Carotenoids play pivotal roles in vision as light filters and precursor of chromophore. Many vertebrates also display the colorful pigments as ornaments in bare skin parts and feathers. Proteins involved in the transport and metabolism of these lipids have been identified including class B scavenger receptors and carotenoid cleavage dioxygenases. Recent research implicates members of the Aster protein family, also known as GRAM domain‐containing (GRAMD), in carotenoid metabolism. These multi‐domain proteins facilitate the intracellular movement of carotenoids from their site of (...) cellular uptake by scavenger receptors to the site of their metabolic processing by carotenoid cleavage dioxygenases. We provide a model how the coordinated interplay of these proteins and their differential expression establishes carotenoid distribution patterns and function in tissues, with particular emphasis on the human retina. (shrink)

The human fovea is known for its distinctive pit‐like appearance, which results from the displacement of retinal layers superficial to the photoreceptors cells. The photoreceptors are found at high density within the foveal region but not the surrounding retina. Efforts to elucidate the mechanisms responsible for these unique features have ruled out cell death as an explanation for pit formation and changes in cell proliferation as the cause of increased photoreceptor density. These findings have led to speculation that (...) mechanical forces acting within and on the retina during development underly the formation of foveal architecture. Here we review eye morphogenesis and retinal remodeling in human embryonic development. Our meta‐analysis of the literature suggests that fovea formation is a protracted process involving dynamic changes in ocular shape that start early and continue throughout most of human embryonic development. From these observations, we propose a new model for fovea development. (shrink)

The ontogeny of the vertebrate retina has been a topic of interest to developmental biologists and human geneticists for many decades. Understanding the unfolding of the genetic program that transforms a field of progenitors cells into a functionally complex and multi‐layered sensory organ is a formidable challenge. Although classical genetic studies succeeded in identifying the key regulators of retina specification, understanding the architecture of their gene network and predicting their behavior are still a distant hope. The emergence (...) of next‐generation sequencing platforms revolutionized the field unlocking the access to genome‐wide datasets. Emerging techniques such as RNA‐seq, ChIP‐seq, ATAC‐seq, or single cell RNA‐seq are used to characterize eye developmental programs. These studies provide valuable information on the transcriptional and cis‐regulatory profiles of precursors and differentiated cells, outlining the trajectories that connect each intermediate state. Here, recent systems biology efforts are reviewed to understand the genetic programs shaping the vertebrate retina. (shrink)

An Atlas of the fine structure of the retina in Primates including humans.

ArgumentThis article explores the entangled histories of three imaging techniques in early nineteenth-century British physical science, techniques in which a dynamic event (such as a sound vibration or an electric spark) was made to leave behind a fixed trace on a sensitive surface. Three categories of “sensitive surface” are examined in turn: first, a metal plate covered in fine dust; second, the retina of the human eye; and finally, a surface covered with a light-sensitive chemical emulsion (a photographic (...) plate). For physicists Michael Faraday and Charles Wheatstone, and photographic pioneer William Henry Fox Talbot, transient phenomena could be studied through careful observation and manipulation of the patterns wrought on these different surfaces, and through an understanding of how the imaging process unfolded through time. This exposes the often-ignored materiality and temporality of epistemic practices around nineteenth-century scientific images said to be “drawn by nature.”. (shrink)

Over 10 years ago, Pax‐6 was shown to play an evolutionarily conserved role in controlling eye formation from Drosophila to humans.1 Since then, the identification of an entire cascade of conserved eye determination genes has brought a new understanding to the developmental relationship between the insect compound eye and the vertebrate camera eye.2 Additional studies are now beginning to suggest that even late aspects of eye development, including cell type specification, also share common molecular machinery. In this commentary, I will (...) discuss some of these findings, with a particular focus on the recent study by Dyer et al.3 describing a novel role for the Prox1 transcription factor in specifying horizontal cells in the mouse retina. As Prospero, the Drosophila homolog of Prox1, also participates in retinal cell specification, these data provide a forum for asking new questions concerning pathways that may regulate retinogenesis across evolution. BioEssays 25:921–925, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

