FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W1992242877> ?p ?o ?g. }

• W1992242877 endingPage "1669" @default.
• W1992242877 startingPage "1663" @default.
• W1992242877 abstract "•Fast (∼hours) emergence of eccentric fixation locus following occluded central vision•Rapid rereferencing of saccades to the eccentric fixation locus•Learned oculomotor plan is retained for weeks with normal (unoccluded) central vision The central region of the human retina, the fovea, provides high-acuity vision. The oculomotor system continually brings targets of interest into the fovea via ballistic eye movements (saccades). Thus, the fovea serves both as the locus for fixations and as the oculomotor reference for saccades. This highly automated process of foveation is functionally critical to vision and is observed from infancy [1Slater A.M. Findlay J.M. The measurement of fixation position in the newborn baby.J. Exp. Child Psychol. 1972; 14: 349-364Crossref PubMed Scopus (44) Google Scholar, 2Aslin R.N. Salapatek P. Saccadic localization of visual targets by the very young human infant.Percept. Psychophys. 1975; 17: 293-302Crossref Scopus (173) Google Scholar]. How would the oculomotor system adjust to a loss of foveal vision (central scotoma)? Clinical observations of patients with central vision loss [3Cummings R.W. Whittaker S.G. Watson G.R. Budd J.M. Scanning characters and reading with a central scotoma.Am. J. Optom. Physiol. Opt. 1985; 62: 833-843Crossref PubMed Scopus (128) Google Scholar, 4Schuchard R.A. Fletcher D.C. Preferred retinal locus: a review with applications in low vision rehabilitation.Ophthalmol. Clin. North Am. 1994; 7: 243-256Google Scholar] suggest a lengthy adjustment period [5Crossland M.D. Culham L.E. Kabanarou S.A. Rubin G.S. Preferred retinal locus development in patients with macular disease.Ophthalmology. 2005; 112: 1579-1585Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar], but the nature and dynamics of this adjustment remain unclear. Here, we demonstrate 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. Once developed, the fixation locus is retained over weeks in the absence of the simulated scotoma. Our data reveal a basic guiding principle of the oculomotor system that prefers control simplicity over optimality. We demonstrate the importance of a visible scotoma on the speed of the adjustment and suggest a possible rehabilitation regimen for patients with central vision loss. The central region of the human retina, the fovea, provides high-acuity vision. The oculomotor system continually brings targets of interest into the fovea via ballistic eye movements (saccades). Thus, the fovea serves both as the locus for fixations and as the oculomotor reference for saccades. This highly automated process of foveation is functionally critical to vision and is observed from infancy [1Slater A.M. Findlay J.M. The measurement of fixation position in the newborn baby.J. Exp. Child Psychol. 1972; 14: 349-364Crossref PubMed Scopus (44) Google Scholar, 2Aslin R.N. Salapatek P. Saccadic localization of visual targets by the very young human infant.Percept. Psychophys. 1975; 17: 293-302Crossref Scopus (173) Google Scholar]. How would the oculomotor system adjust to a loss of foveal vision (central scotoma)? Clinical observations of patients with central vision loss [3Cummings R.W. Whittaker S.G. Watson G.R. Budd J.M. Scanning characters and reading with a central scotoma.Am. J. Optom. Physiol. Opt. 1985; 62: 833-843Crossref PubMed Scopus (128) Google Scholar, 4Schuchard R.A. Fletcher D.C. Preferred retinal locus: a review with applications in low vision rehabilitation.Ophthalmol. Clin. North Am. 1994; 7: 243-256Google Scholar] suggest a lengthy adjustment period [5Crossland M.D. Culham L.E. Kabanarou S.A. Rubin G.S. Preferred retinal locus development in patients with macular disease.Ophthalmology. 2005; 112: 1579-1585Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar], but the nature and dynamics of this adjustment remain unclear. Here, we demonstrate 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. Once developed, the fixation locus is retained over weeks in the absence of the simulated scotoma. Our data reveal a basic guiding principle of the oculomotor system that prefers control simplicity over optimality. We demonstrate the importance of a visible scotoma on the speed of the adjustment and suggest a possible rehabilitation regimen for patients with central vision loss. We simulated a central scotoma in six normally sighted young adults using a gaze-contingent display while the subjects performed a demanding visual search task. The simulated scotoma appeared as a visible gray disc and blocked the screen content at and around the center of gaze. A separate group of six normally sighted subjects participated in a control experiment in which they performed the identical task without a simulated scotoma. The task alternated between two main components (Figure 1A): (1) object following, in which subjects maintained fixation on an object as it was randomly repositioned on the screen against either a uniform or cluttered background, and (2) visual search, in which subjects searched for the target object shown in object following. Subjects were instructed to perform the search task as quickly and accurately as possible during the visual search phase. During the initial period of the experiment, subjects were not told to use a particular eccentric location to guide their eye movements (free exploration). After having performed the experimental task with simulated central scotoma for approximately 3 hr spread over 2 to 3 days (free exploration, Table S1 available online), all six subjects in the experimental condition spontaneously followed the jumping target with eccentric fixation, keeping it out of the central scotoma (Figure S1). Of the six subjects, five (two shown in Figure 2A) spontaneously formed a single preferred retinal locus (PRL) [6Crossland M.D. Engel S.A. Legge G.E. The preferred retinal locus in macular disease: toward a consensus definition.Retina. 