According to an influential philosophical view I call “the relational properties view”, “perspectival” properties, such as the elliptical appearance of a tilted coin, are relational properties of external objects. Philosophers have assessed this view on the basis of phenomenological, epistemological or other purely philosophical considerations. My aim in this paper is to examine whether it is possible to evaluate RPV empirically. In the first, negative part of the paper I consider and reject a certain tempting way of doing so. In (...) the second, positive part of the paper I suggest a novel way of evaluating RPV empirically, relying on the influential object files framework. (shrink)

The world perceived by a person undergoing vision without inversion of the retinal image has traditionally been described as inverted. Drawing on the philosophical work of Maurice Merleau-Ponty and the empirical research of Hubert Dolezal, I argue that this description is more reflective of a representationist conception of vision than of actual visual experience. The world initially perceived in vision without inversion of the retinal image is better described as lacking in lived significance rather than inverted; (...) vision without inversion of the retinal image affects the very content of the perceived world, including, importantly, its expressions and conducts, and not merely the orientation of this content. Moreover, I argue that the enactive approach, rather than a representationist approach, is best able to account for the perception of the world, after prolonged vision without inversion of the retinal image, as both normal and upright, yet still different from the world seen previously. Finally, in their attention to the perception of other people’s facial expressions, I argue that Merleau-Ponty and Dolezal draw out the existential significance of the enactive approach. In encountering another person, the most pressing task is generally not to observe this person’s features but, instead, to engage with this person’s expressions. (shrink)

Sensorimotor theorists of perception have argued that eye movement is a necessary condition for seeing on the basis that subjects whose retinal images do not move undergo a form of blindness. I show that the argument does not work.

A judge springs out of his car on the way to court in downtown Chicago and takes photographs of an inflatable rat. A while later he inserts these photographs into a decision involving another inflatable rodent. Judges now regularly insert pictures in judgments, but there is no study either of the genres or the precedential status of these modern visual emblemata, these pictorial interventions in the record. Using a comparative visual corpus of over three hundred images extracted from diverse common (...) law jurisdictions, the practice of retinal justice, the novelty of vision in decision, is here anatomized, choreographed, and critically classified. (shrink)

Cognition or higher brain activity is sometimes seen as a phenomenon greater than the sum of its parts. This viewpoint however is largely dependent on the state of the art of experimental techniques that endeavor to characterize morphology and its association to function. Retinal ganglion cells are readily accessible for this work and we discuss recent advances in computational techniques in identifying novel parameters that describe structural attributes possibly associated with specific function. These parameters are based on calculating wavelet (...) gradients from cell images followed by the extraction of meaningful measures including 2nd wavelet moment, entropy of orientation, and curvature. For the three cell types analyzed, the mean 2nd wavelet moment, which relates to the field of influence of the dendritic-tree segments was significantly different. cells had the highest mean 2nd wavelet moment, followed by the and cells (134 ± 22, 93 ± 19 and 63 ± 12, respectively). There was no significant difference between cells for entropy of orientation, indicating no class with a preferential orientation of their dendritic tree. Curvature provided similar results to the 2nd wavelet moment with cells having the highest curvature followed by and the cells (mean ± SD: 161 ± 15; 134 ± 22; 121 ± 15). Our feature space analysis also indicated a difference between these cell types. No difference was found between the and cell types and their physiological counterparts the Y and X cells based on wavelet analysis. Both the X and Y cells can be divided into two subtypes, the ON- and OFF-center cells based on the stratification level of the dendritic tree within the retina. Using 2nd wavelet moment, a difference in their morphological attributes, not reported previously, was noted for these subtypes. The 2nd wavelet moment and curvature are further discussed with respect to explaining regularity of spacing and coverage associated with retinal ganglion cell mosaics. (shrink)