The complex sensation of vision begins with the relatively simple photoisomerization of the visual pigment chromophore 11-cis-retinal to its all-trans configuration. This event initiates a series of biochemical reactions that are collectively referred to as phototransduction, which ultimately lead to a change in the electrochemical signaling of the photoreceptor cell. To operate in a wide range of light intensities, however, the phototransduction pathway must allow for adjustments to background light. These take place through physiological adaptation processes that rely primarily on (...) Ca2+ ions. While Ca2+ may modulate some activities directly, it is more often the case that Ca2+-binding proteins mediate between transient changes in the concentration of Ca2+ and the adaptation processes that are associated with phototransduction. Recently, combined genetic, physiological, and biochemical analyses have yielded new insights about the properties and functions of many phototransduction-specific components, including some novel Ca2+-binding proteins. Understanding these Ca2+-binding proteins will provide a more complete picture of visual transduction, including the mechanisms associated with adaptation, and of related degenerative diseases. BioEssays 22:337–350, 2000. © 2000 John Wiley & Sons, Inc. (shrink)

Daily rhythms are a ubiquitous feature of living systems. Generally, these rhythms are not just passive consequences of cyclic fluctuations in the environment, but instead originate within the organism. In mammals, including humans, the master pacemaker controlling 24‐hour rhythms is localized in the suprachiasmatic nuclei of the hypothalamus. This circadian clock is responsible for the temporal organization of a wide variety of functions, ranging from sleep and food intake, to physiological measures such as body temperature, heart rate and hormone release. (...) The retinal circadian clock was the first extra‐SCN circadian oscillator to be discovered in mammals and several studies have now demonstrated that many of the physiological, cellular and molecular rhythms that are present within the retina are under the control of a retinal circadian clock, or more likely a network of hierarchically organized circadian clocks that are present within this tissue. BioEssays 30:624–633, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Early and accurate diagnosis of glaucoma is critical for avoiding human vision deterioration and preventing blindness. A deep-neural-network model has been developed for the diagnosis of glaucoma based on Heidelberg retina tomography, called “Seeking Common Features and Reserving Differences Net” to make full use of the HRT data. In this work, the proposed SCRD-Net model achieved an area under the curve of 94.0%. For the two HRT image modalities, the model sensitivities were 91.2% and 78.3% at specificities of (...) 0.85 and 0.95, respectively. These results demonstrate a significant improvement over earlier results. In addition, we visualized the network outputs to develop an interpretation of the learned mechanism for discriminating glaucoma and normal images. Thus, the SCRD-Net can be an effective diagnostic indicator of glaucoma during clinical screening. To facilitate SCRD-Net utilization by the scientific community, the code implementation will be made publicly available. (shrink)

Colour constancy refers to the ability to extract information about surface colours independently of illumination conditions. A ripe strawberry, for example, appears the same red when viewed under a blue sky or a reddish sunset. Since Land's pioneering work, discussion has centred on the issue whether colour constancy is achieved primarily in the retina or visual cortex. Recently, the debate has shifted to a consideration of the constraints imposed by various psychophysical tasks and instructions. Humans can judge illuminant colour, (...) reflected-light colour, surface colour, and the relationship between surface colours within a scene. Such observations suggest that colour constancy may not be a unitary phenomenon, and that its different aspects may be mediated at different levels in the visual system. Several questions therefore arise: are the tasks of surface estimation and illuminant estimation complementary, insofar as good performance in one implies poor performance in the other? How does retinal adaptation alter performance? Is colour vision tuned to the statistical composition of natural surfaces and illuminants? What role does colour-opponent processing in retina and cortex play in colour constancy? These and related questions are explored here in order to better understand what we mean when we ask: "Why do strawberries look red?". (shrink)

This chapter contains sections titled: * 1 Introduction * 2 Historical Views of Human Nature * 3 Physicalism in Christian Scholarship * 4 Contributions from Contemporary Science * 5 Conclusion * Bibliography.

