Heading detection with simulated visual field defects
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AbstractWe examined how simulated visual field defects influence performance on a heading task to gain insight into the origins of the poorer performance seen in subjects with real visual field defects. We simulated tunnel vision and a central scotoma during ego-translation. Real-time gaze position was used to generate the appropriate optic flow pattern on the screen. The subjects’ task was to direct their gaze at the continuously changing direction of heading. Limiting the peripheral view, as in tunnel vision, or introducing a central scotoma, as in macular degeneration, affected both the accuracy with which subjects could estimate heading direction as well as the time it took them to do this. Under natural circumstances, optic flow patterns can change both smoothly, such as during pursuit of an object, and more abruptly, such as when making saccades. Therefore, we examined performance during both of these types of change. While accuracy was the same under these conditions, processing time was differentially affected. When limiting peripheral view, the influence of the field defect on processing time was larger when the heading changed abruptly than when it changed smoothly. The reverse was the case for simulated central scotomas. The influence of the defect on processing time was largest when the heading changed smoothly. Our results further point out that the calculations underlying heading detection can be performed very quickly, with processing time strongly dependent upon the speed of the simulated translation and the size of the stimulated visual area.Keywords:
Peripheral vision
Visual processing
Visual angle
The visual field records of 45 eyes of 45 patients were evaluated to determine whether examination of the peripheral field of vision in patients with glaucoma and field defects adds useful information about the progression of visual field damage. The central scotoma mass, foveal sensitivity, and the central and peripheral mass of the visual field were quantified from measurements on the Tübinger perimeter. Most of the information on visual field progression was contained in the scotoma mass. When both scotoma mass and foveal sensitivity were known, central or peripheral isoptres did not add statistically significant information on progression. Evaluation of scotomas and assessment of central isoptres or of foveal sensitivity made perimetry of the peripheral isoptres redundant. The appearance of fresh peripheral scotomas or the quantification of changes in peripheral scotomas was not examined in the current study, and they would of course be important when they occurred.
Central scotoma
Peripheral vision
Perimeter
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Purpose: Although foveal vision provides fine spatial information, parafoveal and peripheral vision are also known to be important for efficient reading behaviors. Here we systematically investigate how different types and sizes of visual field defects affect the way visual information is acquired via eye movements during reading. Methods: Using gaze-contingent displays, simulated scotomas were induced in 24 adults with normal or corrected-to-normal vision during a reading task. The study design included peripheral and central scotomas of varying sizes (aperture or scotoma size of 2°, 4°, 6°, 8°, and 10°) and no-scotoma conditions. Eye movements (e.g., forward/backward saccades, fixations, microsaccades) were plotted as a function of either the aperture or scotoma size, and their relationships were characterized by the best fitting model. Results: When the aperture size of the peripheral scotoma decreased below 6° (11 visible letters), there were significant decreases in saccade amplitude and velocity, as well as substantial increases in fixation duration and the number of fixations. Its dependency on the aperture size is best characterized by an exponential decay or growth function in log-linear coordinates. However, saccade amplitude and velocity, fixation duration, and forward/regressive saccades increased more or less linearly with increasing central scotoma size in log-linear coordinates. Conclusions: Our results showed differential impacts of central and peripheral vision loss on reading behaviors while lending further support for the importance of foveal and parafoveal vision in reading. These apparently deviated oculomotor behaviors may in part reflect optimal reading strategies to compensate for the loss of visual information.
Peripheral vision
Microsaccade
Central scotoma
Visual angle
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Background: Cortical remapping after peripheral or central visual deafferentation alters visual perception, but it is unclear whether such a phenomenon impinges on areas remote from a scotoma. To investigate this question, we studied variations of perceptual spatial distortion in the visual field of patients with homonymous paracentral scotoma. Methods: Two patients with right inferior homonymous paracentral scotoma were asked to describe their perception of a series of figures showing two isometric vertical lines symmetrically located on either side of a fixation point. In each figure, the fixation point varied by steps of 2° along a hypothetical vertical line equidistant between the test lines. The lines subtended 20° of visual angle, and the right line passed through the scotoma in both cases. Time for spatial distortion to manifest was recorded. Results: Both subjects reported that the right line was perceived as shorter than the left one. The line shortening varied in magnitude with the distance of the fixation point from the end of the line and was more pronounced when the distance increased. Moreover, perceptual line shortening appeared 5-10 seconds after steady fixation, but values of shortening varied during the following 10 seconds. In addition, the right line appeared uninterrupted or slightly blurred in the scotoma region. Conclusions: These observations reflect long-range cortical reorganization after brain damage. Larger receptive fields in the periphery of the visual map could explain why perceptual shortening is more pronounced with increased eccentricity.
