This paper, which has both a historical and a polemical aspect, investigates the view, dominant throughout the eighteenth and nineteenth centuries, that the sense of sight is, originally, not phenomenally three-dimensional in character, and that we must come to interpret its properly two-dimensional data by reference to the sense of 'touch'. The principal argument for this claim, due to Berkeley, is examined and found wanting. The supposedly confirming findings concerning 'Molyneux subjects' are also investigated and are shown to be either (...) irrelevant or disconfirming. Recent investigations on infant and neonatal perception are discussed and are also found to be disconfirming. An innatist version of the theory is then considered and is shown to be undermined by the largely 'Gibsonian' character of early space-perception. Finally three recent arguments in favour of the theory - two from psychologists, one from a philosopher - are considered and answered. (shrink)

Paul Churchland's philosophical work enjoys an increasing popularity. His imaginative papers on cognitive science and the philosophy of psychology are widely discussed. Scientific Realism and the Plasticity of Mind (1979), his major book, is an important contribution to the debate on realism. Churchland provides us with the intellectual tools for constructing a unified scientific Weltanschauung. His network theory of language implies a provocative view of the relation between science and common sense. This paper contains a critical examination of Churchland's network (...) theory of language, which is the foundation of his philosophy. It is argued that the network theory should be seen as deriving its point from traditional empiricism. The network theory enables the empiricist to resist the phenomenalistic temptations inherent in his position, and to build a realist philosophy on the basis of the representative theory of perception. This interpretation is confirmed by the fact that the representative theory is presupposed by Churchland's main argument in favour of the network view. Churchland tends to conceive of himself as a naturalistic epistemologist. But the philosophical faction to which Churchland belongs is rather that of modern neo?Kantianism. (shrink)

Perceptual constancy, often defined as the perception of stable features under changing conditions, goes hand in hand with variation in how things look. A white wall in the orange afternoon sun still looks white, though its whiteness looks different compared with the same wall in the noon sun. Historically, this variation has often been explained in terms of our experience of “merely sensory” or subjective properties – an approach at odds with the fact that the variation does track objective features (...) of the perceptual situation, such as illumination. One approach, becoming more common, is to account for the variation in terms of further “dimensions” to perceptual experience. Especially in colour perception, this is a natural thought to have but the idea is often left vague. In this paper I argue that the “dimensional” strategy has problems of its own, but is useful in drawing out some interesting complications in the way perceptual experience is structured. Specifically, the structure of “constancy spaces” brings out the different ways in which there is stability and instability in the experience of constancy, without the need for novel or merely subjective features. Instability arises in a contingent structural feature of perceptual experience. (shrink)

My aim … is to show that the celestial machine is likened not to a kind of divine living being but rather to a clockwork. I consider the human body to be a machine … Although it may exaggerate to say that Descartes fathered the mechanization of biology, it is true that his Treatise of Man provided the first systematic development of the idea that a complete understanding of all the phenomena of life, including all abilities and behaviour of animals, (...) can be achieved by viewing living things as machines. To make this out, Decartes had to learn to think about living things in a new way. My first aim here is to identify the fundamental conceptual innovations at work in Descartes’ attempt to extend the new mechanics to include biology. My second aim is to locate the point at which Descartes’ mechanical imagination runs out. This requires study of Descartes’ scientific work on sense. (shrink)

In this innovative study Patricia Kitcher argues that we can only understand the deduction of the categories in Kant's Critique of Pure Reason in terms of his attempt to fathom the psychological prerequisites of thought. Thus a consideration of his conception of psychology is essential to an understanding of his philosophy. Kitcher specifically considers Kant's claims about the unity of the thinking self; the spatial forms of human perceptions; the relations among mental states necessary for them to have content; the (...) relations between perceptions and judgment; and the limits of philosophical insight into psychological processes. (shrink)

Descartes developed an elaborate theory of animal physiology that he used to explain functionally organized, situationally adapted behavior in both human and nonhuman animals. Although he restricted true mentality to the human soul, I argue that he developed a purely mechanistic (or material) ‘psychology’ of sensory, motor, and low-level cognitive functions. In effect, he sought to mechanize the offices of the Aristotelian sensitive soul. He described the basic mechanisms in the Treatise on man, which he summarized in the Discourse. However, (...) the Passions of the soul contains his most ambitious claims for purely material brain processes. These claims arise in abstract discussions of the functions of the passions and in illustrations of those functions. Accordingly, after providing an intellectual context for Descartes’s theory of the passions, especially by comparison with that of Tho- mas Aquinas, I examine its ‘machine psychology’, including the role of habituation and association. I contend that Descartes put forth what may reasonably be called a ‘psychology’ of the unensouled animal body and, correspondingly, of the human body when the soul does not intervene. He thus conceptually distinguished a mechanistically explicable sensory and motor psychology, common to nonhuman and human animals, from true mentality involving higher cognition and volition and requiring (in his view) an immaterial mind. (shrink)