Dans l'Essai pour une nouvelle théorie de la vision (1709) Berkeley critique un usage illégitime de l'optique géométrique dans l'explication de la perception des qualités spatiales. Toutefois, dans la Théorie de la vision défendue et expliquée (1733), il assigne à l'optique géométrique un rôle théorique positif, à côté de sa propre théorie de la vision. Nous défendons la thèse suivant laquelle une image rétinienne, chez Berkeley, est une configuration de corpuscules en mouvement, tangibles de droit. Cette lecture corrobore l'interprétation (...) d'une forme de corpuscularisme dans le système immatérialiste. In An Essay towards a New Theory of Vision (1709) Berkeley objects to an illegitimate use of geometrical optics in the explanation of our perception of spatial qualities. However, in The Theory of Vision, Vindicated and Explained (1733), he grants geometrical optics a positive theoretical role alongside his own philosophical theory of vision. I defend the claim that a retinal image, for Berkeley, is a configuration of moving corpuscles that are tangible in principle. This reading corroborates the interpretation according to which Berkeley accommodates a form of corpuscularism within his immaterialism. (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)

PurposeTo use the power of knowledge acquisition and machine learning in the development of a collaborative computer classification system based on the features of age-related macular degeneration (AMD).MethodsA vocabulary was acquired from four AMD experts who examined 100 ophthalmoscopic images. The vocabulary was analyzed, hierarchically structured, and incorporated into a collaborative computer classification system called IDOCS. Using this system, three of the experts examined images from a second set of digital images compiled from more than 1000 patients with AMD. Images (...) were annotated, and features were identified and defined. Decision trees, a machine learning method, were trained on the data collected and used to extract patterns. Interrelationships between the data from the different clinicians were investigated.ResultsSix drusen classes in the structured vocabulary were largely sufficient to describe all the identified features. The decision trees classified the data with 76.86% to 88.5% accuracy and distilled patterns in the form of hierarchical trees composed of 5 to 15 nodes. Experts were largely consistent in their characterization of soft, and to a lesser extent, hard drusen, but diverge in definition of other drusen. Size and crystalline morphology were the main determinants of drusen type across all experts.ConclusionsMachine learning is a powerful tool for the characterization of disease phenotypes. The creation of a defined feature set for AMD will facilitate the development of an IDOCS-based classification system. (shrink)

Neuroscience hasn’t shown how quite similar sensory circuits encode quite different colors and other qualia, nor how the unified pictorial form of images is encoded, nor how these codes yield conscious images. Neuroscience’s fixation here on cortical codes may be the culprit. Treating conscious images partly as retinal substances may avoid these problems. The evidence for conscious retinal images is that (a) the cortical codes for images are quite problematic, (b) injecting retinas with certain genes turns dichromats into (...) trichromats without cortical help, (c) retinas can discern colors by themselves without cortex, (d) retinal distortions appear in images but cortical distortions don’t, (e) retinal detectors support finely detailed colors, but V4 detectors don’t, due to their big receptive fields, (f) retinal activity has pictorial form, but viable cortical codes for pictorial form don’t exist. So, the colors and unified pictorial form of images arguably arise mainly across arrays of retinal detectors—not from abstract cortical codes. Images may be hidden in retinal activity beyond what EEGs show of it (cf. Strawson’s monism). Also, cortex refines these retinal images but cortical impairment (anesthesia, lesions, etc.) blocks awareness of them, for they’re no longer accessible to the mind’s subject-centered consciousness, resident in cortex. This proposal is largely testable and based in recent evidence. It avoids neuroscience’s elusive, problematic coded images and enigmatic explanations of how they become conscious. (shrink)

No one before Platter and Kepler proposed retinal reception of an inverted visual image. The dominant tradition in visual theory, especially that of Alhazen and his Western followers, subordinated the intra-ocular geometry of visual rays to the requirement for an upright image and to preconceptions about the precise nature of the visual spirit and its part in vision. Henry of Langenstein and an anonymous glossator in the late Middle Ages proposed alternatives to Alhazen, including the suggestion of (...) double inversion of the image. Leonardo da Vinci was aware of both Alhazen's theory and Henry's contradiction, but perhaps not of the anonymous hypothesis of double inversion. Leonardo's visual ‘theory’ has more the character of a critique than of a theoretical alternative, and he did not transcend the medieval concept of visual spirit. (shrink)

