optical coherence tomography may help find photoreceptor dysfunction in cases of idiopathic ERM.
96 citations
TL;DR: The results suggest that the patients' dual reading and non-orthographic recognition impairments have a common underlying mechanism and reflect the loss of high spatial frequency visual information normally coded in the left pFG.
Abstract: Recent visual neuroscience investigations suggest that ventral occipito-temporal cortex is retinotopically organized, with high acuity foveal input projecting primarily to the posterior fusiform gyrus (pFG), making this region crucial for coding high spatial frequency information. Because high spatial frequencies are critical for fine-grained visual discrimination, we hypothesized that damage to the left pFG should have an adverse effect not only on efficient reading, as observed in pure alexia, but also on the processing of complex non-orthographic visual stimuli. Consistent with this hypothesis, we obtained evidence that a large case series (n = 20) of patients with lesions centered on left pFG: 1) Exhibited reduced sensitivity to high spatial frequencies; 2) demonstrated prolonged response latencies both in reading (pure alexia) and object naming; and 3) were especially sensitive to visual complexity and similarity when discriminating between novel visual patterns. These results suggest that the patients' dual reading and non-orthographic recognition impairments have a common underlying mechanism and reflect the loss of high spatial frequency visual information normally coded in the left pFG.
80 citations
TL;DR: It is demonstrated that the oculomotor system can spontaneously and rapidly adopt a peripheral locus for fixation and can rereference saccades to this locus in normally sighted individuals whose central vision is blocked by an artificial scotoma.
79 citations
TL;DR: Direct, objective measures of cone structure may be more sensitive indicators of disease severity than VA or foveal sensitivity in eyes with inherited retinal degenerations.
Abstract: PURPOSE. To study the relationship between cone spacing and density and clinical measures of visual function near the fovea. METHODS. High-resolution images of the photoreceptor mosaic were obtained with adaptive optics scanning laser ophthalmoscopy from 26 patients with inherited retinal degenerations. Cone spacing measures were made close to or at the foveal center (mean [SD] eccentricity, 0.02 [0.03] degree; maximum eccentricity, 0.13 degree) and were converted to Z-scores, fraction of cones, and percentage-of-cones-below-average compared with normal values for each location (based on 37 age-similar visually normal eyes). Z-scores and percentage of cones below average were compared with best-corrected visual acuity (VA) and foveal sensitivity. RESULTS. Visual acuity was significantly correlated with cone spacing (Spearman rank correlation q ¼� 0.60, P ¼ 0.003) and was preserved (‡80 letters), despite cone density measures that were 52% below normal. Foveal sensitivity showed significant correlation with cone spacing (q ¼� 0.47, P ¼ 0.017) and remained normal (‡35 decibels), despite density measures that were approximately 52% to 62% below normal. CONCLUSIONS. Cone density was reduced by up to 62% below normal at or near the fovea in eyes with VA and sensitivity that remained within normal limits. Despite a significant correlation with foveal cone spacing, VA and sensitivity are insensitive indicators of the integrity of the foveal cone mosaic. Direct, objective measures of cone structure may be more sensitive indicators of disease severity than VA or foveal sensitivity in eyes with inherited retinal degenerations. (ClinicalTrials.gov number, NCT00254605.)
78 citations
TL;DR: It is found that unbiased retinotopic map estimates can be obtained in early visual areas, as long as the pRF fitting algorithm takes the scotoma into account and a randomized "multifocal" stimulus sequence is used.
Abstract: There is substantial interest in using functional magnetic resonance imaging (fMRI) retinotopic mapping techniques to examine reorganization of the occipital cortex after vision loss in humans and nonhuman primates. However, previous reports suggest that standard phase encoding and the more recent population Receptive Field (pRF) techniques give biased estimates of retinotopic maps near the boundaries of retinal or cortical scotomas. Here we examine the sources of this bias and show how it can be minimized with a simple modification of the pRF method. In normally sighted subjects, we measured fMRI responses to a stimulus simulating a foveal scotoma; we found that unbiased retinotopic map estimates can be obtained in early visual areas, as long as the pRF fitting algorithm takes the scotoma into account and a randomized “multifocal” stimulus sequence is used.