Suppose it is 2025 and being a technophile, you purchase brain enhancements as they become readily available. First, you add a mobile internet connection to your retina, then, you enhance your working memory by adding neural circuitry. You are now officially a cyborg. Now skip ahead to 2040. Through nanotechnological therapies and enhancements you are able to extend your lifespan, and as the years progress, you continue to accumulate more far-reaching enhancements. By 2060, after several small but cumulatively profound (...) alterations, you are a “posthuman.” To quote philosopher Nick Bostrom, posthumans are possible future beings, “whose basic capacities so radically exceed those of present humans as to be no longer unambiguously human by our current standards” (Bostrom 2003c). At this point, your intelligence is enhanced not just in terms of speed of mental processing; you are now able to make rich connections that you were not able to make before. Unenhanced humans, or “naturals,” seem to you to be intellectually disabled—you have little in common with them—but as a transhumanist, you are supportive of their right to not enhance (Bostrom 2003c; Garreau 2005; Kurzweil 2005). (shrink)

A common view in both philosophy and the vision sciences is that, in human vision, wavelength information is primarily ‘for’ colouring: for seeing surfaces and various media as having colours. In this article we examine this assumption of ‘colour-for-colouring’. To motivate the need for an alternative theory, we begin with three major puzzles from neurophysiology, puzzles that are not explained by the standard theory. We then ask about the role of wavelength information in vision writ large. How might wavelength (...) information be used by any monochromat or dichromat and, finally, by a trichromatic primate with object vision? We suggest that there is no single ‘advantage’ to trichromaticity but a multiplicity, only one of which is the ability to see surfaces and so on as having categorical colours. Instead, the human trichromatic retina exemplifies a scheme for a general encoding of wavelength information given the constraints imposed by high spatial resolution object vision. Chromatic vision, like its partner, luminance vision, is primarily for seeing. Viewed this way, the ‘puzzles’ presented at the outset make perfect sense. 1 Reframing the Problem1.1 Introduction1.2 Three puzzles1.2.1 Why is trichromatic vision an anomaly in diurnal mammals?1.2.2 Why does the colour system occupy such a large and central part in human vision?1.2.3 Why are the blue cones so rare?1.3 Recasting the question2 The Costs and Benefits of Spectral Vision2.1 Spectral information and object vision2.2 Encoding the spectral dimension of light2.2.1 ‘General’ versus ‘specific’ encoding2.2.2 Spectral encoding and the monochromat2.2.3 Spectral encoding and the dichromat2.2.4 Spectral encoding and the human trichromat2.3 Three puzzles revisited2.3.1 Why is trichromatic vision an anomaly in diurnal mammals?2.3.2 Why does the colour system occupy such a large and central part in human vision?2.3.3 Why are the blue cones so rare3 Conclusion. (shrink)

Melatonin, the neuro‐hormone synthesized during the night, has recently seen an unexpected extension of its functional implications toward type 2 diabetes development, visual functions, sleep disturbances, and depression. Transgenic mouse models were instrumental for the establishment of the link between melatonin and these major human diseases. Most of the actions of melatonin are mediated by two types of G protein‐coupled receptors, named MT1 and MT2, which are expressed in many different organs and tissues. Understanding the pharmacology and function of (...) mouse MT1 and MT2 receptors, including MT1/MT2 heteromers, will be of crucial importance to evaluate the relevance of these mouse models for future therapeutic developments. This review will critically discuss these aspects, and give some perspectives including the generation of new mouse models. (shrink)

