Vision

Patients suffering from AIDS develop ocular complications, the most frequent being HIV retinopathy. It is however not clear, if functional visual impairments can be observed as early indicators of ocular complications, before clinical diagnosis of HIV retinopathy is made at fundus examination. To address this issue, we measured colour vision in a group of 49 AIDS subjects with normal clinical fundi using the 'two equation method'. This method, combining red-green Rayleigh and the blue-green Moreland metameric matches, enables more complete and quantitative assessments of colour vision than those based on pigmentary tests. Data were collected on our computer controlled colorimeter and compared to those of normal subjects. While most AIDS subjects without HIV retinopathy demonstrated normal colour vision, a significant portion of them had wider matches than normal subjects (11% for the Rayleigh equation and 16% for the Moreland equation). Furthermore, matching ranges of the Moreland equation were significantly correlated with CD4 lymphocyte counts. Patients with low CD4 values tended to produce larger matching ranges than the patients with high CD4 values. A within subject study on 17 patients confirmed this trend and showed that the patients who increased/decreased their CD4 blood counts generally improved/impaired their colour discrimination in the Moreland match. No such correlation was found between the matching ranges of the Rayleigh equation and the CD4 counts. These results show that colour discrimination is slightly reduced in some AIDS subjects, although there are no detectable ocular complications. They also suggest two different types of colour vision impairments in AIDS patients without retinopathy: one reversible process affecting colour discrimination in the blue-green range; and another irreversible process affecting colour discrimination in the red-green range.

Bisection thresholds are approximately proportional to the separation/eccentricity of the targets. This "Weber's law" for position has been invoked over the past century. Is it the separation of the reference targets, or their eccentricity which determines the threshold? In previous studies separation and eccentricity are confounded. In the present report we have pitted separation against eccentricity. Bisection thresholds were measured for stimuli presented on an isoeccentric arc, so that separation could be varied while holding the eccentricity of the test lines constant. We used a S-fold range of separations from 2210deg. In this regime, the present results provide strong evidence against Weber's law. When separation is varied but eccentricity held constant, there is no Weber's law. Rather the thresholds are approximately constant. Our results suggest that the judgment of the separation of widely separated objects is similar to a distance measurement using a ruler on the cortex, in that the error of measurement is independent of the separation between objects. The results imply that when we attempt to gauge the distance between widely separated objects it is unlikely that we do so on the basis of the outputs of large spatial filters; rather it appears that we make such judgements by estimating the cortical distance which separates the targets of interest.

Autistics often exhibit enhanced perceptual abilities when engaged in visual search, visual discrimination, and embedded figure detection. In similar fashion, while performing a range of perceptual or cognitive tasks, autistics display stronger physiological engagement of the visual system than do non-autistics. To account for these findings, the Enhanced Perceptual Functioning Model proposes that enhanced autistic performance in basic perceptual tasks results from stronger engagement of sensory processing mechanisms, a situation that may facilitate an atypically prominent role for perceptual mechanisms in supporting cognition. Using quantitative meta-analysis of published functional imaging studies from which Activation Likelihood Estimation maps were computed, we asked whether autism is associated with enhanced task-related activity for a broad range of visual tasks. To determine whether atypical engagement of visual processing is a general or domain-specific phenomenon, we examined three different visual processing domains: faces, objects, and words. Overall, we observed more activity in autistics compared to non-autistics in temporal, occipital, and parietal regions. In contrast, autistics exhibited less activity in frontal cortex. The spatial distribution of the observed differential between-group patterns varied across processing domains. Autism may be characterized by enhanced functional resource allocation in regions associated with visual processing and expertise. Atypical adult organizational patterns may reflect underlying differences in developmental neural plasticity that can result in aspects of the autistic phenotype, including enhanced visual skills, atypical face processing, and hyperlexia. Hum Brain Mapp, 2011 © 2011 Wiley-Liss, Inc.