2011; 31: 2109-2114Crossref PubMed Scopus (78) Google Scholar] for fixation near the border of the scotoma, whereas the sixth subject developed two PRLs at roughly opposite sides of the scotoma (S5 in Figure 2A). For the five single-PRL subjects, the variance of the fixational PRL decreased rapidly during this free exploration period (Figure 2B). The variance (defined as bivariate contour ellipse area [BCEA]) measured at the end of this period was significantly smaller than that at the beginning (54% reduction, t(4) = 2.97, p < 0.05). Fixation stability continued to improve with practice in the presence of the simulated scotoma. More importantly, for the five subjects with a single PRL, their first saccade after each target movement placed the target at or near their fixational PRL (Figures 3A and S2) and away from the fovea, demonstrating a shift in oculomotor reference from the fovea to the PRL. Similar to that of the fixational PRL, the variance of the first saccade landing site (i.e., target location on the retina after the first saccade following each target movement) decreased rapidly (Figure 3B). The variance (BCEA) of the first saccade landing site during the last block of free exploration was reduced by 28% in comparison to that of the first block (t(4) = 5.02, p < 0.05). This noticeable change in the first saccade landing site after about 3 hr of exposure to the simulated central scotoma demonstrates a remarkable adaptability of the oculomotor system. The variance of the first saccade landing site was significantly larger than that of the fixational PRL, even for the last block of the free exploration (t(4) = 2.98, p < 0.05). Oculomotor rereferencing may require a longer time to fully develop. The slower time course of saccadic rereferencing has been observed in adult monkeys with bilateral foveal lesions [7Heinen S.J. Skavenski A.A. Adaptation of saccades and fixation to bilateral foveal lesions in adult monkey.Vision Res. 1992; 32: 365-373Crossref PubMed Scopus (40) Google Scholar]. Thus, it appears that the refinement of the fixational PRL preceded the refinement of saccade rereference. Despite the rapid emergence of both fixational PRL and saccade rereference with simulated central scotoma during the free exploration, we observed that the variances of both remained higher than those of the foveal viewing control subjects (fixational PRL: t(8) = 2.70, p < 0.05; saccade rereference: t(8) = 2.69, p < 0.05). We asked whether it would be possible to further reduce the variances with explicit training. We displayed a small white cross at the retinal location of each subject’s emerged fixational PRL (Figure 1B) and instructed subjects to follow the target with this gaze marker (explicit training). Otherwise, subjects performed the identical task as before. With 15 to 25 hr of such explicit training (Table S1), all six subjects were able to refine their oculomotor control such that the variances of the PRL, and the first saccade landing site became comparable to those of the control subjects (Figures 2B and 3B). Contrary to conventional wisdom [8Sansbury R.V. Skavenski A.A. Haddad G.M. Steinman R.M. Normal fixation of eccentric targets.J. Opt. Soc. Am. 1973; 63: 612-614Crossref PubMed Scopus (50) Google Scholar], we found that, using an effective training regimen, the oculomotor control with peripheral vision can be as precise and accurate as that with foveal vision. To investigate whether the learned fixational PRL and saccade rereference could be retained over an extended period of time without practice, subjects were recalled for a retention assessment (retention, Table S1) at least 1 week (up to 1 month) after completion of the explicit training. Subjects performed the same task (visual search and object following in clutter) as they did during the free exploration period of the experiment without any gaze marker. Furthermore, to assess the robustness of the adaptation, we also tested with an invisible scotoma (in separate sessions, Figure 1C) during the object following phase by matching the color and luminance of the scotoma to those of the uniform gray background (invisible scotoma, Table S1). All subjects retained the same PRLs, even in the invisible central scotoma condition (Figures 2A and 3A). However, the variances of both the fixational PRL and first saccade landing site for the retention and invisible scotoma conditions were larger in comparison to those measured at the end of the explicit training period (p < 0.05, both comparisons). The characteristics of eye movements covaried with the development of PRL. We examined the time course of changes in saccade latency, the number of saccades after each object movement, and fixation duration during the object-following component of the task. We found a significant decrease in both saccade latency (42% reduction, Figure 4A) and the number of saccades (60% reduction, Figure 4B). The saccade latency and number of saccades at the end of explicit training