The physiological blind spot corresponds to the optic disc where the retina contains no light-detecting photoreceptor cells. Our perception seemingly fills in this gap in input. Here we suggest that rather than an active process, such perceptual filling-in could instead be a consequence of the integration of visual inputs at higher stages of processing discounting the local absence of retinal input. Using functional brain imaging, we resolved the retinotopic representation of the physiological blind spot in early human visual (...) cortex and measured responses while participants perceived filling-in. Responses in early visual areas simply reflected the absence of visual input. In contrast, higher extrastriate regions responded more to stimuli in the eye containing the blind spot than the fellow eye. However, this signature was independent of filling-in. We argue that these findings agree with philosophical accounts that posit that the concept of filling-in of absent retinal input is unnecessary. (shrink)

A human being viewing a defocused television tube with sweep voltages turned off will see point scintillations at sufficiently low intensities. We show that quantum mechanics predicts these scintillations. Furthermore, by assuming a response of the human nervous system of a type not inconsistent with experiment, measurement theory is used to show that these scintillations will be distributed in proportion to the magnitude squared of the electron wave function incident upon the television tube screen. This nervous system response (...) is to break up the wave incident upon a spot on the retina into a number of similar waves transmitted by different nerves to the brain. The number of these waves is proportional to the incident energy density. Since the theory itself predicts the proper probability distribution, it is unnecessary to introduce a postulate for it. (shrink)

This chapter focuses on one of the common fallacies in Western philosophy called 'homunculus fallacy' (HmF). The HmF was coined by Anthony Kenny in 1971, in his essay by the same name. Following Ludwig Wittgenstein, Kenny describes the fallacy as occurring when we ascribe to the brain attributes that can be ascribed only to the animal as a whole. Historically this fallacy is connected to the theory of vision or what is sometimes called the Cartesian theater. Someone might explain (...) class='Hi'>human vision by saying that when we look around at objects in the world, the light forms an image on the retinas of eyes and something or some little person (where the term homunculus comes from) in the brain looks at these as if they were images on a movie screen. (shrink)

Organoids are three-dimensional biological structures grown in vitro from different kinds of stem cells that self-organise mimicking real organs with organ-specific cell types. Recently, researchers have managed to produce human organoids which have structural and functional properties very similar to those of different organs, such as the retina, the intestines, the kidneys, the pancreas, the liver and the inner ear. Organoids are considered a great resource for biomedical research, as they allow for a detailed study of the development (...) and pathologies of human cells; they also make it possible to test new molecules on human tissue. Furthermore, organoids have helped research take a step forward in the field of personalised medicine and transplants. However, some ethical issues have arisen concerning the origin of the cells that are used to produce organoids and their properties. In particular, there are new, relevant and so-far overlooked ethical questions concerning cerebral organoids. Scientists have created so-called mini-brains as developed as a few-months-old fetus, albeit smaller and with many structural and functional differences. However, cerebral organoids exhibit neural connections and electrical activity, raising the question whether they are or will one day be somewhat sentient. In principle, this can be measured with some techniques that are already available, which are used for brain-injured non-communicating patients. If brain organoids were to show a glimpse of sensibility, an ethical discussion on their use in clinical research and practice would be necessary. (shrink)

When we look at a tree, two images of it are formed, one on each of our retinas. Why, then, asks the child or the philosopher, do we not see two trees?1 Thomas Reid offers an answer to this question in the section of his Inquiry into the Human Mind entitled ‘Of seeing objects single with two eyes’. The principles he invokes in his answer serve at the same time to explain why we do occasionally see objects double. In (...) Part I of this essay, I examine the principles Reid uses to explain single and double vision. This part is mostly an exercise in the history of cognitive science, but it raises questions of interest to philosophers along the way. In Part II, I turn to a hard-core philosophical problem raised by double vision, namely, whether double vision constitutes an objection to the direct realist theory of perception, which was one of Reid's main philosophical purposes to promote. (shrink)

