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- Volume 3, 2017
Annual Review of Vision Science - Volume 3, 2017
Volume 3, 2017
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Inhibitory Interneurons in the Retina: Types, Circuitry, and Function*
Vol. 3 (2017), pp. 1–24More LessVisual signals in the vertebrate retina are shaped by feedback and feedforward inhibition in two synaptic layers. In one, horizontal cells establish fundamental center-surround receptive-field properties via morphologically and physiologically complex synapses with photoreceptors and bipolar cells. In the other, a panoply of amacrine cells imbue ganglion cell responses with spatiotemporally complex information about the visual world. Here, I review current ideas about horizontal cell signaling, considering the evidence for and against the leading, competing theories. I also discuss recent work that has begun to make sense of the remarkable morphological and physiological diversity of amacrine cells. These latter efforts have been aided tremendously by increasingly complete connectivity maps of inner retinal circuitry and new genetic tools that enable study of individual, sparsely expressed amacrine cell types.
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The Transduction Cascade in Retinal ON-Bipolar Cells: Signal Processing and Disease
Vol. 3 (2017), pp. 25–51More LessOur robust visual experience is based on the reliable transfer of information from our photoreceptor cells, the rods and cones, to higher brain centers. At the very first synapse of the visual system, information is split into two separate pathways, ON and OFF, which encode increments and decrements in light intensity, respectively. The importance of this segregation is borne out in the fact that receptive fields in higher visual centers maintain a separation between ON and OFF regions. In the past decade, the molecular mechanisms underlying the generation of ON signals have been identified, which are unique in their use of a G-protein signaling cascade. In this review, we consider advances in our understanding of G-protein signaling in ON-bipolar cell (BC) dendrites and how insights about signaling have emerged from visual deficits, mostly night blindness. Studies of G-protein signaling in ON-BCs reveal an intricate mechanism that permits the regulation of visual sensitivity over a wide dynamic range.
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International Vision Care: Issues and Approaches
Vol. 3 (2017), pp. 53–68More LessGlobally, 32.4 million individuals are blind and 191 million have moderate or severe visual impairment (MSVI); 80% of cases of blindness and MSVI are avoidable. However, great efforts are needed to tackle blindness and MSVI, as eye care in most places is delivered in isolation from and without significant integration with general health sectors. Success stories, including control of vitamin A deficiency, onchocerciasis, and trachoma, showed that global partnerships, multisectoral collaboration, public–private partnerships, corporate philanthropy, support from nongovernmental organizations—both local and international—and governments are responsible for the success of these programs. Hence, the World Health Organization's universal eye health global action plan for 2014–2019 has a goal of reducing the public health problem of blindness and ensuring access to comprehensive eye care; the plan aims to integrate eye health into health systems, thus providing universal eye health coverage (UEHC). This article discusses the challenges faced by low- and middle-income countries in strengthening the six building blocks of the health system. It discusses how the health systems in these countries need to be geared toward tackling the issues of emerging noncommunicable eye diseases, existing infectious diseases, and the common causes of blindness and visual impairment, such as cataract and refractive error. It also discusses how some of the comprehensive eye care models in the developing world have addressed these challenges. Moving ahead, if we are to achieve UEHC, we need to develop robust, sustainable, good-quality, comprehensive eye care programs throughout the world, focusing on the areas of greatest need. We also need to develop public health approaches for more complex problems such as diabetic retinopathy, glaucoma, childhood blindness, corneal blindness, and low vision. There is also a great need to train high-level human resources of all cadres in adequate numbers and quality. In addition to this, we need to exploit the benefits of modern technological innovations in information, communications, biomedical technology, and other domains to enhance quality of, access to, and equity in eye care.