This study recommends changes to the U.S. Army's tactical orders process in order to increase the Army's ability to execute AirLand Battle at the tactical level of war. The thesis exarines the tactical orders process of the Wehrmacht. the Soviet Army and the U.S. Army. The tactical orders process is defined as the process by which a tactical level commander receives or deduces the mission, analyzes the tactical situation, prepares courses of action, makes a decision, issues an order, executes the plan, and adjusts to new situations in order to accomplish the mission. The methodology compared the current U.S. procedures with those of the Wehrmacht and the Soviet Army. The Wehrmacht employed a very decentralized, predominantly verbal, tactical orders process. The Soviet Army employs a very centralized, predominantly graphic, tactical orders process. Both aim at shortening tactical decision cycles and gaining a time advantage through a quick and effective orders process. Research revealed that many units in the U.S. Army do not conduct an effective tactical orders process. Current procedures are "orders intensive" and do not meet the requirements of agility and flexibility demanded by AirLand Battle doctrine. Changes to the orders process, the operations order format and a time linkpri rritpria fnr nrders are suggested , 14. SUBJECT TERMS Combat orders, operation orders, staff planning, 1s. NUMBER OF PAGES synchronization, commander's intent, co-mand and control, troop 227 leading procedures, warning orders, Auftragstaktik, maneuver war-16. PRICE CODE fare. attrition warfare. Soviet Troop Control , decision making.

Arrant-~havioural techniques were used to determine whether cats are able to see subjective contours. Through several stages of testing with increasingly complex displays, cats continued to respond to a figure defined by subjective contours. This result provides the first direct evidence that a nonhuman perceives subjective contours.

People tend to perceive identical top halves (i.e. above the nose) of two face stimuli as being different when they are aligned with distinct bottom halves. This composite face illusion is generally considered as the most compelling evidence that facial features are integrated into a holistic representation. Here, we recorded eye-movements during the composite face illusion in a delayed matching task of top halves of faces. Behavioural results showed a strong composite face effect, participants making more mistakes and taking longer time to match two identical top halves of faces when they were aligned (vs. misaligned) with different bottom halves. Importantly, fixation sites and eyemovements were virtually identical when the top and bottom parts were aligned (composite illusion) or misaligned (no illusion), indicating that holistic face processing can be independent of gaze behaviour. These findings reinforce the view that holistic representations of individual faces can be extracted early on from information at a relatively coarse scale, independently of overt attention.

When two isoluminant colors alternate at frequencies >10 Hz, we perceive only one fused color with a minimal sensation of brightness flicker. In spite of the perception of color fusion, color opponent (CO) cells at early stages of the visual pathway are known to respond to chromatic flicker at frequencies far exceeding the perceptual fusion frequency. To explain color fusion, several groups have predicted that CO cells in Vi-unlike the retina and lateral geniculate nucleus-should not follow high-frequency flicker. To test this prediction we recorded from 12 CC)cells in various V1 layers. We found, contrary to expectations, that these neurons follow high frequency flicker well above heterochromatic fusion frequencies. All followed 15 Hz flicker and 10/12 followed 30 Hz flicker. For three cells, we tested 60 Hz luminance flicker and found clear responses. We thus present evidence of cortical activity in alert, trained monkeys that is clearly representing visual stimulation, yet is not perceived. Our data call into question explanations of perceptual phenomena that invoke a low temporal frequency cutoff of CO cells in VI to account for the failure to perceive fast temporal changes in the chromatic domain.

We have initiated a genetic analysis of the zebrafish visual system to identify novel molecules involved in vertebrate retinal function. Zebrafish are highly visual; they have four types of cones as well as rod photoreceptors, making it possible to study both rod and cone-mediated visual responses. To identify visual mutants, optokinetic responses of mutagenized larvae are measured in a three-generation screen for recessive mutations. By measuring visual behavior our genetic screen has been targeted towards identifying mutants that do not have gross morphological abnormalities. The electroretinogram (ERG) of optokinetic-defective mutants is recorded and their retinas are examined histologically to localize defects to the retina. In this report, we summarize our screening results and ERG and histological analyses of the five morphologically normal mutants we have analyzed to date. Additionally, the more detailed characterization of a red-blind mutant that we have isolated is summariz...

The aim of this study was to integrate a gaze training intervention (i.e., quiet eye training; QET) that has been shown to improve the throwing and catching skill of children with Developmental Coordination Disorder (DCD), within an approach (i.e., group therapy) that might alleviate the negative psychosocial impact of these motor skill deficits. Twenty-one children with DCD were split into either QET (8 male 3 female, mean age of 8.6 years (SD = 1.04) or technical training (TT) groups (7 male 3 female, mean age of 8.6 years (SD = 1.84). The TT group were given movement-related instructions via video, relating to the throw and catch phases, while the QET group were also taught to fixate a target location on the wall prior to the throw (QE1) and to track the ball prior to the catch (QE2). Each group partook in a 4-week, group therapy intervention and measurements of QE duration and catching performance were taken before and after training, and at a 6-week delayed retention test. Pare...