became comparable to those of controls (saccade latency: t(8) = 1.36, p = 0.21; number of saccades: t(8) = 1.30, p = 0.23). Although there were no significant changes in fixation duration, there was a slight upward trend during the course of the experiment (Figure 4C). The rate of change in both saccade latency and the number of saccades mirrored those of the refinement of the fixational PRL and the saccadic rereference: a rapid decrease during the free exploration followed by a persistent decrease during explicit training to levels that were comparable to controls. Performance during the visual search component of the task also improved over the course of PRL development (Figure 5). Search accuracy was high (∼89% ± 2.1% SD, relative to the chance level of 50%, Figure 5A) and remained unchanged throughout the experiment. The average search time showed a considerable decrease (42% reduction, Figure 5B) during the free exploration period followed by a gradual decrease during explicit training. A corresponding decrease was observed in the number of saccades that was required to find the target (60% reduction, Figure 5C). At the end of explicit training, subjects were performing the search task as fast as (t(8) = −0.94, p = 0.38) and with as few saccadic eye movements as (t(8) = 1.30, p = 0.23) the foveal viewing controls. We found that a stable PRL spontaneously emerges within hours of performing a visual task with a simulated central scotoma. Saccades were rereferenced to the PRL. The acquired PRL was retained for at least 1 week, during which subjects went about their daily lives with normal central vision. The same PRL was used even when the simulated scotoma was not visible. With explicit training using a gaze marker, the fixation stability at the PRLs and the precision of the targeting saccades became as good as those with normal foveal vision. These findings imply a flexible and adaptive oculomotor system. Akin to learning a motor skill such as riding a bicycle, the system can rapidly develop a new motor plan even with limited and sporadic exposure. Moreover, the motor plan improves with use and is retained without continuous practice. Our findings suggest that the oculomotor system prefers developing a motor plan that is simple over one that may be optimal with respect to saccade amplitude and accuracy. With intact central vision, the fovea has the highest acuity and, therefore, is a unique point in the visual field. The oculomotor system is presented with the simple goal of bringing the high-resolution fovea to the target of interest. Losing central vision eliminates this unique point. It is conceivable that there exists a unique “best” point in the spared peripheral retina for optimal form vision, and the location of this point may be partly determined by oculomotor factors, such as fixational drift, that contribute to spatiotemporal sensitivity [9Kuang X. Poletti M. Victor J.D. Rucci M. Temporal encoding of spatial information during active visual fixation.Curr. Biol. 2012; 22: 510-514Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar, 10Rucci M. Iovin R. Poletti M. Santini F. Miniature eye movements enhance fine spatial detail.Nature. 2007; 447: 851-854Crossref PubMed Scopus (238) Google Scholar]. However, the difference in functional acuity between the best peripheral point and the next best is likely to be small and certainly smaller than the difference between normal fovea and parafovea. Indeed, preliminary data from a recent study showed that local acuity did not predict the location of PRL in macular degeneration (MD) patients [11Chung S. Bernard J.-B. Does the location of the PRL correspond to the retinal location with the best acuity?.Invest. Ophthalmol. Vis. Sci. 2013; 54: 2183Crossref Scopus (13) Google Scholar]. Hence, given a target of interest, there are most likely multiple points (or contours) on the peripheral retina that are equally adequate. As such, the oculomotor system could choose a point that is closest to the target in order to minimize saccade amplitude and, thus, improve accuracy. Alternatively, it could choose a point on the peripheral retina that avoids occluding the informative parts of the target with the scotoma (i.e., for reading English text, placing the current word below the scotoma could be advantageous). Despite these possibilities for an on-demand variable fixation strategy that is perhaps more efficient in terms of accuracy or information gain, the oculomotor system opts for a strategy that is, from a control perspective, exceedingly simple: using a single point in the periphery as the preferred locus for fixation. This amounts to adding a constant vector offset to the existing oculomotor control system. Our observations are qualitatively different from what is generally known as saccadic adaptation [12Hopp J.J. Fuchs A.F. The characteristics and neuronal substrate of saccadic eye movement plasticity.Prog. Neurobiol. 2004; 72: 27-53Crossref PubMed Scopus (251) Google Scholar]. Saccadic adaptation is a continuous recalibration process that minimizes the perceived saccade error; it is thought to be necessary for adapting to an ever-changing oculomotor plan due to growth, aging, and diseases. Saccadic adaptation, although rapid in humans (in the order of a couple hundred saccades), is magnitude and direction specific [13Albano J.E. Adaptive changes in saccade amplitude: oculocentric or orbitocentric mapping?.Vision Res. 1996; 36: 2087-2098Crossref PubMed Scopus (69) Google Scholar, 14Abel L.A. Schmidt D. Dell’Osso L.F. Daroff R.B. Saccadic system plasticity in humans.Ann. Neurol. 