77 citations
TL;DR: Analyses carried out on a large corpus of eye movement data were used to comment on four contentious theoretical issues, and there is evidence that information about word class modulates processing over a span greater than a single word.
Abstract: Analyses carried out on a large corpus of eye movement data were used to comment on four contentious theoretical issues. The results provide no evidence that word frequency and word predictability have early interactive effects on inspection time. Contrary to some earlier studies, in these data there is little evidence that properties of a prior word generally spill over and influence current processing. In contrast, there is evidence that both the frequency and the predictability of a word in parafoveal vision influence foveal processing. In the case of predictability, the direction of the effect suggests that more predictable parafoveal words produce longer foveal fixations. Finally, there is evidence that information about word class modulates processing over a span greater than a single word. The results support the notion of distributed parallel processing.
73 citations
TL;DR: This review summarises retinal physiology and foveal visual dysfunction in PD and quantification of retinal thinning as reported in different studies and using different instruments, with some promising results suggesting the potential applicability of ST-Oct as a biomarker in PD.
TL;DR: The methodology was evaluated on 1200 fundus images from the publicly available MESSIDOR database, 660 of which present signs of diabetic retinopathy, and results outperform all the reviewed methodologies available in literature.
TL;DR: The authors showed that increasing the fixation probability on function words with a manipulation of the expected difficulty and frequency of questions reduces an age difference in skipping probability and helps to uncover significant parafoveal-on-foveal effects in this group of old adults.
Abstract: Task demands and individual differences have been linked reliably to word skipping during reading. Such differences in fixation probability may imply a selection effect for multivariate analyses of eye-movement corpora if selection effects correlate with word properties of skipped words. For example, with fewer fixations on short and highly frequent words the power to detect parafoveal-on-foveal effects is reduced. We demonstrate that increasing the fixation probability on function words with a manipulation of the expected difficulty and frequency of questions reduces an age difference in skipping probability (i.e., old adults become comparable to young adults) and helps to uncover significant parafoveal-on-foveal effects in this group of old adults. We discuss implications for the comparison of results of eye-movement research based on multivariate analysis of corpus data with those from display-contingent manipulations of target words.
TL;DR: In this paper, a three-dimensional topographic map of the healthy and Parkinson's foveal pit was created, where the difference becomes evident in an annular zone between 0.5 and 2 mm from the foveola and the optimal zone is from 0.75 to 1.5 mm.
Abstract: To quantify the thickness of the inner retinal layers in the foveal pit where the nerve fiber layer (NFL) is absent, and quantify changes in the ganglion cells and inner plexiform layer. Pixel-by-pixel volumetric measurements were obtained via Spectral-Domain optical coherence tomography (SD-OCT) from 50 eyes of Parkinson disease (PD) (n = 30) and 50 eyes of healthy control subjects (n = 27). Receiver operating characteristics (ROC) were used to classify individual subjects with respect to sensitivity and specificity calculations at each perifoveolar distance. Three-dimensional topographic maps of the healthy and PD foveal pit were created. The foveal pit is thinner and broader in PD. The difference becomes evident in an annular zone between 0.5 and 2 mm from the foveola and the optimal (ROC-defined) zone is from 0.75 to 1.5 mm. This zone is nearly devoid of NFL and partially overlaps the foveal avascular zone. About 78 % of PD eyes can be discriminated from HC eyes based on this zone. ROC applied to OCT pixel-by-pixel analysis helps to discriminate PD from HC retinae. Remodeling of the foveal architecture is significant because it may provide a visible and quantifiable signature of PD. The specific location of remodeling in the fovea raises a novel concept for exploring the mechanism of oxidative stress on retinal neurons in PD. OCT is a promising quantitative tool in PD research. However, larger scale studies are needed before the method can be applied to clinical follow-ups.
TL;DR: In this article, the feasibility of handheld ultra-high-resolution spectral-domain optical coherence tomography (SD-OCT) in young children with nystagmus was investigated.
TL;DR: The authors used a gaze-contingent moving window paradigm in a rapid automatized naming task and found that dyslexics extract less parafoveal information than control children.
17 Jun 2013
TL;DR: The debut demonstration of the blind spot in the visual field is comparably surprising and indicates the existence of the perceptual blind spot is owed to the specific architecture of the retina.