Ein Homunkulus im philosophischen Sprachgebrauch ist eine postulierte menschenähnliche Instanz, die ausdrücklich oder unausdrücklich zur Erklärung der Arbeitsweise des menschlichen Geistes herangezogen wird. Als Homunkulus-Fehlschluß wird die Praxis bezeichnet, Prädikate, die auf kognitive oder perzeptive Leistungen einer ganzen Person zutreffen, auch auf Teile von Personen oder auf subpersonale Vorgänge anzuwenden, was typischerweise zu einem Regreß führt. Der vorliegende Beitrag erörtert den Homunkulus-Fehlschluß zunächst in argumentationstheoretischer Hinsicht und stellt dabei ein Diagnoseschema auf. Dann werden zwei Anwendungsfelder erörtert: Instanzenmodelle der Psyche (Platon, (...) Freud) sind ihrer Natur nach homunkulusgefährdet, denn es ist aufgrund der holistischen Zuschreibungsbedingungen mentaler Fähigkeiten schwer plausibel zu machen, wie eine innerpsychische Instanz den ihr zugedachten Beitrag leisten soll, ohne über eine eigene Psyche zu verfügen. Der zweite Anwendungsfall ist das Problem des invertierten Netzhautbildes in der Philosophie der Wahrnehmung, das wissenschafts- und philosophiegeschichtlich eingebettet und unter besonderer Berücksichtigung von Descartes diskutiert wird. Schließlich werden offensive Rechtfertigungen homunkularer Redeweisen erörtert und größtenteils zurückgewiesen. -- The homunculus fallacy is committed when someone tries to explain how the human mind works by postulating a little man within the mind or the brain. Homunculi are rarely posited with one’s eyes open. Rather, the fallacy occurs when predicates that properly apply to cognitive or perceptual achievements of persons get applied to subpersonal processes or to parts of persons (e.g., brains). The paper suggests a pattern for diagnosing homunculus fallacies. After taking a look at Freud’s and Platon’s homuncular metapsychologies, a case study is discussed in detail: the problem of the inverted retinal image which plagued the philosophy of perception since Kepler formulated it in 1604. It is argued that the irradiation patterns on the retina are not images, on pain of committing the homunculus fallacy. The paper closes with the repudiation of some frank apologies of homuncular explanations. (shrink)

Deciphering the neural basis of subjective experience remains one of the great challenges in the natural sciences. The structural complexity and the limitations around invasive experimental manipulations of the human brain have impeded progress towards this goal. While animals cannot directly report first-person subjective experiences, their ability to exhibit flexible behaviours such as motivational trade-offs are generally considered evidence of sentience. The worm _Caenorhabditis elegans_ affords the unique opportunity to describe the circuitry underlying subjective experience at a single cell (...) level as its whole neural connectome is known and moreover, these animals exhibit motivational trade-offs. We started with the premise that these worms were sentient and then sought to understand the neurons that were both necessary and sufficient for a motivational trade-off involving the rewarding experience of food and the negative experience of an aversive odour. A simple hierarchical network consisting of two chemosensory neurons and three interneurons was found to produce an output to motoneurons that enabled worms to respond in a contextually appropriate manner to an aversive odour according to the worm's hunger state. Given that this circuitry is like that found in the human spinal cord, retina, and primary visual cortex, three regions which are neither necessary nor sufficient for subjective experience, we conclude that motivational trade-offs are not a criterion for subjective experience in worms. Furthermore, once the neural substrate for a behaviour is described, we question the explanatory role of subjective experience in behaviour. (shrink)