This article seeks the origin, in the theories of Ibn al-Haytham (Alhazen), Descartes, and Berkeley, of two-stage theories of spatial perception, which hold that visual perception involves both an immediate representation of the proximal stimulus in a two-dimensional ‘‘sensory core’’ and also a subsequent perception of the three dimensional world. The works of Ibn al-Haytham, Descartes, and Berkeley already frame the major theoretical options that guided visual theory into the twentieth century. The field of visual perception was the first area (...) of what we now call psychology to apply mathematics, through geometrical models as used by Euclid, Ptolemy, Ibn al-Haytham, and Descartes (among others). The article shows that Kepler’s discovery of the retinal image, which revolutionized visual anatomy and entailed fundamental changes in visual physiology, did not alter the basic structure of theories of spatial vision. These changes in visual physiology are advanced especially in Descartes' Dioptrics and his L'Homme. Berkeley develops a radically empirist theory vision, according to which visual perception of depth is learned through associative processes that rely on the sense of touch. But Descartes and Berkeley share the assertion that there is a two-dimensional sensory core that is in principle available to consciousness. They also share the observation that we don't usually perceived this core, but find depth and distance to be phenomenally immediate, a point they struggle to accommodate theoretically. If our interpretation is correct, it was not a change in the theory of the psychology of vision that engendered the idea of a sensory core, but rather the introduction of the theory into a new metaphysical context. (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)

This study examines the theology of the fourth-century bishop, Hilary of Poitiers, concentrating particularly on two commentaries written at different times in his life. The main focus of the study is on Hilary's anthropological theology.

Abstract:The notions "retinal images" and "retinal projection" are ubiquitous in both the scientific and philosophical literature on perception. However, this article argues that they belong to the former and should be kept out of the latter. In the context of the empirical investigation of perception, projections play a crucial role, and help articulate pressing research problems. But, as part of the phenomenological and conceptual analysis of perception, projections give rise to untenable models and to avoidable conundrums, such as (...) the much discussed issue of perceptual constancy. Why are projections and retinal images so prevalent in the philosophical literature? The author conjectures that the reason has to do with conceptual fallouts of the effort to give a geometric representation to changes of perspective, a mission more daunting than it initially appears to be, and one that leads to the problematic insertion of projections into phenomenology. He suggests that correcting this shows perceptual constancy to be a starting point rather than a challenge for phenomenology. (shrink)

When a circular coin is rotated in depth, is there any sense in which it comes to resemble an ellipse? While this question is at the center of a rich and divided philosophical tradition (with some scholars answering affirmatively and some negatively), Morales et al. (2020, 2021) took an empirical approach, reporting 10 experiments whose results favor such perspectival similarity. Recently, Burge and Burge (2022) offered a vigorous critique of this work, objecting to its approach and conclusions on both philosophical (...) and empirical grounds. Here, we answer these objections on both fronts. We show that Burge and Burge’s critique rests on misunderstandings of Morales et al.’s claims; of the relation between the data and conclusions; and of the philosophical context in which the work appears. Specifically, Burge and Burge attribute to us a much stronger (and stranger) view than we hold, involving the introduction of “a new entity” located “in some intermediate position(s) between the distal shape and the retinal image.” We do not hold this view. Indeed, once properly understood, most of Burge and Burge’s objections favor Morales et al.’s claims rather than oppose them. Finally, we discuss several questions that remain unanswered, and reflect on a productive path forward on these issues of foundational scientific and philosophical interest. (shrink)