Abstract: It comes as a surprise to discover that the foveal area in which one has
high resolution and high acuity vision is minute; it encompasses a mere
2° of visual angle-roughly, the area of the thumbnail at arm's length.
The introspective guess concerning acuity in depth likewise errs on the
side of extravagance; the region of crisp, fused perception is, at arm's
length, only a few centimeters deep; closer in, the area of fused
perception is even narrower. The eyes make a small movement-a
saccade-about every 200-300 milliseconds, sampling the scene by
shifting continuously the location of the fovea. Presumably
interpolation across intervals of time to yield an integrated spatiotemporal representation is a major component of what brains do.
Interpolation in perception probably enables generation of an internal
representation of the world that is useful in the animal's struggle for
survival.
TL;DR: This work used the gaze-contingent boundary paradigm to manipulate the parafoveal information that subjects received before or while fixating a target word within a sentence, and presented a simple model framework that can account for these effects.
Abstract: Readers continuously receive parafoveal information about the upcoming word in addition to the foveal information about the currently fixated word. Previous research (Inhoff, Radach, Starr, & Greenberg, 2000) showed that the presence of a parafoveal word that was similar to the foveal word facilitated processing of the foveal word. We used the gaze-contingent boundary paradigm (Rayner, 1975) to manipulate the parafoveal information that subjects received before or while fixating a target word (e.g., news) within a sentence. Specifically, a reader's parafovea could contain a repetition of the target (news), a correct preview of the posttarget word (once), an unrelated word (warm), random letters (cxmr), a nonword neighbor of the target (niws), a semantically related word (tale), or a nonword neighbor of that word (tule). Target fixation times were significantly lower in the parafoveal repetition condition than in all other conditions, suggesting that foveal processing can be facilitated by parafoveal repetition. We present a simple model framework that can account for these effects.
TL;DR: The findings suggest that the involuntary eye movements produced during attempted fixation do not always prevent fading—in either the fovea or the periphery—and that microsaccades can restore perception, when fading does occur, and that micro saccades are relevant to human perception of foveal stimuli.
Abstract: Stationary targets can fade perceptually during steady visual fixation, a phenomenon known as Troxler fading. Recent research found that microsaccades—small, involuntary saccades produced during attempted fixation—can restore the visibility of faded targets, both in the visual periphery and in the fovea. Because the targets tested previously extended beyond the foveal area, however, the ability of microsaccades to restore the visibility of foveally-contained targets remains unclear. Here, subjects reported the visibility of low-to-moderate contrast targets contained entirely within the fovea during attempted fixation. The targets did not change physically, but their visibility varied intermittently during fixation, in an illusory fashion (i.e., foveal Troxler fading). Microsaccade rates increased significantly before the targets became visible, and decreased significantly before the targets faded, for a variety of target contrasts. These results support previous research linking microsaccade onsets to the visual restoration of peripheral and foveal targets, and extend the former conclusions to minute targets contained entirely within the fovea. Our findings suggest that the involuntary eye movements produced during attempted fixation do not always prevent fading—in either the fovea or the periphery—and that microsaccades can restore perception, when fading does occur. Therefore, microsaccades are relevant to human perception of foveal stimuli.
TL;DR: The difference between foveal structure in amblyopic participants relative to structure in subjects with normal vision persisted even when variables such as age, ethnicity, axial length, and sex were taken into account.
TL;DR: A computational model with two compartments is implemented, approximating spatial aspects of processing by foveal and peripheral activations that change according to a small set of dynamical rules, which reproduced distributions of fixation durations from all experimental conditions by variation of few parameters that were affected by specific filtering conditions.