The generalisation of the Internet and the recent technological developments in embedded systems and wireless networks contribute to the realisation of a vision where access to information is possible at any moment and from anywhere. This is particularly attractive with information that is relevant to a specific geographic location. Applications that rely on locationbased services to provide information to mobile users, or that support interaction with real devices in the user neighbourhood, are called location-dependent applications and enhance the relationship between mobile users and a specific geographic location. However, the design of such applications breaks with the existing paradigms and methodologies as the mobile devices and the wireless communication infrastructures have characteristics that are very different from those of desktop computers and wired communication systems. The Around architecture is an open and extensible framework for location-based services that allows network services to be associated with specific geographic locations. By using this architecture applications can select services that are relevant for specific locations. Within the context of the Around project we have developed a prototype system with multiple locationbased services and an application that accesses these services to provide information related to a town transportation system. This paper reports on the design and development of this location-based application. Its design raised several new issues, going from the computational model to the interface paradigm, which are also discussed in this paper. The developed application is composed of several modules: a set of agents which are autonomous units with the knowledge necessary to select and use location-based services in a specific thematic area (e.g. transportation); an HTML output area based on a browser metaphor; and a location-context module responsible for determining the user context. The results show that an application architecture based on a modular approach turns to be very flexible as it becomes very easy to extend its functionality by simply adding or changing the agents that deal with each location-based service.

Birds gather information about their environment mainly through vision by scanning their surroundings. Many prevalent models of social foraging assume that foraging and scanning are mutually exclusive. Although this assumption is valid for birds with narrow visual fields, these models have also been applied to species with wide fields. In fact, available models do not make precise predictions for birds with large visual fields, in which the head-up, head-down dichotomy is not accurate and, moreover, do not consider the effects of detection distance and limited attention. Studies of how different types of visual information are acquired as a function of body posture and of how information flows within flocks offer new insights into the costs and benefits of living in groups. Box 1. The big picture † Foraging animals use their senses to respond to food distribution and predator danger, and many forage in groups to deal appropriately with these needs. † Social foragers receive information through their own monitoring of external events and through monitoring the behaviour of their neighbours. † These different information inputs conflict with each other, and maximally efficient predator detection, food finding and neighbor monitoring are achieved by different body postures and head orientation. † Current models rarely take into account that, to infer visual targets from body postures, it is necessary to consider the organization of vision, which can vary dramatically among species. † We argue that specific features of visual systems should be incorporated into theoretical social foraging models and that doing so will change predictions and validate the use of behavioural observations as tests of functional hypotheses.

We have employed methodologies of human centered design to inspire and guide the engineering of a definitive low-cost aesthetic multimodal experience intended to stimulate cultural growth. Using a combination of design research, trend analysis and the programming of immersive virtual 3D worlds, over 250 innovative concepts have been brainstormed, prototyped, evaluated and refined. These concepts have been used to create a strategic map for the development of highimpact virtual art experiences, the most promising of which have been incorporated into a multimodal environment programmed in the online interactive 3D platform XVR. A group of test users have evaluated the experience as it has evolved, using a multimodal interface with stereo vision, 3D audio and haptic feedback. This paper discusses the process, content, results, and impact on our engineering laboratory that this research has produced.

The Fourier phase spectrum plays a central role regarding where in an image contours occur, thereby defining the spatial relationship between those structures in the overall scene. Only a handful of studies have demonstrated
psychophysically the relevance of the Fourier phase spectrum with respect to human visual processing, and none have demonstrated the relative amount of local cross-scale spatial phase alignment needed to perceptually
extract meaningful structure from an image. We investigated the relative amount of spatial phase alignment needed for humans to perceptually match natural scene image structures at three different spatial frequencies [3, 6, and 12 cycles per degree (cpd)] as a function of the number of structures within the image (i.e., “structural sparseness”). The results showed that (1) the amount of spatial phase alignment needed to match structures depends on structural sparseness, with a bias for matching structures at 6 cpd and (2) the ability to match partially phase-randomized images at a given spatial frequency is independent of structural sparseness at other spatial frequencies. The findings of the current study are discussed in terms of a network of feature integrators in the human visual system.

We examine whether holes (two separate cutout rectangles in a surface) appearing as if on a homogeneous background produce object-based effects similar to those observed when the same regions appear as separate items in front of that surface (commonly called objects). We used a version of the two-rectangle design described by R. Egly, J. Driver, and R. D. . Viewing modified patterns through stereoscopic goggles created the perception of the rectangles as either part of the background or as foreground objects. In Experiment 1, we replicated Egly et al. when the regions were perceived as objects but not when they were perceived as holes. In Experiment 2, we included a condition where the background was split: The rectangles in the holes condition were perceived as part of two separate background regions. In this case, the object-based effects were the same as when the rectangles were foreground objects. The findings of Experiment 2 demonstrate that those of Experiment 1 were not due to depth per se, but rather to the background being treated as a single region. More importantly, these results demonstrate that identically shaped regions in the stimulus engage object-based attention differently, depending on how the regions are perceptually organized.