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EK (DLEK, DSEK, DMEK): New Frontier in Cornea Surgery
Vol. 3 (2017), pp. 69–90More LessEndothelial keratoplasty (EK) has revolutionized treatment of corneal endothelial dysfunction. Compared with penetrating keratoplasty (PK), EK provides faster and more reliable visual rehabilitation while maintaining the eye's structural integrity. The number of EK procedures is growing annually and surpassed PK in the United States in 2012. The most widely used iteration, Descemet stripping endothelial keratoplasty (DSEK), implants healthy donor endothelium, Descemet membrane, and posterior stroma. Descemet membrane endothelial keratoplasty (DMEK) eliminates the donor stromal layer. Although more surgically challenging than DSEK, DMEK provides even faster visual rehabilitation and reduced risk of immunologic rejection, so its use is growing. Potential future alternatives to EK that could help address the unmet demand for donor corneas include removing central guttae and regenerating a central endothelial cell layer from healthy peripheral cells in patients with Fuchs’ dystrophy or injecting cultured human corneal endothelial cells to rehabilitate eyes without residual healthy endothelium.
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Neuroprotection in Glaucoma: Animal Models and Clinical Trials
Vol. 3 (2017), pp. 91–120More LessGlaucoma is a progressive neurodegenerative disease that frequently results in irreversible blindness. Glaucoma causes death of retinal ganglion cells (RGCs) and their axons in the optic nerve, resulting in visual field deficits and eventual loss of visual acuity. Glaucoma is a complex optic neuropathy, and a successful strategy for its treatment requires not only better management of known risk factors such as elevated intraocular pressure and the development of improved tools for detecting RGC injury but also treatments that address this injury (i.e., neuroprotection). Experimental models of glaucoma provide insight into the cellular and molecular mechanisms of glaucomatous optic neuropathy and aid the development of neuroprotective therapies.
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Vectors and Gene Delivery to the Retina
Vol. 3 (2017), pp. 121–140More LessOne of the great advantages of the retina as a target tissue for gene delivery is the wide array of genetic tools that have been developed in the past decade. This includes a variety of vectors for therapeutic gene delivery to most types of retinal neurons and glia, as well as cell type–specific promoters for restricted gene expression in distinct neuronal subtypes. Within the scope of neuroscience applications and for gene therapy, it is now routine to express reporter genes, replacement genes, neuronal activity indicators, and microbial opsins in specific neuronal types in the mouse retina. However, there are considerable anatomical, physiological, immunological, and behavioral differences between the mouse and the human that limit the usefulness of these tools in humans and nonhuman primates. Several advances are now being made toward the goal of applying viral targeting tools to understand the primate retina. Here, we describe these advances, consider their potential to advance our understanding of the primate retina, and describe what will be needed to move forward.
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Electrical Stimulation of Visual Cortex: Relevance for the Development of Visual Cortical Prosthetics
Vol. 3 (2017), pp. 141–166More LessElectrical stimulation of the cerebral cortex is a powerful tool for exploring cortical function. Stimulation of early visual cortical areas is easily detected by subjects and produces simple visual percepts known as phosphenes. A device implanted in visual cortex that generates patterns of phosphenes could be used as a substitute for natural vision in blind patients. We review the possibilities and limitations of such a device, termed a visual cortical prosthetic. Currently, we can predict the location and size of phosphenes produced by stimulation of single electrodes. A functional prosthetic, however, must produce spatial temporal patterns of activity that will result in the perception of complex visual objects. Although stimulation of later visual cortical areas alone usually does not lead to a visual percept, it can alter visual perception and the performance of visual behaviors, and training subjects to use signals injected into these areas may be possible.
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The Functional Neuroanatomy of Human Face Perception
Vol. 3 (2017), pp. 167–196More LessFace perception is critical for normal social functioning and is mediated by a network of regions in the ventral visual stream. In this review, we describe recent neuroimaging findings regarding the macro- and microscopic anatomical features of the ventral face network, the characteristics of white matter connections, and basic computations performed by population receptive fields within face-selective regions composing this network. We emphasize the importance of the neural tissue properties and white matter connections of each region, as these anatomical properties may be tightly linked to the functional characteristics of the ventral face network. We end by considering how empirical investigations of the neural architecture of the face network may inform the development of computational models and shed light on how computations in the face network enable efficient face perception.