Arguably the most foundational principle in perception research is that our experience of the world goes beyond the retinal image; we perceive the distal environment itself, not the proximal stimulation it causes. Shape may be the paradigm case of such “unconscious inference”: When a coin is rotated in depth, we infer the circular object it truly is, discarding the perspectival ellipse projected on our eyes. But is this really the fate of such perspectival shapes? Or does a tilted (...) coin retain an elliptical appearance even when we know it’s circular? This question has generated heated debate from Locke and Hume to the present; but whereas extant arguments rely primarily on introspection, this problem is also open to empirical test. If tilted coins bear a representational similarity to elliptical objects, then a circular coin should, when rotated, impair search for a distal ellipse. Here, nine experiments demonstrate that this is so, suggesting that perspectival shapes persist in the mind far longer than traditionally assumed. Subjects saw search arrays of three-dimensional “coins,” and simply had to locate a distally elliptical coin. Surprisingly, rotated circular coins slowed search for elliptical targets, even when subjects clearly knew the rotated coins were circular. This pattern arose with static and dynamic cues, couldn’t be explained by strategic responding or unfamiliarity, generalized across shape classes, and occurred even with sustained viewing. Finally, these effects extended beyond artificial displays to real-world objects viewed in naturalistic, full-cue conditions. We conclude that objects have a remarkably persistent dual character: their objective shape “out there,” and their perspectival shape “from here.”. (shrink)

Perceptual representations have distal content: they represent external objects and their properties, not light waves or retinal images. This basic fact presents a fundamental problem for ‘input-oriented’ theories of perceptual content. As I show in the first part of this paper, this even holds for what is arguably the most sophisticated input-oriented theory to date, namely Karen Neander's informational teleosemantics. In the second part of the paper, I develop a new version of informational teleosemantics, drawing partly on empirical psychology, (...) and partly on philosophical considerations. I shall argue that this version has all the virtues of Neander's original theory, but also the further crucial advantage of being able to account for the distality of perceptual content. (shrink)

Based on electrophysiological and anatomical studies, a prevalent conception is that the visual system recovers features of the world from retinal images to generate perceptions and guide behavior. This paradigm, however, is unable to explain why visual perceptions differ from physical measurements, or how behavior could routinely succeed on this basis. An alternative is that vision does not recover features of the world, but assigns perceptual qualities empirically by associating frequently occurring stimulus patterns with useful responses on the basis (...) of survival and reproductive success. The purpose of the present article is to briefly describe this strategy of vision and the evidence for it. (shrink)

Ecological Psychology and Enactivism both challenge representationist cognitive science, but the two approaches have only begun to engage in dialogue. Further conceptual clarification is required in which differences are as important as common ground. This paper enters the dialogue by focusing on important differences. After a brief account of the parallel histories of Ecological Psychology and Enactivism, we cover incompatibility between them regarding their theories of sensation and perception. First, we show how and why in ecological theory perception is, crucially, (...) not based on sensation. We elucidate this idea by examining the biological roots of work in the two fields, concentrating on Gibson and Varela and Maturana. We expound an ecological critique of any sensation-based approach to perception by detailing two topics: classic retinal image theories and perception in single-celled organisms. The second main point emphasizes the importance of the idea of organism-environment mutuality and its difference from structural coupling of sensations and motor behavior. We point out how ecological - phenomenological methods of inquiry grow out of mutualism and compare Gibson’s idea of visual kinesthesis to Merleau-Ponty’s idea of the lived body. Third, we conclude that Ecological Psychology and varieties of Enactivism are laying down different paths to pursue related goals. Thus, convergence of Ecological Psychology and Enactivism is not possible given their conflicting assumptions, but cross-fertilization is possible and desirable. (shrink)