This chapter examines a question at the intersection of the mind-body problem and the analysis of mental representation: the question of the direction of constraint between psychological fact and theory and neurophysiological or physical fact and theory. Does physiology constrain psychology? Are physiological facts more basic than psychological facts? Or do psychological theories, including representational analyses, guide and constrain physiology? Despite the antireductionist bent of functionalist positions, it has generally been assumed that physics or physiology are more basic than, and (...) hence contraining on, psychological fact and theory. Section 1 sketches the intuitions that would lead one to adopt such a view. The chapter then examines whether one-sided constraint has been and should be found in practice. It argues that philosophical analysis of psychological science shows that rigorous functional analyses can be carried out in advance of physiological knowledge. Indeed, in the investigation of sensory perception, ascription of psychological function leads the way in the individuation and investigation of neurophysiology. We shall look at several cases in visual perception (binocular single vision, stereopsis, and color vision), in which psychological results have provided a basis for physiological research. It is tempting to think that the psychological functions that enable physiological investigation would be Wrightian teleofunctions. It is, thus, natural to suppose that psychologists and neurophysiologists have proceeded with a conception of the purpose of a given neural structure, and have viewed neural anatomy and neural activity as the substrate for or instantiation of various properly psychological functions. For example, neuroscientists surely understand that the eye and visual system are for seeing, rather than for detecting an electric discharge in the vicinity of the retina (which sighted humans can do, via the subjective light produced by such discharges), and they guide their investigations of the eye, visual cortex, and intervening pathways accordingly. As a result, they will view rods and cones in the eye as photoreceptors, even though these structures will produce "output" (will respond with hyperpolarization) to other forms of energy. At the same time, there may be cases in which the functions that have guided research are in fact precisely determined input-output functions, whose teleofunctional status is absent or misdescribed. I will argue that in the case of trichromatic color matches, the psychological function involved is an input-output function, and that this result has implications for the description of color vision as a psychological capacity. (shrink)

For millions of years, biological creatures have dealt with the world without being able to see it; however, the change in the atmospheric condition during the Cambrian period and the subsequent increase of light, triggered the sudden evolution of vision and the consequent evolutionary benefits. Nevertheless, how from simple organisms to more complex animals have been able to generate meaning from the light who fell in their eyes and successfully engage the visual world remains unknown. As shown by many psychophysical (...) experiments, biological visual systems cannot measure the physical properties of the world. The light projected onto the retina is, in fact, unable to specify the physical properties of the world in which humans and other visually ‘intelligent’ animals behave; however, visual behaviours are habitually successful. Through psychophysical evidence, examples of the functioning of Artificial Neural Networks and a reflection upon visual appreciation in the cultural and artistic context, this paper shows how vision emerged by random trial and error during evolution and lifetime learning; how the functioning of ANNs may provide evidence and insights on how machine and human vision works; and how rethinking vision theory in terms of trial and error may offer a new approach to better understand vision—biological and artificial—and reveal new insights into why we like what we like. (shrink)

The efficient coding hypothesis posits that sensory systems are tuned to the regularities of their natural input. The statistics of natural image databases have been the topic of many studies, which have revealed biases in the distribution of orientations that are related to neural representations as well as behavior in psychophysical tasks. However, commonly used natural image databases contain images taken with a camera with a planar image sensor and limited field of view. Thus, these images do not incorporate the (...) physical properties of the visual system and its active use reflecting body and eye movements. Here, we investigate quantitatively, whether the active use of the visual system influences image statistics across the visual field by simulating visual behaviors in an avatar in a naturalistic virtual environment. Images with a field of view of 120° were generated during exploration of a virtual forest environment both for a human and cat avatar. The physical properties of the visual system were taken into account by projecting the images onto idealized retinas according to models of the eyes' geometrical optics. Crucially, different active gaze behaviors were simulated to obtain image ensembles that allow investigating the consequences of active visual behaviors on the statistics of the input to the visual system. In the central visual field, the statistics of the virtual images matched photographic images regarding their power spectra and a bias in edge orientations toward cardinal directions. At larger eccentricities, the cardinal bias was superimposed with a gradually increasing radial bias. The strength of this effect depends on the active visual behavior and the physical properties of the eye. There were also significant differences between the upper and lower visual field, which became stronger depending on how the environment was actively sampled. Taken together, the results show that quantitatively relating natural image statistics to neural representations and psychophysical behavior requires not only to take the structure of the environment into account, but also the physical properties of the visual system, and its active use in behavior. (shrink)