There is a strong philosophical intuition that direct study of the brain can and will constrain the development of psychological theory. When this intuition is tested against case studies on the neurophysiology and psychology of perception and memory, it turns out that psychology has led the way toward knowledge of neurophysiology. An abstract argument is developed to show that psychology can and must lead the way in neuroscientific study of mental function. The opposing intuition is based on mainly weak arguments (...) about the fundamentality or objectivity of physics or physiology in relation to psychology. -/- Philosophy of Science, Vol. 67, Supplement. Proceedings of the 1998 Biennial Meetings of the Philosophy of Science Association. Part II: Symposia Papers (Sep., 2000). (shrink)

Psychology considered as a natural science began as Aristotelian "physics" or "natural philosophy" of the soul. C. Wolff placed psychology under metaphysics, coordinate with cosmology. Scottish thinkers placed it within moral philosophy, but distinguished its "physical" laws from properly moral laws (for guiding conduct). Several Germans sought to establish an autonomous empirical psychology as a branch of natural science. British and French visual theorists developed mathematically precise theories of size and distance perception; they created instruments to test these theories and (...) to measure visual phenomena such as the duration of visual impressions. These investigators typically were dualists who included mental phenomena within nature. (shrink)

Some experiments in perceptual psychology measure perceivers’ phenomenal experiences of objects versus their cognitive assessments of object properties. Analyzing such experiments, this article responds to Pizlo’s claim that much work on shape constancy before 1985 confused problems of shape ambiguity with problems of shape constancy. Pizlo fails to grasp the logic of experimental designs directed toward phenomenal aspects of shape constancy. In the domain of size perception, Granrud’s studies of size constancy in children and adults distinguish phenomenal from cognitive factors.

According to Kepler and Descartes, the geometry of the triangle formed by the two eyes when focused on a single point affords perception of the distance to that point. Kepler characterized the processes involved as associative learning. Descartes described the processes as a “ natural geometry.” Many interpreters have Descartes holding that perceivers calculate the distance to the focal point using angle-side-angle, calculations that are reduced to unnoticed mental habits in adult vision. This article offers a purely psychophysiological interpretation of (...) Descartes’s natural geometry. In his account of perceived limb position from the Treatise on Man, he envisioned a central brain state that controls ocular convergence and thereby co-varies with the distance from observer to object. A psychophysiological law relates the visual perception of distance to this brain state. Descartes also invokes more traditional theories of distance and size perception based on unnoticed judgments, yielding a hybrid account. (shrink)

L’Homme presents what has been termed Descartes’ “physiological psychology”. It envisions and seeks to explain how the brain and nerves might yield situationally appropriate behavior through mechanical means. On occasion in the past 150 years, this aim has been recognized, described, and praised. Still, acknowledgement of this aspect of Descartes’ writing has been spotty in histories of neuroscience and histories of psychology. In recent years, there has been something of a resurgence. This chapter argues that, in seeking to explain psychological (...) functions such as sense perception, attention, memory, and emotional response, Descartes ascribed a range of active functions to the brain acting on its own (independently of mind). (shrink)

Review of THEO C. MEYERING, Historical Roots of Cognitive Science : The Rise of a Cognitive Theory of Perception from Antiquity to the Nineteenth Century. Boston: Kluwer, xix + 250 pp. $69.00. Examines the author's interpretation of Aristotelian theories of perceptual cognition, early modern theories, and Helmholtz's theory.

Descartes analysed the mind into various faculties or powers, including pure intellect, imagination, senses, and will. This article focuses on his account of the sensory power, in relation to its Aristotelian background. Descartes accepted from the Aristotelians that the senses serve to preserve the body by detecting benefits and harms. He rejected the scholastic Aristotelian sensory ontology of resembling species, or ‘forms without matter’. For the visual sense, Descartes offered a mechanistic ontology and a partially mechanized account of sensory processes, (...) including some previously ascribed to judgement. He did this in the context of his theory of brain signs that prompt sensations. The article contends that Descartes’s use of the sign-relation was modelled on standard discussions of non-resembling signs in commentaries on Aristotle’s De interpretatione. It follows three uses of the sign-relation: brain states that cause colour sensations; brain states that cause experiences of spatialized contents, such as shapes; and brain states that realize a ‘natural geometry’. It argues that Descartes’s natural geometry does not involve mental operations but physiological mechanisms that co-vary with the distance to seen objects. While retaining the language of sensory powers, Descartes offered a partial mechanization of those powers. (shrink)