1978; 4: 313-318Crossref PubMed Scopus (137) Google Scholar, 15Moidell B.G. Bedell H.E. Changes in oculocentric visual direction induced by the recalibration of saccades.Vision Res. 1988; 28: 329-336Crossref PubMed Scopus (41) Google Scholar]. Establishing a PRL with saccadic adaptation would require one to adapt to a large, if not infinite, number of magnitudes and directions. More importantly, saccadic adaption affects the current state of the oculomotor controller. It takes time to adapt and to recover from adaptation. This contradicts the observations that (1) our subjects’ normal foveation behavior was not affected by performing the task with their PRL and that (2) subjects retained their PRL between the daily experimental sessions and after weeks of not performing the task. Hence, the development of PRL that we observed is unlikely to be due to saccadic adaptation. Our results with simulated central scotoma echo some of the clinical findings. A majority of MD patients with bilateral central vision loss utilize a single PRL for viewing or fixating [16Von Noorden G.K. MacKensen G. Phenomenology of eccentric fixation.Am. J. Ophthalmol. 1962; 53: 642-660Abstract Full Text PDF PubMed Scopus (135) Google Scholar, 17Whittaker S.G. Budd J. Cummings R.W. Eccentric fixation with macular scotoma.Invest. Ophthalmol. Vis. Sci. 1988; 29: 268-278PubMed Google Scholar, 18Fletcher D.C. Schuchard R.A. Preferred retinal loci relationship to macular scotomas in a low-vision population.Ophthalmology. 1997; 104: 632-638Abstract Full Text PDF PubMed Scopus (267) Google Scholar], whereas some patients develop two or three task-dependent PRLs [19Timberlake G.T. Mainster M.A. Peli E. Augliere R.A. Essock E.A. Arend L.E. Reading with a macular scotoma. I. Retinal location of scotoma and fixation area.Invest. Ophthalmol. Vis. Sci. 1986; 27: 1137-1147PubMed Google Scholar]. A portion of these patients make saccades that are rereferenced to their fixational PRLs [20White J.M. Bedell H.E. The oculomotor reference in humans with bilateral macular disease.Invest. Ophthalmol. Vis. Sci. 1990; 31: 1149-1161PubMed Google Scholar]. Patients’ visual performance is closely correlated with the establishment of a stable PRL [17Whittaker S.G. Budd J. Cummings R.W. Eccentric fixation with macular scotoma.Invest. Ophthalmol. Vis. Sci. 1988; 29: 268-278PubMed Google Scholar, 21Falkenberg H.K. Rubin G.S. Bex P.J. Acuity, crowding, reading and fixation stability.Vision Res. 2007; 47: 126-135Crossref PubMed Scopus (60) Google Scholar, 22Tarita-Nistor L. González E.G. Markowitz S.N. Steinbach M.J. Plasticity of fixation in patients with central vision loss.Vis. Neurosci. 2009; 26: 487-494Crossref PubMed Scopus (92) Google Scholar], further suggesting that variable fixation is not an option used by the oculomotor system. However, unlike MD patients, who apparently take months to develop PRLs and rereference the oculomotor system to the PRLs [5Crossland M.D. Culham L.E. Kabanarou S.A. Rubin G.S. Preferred retinal locus development in patients with macular disease.Ophthalmology. 2005; 112: 1579-1585Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar], we found that PRL development was rapid with a (visible) simulated central scotoma. Our results are consistent with a report of a similarly rapid development in the case of pursuit eye movements with a sinusoidally moving target [23Pidcoe P.E. Wetzel P.A. Oculomotor tracking strategy in normal subjects with and without simulated scotoma.Invest. Ophthalmol. Vis. Sci. 2006; 47: 169-178Crossref PubMed Scopus (31) Google Scholar] and qualitative accounts of the fast emergence of visual-field preference for target identification [24Ness J.W. Zwick H. Molchany J.W. Preferred retinal location induced by macular occlusion in a target recognition task.Proc. SPIE. 1996; 2674: 131-135Crossref Google Scholar, 25Varsori M. Perez-Fornos A. Safran A.B. Whatham A.R. Development of a viewing strategy during adaptation to an artificial central scotoma.Vision Res. 2004; 44: 2691-2705Crossref PubMed Scopus (24) Google Scholar]. In contrast, although the natural development of PRLs may occur in some patients within weeks of vision loss, saccade rereferencing to PRLs in macular patients is a slow process that has a median time ranging from 1 to 6 months, depending on the age of MD onset [5Crossland M.D. Culham L.E. Kabanarou S.A. Rubin G.S. Preferred retinal locus development in patients with macular disease.Ophthalmology. 2005; 112: 1579-1585Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar]. The difference in the time courses between simulated and real scotoma is even more remarkable when considering the fact that the simulated scotoma in our experiment was imposed for only about 1 hr per day. It is quite plausible that the gradual deterioration of vision in MD patients interferes with the development of adaptive oculomotor behavior. Age may also be a contributing factor to the slow development. Patients have better fixation stability if their central vision loss occurred at an early age [20White J.M. Bedell H.E. The oculomotor reference in humans with bilateral macular disease.Invest. Ophthalmol. Vis. Sci. 1990; 31: 1149-1161PubMed Google Scholar]. In a recent study, we found that older adults were slower and used excessive eye movements during a visual search task with simulated central scotoma [26Kwon M. Ramachandra C. Satgunam P. Mel B.W. Peli E. Tjan B.S. Contour enhancement benefits older adults with simulated central field loss.Optom. Vis. Sci. 2012; 89: 1374-1384Crossref PubMed Scopus (27) Google Scholar], although the same study did not examine PRL development. Another likely cause for the slow development is that real scotomas are often invisible or with unclear boundary [27Schuchard R.A. Validity and interpretation of Amsler grid reports.Arch. Ophthalmol. 