Psychology and philosophy have long reflected on the role of perspective in vision. Since the dawn of modern vision science—roughly, since Helmholtz in the late 1800s—scientific explanations in vision have focused on understanding the computations that transform the sensed retinal image into percepts of the three-dimensional environment. The standard view in the science is that distal properties—viewpoint-independent properties of the environment (object shape) and viewpoint-dependent relational properties (3D orientation relative to the viewer)–are perceptually represented and that properties of (...) the proximal stimulus (in vision, the retinal image) are not. This view is woven into the nature of scientific explanation in perceptual psychology, and has guided impressive advances over the past 150 years. A recently published article suggests that in shape-perception, the standard view must be revised. It argues, on the basis of new empirical data, that a new entity—perspectival shape—should be introduced into scientific explanations of shape perception. Specifically, the article’s centrally advertised claim is that, in addition to distal shape, perspectival shape is perceived. We argue that this claim rests on a series of mistakes. Problems in experimental design entail that the article provides no empirical support for any claims regarding either perspective or the perception of shape. There are further problems in scientific reasoning and conceptual development. Detailing these criticisms and explaining how science treats these issues is meant to clarify method and theory, and to improve exchanges between the science and philosophy of perception. (shrink)

Psychophysical scaling models of the form R = f, with R the response and I some intensity of an attribute, all assume that people judge the amounts of an attribute. With simple biases excepted, most also assume that judgments are independent of space, time, and features of the situation other than the one being judged. Many data support these ideas: Magnitude estimations of brightness increase with luminance. Nevertheless, I argue that the general model is wrong. The stabilized retinal (...) class='Hi'>image literature shows that nothing is seen if light does not change over time. The classification literature shows that dimensions often combine to produce emergent properties that cannot be described by the elements in the stimulus. These and other effects cannot be adjusted for by simply adding variables to the general model because some factors do not combine linearly. The proposed alternative is that people initially judge the entire stimulus – the object in terms of its environment. This agrees with the constancy literature that shows that objects and their attributes are identified through their relations to other aspects of the scene. That the environment determines judgments is masked in scaling studies where the standard procedure is to hold context constant. In a typical brightness study the essential stimulus might be the intensity of the light or a difference between the light and the background. The two are perfectly confounded. This issue is examined in the case of audition. Judgments of the loudness of a tone depend on how much that tone differs from the previous tone in both pitch and loudness. To judge loudness people first seem to process the stimulus object in terms of differences between it and other aspects in the situation; only then do they assess the feature of interest. Psychophysical judgments will therefore be better interpreted by theories of attention that are based in biology or psychology than those that are based in classical physics. (shrink)