Galileo's Philosophy of Science - or: Contra Feyerabend. In analyzing Galileo's methodology, philosophers of science were using, misusing, and abusing his ideas rather unashamedly to suit their own purposes. Like so many others before him, Paul Feyerabend had come to the conclusion that his methodological ideas might gain momentum by demonstrating their compatibility with those of Galileo. The reinterpretation of Galileo as a true, though disguised, anarchist, was considered by Feyerabend as the most forceful, and indeed conclusive, case against rationalism (...) in methodology which might be conceived in view of the privileged position ascribed to Galileo by both philosophers which might be conceived in view of the privileged position ascribed to Galileo by both philosophers and historians of science. The paper argues - against Feyerabend - that Galileo was not a methodological anarchist, neither in theory nor in practice. He had firm methodological convictions that remained basically the same throughout his entire career. In his view, essential and accidental causes of phenomena were not given by experience. Although mathematical and geometrical analysis was needed to discriminate between them, experience and experiment was considered by Galileo from his middle periode on as a means to identify among the set of explanations, demonstrable "ex suppositione" as being mathematically correct, those which could in addition be applied to reality. Thus, Galileo was neither an inductivist nor a naive falsificationist, nor a Copernican zealot adapting his methodology to the needs of his presumed fight for heliocentrism, come what be. Only after the reconstruction of mechanics was in a fairly advanced stage, and after his own telescopic observations had provided independent evidence in favor of the new astronomy, Galileo was in a position to appreciate the Copernican system as a most forceful ally in his fight for the recognition of his physical achievements. Through the end of his life, his view of the heliocentric system remained rather traditional in adhering firmly to the principles of epicyclic and circular motion, as far as the heavens were concerned. (shrink)

Ever since Berkeley discussed the problem at length in his Essay Toward a New Theory of Vision, theorists of vision have attempted to explain why the moon appears larger on the horizon than it does at the zenith. Prevailing opinion has it that the contemporary perceptual psychologists Kaufman and Rock have finally explained the illusion. This paper argues that Kaufman and Rock have not refuted a Berkeleyan account of the illusion, and have over-interpreted their own experimental results. The moon illusion (...) remains unexplained, and a Berkeleyan account is still a contender. (shrink)

Do the physical facts of the viewed environment account for the ordinary experiences we have of that environment? According to standard philosophical views, distal facts do account for our experiences, a phenomenon explained by appeal to perceptual constancy, the phenomenal stability of objects and environmental properties notwithstanding physical changes in proximal stimulation. This essay reviews a significant but neglected research tradition in experimental psychology according to which percepts systematically do not correspond to mind-independent distal facts. Instead, stability of percept values (...) comes in degrees, and physical facts about the viewed environment alone do not account for our ordinary experiences of the world. I conclude that more attention to descriptive research in psychophysics is warranted if what is sought is a philosophical theory of the nature of our perceptual relation with the world. (shrink)

This chapter discusses eighteenth-century British theories of perception, beginning with George Berkeley’s Essay Towards a New Theory of Vision. The chapter traces Berkeley’s influence through Thomas Reid, David Hume, David Hartley, Adam Smith and Dugald Stewart. The chapter presents theories of perception in this time a place a primarily concerned with metaphysics, mind and methodology rather than epistemology.

How does Descartes characterize the peculiar way in which each of us is aware of our bodies? I argue that Descartes recognizes a sense of bodily ownership, such that the body sensorily appears to be one's own in bodily awareness. This sensory appearance of ownership is ubiquitous, for Descartes, in that bodily awareness always confers a sense of ownership. This appearance is confused, in so far as bodily awareness simultaneously represents the subject as identical to, partially composed by, and united (...) to her body, without distinguishing these relations. Finally, the appearance of ownership is grounded in multiple other ways in which the body sensorily appears: namely, in the fact that the body appears to be inescapable, modified by bodily sensations, and an object of special concern. (shrink)

In this paper I present a transcendental argument based on the findings of cognitive psychology and neurophysiology which invites two conclusions: First and foremost, that a pre-condition of visual perception itself is precisely what the Aristotelian and other commonsense realists maintain, namely, the independent existence of a featured, or pre-packaged world; second, this finding, combined with other reflections, suggests that, contra McDowell and other neo-Kantians, human beings have access to things as they are in the world via non-projective perception. These (...) two conclusions taken together form the basis of Aristotelian metaphysical realism and a refutation of the neo-Kantian two-factor approach to perception. (shrink)