1993; 111: 776-780Crossref PubMed Scopus (149) Google Scholar, 28Schuchard R.A. Preferred retinal loci and macular scotoma characteristics in patients with age-related macular degeneration.Can. J. Ophthalmol. 2005; 40: 303-312Abstract Full Text PDF PubMed Scopus (94) Google Scholar, 29Fletcher D.C. Schuchard R.A. Renninger L.W. Patient awareness of binocular central scotoma in age-related macular degeneration.Optom. Vis. Sci. 2012; 89: 1395-1398Crossref PubMed Scopus (33) Google Scholar]. A visible scotoma can provide accurate positional feedback and, thus, may speed up PRL development. Given our results of a robust development of PRL and oculomotor rereferencing with a visible scotoma and the persistence of a PRL even when the scotoma was rendered invisible, it might be possible to speed up the process of PRL development in patients by superimposing a simulated scotoma on the real scotoma, thereby creating a visible border. The remarkable ability of the oculomotor system to rapidly adjust to an occluded central vision reveals a basic guiding principle of oculomotor control. Given the time pressure underlying saccadic eye movements, the system strives to maintain simplicity—a new motor plan is formed by adding a constant vector offset to the existing and well-practiced motor plan. Our finding opens up the rich possibility of exploring plasticity in the cortical and subcortical structures associated with oculomotor control and in the visual areas that are retinotopically associated with the newly formed PRL. We recruited 12 normally sighted subjects from the University of Southern California campus (ages ranging from 19 to 30 years, one female). Six subjects participated in the simulated scotoma experiments. The other six subjects participated in the control experiment. They all had normal or corrected-to-normal vision without known cognitive or neurological impairments. The mean acuity (assessed with a lighthouse distance acuity chart) was −0.1 logMar (Snellen 20/15). Subjects received monetary compensation for their participation. The experimental protocols were approved by the internal review board of the University of Southern California, and written informed consent was obtained from all subjects prior to the experiment. All stimuli were high-contrast 24 bit RGB color images of indoor scenes and objects. Images of 49 indoor scenes (1,024 × 768 pixels) were selected from an image database [30Luo G. Satgunam P. Peli E. Visual search performance of patients with vision impairment: effect of JPEG image enhancement.Ophthalmic Physiol. Opt. 2012; 32: 421-428Crossref PubMed Scopus (16) Google Scholar]. Images of 140 objects (average diagonal size of 2.4° with a range of 2° to 2.7°) were selected from a commercially available set of photographs of real objects at www.photos.com (now at www.thinkstockphotos.com). The stimuli were generated and controlled with MATLAB (version 7.9) and Psychophysics Toolbox extensions (Windows 7 OS) [31Brainard D.H. The psychophysics toolbox.Spat. Vis. 1997; 10: 433-436Crossref PubMed Scopus (13433) Google Scholar, 32Pelli D.G. The VideoToolbox software for visual psychophysics: transforming numbers into movies.Spat. Vis. 1997; 10: 437-442Crossref PubMed Scopus (8017) Google Scholar] running on a Dell PC. The display was a 19” CRT monitor (refresh rate, 85 Hz; resolution, 1,024 × 768). The stimuli were presented at a viewing distance of 57 cm. The displayed scenes subtended visual angles of 39° × 29°. Subjects’ eye movements were monitored with an infrared video-based eye tracker sampled at 2,000 Hz (EyeLink 1000 Tower Mount monocular eyetracker, SR Research) with a maximum spatial resolution of 0.02°. A nine-point calibration and/or validation sequence was performed at the beginning of every block, and drift correction was made at the beginning of every trial. Calibration and/or validation were repeated until the validation error was smaller than 1° on average. The average gaze error was 0.5°, ranging from 0.1° to 1°. A gaze-contingent visual display was used to simulate central visual field loss in normally sighted subjects. This paradigm, referred to as “artificial scotoma” [33Aguilar C. Castet E. Gaze-contingent simulation of retinopathy: some potential pitfalls and remedies.Vision Res. 2011; 51: 997-1012Crossref PubMed Scopus (48) Google Scholar], has been used in previous studies to investigate various issues related to central field loss [23Pidcoe P.E. Wetzel P.A. Oculomotor tracking strategy in normal subjects with and without simulated scotoma.Invest. Ophthalmol. Vis. Sci. 2006; 47: 169-178Crossref PubMed Scopus (31) Google Scholar, 34Fine E.M. Rubin G.S. Effects of cataract and scotoma on visual acuity: a simulation study.Optom. Vis. Sci. 1999; 76: 468-473Crossref PubMed Scopus (22) Google Scholar, 35Bernard J.B. Scherlen A.C. Castet E. Page mode reading with simulated scotomas: a modest effect of interline spacing on reading speed.Vision Res. 2007; 47: 3447-3459Crossref PubMed Scopus (37) Google Scholar]. The real-time gaze position was sent to the display computer through a high-speed Ethernet link. The continuous gaze information