Action is a means of acquiring perceptual information about the environment. Turning around, for example, alters your spatial relations to surrounding objects and, hence, which of their properties you visually perceive. Moving your hand over an object’s surface enables you to feel its shape, temperature, and texture. Sniffing and walking around a room enables you to track down the source of an unpleasant smell. Active or passive movements of the body can also generate useful sources of perceptual information (Gibson 1966, (...) 1979). The pattern of optic flow in the retinal image produced by forward locomotion, for example, contains information about the direction in which you are heading, while motion parallax is a “cue” used by the visual system to estimate the relative distances of objects in your field of view. In these uncontroversial ways and others, perception is instrumentally dependent on action. According to an explanatory framework that Susan Hurley (1998) dubs the “Input-Output Picture”, the dependence of perception on action is purely instrumental: "Movement can alter sensory inputs and so result in different perceptions… changes in output are merely a means to changes in input, on which perception depends directly" (1998: 342). -/- The action-based theories of perception, reviewed in this entry, challenge the Input-Output Picture. They maintain that perception can also depend in a noninstrumental or constitutive way on action (or, more generally, on capacities for object-directed motor control). This position has taken many different forms in the history of philosophy and psychology. Most action-based theories of perception in the last 300 years, however, have looked to action in order to explain how vision, in particular, acquires either all or some of its spatial representational content. Accordingly, these are the theories on which we shall focus here. -/- We begin in Section 1 by discussing George Berkeley’s Towards a New Theory of Vision (1709), the historical locus classicus of action-based theories of perception, and one of the most influential texts on vision ever written. Berkeley argues that the basic or “proper” deliverance of vision is not an arrangement of voluminous objects in three-dimensional space, but rather a two-dimensional manifold of light and color. We then turn to a discussion of Lotze, Helmholtz, and the local sign doctrine. The “local signs” were felt cues for the mind to know what sort of spatial content to imbue visual experience with. For Lotze, these cues were “inflowing” kinaesthetic feelings that result from actually moving the eyes, while, for Helmholtz, they were “outflowing” motor commands sent to move the eyes. -/- In Section 2, we discuss sensorimotor contingency theories, which became prominent in the 20thcentury. These views maintain that an ability to predict the sensory consequences of self-initiated actions is necessary for perception. Among the motivations for this family of theories is the problem of visual direction constancy—why do objects appear to be stationary even though the locations on the retina to which they reflect light change with every eye movement?—as well as experiments on adaptation to optical rearrangement devices (ORDs) and sensory substitution. -/- Section 3 examines two other important 20th century theories. According to what we shall call the motor component theory, efference copies generated in the oculomotor system and/or proprioceptive feedback from eye-movements are used together with incoming sensory inputs to determine the spatial attributes of perceived objects. Efferent readiness theories, by contrast, look to the particular ways in which perceptual states prepare the observer to move and act in relation to the environment. The modest readiness theory, as we shall call it, claims that the way an object’s spatial attributes are represented in visual experience can be modulated by one or another form of covert action planning. The bold readiness theory argues for the stronger claim that perception just is covert readiness for action. -/- In Section 4, we move to the disposition theory, most influentially articulated by Gareth Evans (1982, 1985), but more recently defended by Rick Grush (2000, 2007). Evans’ theory is, at its core, very similar to the bold efferent readiness theory. There are some notable differences, though. Evans’ account is more finely articulated in some philosophical respects. It also does not posit a reduction of perception to behavioral dispositions, but rather posits that certain complicated relations between perceptual input and behavioral provide spatial content. Grush proposes a very specific theory that is like Evans’ in that it does not posit a reduction, but unlike Evans’ view, does not put behavioral dispositions and sensory input on an undifferentiated footing. (shrink)

Philosophers and scientists are concerned with the why and the how of things. Questions like the following are so much grist for the philosopher’s and scientist’s mill: How can we be free and yet live in a deterministic universe?, How do neural processes give rise to conscious experience?, Why does conscious experience accompany certain physiological events at all?, How is a three-dimensional perception of depth generated by a pair of two-dimensional retinal images?. Since Belnap and Steel’s pioneering work on (...) the logic of questions, Van Fraassen has managed to apply their approach in constructing an account of the logic of why-questions. Comparatively little, by contrast, has been written on the logic of how-questions despite the apparent centrality of questions such as How is it possible for us to be both free and determined? to philosophical enterprise.1 In what follows I develop a logic for how-questions of various sorts including how-questions of cognitive resolution, how-questions of manner, how-questions of method, of means, and of mechanism. (shrink)

Aristotle held that perception consists in the reception of external sensory qualities (or sensible forms) in the sensorium. This idea is repeated in many forms in contemporary philosophy, including, with regard to vision, in the idea (still not firmly rejected) that the retinal image consists of points of colour. In fact, this is false. Colour is a quality that is constructed by the visual system, and though it is possible to be a realist about colour, it is completely (...) misleading to think of it as received by the retina. Moreover, such supposedly “charitable” interpretations of Aristotle’s doctrines, based on miscon- ceptions of perception-science, distort our understanding of his historical context. (shrink)