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Circuits for Action and Cognition: A View from the Superior Colliculus
Vol. 3 (2017), pp. 197–226More LessThe superior colliculus is one of the most well-studied structures in the brain, and with each new report, its proposed role in behavior seems to increase in complexity. Forty years of evidence show that the colliculus is critical for reorienting an organism toward objects of interest. In monkeys, this involves saccadic eye movements. Recent work in the monkey colliculus and in the homologous optic tectum of the bird extends our understanding of the role of the colliculus in higher mental functions, such as attention and decision making. In this review, we highlight some of these recent results, as well as those capitalizing on circuit-based methodologies using transgenic mice models, to understand the contribution of the colliculus to attention and decision making. The wealth of information we have about the colliculus, together with new tools, provides a unique opportunity to obtain a detailed accounting of the neurons, circuits, and computations that underlie complex behavior.
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Visual Decision-Making in an Uncertain and Dynamic World
Vol. 3 (2017), pp. 227–250More LessThe right decision today may be the wrong decision tomorrow. We live in a world in which expectations, contingencies, and goals continually evolve and change. Thus, decisions do not occur in isolation but rather are tightly embedded in these streams of temporal dependencies. Accordingly, even relatively straightforward visual decisions must take into account not just the immediate sensory input but also past experiences and future goals and expectations. Here, we evaluate recent progress in understanding how the brain implements these dependencies. We show that visual decision-making relies on mechanisms of evidence accumulation and commitment that have been studied extensively under relatively static, isolated conditions but in general can operate much more flexibly. A deeper understanding of these mechanisms will require identifying the principles that govern this flexibility, which must operate across different timescales to produce effective decisions in uncertain and dynamic environments.
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Higher-Order Areas of the Mouse Visual Cortex
Vol. 3 (2017), pp. 251–273More LessThe brain has evolved to transform sensory information in the environment into neural representations that can be used for perception and action. Higher-order sensory cortical areas, with their increasingly complex receptive fields and integrative properties, are thought to be critical nodes for this function. This is especially true in the primate visual cortex, in which functionally specialized areas are engaged in parallel streams to support diverse computations. Recent anatomical and physiological studies of the mouse visual cortex have revealed a similarly complex network of specialized higher-order areas. This structure provides a useful model for determining the synaptic and circuit mechanisms through which information is transformed across distinct processing stages. In this review, we summarize the current knowledge on the layout, connectivity, and functional properties of the higher visual areas in the mouse. In addition, we speculate on the contribution of these areas to perception and action, and how knowledge of the mouse visual system can inform us about the principles that govern information processing in integrated networks.
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Textures as Probes of Visual Processing
Vol. 3 (2017), pp. 275–296More LessVisual textures are a class of stimuli with properties that make them well suited for addressing general questions about visual function at the levels of behavior and neural mechanism. They have structure across multiple spatial scales, they put the focus on the inferential nature of visual processing, and they help bridge the gap between stimuli that are analytically convenient and the complex, naturalistic stimuli that have the greatest biological relevance. Key questions that are well suited for analysis via visual textures include the nature and structure of perceptual spaces, modulation of early visual processing by task, and the transformation of sensory stimuli into patterns of population activity that are relevant to perception.
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Binocular Mechanisms of 3D Motion Processing
Vol. 3 (2017), pp. 297–318More LessThe visual system must recover important properties of the external environment if its host is to survive. Because the retinae are effectively two-dimensional but the world is three-dimensional (3D), the patterns of stimulation both within and across the eyes must be used to infer the distal stimulus—the environment—in all three dimensions. Moreover, animals and elements in the environment move, which means the input contains rich temporal information. Here, in addition to reviewing the literature, we discuss how and why prior work has focused on purported isolated systems (e.g., stereopsis) or cues (e.g., horizontal disparity) that do not necessarily map elegantly on to the computations and complex patterns of stimulation that arise when visual systems operate within the real world. We thus also introduce the binoptic flow field (BFF) as a description of the 3D motion information available in realistic environments, which can foster the use of ecologically valid yet well-controlled stimuli. Further, it can help clarify how future studies can more directly focus on the computations and stimulus properties the visual system might use to support perception and behavior in a dynamic 3D world.