Michael Baxandall was probably the most important art historian of his generation, not just in Britain but in the world. In a series of books published between 1971 and 2003 he kept expanding the frontiers of the discipline, introducing new topics, new ways of writing, and new explanatory models, always demanding of himself and his readers an undissembling clarity of thought and expression. If art history is now a field that can hold its own with more established areas of the (...) humanities, it is largely because Baxandall had a talent to transmit to others through the printed page the powerful intellectual resources he had built up through tireless inward reflection. These resources he applied with equal engagement to Italian Renaissance art criticism, German wood sculpture, the understanding of shadows in the 18th century, the planning of the Forth Bridge, and the functions of the neural structure of the retina. (shrink)

This study evaluated the potential contribution of extrageniculate visual pathways to oculomotor orienting reflexes in hemianopic patients. It tested whether extrageniculate pathways mediate inhibition of return —a phenomenon characterized by slowed target detections at recently stimulated locations . Because hemianopic subjects cannot overtly respond to stimuli presented within their hemianopic field, we utilized a spatial cueing paradigm that capitalized on the fact that IOR operates in spatiotopic coordinates. Subjects moved their eyes so that a cue and a target presented at (...) the same spatial location were imaged successively onto blind and seeing portions of their retinas. One hemianopic patient showed a similar IOR effect from cues presented within both the seeing and the hemianopic fields. With a second hemianopic patient, only presentations of the cue to the subject's seeing field produced IOR. The explanation for this discrepancy is not evident. These observations highlight both the potential value and the pitfalls inherent in using “blindsight” as a window into human consciousness. (shrink)

It may be possible, one day, to use gene therapy to treat diseases whose genetic defects have been discerned. Because many genes responsible for inherited eye disorders within the retina have been identified, diseases of the eye are prime candidates for this form of therapy. The eye also has the advantage of being highly accessible with altered immunological properties, important considerations for easy delivery of virus and avoidance of systemic immune responses. Currently, adenovirus, adeno‐associated virus and lentivirus have been (...) used to successfully transfer genetic material to retinal pigment epithelium and photoreceptor cells. By harnessing therapeutic genes to these viruses, researchers have been able to demonstrate rescue in rodent models of retinitis pigmentosa, providing evidence that this form of therapy can be effective in delaying photoreceptor cell death. Future challenges include confirming therapeutic effects in animal models with eyes more anatomically similar to those of humans and demonstrating long‐term rescue with minimal toxicity. BioEssays 23:662–668, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:The Journal of Aesthetic Education 39.1 (2005) 77-92 [Access article in PDF] Art and the Teaching of Love Didier Maleuvre Art is rightly thought to be the domain of expression and illusion. It is expression because every work of art, however stone-faced or impersonal in aspect, is the product of human intention. And it is illusion because, however concrete, vivid, or raw, it holds up only images. These (...) two points — that art is expression and fiction — are deeply entrenched in the modern understanding of art. They are the twin pillars of our aesthetics.In the following I wish to argue that this focus on the expressive and the representative eclipse the most important dynamic of art — what I propose to call the communicative and the iconoclastic. By the former, I mean that art is primarily, not a subjectivity giving shape to a private vision, but a form of sanctifying the human conversation, that is, the encounter between subjectivities; by the latter, I mean to suggest that art is an image that paradoxically strives to go beyond the realm of images. On this account we will see that an image is artistic to the extent that it breaks through representation.Briefly put, art has a destination beyond itself. One should not imagine, as postmodernism ruled ex officio, that the essence of art is formal or social self-reflectivity. Certainly, self-mirroring occurs in art, but no more or less than in any act of intelligence. Moreover, it is not enough to affix tokens of self-consciousness onto an object to turn it into art. The aim of art is not art. Its destination is elsewhere; its aim is reality encountered and lived with.And the vehicle by which art travels into reality is not just skill, insight, knowledge, or intelligence. It is love. To defend these two propositions will be the gist of the following essay.The aim of education is rightly thought to be knowledge of the world. Knowledge, however, is of two kinds: one is concerned with storage of facts, the other with modes of relating to the world. The first is a technical pursuit; the second, moral practice. The sort of education fostered by art clearly belongs with the second sort. Art is less concerned with delivering [End Page 77] information about the world than teaching us about how to stand in relation to it, how to find our place in it, and live with it: through art we do not seek to master the world so much as become its denizens. It is a teaching of love. Art, Mind, and Reality Now, the idea that art is religious embrace of reality runs against a powerful philosophic doctrine: the idea, known as subjectivism — that the human mind is kept from reality by its own knowledge of reality. We perceive reality only through mental representations. I see a tree, I hear laughter, I taste tea. When my mind alights on these objects, they have already been retouched and recomposed by my senses. By the time I am aware of them, I have reordered the perceptual datum into the concepts of "tree," "laugher," "tea." So we really deal with conceptual images of things, even when those things fall on our head like rain, or trip us like an untied shoelace.Subjectivism takes art to be proof of its doctrine. No two artists have transposed the same landscape or object in exactly the same hues and forms. Monet may have wanted to put in his paintings only what the retina mirrored; still, in the end he painted like no other before him and an indisputable infusion of the Monet personality stamps his paintings. Likewise there is a Titian "take" on reality that is not Rubens's, a Constable way of painting gray watery skies that is not Corot's, or again a Twombly way of rendering the four seasons that is nothing like Vivaldi's. This, then, should be where art's commitment to reality expires — on the evidence that no two artworks have ever been able to... (shrink)