was used to draw a scotoma on the display screen at a refresh and update rate of 85 Hz. The size and shape of the scotoma were derived from the visual field measurement obtained from a patient with age-related MD [36Chung S.T.L. Improving reading speed for people with central vision loss through perceptual learning.Invest. Ophthalmol. Vis. Sci. 2011; 52: 1164-1170Crossref PubMed Scopus (81) Google Scholar]. The scotoma, as shown in Figure 1A, was a nearly circular disc, subtended about 10° of visual angle, and was rendered as a uniform gray patch (luminance 18 cd/m2) on the screen. We also ran an invisible scotoma condition with a slightly lighter gray patch, the luminance of which was matched to that of the gray background (22 cd/m2). The average delay between actual eye movement and screen update was estimated to be approximately 10 ms (range from 2 ms to 15 ms on the basis of the eye data to frame time latencies that we measured on the stimulus computer and on the manufacturer’s data on minimum eye data latency). The gaze position error (i.e., the difference between target position and computed gaze position) was estimated during the nine-point validation process. A chin-and-forehead rest was used throughout the experiment in order to minimize head movements and trial-to-trial variability in the estimate of gaze position. The emergence of an eccentric retinal locus with rereferenced saccades observed in the free exploration period of the experiment, in contrast to the normal foveating behavior observed in the control experiment, served as confirmation that the slight amount of spatiotemporal imprecision in the eye-tracking system was not sufficient to interfere with the effectiveness of the simulated central scotoma. Subjects performed a demanding visual task in uninterrupted blocks of 30 trials each. On average, subjects took 30 hr to complete the entire experiment (excluding breaks and calibration time). This was spread into several sessions spanning two months. Each block took approximately 25 min to complete. Subjects performed the task in a dimly lit room while they were seated in a comfortable position with chin and forehead supports. Each block started with the calibration and/or validation sequence described earlier (∼5 min) followed by drift correction. The trial started with an auditory beep immediately after drift correction. For each trial, subjects had to complete four task phases: object following, gaze centering, visual search, and a second object following (Figure 1A). During object following, subjects followed a target object as it was randomly repositioned four times against a gray background (Figure 1A, i). The center of the object was uniformly distributed within the central 31° × 22° region of the display. Each move was initiated only when the onscreen position of the subjects’ scotoma did not occlude the target object for at least 1.5 s. This was done to encourage eccentric fixation. Subjects were told to examine the target object as accurately as possible, given that it was the search target for the upcoming visual search phase. Otherwise, subjects did not receive any explicit instructions on how to use their gaze. During gaze centering, subjects centered their gaze in the middle of the screen so that their scotoma was placed inside a black rectangular box for 1.5 s (Figure 1A, ii). This was performed right before the onset of visual search in order to minimize any positional bias. During visual search, subjects searched for the target object (the same object as in phase 1) amidst a cluttered background with an array of nontarget distracters (Figure 1A, iii). Both the target and nontarget distracters were superimposed on the scene rather than being part of the scene. This was done in order to minimize any contextual effects on search performance. Subjects were given an unlimited amount of time to perform the search, after which they indicated the presence or absence of the search target by a key press (“p” for presence and “a” for absence). The probability of the target being present was 0.5. Subjects were instructed to perform the search task as quickly and as accurately as possible. An auditory feedback was provided for a correct response. A second object following phase was conducted similarly to the first object following phase, except that the target was a randomly drawn object that appeared on a cluttered background (Figure 1A, iv). Oculomotor performance (fixational PRL and saccadic rereference) was assessed during the two object following phases (phases 1 and 4) under the assumption that the target object was the intended target of gaze. Subjects performed at least two or three blocks per day and completed 9 to 30 blocks of the task during free exploration. Subjects then received explicit training (42 to 72 blocks) for refining the emerged PRL. This was accomplished by having the subjects perform the same task as in the free exploration period except that their PRLs were marked with a small 0.7° white cross (Figure 1B), and subjects were instructed to use the cross as the point of gaze. This effectively encouraged the subjects to rely on the emerged PRLs for the task and possibly improve fixation accuracy with the peripheral locus. For normal foveal vision, a significant decrease in the accuracy of eye positions has been reported in the absence of a fixation marker [37Cherici C. Kuang X. Poletti M. Rucci M. Precision of sustained fixation in trained and untrained observers.J. Vis. 2012; 12: 1-16Crossref Scopus (91) Google