A ®gure combination task, in which three components are combined into an object, was administered under imagery-alone and externalization conditions to subjects with dierent levels of sketching expertise. In externalization conditions the imaged combinations were sketched. In accordance with earlier studies, the combinations were rated equally creative across conditions. The combinations were scored with regard to the novelty of their spatial con®gurations of the components (combining score), and with regard to the novelty of the structure of the components (restructuring score). For expert sketchers the latter score was found to be increased by sketching. Creativity ratings correlated with both combining and restructuring scores in the sketching condition, but only with combining scores in the imagery condition. The results are interpreted in terms of a model in which creative processes use combining and restructuring strategies in a¯exible way. Whereas restructuring draws heavily on both externalization and expertise in externalization, combining can be used independently of externalization and expertise. Ó

We examined familial aggregation and risk of age-related macular degeneration in the Utah population using a population-based case-control study. Over one million unique patient records were searched within the University of Utah Health Sciences Center and the Utah Population Database (UPDB), identifying 4764 patients with AMD. Specialized kinship analysis software was used to test for familial aggregation of disease, estimate the magnitude of familial risks, and identify families at high risk for disease. The population-attributable risk (PAR) for AMD was calculated to be 0.34. Recurrence risks in relatives indicate increased relative risks in siblings (2.95), first cousins (1.29), second cousins (1.13), and parents (5.66) of affected cases. There were 16 extended large families with AMD identified for potential use in genetic studies. Each family had five or more living affected members. The familial aggregation of AMD shown in this study exemplifies the merit of the UPDB and supports recent research demonstrating significant genetic contribution to disease development and progression.

Background Many causes of vision impairment can be prevented or treated. With an ageing global population, the demands for eye health services are increasing. We estimated the prevalence and relative contribution of avoidable causes of blindness and vision impairment globally from 1990 to 2020. We aimed to compare the results with the World Health Assembly Global Action Plan (WHA GAP) target of a 25% global reduction from 2010 to 2019 in avoidable vision impairment, defined as cataract and undercorrected refractive error. We did a systematic review and meta-analysis of population-based surveys of eye disease from January, 1980, to October, 2018. We fitted hierarchical models to estimate prevalence (with 95% uncertainty intervals [UIs]) of moderate and severe vision impairment (MSVI; presenting visual acuity from <6/18 to 3/60) and blindness (<3/60 or less than 10° visual field around central fixation) by cause, age, region, and year. Because of data sparsity at younger ages, our analysis focused on adults aged 50 years and older. Findings Global crude prevalence of avoidable vision impairment and blindness in adults aged 50 years and older did not change between 2010 and 2019 (percentage change -0•2% [95% UI -1•5 to 1•0]; 2019 prevalence 9•58 cases per 1000 people [95% IU 8•51 to 10•8], 2010 prevalence 96•0 cases per 1000 people [86•0 to 107•0]). Age-standardised prevalence of avoidable blindness decreased by -15•4% [-16•8 to -14•3], while avoidable MSVI showed no change (0•5% [-0•8 to 1•6]). However, the number of cases increased for both avoidable blindness (10•8% [8•9 to 12•4]) and MSVI (31•5% [30•0 to 33•1]). The leading global causes of blindness in those aged 50 years and older in 2020 were cataract (15•2 million cases [9% IU 12•7-18•0]), followed by glaucoma (3•6 million cases [2•8-4•4]), undercorrected refractive error (2•3 million cases [1•8-2•8]), age-related macular degeneration (1•8 million cases [1•3-2•4]), and diabetic retinopathy (0•86 million cases [0•59-1•23]). Leading causes of MSVI were undercorrected refractive error (86•1 million cases [74•2-101•0]) and cataract (78•8 million cases [67•2-91•4]). Interpretation Results suggest eye care services contributed to the observed reduction of age-standardised rates of avoidable blindness but not of MSVI, and that the target in an ageing global population was not reached.