Esoteric knowledge, reserved for a few specially trained thinkers, as opposed to an exoteric faith disseminated to the masses, is not usually associated with scholastic theology. It is therefore interesting to find that William of Auvergne, longtime theologian at the University of Paris and bishop of that city from 1228 until his death in 1249, applied the concept to his account of the fires of hell and purgatory. Because he considered the infernal and purgatorial fires as deterrents to antisocial acts, (...) William was very concerned to protect belief in the physical nature of punishment after death. Yet, as a theologian abreast of the Aristotelian and Arabic philosophical literature recently translated into Latin, he understood the challenge that this sophisticated tradition posed for Christian orthodoxy. He also knew that contemporary heretics, the Albigensians, or Cathars, denied hell and purgatory altogether. To prevent these competing views from confusing the mass of believers, he advocated the dissemination of a simple, literal view to the faithful, even while he elaborated an esoteric, metaphorical position of his own. In so doing, William adapted ideas drawn from the Arabic philosopher Avicenna and fashioned an innovative theory of infernal and purgatorial fire. (shrink)

The sensation-perception distinction did not appear before the seventeenth century, but since then various formulations of it have gained wide acceptance. This is not an historical accident and the article suggests an explanation for its appearance. Section 1 describes a basic assumption underlying the sensation-perception distinction, to wit, the postulation of a pure sensory stage--viz. sensation--devoid of active influence of the agent's cognitive, emotional, and evaluative frameworks. These frameworks are passive in that stage. I call this postulation the passivity assumption. (...) Section 2 suggests three major reasons for the emergence of this assumption in the seventeenth century: the mental-physical gap, the causal theory of perception, and epistemological considerations regarding the status of the sensory given. In the last section a critical discussion is presented. The passivity assumption is found to have serious empirical and theoretical flaws. (shrink)

Although current debates in epistemology and philosophy of mind show a renewed interest in perceptual illusions, there is no systematic work in the philosophy of perception and in the psychology of perception with respect to the concept of illusion and the relation between illusion and error. This book aims to fill that gap.

Philosophy and Memory Traces defends two theories of autobiographical memory. One is a bewildering historical view of memories as dynamic patterns in fleeting animal spirits, nervous fluids which rummaged through the pores of brain and body. The other is new connectionism, in which memories are 'stored' only superpositionally, and reconstructed rather than reproduced. Both models, argues John Sutton, depart from static archival metaphors by employing distributed representation, which brings interference and confusion between memory traces. Both raise urgent issues about control (...) of the personal past, and about relations between self and body. Sutton demonstrates the role of bizarre body fluids in moral physiology, as philosophers from Descartes and Locke to Coleridge struggled to control their own innards and impose cognitive discipline on 'the phantasmal chaos of association'. Going on to defend connectionism against Fodor and critics of passive mental representations, he shows how problems of the self are implicated in cognitive science. (shrink)

The concept of an "idea" played a central role in 17th-century theories of mind and knowledge, but philosophers were divided over the nature of ideas. This book examines an important, but little-known, debate on this question in the work of Leibniz, Malebranche, and Descartes. Looking closely at the issues involved, as well as the particular context in which the debate took place, Jolley demonstrates that the debate has serious implications for a number of major topics in 17th-century philosophy.

Psychology considered as a natural science began as Aristotelian "physics" or "natural philosophy" of the soul, conceived as an animating power that included vital, sensory, and rational functions. C. Wolff restricted the term " psychology " to sensory, cognitive, and volitional functions and placed the science under metaphysics, coordinate with cosmology. Near the middle of the eighteenth century, Krueger, Godart, and Bonnet proposed approaching the mind with the techniques of the new natural science. At nearly the same time, Scottish thinkers (...) placed psychology within moral philosophy, but distinguished its "physical" laws from properly moral laws. British and French visual theorists developed mathematically precise theories of size and distance perception; they created instruments to test these theories and to measure visual phenomena such as the duration of visual impressions. By the end of the century there was a flourishing discipline of empirical psychology in Germany, with a professorship, textbooks, and journals. The practitioners of empirical psychology at this time typically were dualists who included mental phenomena within nature. Accordingly, psychology as a natural scientific disciplines was not invented in the 18th and 19th centuries, but *remade* from the extant empirical psychology. (shrink)