Scholar]. Upon the completion of explicit training, subjects took a break for at least 1 week before being recalled for another round of the task for five to seven blocks (retention assessment). After the retention assessment, subjects performed five additional blocks of the object following and visual search tasks against a gray background, a process that was identical to the first object following phase and the third visual search phase of the free exploration period of the experiment but with one exception: the luminance of the simulated scotoma was matched to that of the background (Figure 1C). As a result, the simulated central scotoma was not visible to the subjects (invisible scotoma). Thus, the invisible scotoma experiment consisted of two phases: object following (Figure 1C, i) and visual search (Figure 1C, ii). A separate group of six subjects participated in a control experiment (a total of five blocks) identical to free exploration but without the simulated scotoma (control experiment). The specific numbers of blocks each subject performed in the different stages of the experiment are listed in Table S1. Gaze position data were first preprocessed by an edge-preserving median filter with a 200 ms window in order to remove transient noise. Then, a modified version of a standard parsing algorithm [38Fischer B. Biscaldi M. Otto P. Saccadic eye movements of dyslexic adult subjects.Neuropsychologia. 1993; 31: 887-906Crossref PubMed Scopus (54) Google Scholar, 39Gitelman D.R. ILAB: a program for postexperimental eye movement analysis.Behav. Res. Methods Instrum. Comput. 2002; 34: 605-612Crossref PubMed Scopus (183) Google Scholar] was applied to the preprocessed data in order to robustly classify saccades and fixations while excluding microsaccades [40Engbert R. Mergenthaler K. Microsaccades are triggered by low retinal image slip.Proc. Natl. Acad. Sci. USA. 2006; 103: 7192-7197Crossref PubMed Scopus (377) Google Scholar]. We defined a period of eye movement as a saccade if the following conditions were met: (1) the eye velocity exceeded 20° per s during the entire period, (2) the peak velocity during this period was in the top 25th percentile of the recording phase, (3) the beginning and end of this period had a velocity of at least 15% of the peak velocity, and (4) the amplitude of the eye movement during this period exceeded 0.9°. Periods that were not saccades were candidates for fixations. A candidate period was classified as a fixation if it started with at least 50 ms of stable gaze (SD in gaze position did not exceed 0.5° in any direction) and ended with one of the following conditions: (1) a period of missing data (a blink) exceeding 500 ms, (2) the start of a saccade, or (3) the start of a reliable drift that exceeded 1°. Fixation density maps were derived from the retinal positions of the target objects during periods of fixation via kernel density estimation with a bivariate Gaussian kernel [41Botev Z.I. Grotowski J.F. Kroese D.P. Kernel density estimation via diffusion.Ann. Stat. 2010; 38: 2916-2957Crossref Scopus (1313) Google Scholar]. The PRL was defined as the peak of the density. Fixation stability has traditionally been quantified by calculating the area of the ellipse that encompasses a given proportion of eye positions during fixation [42Crossland M.D. Sims M. Galbraith R.F. Rubin G.S. Evaluation of a new quantitative technique to assess the number and extent of preferred retinal loci in macular disease.Vision Res. 2004; 44: 1537-1546Crossref PubMed Scopus (91) Google Scholar]. This area is termed the BCEA [43Steinman R.M. Effect of target size, luminance, and color on monocular fixation.J Opt Soc Am. 1965; 55: 1158-1165Crossref Google Scholar]. A more stable fixation corresponds to a smaller BCEA. In the current study, the variance of fixation was defined as the BCEA that encompassed 68% of fixations around the mean [42Crossland M.D. Sims M. Galbraith R.F. Rubin G.S. Evaluation of a new quantitative technique to assess the number and extent of preferred retinal loci in macular disease.Vision Res. 2004; 44: 1537-1546Crossref PubMed Scopus (91) Google Scholar] and was used as an indicator of fixation stability. BCEAs were calculated from the density maps. (The fixational BECAs measured from the current experiment are most likely to be overestimations because we instructed our subjects to simply “follow and examine” an object, 2° to 2.7° in size without specifying where on the object a subject must fixate.) The density maps for the first saccade landing site were obtained in a similar manner from the retinal positions of the target objects at the end point of the first saccade after object movement. This work was supported by National Institutes of Health grants R01EY017707 and R01EY016093. The authors would like to thank A. Disney, G. Legge, G. Timberlake, and two anonymous reviewers for their helpful comments and discussion of the manuscript and J.L. Gonzales and E. Trinh for their help with subject recruitment and data collection. Download .pdf (.38 MB) Help with pdf files Document S1. Figures S1 and S2 and Table S1" @default.
• W1992242877 created "2016-06-24" @default.
• W1992242877 creator A5000739640 @default.
• W1992242877 creator A5009198945 @default.
• W1992242877 creator A5076317027 @default.
• W1992242877 date "2013-09-01" @default.
• W1992242877 modified "2023-10-01" @default.
• W1992242877 title "Rapid and Persistent Adaptability of Human Oculomotor Control in Response to Simulated Central Vision Loss" @default.