Microsaccades are small rapid and involuntary eye movements that occur during fixation in an apparently stochastic manner. They are known to be inhibited in response to sensory transients, with a time course that depends on the stimulus parameters and attention. However, the temporal precision of their onsets and the degree to which they can be used to assess the response of the visual system to basic stimulus parameters is currently unknown. Here we studied microsaccade response properties as a function of the contrast and spatial frequency of visual onsets. Observers (n ¼ 18) viewed and silently counted 2-min sequences of Gabor patches presented briefly (100 ms) at 1 Hz. Contrast and spatial frequency were randomized in different experiments. We found that the microsaccade response time, as measured by the latency of the first microsaccade relative to stimulus onset following its release from inhibition, was sensitive to the contrast and spatial frequency of the stimulus and could be used to extract a contrast response function without the observers' response. We also found that contrast detection thresholds, measured behaviorally for different spatial frequencies, were highly and positively correlated (R ¼ 0.87) with the microsaccade response time measured at high contrast (.4 times the threshold). These results show that different measures of microsaccade inhibition, especially the microsaccade response time, can provide accurate and involuntary measures of low-level visual properties such as contrast response and sensitivity.

We have measured the spread of contrast adaptation across the dimension of spatial frequency. Threshold elevation was tightly tuned to the adapting spatial frequency but became much broader as test contrast was increased. This means that, for a given test frequency, there arc some frequencies which do not raise threshold but do result in a loss of perceived contrast. The contrast dependence, retinal specificity and interocular transfer of adaptation effects elicited from sameand remote-frequency adaptation were compared. While we were able to show some distinct differences between threshold and suprathreshold tests, we were unable to demonstrate any reliable differences in the retinal specificity and interocular transfer between same-and remotefrequency adaptation.

Objective: To present an overview of possible effects of Arnold-Chiari malformation (ACM) and to offer chiropractic approaches and theories for treatment of a patient with severe visual dysfunction complicated by ACM. Clinical Features: A young woman had complex optic nerve neuritis exacerbated by an ACM type I of the brain. Intervention and Outcome: Applied kinesiology chiropractic treatment was used for treatment of loss of vision and nystagmus. After treatment, the patient's ability to see, read, and perform smooth eye tracking showed improvement. Conclusion: Further studies into applied kinesiology and cranial treatments for visual dysfunctions associated with ACM may be helpful to evaluate whether this single case study can be representative of a group of patients who might benefit from this care.

The ontogeny of orientation mechanisms in migratory birds involves a complex of programmed learning rules and calibrations between the several compasses used during migration. Visual information at sunset, especially the pattern of polarized skylight, provides a primary source of orientation information for night-migrating species. To examine the development of visual orientation mechanisms at sunset, hand-raised Savannah sparrows, Passerculus sandwichensis, were given controlled experience with the clear daytime sky during the first 3 months of life. One group of birds saw the daytime sky only within an earth-strength magnetic field with magnetic north shifted 90 clockwise to true east; a control group had similar exposure to the sky within a normal, unshifted magnetic field. Orientation tests were performed on clear evenings between the time of sunset and the first appearance of stars within a vertical magnetic field of normal earth intensity (no directional magnetic information). There was no difference in the orientation of the two groups: both showed southwestward orientation. Contrary to indications from earlier experiments, the visual orientation mechanism at sunset develops independently of magnetic directions and, in this context, is similar to the ontogeny of stellar orientation.

A new approach to historical research traces the rise and fall of concepts by computational analysis of millions of documents. Based on approximately 4% of all books ever published, Google has created a database of the annual frequency of 1to 5-word phrases, termed n-grams (eTable 1 in Supplement). 1,2 We studied the database to gain insights about the history of visionrelated concepts. In addition, we documented the earliest references in English to these terms by reviewing historical articles and online databases.

We used an opportunistic review of photographs of different adult and juvenile horses walking, trotting, and cantering (n 5 828) to compare the angle of the nasal plane relative to vertical in feral and domestic horses at liberty (n 5 450) with ridden horses advertised in a popular Australian horse magazine (n 5 378). We assumed that horses in advertisements were shown at, what was perceived by the vendors to be, their best. Of the ridden horses, 68% had their nasal plane behind the vertical. The mean angle of the unridden horses at walk, trot, and canter (30.7 6 11.5; 27.3 6 12.0; 25.5 6 11.0) was significantly greater than those of the ridden horses (1.4 6 14.1; 25.1 6 211.1; 3.1 6 15.4, P , 0.001). Surprisingly, unridden domestic horses showed greater angles than feral horses or domestic horses at liberty. We compared adult and juvenile horses in all 3 gaits and found no significant difference. Taken together, these findings demonstrate that the longitudinal neck flexion of the degree desirable by popular opinion in ridden horses is not a common feature of unridden horses moving naturally. Moreover, they suggest that advertised horses in our series are generally being ridden at odds with their natural carriage and contrary to the international rules of dressage (as published by the International Equestrian Federation). These findings are discussed against the backdrop of the established doctrine, which states that carrying a rider necessitates changes in longitudinal flexion, and in the context of the current debate around hyperflexion.