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Probabilistic Computations for Attention, Eye Movements, and Search
Vol. 3 (2017), pp. 319–342More LessThe term visual attention immediately evokes the idea of limited resources, serial processing, or a zoom metaphor. But evidence has slowly accumulated that computations that take into account probabilistic relationships among visual forms and the target contribute to optimizing decisions in biological and artificial organisms, even without considering these limited-capacity processes in covert attention or even foveation. The benefits from such computations can be formalized within the framework of an ideal Bayesian observer and can be related to the classic theory of sensory cue combination in vision science and context-driven approaches to object detection in computer vision. The framework can account for a large range of behavioral findings across distinct experimental paradigms, including visual search, cueing, and scene context. I argue that these forms of probabilistic computations might be fundamental to optimizing decisions in many species and review human experiments trying to identify scene properties that serve as cues to guide eye movements and facilitate search. I conclude by discussing contributions of attention beyond probabilistic computations but argue that the framework's merit is to unify many basic paradigms to study attention under a single theory.
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Visual Perceptual Learning and Models
Vol. 3 (2017), pp. 343–363More LessVisual perceptual learning through practice or training can significantly improve performance on visual tasks. Originally seen as a manifestation of plasticity in the primary visual cortex, perceptual learning is more readily understood as improvements in the function of brain networks that integrate processes, including sensory representations, decision, attention, and reward, and balance plasticity with system stability. This review considers the primary phenomena of perceptual learning, theories of perceptual learning, and perceptual learning's effect on signal and noise in visual processing and decision. Models, especially computational models, play a key role in behavioral and physiological investigations of the mechanisms of perceptual learning and for understanding, predicting, and optimizing human perceptual processes, learning, and performance. Performance improvements resulting from reweighting or readout of sensory inputs to decision provide a strong theoretical framework for interpreting perceptual learning and transfer that may prove useful in optimizing learning in real-world applications.
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Material Perception
Vol. 3 (2017), pp. 365–388More LessUnder typical viewing conditions, human observers effortlessly recognize materials and infer their physical, functional, and multisensory properties at a glance. Without touching materials, we can usually tell whether they would feel hard or soft, rough or smooth, wet or dry. We have vivid visual intuitions about how deformable materials like liquids or textiles respond to external forces and how surfaces like chrome, wax, or leather change appearance when formed into different shapes or viewed under different lighting. These achievements are impressive because the retinal image results from complex optical interactions between lighting, shape, and material, which cannot easily be disentangled. Here I argue that because of the diversity, mutability, and complexity of materials, they pose enormous challenges to vision science: What is material appearance, and how do we measure it? How are material properties estimated and represented? Resolving these questions causes us to scrutinize the basic assumptions of mid-level vision.
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Vision and Action
Vol. 3 (2017), pp. 389–413More LessInvestigation of natural behavior has contributed a number of insights to our understanding of visual guidance of actions by highlighting the importance of behavioral goals and focusing attention on how vision and action play out in time. In this context, humans make continuous sequences of sensory-motor decisions to satisfy current behavioral goals, and the role of vision is to provide the relevant information for making good decisions in order to achieve those goals. This conceptualization of visually guided actions as a sequence of sensory-motor decisions has been formalized within the framework of statistical decision theory, which structures the problem and provides the context for much recent progress in vision and action. Components of a good decision include the task, which defines the behavioral goals, the rewards and costs associated with those goals, uncertainty about the state of the world, and prior knowledge.
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