Peripheral vision
Central scotoma
Filling-in
Visual angle
Fixation point
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Fixation durations are normally adapted to the difficulty of the foveal analysis task. We examine to what extent artificial central and peripheral visual field defects interfere with this adaptation process.Subjects performed a visual search task while their eye movements were registered. The latter were used to drive a real-time gaze-dependent display that was used to create artificial central and peripheral visual field defects. Recorded eye movements were used to determine saccadic amplitude, number of fixations, fixation durations, return saccades, and changes in saccade direction.For central defects, although fixation duration increased with the size of the absolute central scotoma, this increase was too small to keep recognition performance optimal, evident from an associated increase in the rate of return saccades. Providing a relatively small amount of visual information in the central scotoma did substantially reduce subjects' search times but not their fixation durations. Surprisingly, reducing the size of the tunnel also prolonged fixation duration for peripheral defects. This manipulation also decreased the rate of return saccades, suggesting that the fixations were prolonged beyond the duration required by the foveal task.Although we find that adaptation of fixation duration to task difficulty clearly occurs in the presence of artificial scotomas, we also find that such field defects may render the adaptation suboptimal for the task at hand. Thus, visual field defects may not only hinder vision by limiting what the subject sees of the environment but also by limiting the visual system's ability to program efficient eye movements. We speculate this is because of how visual field defects bias the balance between saccade generation and fixation stabilization.
Peripheral vision
Visual Search
Central scotoma
Microsaccade
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Contrary to our perceptual impression, visual processing is not homogeneous across the visual field. While foveal vision offers fine spatial detail with high precision, peripheral vision provides coarser yet crucial previewing that helps direct our attention and future saccades. Together, the two types of visual processing allow us to perform everyday visual tasks, such as reading or visual search. Thus, the question arises as to how the oculomotor system would adapt when one or the other processing is compromised. Here, using a gaze-contingent display, we simulated scotomas with various shapes, sizes, and locations to see whether/how different disruptions in the visual field would impact the pattern of eye movements during reading. Simulated scotoma was induced in 12 young normally-sighted adults and their eye movements were continuously recorded during reading. Our visual-field defects included no scotoma, central scotomas with diameters ranging from 2 – 10 degrees, peripheral scotomas (with the intact central visual-field ranging from 2 – 10 degrees in diameter), and hemifield scotomas that induce left, right, upper, or lower visual-field loss. Eye movements were analyzed in terms of forward and backward saccades, microsaccades, and fixations. As expected, under severe peripheral and central scotoma, reading speed decreased by 47% and 51%. Compared to no scotoma, severe peripheral scotoma induced increased fixation duration (17%), decreased saccade amplitude (37%), increased number of fixations (71%), and increased rate of microsaccades (150%). When blocking the right visual hemifield, saccade amplitude decreased by 26% and showed the largest increase in the number of forward saccades (186%) compared to other hemifield scotomas. Eye movements often represents active choices of sampling the environment required to accomplish visual tasks. Our findings suggest that, during reading under various disruptions of the integration of information in the visual field, the oculomotor system exhibits changes in strategies to optimize the information uptake.
Microsaccade
Peripheral vision
Visual angle
Central scotoma
Visual processing
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Patients suffering from pathologies leading to central vision loss, such as macular degeneration (MD), tend to spontaneously develop compensatory oculomotor strategies to overcome their lack of foveal vision. One of the most commonly used strategies is the adoption of a preferred retinal locus, or PRL, a peripheral area outside the region of vision loss (scotoma) which they use for tasks such as reading, recognizing faces and fixation. The mechanisms underlying PRL development and its spatial location are still not completely understood: studies in MD patients show that the PRL is not necessarily the peripheral region with the highest resolution, while studies using simulated central vision loss seem to suggest that pre-existing attentional capabilities might be relevant in selecting the PRL location. The process of PRL development most likely involves multiple components, some related to resolution, others to integration and attention. In this study we measured visual acuity, visual crowding and spatial attention in four peripheral locations (‘PRL candidate regions’) before training participants to perform a demanding visual discrimination task in conditions of simulated central vision loss. We examine the extent to which these measures of visual performance across peripheral locations individually and jointly predict which of the PRL candidate regions the participant would use during the simulated scotoma task. Additionally, we measured how visual performance predicts PRL locations in a transfer task that allowed participants to place the target anywhere within a ring around the simulated scotoma. Similar to previous findings in the clinical literature, our results show individual differences in patterns across participants that will be discussed.
Peripheral vision
Central scotoma
Visual Search
Crowding
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Purpose: Search in repeatedly presented visual search displays can benefit from implicit learning of the display items' spatial configuration. This effect has been named contextual cueing. Previously, contextual cueing was found to be reduced in observers with foveal or peripheral vision loss. Whereas this previous work used symbolic (T among L-shape) search displays with arbitrary configurations, here we investigated search in realistic scenes. Search in meaningful realistic scenes may benefit much more from explicit memory of the target location. We hypothesized that this explicit recall of the target location reduces visuospatial working memory demands on search considerably, thereby enabling efficient search guidance by learnt contextual cues in observers with vision loss. Methods: Two experiments with gaze-contingent scotoma simulation (Experiment 1: central scotoma, Experiment 2: peripheral scotoma) were carried out with normal-sighted observers (total n = 39/40). Observers had to find a cup in pseudorealistic indoor scenes and discriminate the direction of the cup's handle. Results: With both central and peripheral scotoma simulation, contextual cueing was observed in repeatedly presented configurations. Conclusions: The data show that patients suffering from central or peripheral vision loss may benefit more from memory-guided visual search than would be expected from scotoma simulation and patient studies using abstract symbolic search displays. Translational Relevance: In the assessment of visual search in patients with vision loss, semantically meaningless abstract search displays may gain insights into deficient search functions, but more realistic meaningful search scenes are needed to assess whether search deficits can be compensated.