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities .

Among mammals, birds, most reptiles and chondrichthians, only rhodopsins are present. Among agnathans, osteichthians, amphibians and certain freshwater turtles there are species having only porphyropsins or only rhodopsins or, more interestingly, both pigments, either sequentially or together. This latter grouping represents the paired-pigment species. Associated with the presence of pairedpigments is the possibility that the proportions of rhodopsin and porphyropsin may change. Depending on the characteristics of each paired-pigment species, naturally occurring changes in visual pigment ratios are related to migrations in anadromous and catadromous teleosts and anadromous cyclostomes and to seasonal variation in several teleosts. In addition, the visual pigment composition of certain species of teleosts has been altered by the specific effects of light, temperature, diet and hormones. Of two possible mechanisms for altering spectral sensitivity, varying the proportion of rhodopsin and porphyropsin is far more common than utilizing a single chromophore and changing the opsin. In addition to the long established evidence that extractable rod pigment ratios may change during the life cycle or in response to specific exogenous factors, there is the more recent recognition from microspectrophotometry that cone pigment ratios may also change in concert. The effect of lighting conditions and temperature on the visual pigment composition of certain paired-pigment species is presented.

Towards an ecological approach to visual anticipation for expert performance in sport ... University of Illinois at Urbana–Champaign, USA ... Corresponding author. Duarte Araújo, Faculty of Human Kinetics, Technical University of Lisbon, Portugal. Tel.: +351 - 214149209; fax.: + 351 – 21 4144712 E-mail address: [email protected] ... Much research attention has been dedicated to investigating visual anticipation ... Goodale (MG model) to the study of visual anticipation, Van der Kamp et al. argue that ... However, the theoretical perspective of Van der Kamp et al. may be ...

An unresolved question is how much information can be remembered from visual scenes when they are inspected by saccadic eye movements. Subjects used saccadic eye movements to scan a computer-generated scene, and afterwards, recalled as many objects as they could. Scene memory was quite good: it improved with display duration, it persisted over time long after the display was removed, and it continued to accumulate with additional viewings of the same display (Melcher, D. The persistance of memory for scenes. Nature 412, 401). The occurrence of saccadic eye movements was important to ensure good recall performance, even though subjects often recalled non-fixated objects. Inter-saccadic intervals increased with display duration, showing an influence of duration on global scanning strategy. The choice of saccadic target was predicted by a Random Selection with Distance Weighting (RSDW) model, in which the target for each saccade is selected at random from all available objects, weighted according to distance from fixation, regardless of which objects had previously been fixated. The results show that the visual memory that was reflected in the recall reports was not utilized for the immediate decision about where to look in the scene. Visual memory can be excellent, but it is not always reflected in oculomotor measures, perhaps because the cost of rapid on-line memory retrieval is too great.

Older adults have serious difficulty seeing under low illumination and at night, even in the absence of ocular disease. Optical changes in the aged eye, such as pupillary miosis and increased lens density, cannot account for the severity of this problem, and little is known about its neural basis. Dark adaptation functions were measured on 94 adults ranging in age from the 20s to the 80s to assess the rate of rod-mediated sensitivity recovery after exposure to a 98% bleach. Fundus photography and a grading scale were used to characterize macular health in subjects over age 49 in order to control for macular disease. Thresholds for each subject were corrected for lens density based on individual estimates, and pupil diameter was controlled. Results indicated that during human aging there is a dramatic slowing in rod-mediated dark adaptation that can be attributed to delayed rhodopsin regeneration. During the second component of the rod-mediated phase of dark adaptation, the rate of sensitivity recovery decreased 0.02 log unit/min per decade, and the time constant of rhodopsin regeneration increased 8.4 s/decade. The amount of time to reach within 0.3 log units of baseline scotopic sensitivity increased 2.76 min/decade. These aging-related changes in rod-mediated dark adaptation may contribute to night vision problems commonly experienced by the elderly.