Abstract: Processing in our visual system is functionally segregated, with the fovea specialized in processing fine detail (high spatial frequencies) for object identification, and the periphery in processing coarse information (low frequencies) for spatial orienting and saccade target selection. Here we investigate the consequences of this functional segregation for the control of fixation durations during scene viewing. Using gaze-contingent displays, we applied high-pass or low-pass filters to either the central or the peripheral visual field and compared eye-movement patterns with an unfiltered control condition. In contrast with predictions from functional segregation, fixation durations were unaffected when the critical information for vision was strongly attenuated (foveal low-pass and peripheral high-pass filtering); fixation durations increased, however, when useful information was left mostly intact by the filter (foveal high-pass and peripheral low-pass filtering). These patterns of results are difficult to explain under the assumption that fixation durations are controlled by foveal processing difficulty. As an alternative explanation, we developed the hypothesis that the interaction of foveal and peripheral processing controls fixation duration. To investigate the viability of this explanation, we implemented a computational model with two compartments, approximating spatial aspects of processing by foveal and peripheral activations that change according to a small set of dynamical rules. The model reproduced distributions of fixation durations from all experimental conditions by variation of few parameters that were affected by specific filtering conditions.
TL;DR: Results indicate that contour interaction of foveal acuity targets occurs within a fixed angular zone of a few min arc, regardless of the size or contrast of the acuity target.
TL;DR: Overall, meadowlark vision does not fit the profile of vertebrates living in open habitats and may be used for detecting and tracking aerial stimuli (predators, conspecifics).
Abstract: Visual systems of open habitat vertebrates are predicted to have a band of acute vision across the retina (visual streak) and wide visual coverage to gather information along the horizon. We tested whether the eastern meadowlark (Sturnella magna) had this visual configuration given that it inhabits open grasslands. Contrary to our expectations, the meadowlark retina has a localized spot of acute vision (fovea) and relatively narrow visual coverage. The fovea projects above rather than towards the horizon with the head at rest, and individuals modify their body posture in tall grass to maintain a similar foveal projection. Meadowlarks have relatively large binocular fields and can see their bill tips, which may help with their probe-foraging technique. Overall, meadowlark vision does not fit the profile of vertebrates living in open habitats. The binocular field may control foraging while the fovea may be used for detecting and tracking aerial stimuli (predators, conspecifics).
TL;DR: Using transcranial magnetic stimulation, it is found that relatively late disruption of foveal retinotopic cortex impaired perceptual discrimination of objects in the periphery, consistent with the hypothesis that feedback to the fovea is crucial for extra-foveal perception and provide additional evidence for 'constructive' feedback in human vision.
TL;DR: Foveal hyperfluorescence is an early sign of achromatopsia that can aid in clinical diagnosis and may be useful in charting the natural course of the disease and in defining a therapeutic window for treatment.
TL;DR: A possible reconciliation for mixed results in sentence reading experiments is suggested via two ERP studies in which volunteers read sentences presented word by word at fixation, flanked bilaterally by the next word to its right and the previous words to its left.
Abstract: During natural reading, parafoveal information is processed to some degree. Although isolated words can be fully processed in the parafovea, not all sentence reading experiments have found evidence of semantic processing in the parafovea. We suggest a possible reconciliation for these mixed results via two ERP studies in which volunteers read sentences presented word by word at fixation, flanked bilaterally by the next word to its right and the previous word to its left. Half the words in the right parafovea of critical triads and in the fovea for the subsequent triad were semantically incongruent. The conditions under which parafoveal words elicit canonical visual N400 congruity effects suggest that they are processed in parallel with foveal words, but that the extraction of semantic information parafoveally is a function of contextual constraint and presentation rate, most likely under high contextual constraint and at slower rates.
TL;DR: This study studied the influence of task instructions on memory performance and fixation allocation in a real-world setting, in which participants were free to move around, to suggest that the manner in which information is extracted and retained varies with the instructions given to participants.
Abstract: The representations that are formed as we view real environments are still not well characterized. We studied the influence of task instructions on memory performance and fixation allocation in a real-world setting, in which participants were free to move around. Object memories were found to be task sensitive, as was the allocation of foveal vision. However, changes in the number of fixations directed at objects could not fully explain the changes in object memory performance that were found between task instruction conditions. Our data suggest that the manner in which information is extracted and retained from fixations varies with the instructions given to participants, with strategic prioritization of information retention from fixations made to task-relevant objects and strategic deprioritization of information retention from fixations directed to task-irrelevant objects.
TL;DR: It is found that the degree to which spatial contexts induced illusory orientation perception, namely, the magnitude of the tilt illusion, varied across healthy human adults in a trait-like fashion independent of stimulus size or contrast.