Visual Search
Peripheral vision
Central scotoma
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Observers with central field loss typically fixate within a non-foveal region called the preferred retinal locus, which can include localized sensitivity losses, or micro-scotomas (Krishnan and Bedell, 2018). In this study, we simulated micro-scotomas at the fovea and in the peripheral retina to assess their impact on reading speed. Ten younger (<36 years old) and 8 older (>50 years old) naïve observers with normal vision monocularly read high and/or low contrast sentences, presented at or above the critical print size for young observers at the fovea and at 5 and 10 deg in the inferior visual field. Reading material comprised MNREAD sentences and sentences taken from novels that were presented in rapid serial visual presentation (RSVP) format. Randomly distributed 13 × 13 arc min blocks corresponding to 0–78% of the text area (corresponding to ∼0–17 micro-scotomas/deg2) were set to the background luminance to simulate micro-scotomas. A staircase algorithm estimated maximum reading speed from the threshold exposure duration for each combination of retinal eccentricity, contrast and micro-scotoma density in both age groups. Log10(RSVP reading speed) decreased significantly with simulated micro-scotoma density and eccentricity. Across conditions, reading speed was slower with low-compared to high-contrast text and was faster in younger than older normal observers. For a given eccentricity and contrast, a higher density of random element losses maximally affected older observers with normal vision. These outcomes may explain some of the reading deficits observed in older observers with central field loss.
Peripheral vision
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In current theories of scene perception, the construct of scene gist plays a critical role in guiding attention, facilitating object recognition, and influencing memory. Yet an important and frequently overlooked issue in research and theory on scene gist is the relative contributions of central versus peripheral vision in its acquisition. The current study investigated this issue, while testing how well the conclusions of Larson and Loschky (2009) generalize to more realistic viewing conditions. Larson and Loschky used 27° x 27° images (i.e., maximum retinal eccentricity = 13.5°--near peripheral vision), whereas the current study used a 180° (H) x 40° (V) screen (i.e., maximum eccentricity = 90°--the extreme periphery). We similarly used the Window/Scotoma paradigm, comparing perception of full scenes centered at fixation versus scenes viewed through a "Window" (circular region centered at fixation, with no imagery outside the circle), or a "Scotoma" (the inverse--a blank circular region centered at fixation, with normal imagery outside the circle). Window radii varied from 1-24°, Scotoma radii varied from 10-70°, with both compared to the full image. We flashed images for 33 ms and ensured central fixation using an eyetracker. Stimuli were 512 full color panoramic photographs in 8 basic level scene categories. The results confirmed the main findings of Larson and Loschky (2009) but more dramatically. First, peripheral vision was more important for scene gist than central vision. Removing all information ≤ 30° eccentricity was equal to viewing the entire image, but showing only information within the central 5° eccentricity was significantly worse. Second, although central vision was less important, it was far more efficient than peripheral vision in terms of scene gist extracted per image pixel viewed. Window and Scotoma regression slopes for non-asymptotic proportion accuracy as a function of proportion of image shown were 9.55 versus 1.05, respectively. Meeting abstract presented at VSS 2015
Peripheral vision
Eccentricity (behavior)
Visual angle
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We address two questions concerning eye guidance during visual search in naturalistic scenes. First, search has been described as a task in which visual salience is unimportant. Here, we revisit this question by using a letter-in-scene search task that minimizes any confounding effects that may arise from scene guidance. Second, we investigate how important the different regions of the visual field are for different subprocesses of search (target localization, verification). In Experiment 1, we manipulated both the salience (low vs. high) and the size (small vs. large) of the target letter (a "T"), and we implemented a foveal scotoma (radius: 1°) in half of the trials. In Experiment 2, observers searched for high- and low-salience targets either with full vision or with a central or peripheral scotoma (radius: 2.5°). In both experiments, we found main effects of salience with better performance for high-salience targets. In Experiment 1, search was faster for large than for small targets, and high-salience helped more for small targets. When searching with a foveal scotoma, performance was relatively unimpaired regardless of the target's salience and size. In Experiment 2, both visual-field manipulations led to search time costs, but the peripheral scotoma was much more detrimental than the central scotoma. Peripheral vision proved to be important for target localization, and central vision for target verification. Salience affected eye movement guidance to the target in both central and peripheral vision. Collectively, the results lend support for search models that incorporate salience for predicting eye-movement behavior.
Salience (neuroscience)
Visual Search
Naturalism
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Citations (18)