Novel binocular depth ilhrsions obtained from two-dimensional colour images are presented. It is demonstrated that the magnitude of these illusions is based on transverse chromatic aberation (TCA), however, the depth obtained caNlot be observed unless specific astir are met even if the TCA is present, Some form of perceptual organization occurring at and/or beyond tbe binocular fusion site of the brain, is required for some of these effects to occur. An example of a paradoxical finding leading to this conclusion is the observation that uader some conditious the same colour can be perceived on separate depth planes while spatially adjacent colours from opposing ends of the visible spectrum (i.e. red and blue or green) can be perceived on the same depth plane ~~ta~~ly within the same image. Further, results show that some form of reference pibe is required by the brain to use the colour induced disparity, without which, depth connot be perceived even if the disparity information is preseut. This phenomenon is spatially tuned for medium to high frequency components aud is still detectable under isoluminant conditions which would support the notion that it requires information from the parvocelhdar pathway. Binocular hrstre and rivaldepth are ruled out as being significant factors in the effect. It is argued that this phenomenon represents an instance of global interactive processes induced by TCA whife previous studies on c~o~ter~~ have cou~en~ated on locai aspects. Results of the present study may explain wby under certain situations depth can be perceived in coloured images and not under other circumstances where TCA is still present. Depth perception Colour Chromostereopsis Binocular Stereopsis Chromatic aberration The illusion

Summary Background Many causes of vision impairment can be prevented or treated. With an ageing global population, the demands for eye health services are increasing. We estimated the prevalence and relative contribution of avoidable causes of blindness and vision impairment globally from 1990 to 2020. We aimed to compare the results with the World Health Assembly Global Action Plan (WHA GAP) target of a 25% global reduction from 2010 to 2019 in avoidable vision impairment, defined as cataract and undercorrected refractive error. Methods We did a systematic review and meta-analysis of population-based surveys of eye disease from January, 1980, to October, 2018. We fitted hierarchical models to estimate prevalence (with 95% uncertainty intervals [UIs]) of moderate and severe vision impairment (MSVI; presenting visual acuity from &lt;6/18 to 3/60) and blindness (&lt;3/60 or less than 10° visual field around central fixation) by cause, age, region, and year. Because of data sparsity at...

The proposal that peripheral visual changes (cues) tend to summon attention automatically was tested by studying the effect of peripheral cueing on simple detection latency. Delay between cue onset and target onset, the contingent relationship between cue location and target location, and instructions to subjects were manipulated. Results showed that a peripheral display change could capture attention even when the target was far more likely to appear at an uncued location. When subjects were explicitly informed that targets were likely to appear away from the cued location they were able to suppress this effect, but were unable completely to reverse it by rapidly orienting attention towards the uncued side. Hence the process appears to be automatic in the sense that it occurs unless there are explicit instructions to the contrary. With explicit instructions the processing operation can be suppressed, but not completely reversed.

A neural network model is developed to explain how visual thalamocortical interactions give rise to boundary percepts such as illusory contours and surface percepts such as filled-in brightnesses. Top-down feedback interactions are needed in addition to bottom-up feed-forward interactions to simulate these data. One feedback loop is modeled between lateral geniculate nucleus (LGN) and cortical area V1, and another within cortical areas V1 and V2. The first feedback loop realizes a matching process which enhances LGN cell activities that are consistent with those of active cortical cells, and suppresses LGN activities that are not. This corticogeniculate feedback, being endstopped and oriented, also enhances LGN ON cell activations at the ends of thin dark lines, thereby leading to enhanced cortical brightness percepts when the lines group into closed illusory contours. The second feedback loop generates boundary representations, including illusory contours, that coherently bind dist...

Accommodation stimulus-response function (ASRF) and its relationship to retinal image quality were investigated using a modified wavefront sensor. Ten subjects were presented with six vergence stimuli between 0.17 D and 5 D. For each vergence distance, ocular wavefronts and subjective visual acuity were measured. Wavefronts were analysed for a fixed 3-mm pupil diameter and for natural pupil sizes. Visual Strehl ratio computed in the frequency domain (VSOTF) and retinal images were calculated for each condition tested. Subjective visual acuity was significantly improved at intermediate vergence distances (1 D and 2 D; p < 0.01), and only decreased significantly at 5 D compared with 0.17 D (p < 0.05). VSOTF magnitude was associated with subjective visual acuity and VSOTF peak location correlated with accommodation error. Apparent accommodation errors due to spherical aberration were highly correlated with accommodation lead and lag for natural pupils (R 2 = 0.80) but not for fixed 3-mm pupils (R 2 < 0.00). The combination of higher-order aberrations and accommodation errors improved retinal image quality compared with accommodation errors or higher order aberrations alone. Pupil size and higher order aberrations play an important role in the ASRF.