The experiments described in this publication had their start during the Second World War under the direction of Professor Sir Frederick Bartlett at Cambridge. The immediate aim was to compare the various tests that had been devised at one time or another to help in selecting people for such night tasks as required keen night vision. The work gradually turned into a laboratory investigation for studying the outstanding traits of the key tests. When the war came to an end, the (...) research was continued because it was seen to have importance for the theory of human vision in general. In the post-war investigations, special attention was paid to the way in which quantum properties of light might be related to excitation of the retina. (shrink)

Pericytes, like vascular smooth muscle cells, are perivascular cells closely associated with blood vessels throughout the body. Pericytes are necessary for vascular development and homeostasis, with particularly critical roles in the brain, where they are involved in regulating cerebral blood flow and establishing the blood-brain barrier. A role for pericytes during neurovascular disease pathogenesis is less clear—while some studies associate decreased pericyte coverage with select neurovascular diseases, others suggest increased pericyte infiltration in response to hypoxia or traumatic brain injury. Here, (...) we used an endothelial loss-of-function Recombination signal binding protein for immunoglobulin kappa J region (Rbpj)/Notch mediated mouse model of brain arteriovenous malformation (AVM) to investigate effects on pericytes during neurovascular disease pathogenesis. We tested the hypothesis that pericyte expansion, via morphological changes, and Platelet-derived growth factor B/Platelet-derived growth factor receptor β (Pdgf-B/Pdgfrβ)-dependent endothelial cell-pericyte communication are affected, during the pathogenesis of Rbpj mediated brain AVM in mice. Our data show that pericyte coverage of vascular endothelium expanded pathologically, to maintain coverage of vascular abnormalities in brain and retina, following endothelial deletion of Rbpj. In Rbpj-mutant brain, pericyte expansion was likely attributed to cytoplasmic process extension and not to increased pericyte proliferation. Despite expanding overall area of vessel coverage, pericytes from Rbpj-mutant brains showed decreased expression of Pdgfrβ, Neural (N)-cadherin, and cluster of differentiation (CD)146, as compared to controls, which likely affected Pdgf-B/Pdgfrβ-dependent communication and appositional associations between endothelial cells and pericytes in Rbpj-mutant brain microvessels. By contrast, and perhaps by compensatory mechanism, endothelial cells showed increased expression of N-cadherin. Our data identify cellular and molecular effects on brain pericytes, following endothelial deletion of Rbpj, and suggest pericytes as potential therapeutic targets for Rbpj/Notch related brain AVM. (shrink)