• W1992242877 cites W1966067027 @default.
• W1992242877 cites W1968908436 @default.
• W1992242877 cites W1969202206 @default.
• W1992242877 cites W1977966784 @default.
• W1992242877 cites W1979768732 @default.
• W1992242877 cites W1982306361 @default.
• W1992242877 cites W1992039040 @default.
• W1992242877 cites W1997062280 @default.
• W1992242877 cites W1997742420 @default.
• W1992242877 cites W1998639902 @default.
• W1992242877 cites W1999038885 @default.
• W1992242877 cites W1999467054 @default.
• W1992242877 cites W2013803214 @default.
• W1992242877 cites W2017108196 @default.
• W1992242877 cites W2022020105 @default.
• W1992242877 cites W2023589236 @default.
• W1992242877 cites W2024521795 @default.
• W1992242877 cites W2038529966 @default.
• W1992242877 cites W2046205373 @default.
• W1992242877 cites W2046698945 @default.
• W1992242877 cites W2052443849 @default.
• W1992242877 cites W2054502476 @default.
• W1992242877 cites W2056187454 @default.
• W1992242877 cites W2061759044 @default.
• W1992242877 cites W2073287733 @default.
• W1992242877 cites W2073322462 @default.
• W1992242877 cites W2079603962 @default.
• W1992242877 cites W2080174491 @default.
• W1992242877 cites W2089834181 @default.
• W1992242877 cites W2089900581 @default.
• W1992242877 cites W2094744388 @default.
• W1992242877 cites W2109193744 @default.
• W1992242877 cites W2141611146 @default.
• W1992242877 cites W2144917418 @default.
• W1992242877 cites W2163957510 @default.
• W1992242877 cites W3104298728 @default.
• W1992242877 cites W4294214781 @default.
• W1992242877 doi "https://doi.org/10.1016/j.cub.2013.06.056" @default.
• W1992242877 hasPubMedCentralId "https://www.ncbi.nlm.nih.gov/pmc/articles/3773263" @default.
• W1992242877 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/23954427" @default.
• W1992242877 hasPublicationYear "2013" @default.
• W1992242877 type Work @default.
• W1992242877 sameAs 1992242877 @default.
• W1992242877 citedByCount "76" @default.
• W1992242877 countsByYear W19922428772013 @default.
• W1992242877 countsByYear W19922428772014 @default.
• W1992242877 countsByYear W19922428772015 @default.
• W1992242877 countsByYear W19922428772016 @default.
• W1992242877 countsByYear W19922428772017 @default.
• W1992242877 countsByYear W19922428772018 @default.
• W1992242877 countsByYear W19922428772019 @default.
• W1992242877 countsByYear W19922428772020 @default.
• W1992242877 countsByYear W19922428772021 @default.
• W1992242877 countsByYear W19922428772022 @default.
• W1992242877 countsByYear W19922428772023 @default.
• W1992242877 crossrefType "journal-article" @default.
• W1992242877 hasAuthorship W1992242877A5000739640 @default.
• W1992242877 hasAuthorship W1992242877A5009198945 @default.
• W1992242877 hasAuthorship W1992242877A5076317027 @default.
• W1992242877 hasBestOaLocation W19922428771 @default.
• W1992242877 hasConcept C169760540 @default.
• W1992242877 hasConcept C177606310 @default.
• W1992242877 hasConcept C18903297 @default.
• W1992242877 hasConcept C86803240 @default.
• W1992242877 hasConceptScore W1992242877C169760540 @default.
• W1992242877 hasConceptScore W1992242877C177606310 @default.
• W1992242877 hasConceptScore W1992242877C18903297 @default.
• W1992242877 hasConceptScore W1992242877C86803240 @default.
• W1992242877 hasIssue "17" @default.
• W1992242877 hasLocation W19922428771 @default.
• W1992242877 hasLocation W19922428772 @default.
• W1992242877 hasLocation W19922428773 @default.
• W1992242877 hasLocation W19922428774 @default.
• W1992242877 hasOpenAccess W1992242877 @default.
• W1992242877 hasPrimaryLocation W19922428771 @default.
• W1992242877 hasRelatedWork W1967419200 @default.
• W1992242877 hasRelatedWork W1981668633 @default.
• W1992242877 hasRelatedWork W2070040999 @default.
• W1992242877 hasRelatedWork W2082860237 @default.
• W1992242877 hasRelatedWork W2348924972 @default.
• W1992242877 hasRelatedWork W2357124094 @default.
• W1992242877 hasRelatedWork W2365736347 @default.
• W1992242877 hasRelatedWork W2387399993 @default.
• W1992242877 hasRelatedWork W2389739210 @default.
• W1992242877 hasRelatedWork W4255820752 @default.
• W1992242877 hasVolume "23" @default.
• W1992242877 isParatext "false" @default.
• W1992242877 isRetracted "false" @default.
• W1992242877 magId "1992242877" @default.
• W1992242877 workType "article" @default.