One of the remaining obstacles to the widespread application of industrial robots is their inability to deal with parts: that are not precisciy po~itioned. In the case of manual asscm'nly, componentq are often presented in bins. Current automated systems, on the olher hand, require separate feeders which present the parts with carefully controlled position and attitude. Here we show how results in rnachicc vision provide techn:ques for automatically directing a mechanical manipulator to pick one object at a time out of a pile. The attitude of the object to be picked up is determined using a histogram of the orientations of visible surface patches. Surface orientation, in turn, is determined using photometric stereo applied to multiple images. These images are taken with the same camera but differing l~ghting. The resulting needle map, giving the orientations of surface patches, is used to create an orientation histograni which is a discrete approximation to the est,ended Gaussian image. This can be rmtched against a synthetic orientation histogram obtsined from protoypica1 models of the objects to be n~anipulated. Such models may be obtained from computer aided design (CAI)) databases. The method thus requires t h a t the shape of the objects be described, but it is not restricted to particular types of objects.

Previous findings suggest that planning an action "backward-primes" perceptual dimension related to this action: planning a grasp facilitates the processing of visual size information, while planning a reach facilitates the processing of location information. Here we show that dimensional priming of perception through action occurs even in the absence of active action planning. Subjects watched video clips showing a grasping or reaching action before detecting size-or location-defined deviants in visual stimulus sequences. Size deviants were detected faster after seeing a grasp and location deviants were detected faster after seeing a reach. This supports the assumption that perceptual codes and action plans share a common representational medium, and that "attention to action" controls "attention to stimuli".

1 2 3 Probability that light is perceived left of touch 0.0 0.2 0.4 0.6 0.8 1.0 Asynchronous presentation of light and touch Synchronous presentation of light and touch Light left of touch Light/touch same position Light right of touch significant interaction between position and timing p=.013

2 words are presented successively within 500 ms, subjects often miss the 2nd word. This attentional blink reflects a limited capacity to attend to incoming information. Memory effects were studied for words that fell within an attentional blink. Unrelated words were presented in a modified rapid serial visual presentation task at varying stimulus-onset asynchronies, and attention was systematically manipulated. Subsequently, recognition, repetition priming, and semantic priming were measured separately in 3 experiments. Unidentified words showed no recognition and no repetition priming. However, blinked (i.e., unidentified) words did produce semantic priming in related words. When, for instance, ring was blinked, it was easier to subsequently identify wedding than apple. In contrast, when the blinked word itself was presented again, it was not easier to identify than an unrelated word. Possible interpretations of this paradoxical finding are discussed.

The sensory brain areas of a sample of < 100 deep-sea fish species were studied, and the relative volumes of the olfactory bulb, optic tectum, octavolateral area and gustatory area were determined. In the absence of direct observations on the behaviour of this ichthyofauna these data allow deductions to be made about the kinds of sensory modalities used preferentially in the deep-sea environment. Here, members of three families are compared that have representatives living on or near the sea floor ("demersal") and in the open water between 200 and 1,000 m (mesopelagic). The findings indicate that both regions present fish with rich and diverse sensory environments. While vision emerges as the dominant sense of the mesopelagic realm, olfaction seems more important on or near the bottom of the sea. However, other sensory modalities supplement these senses in species-specific patterns. Considerations of the phyletic relationships indicate different degrees of pervasiveness. Whilst in slickheads the dominance of vision appears to be a family-related trait, a similar relationship is not found in either eels or grenadiers. By contrast, the common trait in these two families seems to be the greater adaptability to the environment.

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers ( Rynchops , Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique 'skimming' foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision-pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5 ° wide and extending 5 ° above the horizontal, looks in the direction of travel. The small size of this forward-facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.

We measured the kinetics of recombination of 11-cis-retinal with opsin in intact frog rod outer segment (ROS). The rhodopsin in ROS was bleached and allowed to decay to ''indicator yellow,'' a photoproduct where all-trans-retinal is partly free, and partly bound to non-specific amino groups of disk membranes. By briefly illuminating the ''indicator yellow'' by an intense 465 or 380nm flash, we then photoconverted all-trans-retinal to (mostly) the 11-cis-form thus introducing into ROS a certain amount of cis-chromophore. The recombination of cis-retinal with opsin and the formation of rhodopsin were followed by fast single-cell microspectrophotometry. Regeneration proceeded with a time constant of $3.5 min; up to 27% of bleached visual pigment was restored. The regenerated pigment consisted of 91% rhodopsin (11-cis-chromophore) and 9% of presumably isorhodopsin (9-cischromophore). The recombination of 11-cis-retinal with opsin inside the ROS proceeds substantially faster than rhodopsin regeneration in the intact eye and, hence, is not the rate-limiting step in the visual cycle.