Abstract: Visual perception depends strongly on spatial context. A classic example is the tilt illusion where the perceived orientation of a central stimulus differs from its physical orientation when surrounded by tilted spatial contexts. Here we show that such contextual modulation of orientation perception exhibits trait-like interindividual diversity that correlates with interindividual differences in effective connectivity within human primary visual cortex. We found that the degree to which spatial contexts induced illusory orientation perception, namely, the magnitude of the tilt illusion, varied across healthy human adults in a trait-like fashion independent of stimulus size or contrast. Parallel to contextual modulation of orientation perception, the presence of spatial contexts affected effective connectivity within human primary visual cortex between peripheral and foveal representations that responded to spatial context and central stimulus, respectively. Importantly, this effective connectivity from peripheral to foveal primary visual cortex correlated with interindividual differences in the magnitude of the tilt illusion. Moreover, this correlation with illusion perception was observed for effective connectivity under tilted contextual stimulation but not for that under iso-oriented contextual stimulation, suggesting that it reflected the impact of orientation-dependent intra-areal connections. Our findings revealed an interindividual correlation between intra-areal connectivity within primary visual cortex and contextual influence on orientation perception. This neurophysiological-perceptual link provides empirical evidence for theoretical proposals that intra-areal connections in early visual cortices are involved in contextual modulation of visual perception.
Journal Article•
TL;DR: In this article, the authors investigated the consequences of functional segregation for the control of fixation durations during scene viewing using gaze-contingent displays, using high-pass or low-pass filters to either the central or the peripheral visual field and compared eye-movement patterns with an unfiltered control condition.
Abstract: Processing in our visual system is functionally segregated, with the fovea specialized in processing fine detail (high spatial frequencies) for object identification, and the periphery in processing coarse information (low frequencies) for spatial orienting and saccade target selection. Here we investigate the consequences of this functional segregation for the control of fixation durations during scene viewing. Using gaze-contingent displays, we applied high-pass or low-pass filters to either the central or the peripheral visual field and compared eye-movement patterns with an unfiltered control condition. In contrast with predictions from functional segregation, fixation durations were unaffected when the critical information for vision was strongly attenuated (foveal low-pass and peripheral high-pass filtering); fixation durations increased, however, when useful information was left mostly intact by the filter (foveal high-pass and peripheral low-pass filtering). These patterns of results are difficult to explain under the assumption that fixation durations are controlled by foveal processing difficulty. As an alternative explanation, we developed the hypothesis that the interaction of foveal and peripheral processing controls fixation duration. To investigate the viability of this explanation, we implemented a computational model with two compartments, approximating spatial aspects of processing by foveal and peripheral activations that change according to a small set of dynamical rules. The model reproduced distributions of fixation durations from all experimental conditions by variation of few parameters that were affected by specific filtering conditions.
TL;DR: Processing times did not differ between the two ERP conditions indicating that “cognitive readiness” during self-paced processing can be ruled out as an alternative explanation for differences in processing times between the ERP and the FRP conditions.
Abstract: The boundary paradigm, in combination with parafoveal masks, is the main technique for studying parafoveal preprocessing during reading. The rationale is that the masks (e.g., strings of X’s) prevent parafoveal preprocessing, but do not interfere with foveal processing. A recent study, however, raised doubts about the neutrality of parafoveal masks. In the present study, we explored this issue by means of fixation-related brain potentials (FRPs). Two FRP conditions presented rows of 5 words. The task of the participant was to judge whether the final word of a list was a “new” word, or whether it was a repeated (i.e., “old”) word. The critical manipulation was that the final word was X-masked during parafoveal preview in one condition, whereas another condition presented a valid preview of the word. In two additional event-related brain potential (ERP) conditions, the words were presented serially with no parafoveal preview available; in one of the conditions with a fixed timing, in the other word presentation was self-paced by the participants. Expectedly, the valid-preview FRP condition elicited the shortest processing times. Processing times did not differ between the two ERP conditions indicating that “cognitive readiness” during self-paced processing can be ruled out as an alternative explanation for differences in processing times between the ERP and the FRP conditions. The longest processing times were found in the X-mask FRP condition indicating that parafoveal X-masks interfere with foveal word recognition.