Merleau-Ponty's views are the fruit of the method of "phenomenological description," in part taken over from Husserl. This consists of describing our "original" experience of the world without assuming the truth or validity of any statements we may know about it. Unlike the Cartesian method it does not mean that we should suppose false those statements we know are true, but rather that we should "put these in brackets," or "suspend" their rel- evance, consider them as void of ontological implications. (...) For only if we succeed in doing so, the theory runs, will our description be "pure" or "presuppositionless," free of prejudice with respect to the nature of that which we are trying to describe. In doing the phenomenology of perception, then, we must deliberately discount all that we may chance to know about the "how" or the "why" of perception. In describing our "original" experience of the world, we must not let ourselves be influenced by any empirical or philosophical theory of perception, any hypotheses concerning its nature, causes, or physiological or other underlying processes involved. To cite a concrete example, in describing our perception of some visible scene we must discount anything we may chance to know about light rays impinging upon the retina, etc. Failure to do so might lead to a description not of that which we do see, but that which, given the retinal image, we ought to see, i.e., that portion of the visual scene, light rays from which, impinge upon our retina, and not the visual scene itself. Here, then, is one of the reasons for which we must go through a process of "phenomenological reduction" with respect to our knowledge of the world. But it is not the only reason. In fact the interdict goes further. We are not even entitled to use the usual categories of everyday or scientific descriptive discourse. Nor should we use the language of sense data, or that of the introspectionists. For both of these "presuppose" the validity of some at any rate of its categories. Both rest in the last resort on some theory regarding the nature of the "objective" world, or of our experience of it. (shrink)

Available from UMI in association with The British Library. Requires signed TDF. ;Metaphor and analogy are the scaffolding of science. Kepler's theory of the retinal picture could not have been built without the analogy between an eye and a camera obscura, and, two hundred and fifty years later, Charles Darwin devoted most of the first chapter of The origin of Species to discussion of pigeon fanciers. Unlike Darwin, Kepler was bewitched by his own imagination and was led to wonder (...) "how this image or picture is joined to the visual faculty, which is situated in the retina and in the nerve, and whether it is placed within the hollows of the brain, before the soul or tribunal of the visual faculty, or whether the visual faculty, like a magistrate sent by the soul from the administrative chamber of the brain, descends into the optic nerve or retina to meet this image, as though to a lower court" . ;The theory of the retinal image answered the crucial question of medieval optics: the scaffolding had served its purpose and should have been dismantled. Instead, Kepler mistook it for a part of the building: what he construed as a scientific problem was nothing more than the extension of a metaphor. As a result, and in spite of his remarkable achievement, he left the theory of vision in a state of confusion. ;I intend to show that Descartes revolutionized visual theory by manipulating the pair of analogies which had dominated visual theory since its inception and by advancing a theory of depiction which has since become orthodox. Advocates of the first analogy suggest that seeing the world is rather like seeing pictures of it; Kepler's analogy between the eye and a camera obscura, which was anticipated by Leonardo de Vinci, was a variation on this theme. Advocates of the second analogy compare vision to the use of a walking-stick: the air transmits an impression of a visible object to the eye rather as a walking-stick enables us to find our way around in the dark by transmitting pressures to the hand. As I shall show, Descartes' rejection of the pictorial analogy in favour of the walking-stick analogy and his theory of depiction were designed to salvage Kepler's theory of the retinal picture, a pearl of great price, from its murky setting. ;Descartes aimed to show that whilst Kepler's theory of the retinal picture correctly described the optics of the eye, the pictorial analogy was misleading and stood in the way of a mechanistic theory of perception. ;Current visual theory is Cartesian in some respects and un-Cartesian in others. The walking-stick analogy is no longer used, but the explanatory pattern that it served to illustrate is adhered to closely where the perception of brightness and colour are concerned, and the causal theory of depiction commands widespread support. At the same time, the pictorial analogy has not lost its appeal. (shrink)

Change blindness illustrates a remarkable limitation in visual processing by demonstrating that substantial changes in a visual scene can go undetected. Because these changes can ultimately be detected using top–down driven search processes, many theories assign a central role to spatial attention in overcoming change blindness. Surprisingly, it has been reported that change blindness can occur during blink-contingent changes even when observers fixate the changing location [O’Regan, J. K., Deubel, H., Clark, J. J., & Rensink, R. A. . Picture changes (...) during blinks: Looking without seeing and seeing without looking. Visual Cognition, 7, 191–212]. However, eye blinks produce a transient disruption of vision that is independent of any associated changes in the retinal image. We determined whether these ‘attentive blank stares’ could occur in the absence of blink-mediated visual suppression. Using a flicker change-blindness paradigm we confirm that despite direct attentive fixations, obvious scene changes often remain undetected. We conclude that change detection involves object or feature based attentional mechanisms, which can be ‘misdirected’ despite the allocation of spatial attention to the position of the change. (shrink)

According to the traditional inferential theory of perception, percepts of object motion or stationarity stem from an evaluation of afferent retinal signals (which encode image motion) with the help of extraretinal signals (which encode eye movements). According to direct perception theory, on the other hand, the percepts derive from retinally conveyed information only. Neither view is compatible with a perceptual phenomenon that occurs during visually induced sensations of ego motion (vection). A modified version of inferential theory yields a (...) model in which the concept of extraretinal signals is replaced by that of reference signals, which do not encode how the eyes move in their orbits but how they move in space. Hence reference signals are produced not only during eye movements but also during ego motion (i.e., in response to vestibular stimulation and to retinal image flow, which may induce vection). The present theory describes the interface between self-motion and object-motion percepts. An experimental paradigm that allows quantitative measurement of the magnitude and gain of reference signals and the size of the just noticeable difference (JND) between retinal and reference signals reveals that the distinction between direct and inferential theories largely depends on: (1) a mistaken belief that perceptual veridicality is evidence that extraretinal information is not involved, and (2) a failure to distinguish between (the perception of) absolute object motion in space and relative motion of objects with respect to each other. The model corrects these errors, and provides a new, unified framework for interpreting many phenomena in the field of motion perception. (shrink)

The question of how the brain can construct a stable representation of the external world despite eye movements is a very old one. If there have been some wrong statements of problems (such as the inverted retinal image), other statements are less naive and have led to analytic solutions possibly adopted by the brain to counteract the spurious effects of eye movements. Following the MacKay (1973) objections to the analytic view of perceptual stability, Bridgeman et al. claim that (...) the idea that signals canceling the effects of saccadic eye movements are needed is also a misconception, as is the claim that stability and position encoding are two distinct problems. It must be remembered, however, that what made the theory of “cancellation” formulated by von Holst and Mittelstaedt (1950) so appealing was the clinical observation of perceptual instability following ocular paralysis. Following the concept of corollary discharge, the theory of efference copy had the advantage of simultaneously solving three problems: the stability of the visual world during the saccade, the same visual stability across saccades, and the visual constancy problem of allowing the subject to know where an object in space is. (shrink)

The much larger appearance of the moon near horizon than the perceived size of the moon at zenith has motivated many scientists to develop theories that aim at explaining this puzzling phenomenon. Considering that the size of retinal images of the moon in these positions are very similar, the explanation of difference in their apparent sizes has relied on perceptual cues of distance embedded in the retinal image of their respective contexts. Although this account of the moon (...) illusion is quite popular, it does not explain all aspects of this phenomenon. The theoretical formulation of the moon illusion based on other factors such as size contrast later may have had some advantages but has also created some new problems. Although the moon is perceived in a three-dimensional (3D) environment, the present analysis proposes that an explanation of the moon illusion based on two-dimensional (2D) cues can remove some of the unnecessary problems. The empty space and size contrast that have already been considered in explaining classic geometric-optical illusions play a parallel role in explaining the moon illusion. In other words, the role of open space in interaction with the image of the moon and different objects near horizon, all reflected on the retina, are considered as the main explaining factors. The advantages of this approach will be discussed and some of the facts pertaining to the moon illusion will be explained within this theoretical framework. (shrink)