The seventeenth century witnesses the demise of two core doctrines in the theory of perception: naive realism about color, sound, and other sensible qualities and the empirical theory, drawn from Alhacen and Roger Bacon, which underwrote it. This created a problem for seventeenth century philosophers: how is that we use qualities such as color, feel, and sound to locate objects in the world, even though these qualities are not real? -/- Ejecting such sensible qualities from the mind-independent world at once (...) makes for a cleaner ontology, since bodies can now be understood in purely geometrical terms, and spawns a variety of fascinating complications for the philosophy of perception. If sensible qualities are not part of the mind-independent world, just what are they, and what role, if any, do they play in our cognitive economy? We seemingly have to use color to visually experience objects. Do we do so by inferring size, shape, and motion from color? Or is it a purely automatic operation, accomplished by divine decree? -/- This volume traces the debate over perceptual experience in early modern France, covering such figures as Antoine Arnauld, Robert Desgabets, and Pierre-Sylvain Regis alongside their better-known countrymen Rene Descartes and Nicolas Malebranche. (shrink)

A.D. Smith opens his excellent paper, “Space and Sight,” by remarking, One of the most notable features of both philosophy and psychology throughout the eighteenth and nineteenth centuries is the almost universal denial that we are immediately aware through sight of objects arrayed in three-dimensional space. This was not merely a denial of Direct Realism, but a denial that truly visual objects are even phenomenally presented in depth (481). Times have changed. As Smith writes, “It is hard to think of (...) a more radical reversal in thinking than the one that separates such an outlook from that which prevails today; for this erstwhile orthodoxy is hardly given even serious consideration in our own times, at least among philosophers” (482). Even so, how could this doctrine come and go? How can there be fashion in phenomenology?1 Let me answer the question indirectly, by considering Locke’s reasons for advancing the doctrine. He writes, “When we set before our Eyes a round Globe, of any uniform colour, v.g. Gold, Alabaster, or Jet, ‘tis certain, that the Idea thereby imprinted in our Mind, is of a flat Circle variously shadow’d, with several degrees of Light and Brightness coming to our Eyes” (2.9.8).2 Adults have acquired ideas of three-dimensional objects (presumably by.. (shrink)

In this chapter I examine past and recent theories of unconscious inference. Most theorists have ascribed inferences to perception literally, not analogically, and I focus on the literal approach. I examine three problems faced by such theories if their commitment to unconscious inferences is taken seriously. Two problems concern the cognitive resources that must be available to the visual system (or a more central system) to support the inferences in question. The third problem focuses on how the conclusions of inferences (...) are supposed to explain the phenomenal aspects of visual experience, the looks of things. Finally, in comparing past and recent responses to these problems, I provide an assessment of the current prospects for inferential theories. (This paper is reprinted in Hatfield 2009, Perception and Cognition: Essays in the Philosophy of Psychology, Clarendon Press, 124-152.). (shrink)

This paper serves to introduce the papers from the symposium by the same title, by describing the sort of work done in philosophy of psychology conceived as a branch of the philosophy of science, distinguishing it from other discussions of psychology in philosophy, and criticizing the claims to set limits on scientific psychology in the largely psychologically uninformed literatures concerning "folk psychology' and "wide" and "narrow" content. Philosophy of psychology as philosophy of science takes seriously and analyzes the explanatory structures, (...) conceptual problems, and evidentiary practices of extant scientific psychology. (shrink)

The chapter focuses on attributions of the transparency of thought to early modern figures, most notably Descartes. Many recent philosophers assume that Descartes believed the mind to be “transparent”: since all mental states are conscious, we are therefore aware of them all, and indeed incorrigibly know them all. Descartes, and Berkeley too, do make statements that seem to endorse both aspects of the transparency theses (awareness of all mental states; incorrigibility). However, they also make systematic theoretical statements that directly countenance (...) “unnoticed” thoughts or mental states, that is, thoughts or mental states of which the subject is unaware and has no knowledge. Descartes, having identified the essence of mind with thought or representation, distinguishes bare states of mind from states of which we have reflective awareness, thereby providing a theoretical tool for understanding both his seeming endorsement of transparency and his actual denial of it: Descartes distinguished between a basic perceptual state, or a basic awareness, and reflectively conscious states that involve explicit noticing and cognizing on the part of the subject. Leibniz (as is better known) directly endorsed a similar distinction between bare perception and reflective consciousness, using the term “perception” for the first and “apperception” for the second. In these cases, bare perceptions are not transparently available to the subject, and so in fact the subject does not have knowledge, hence does not have incorrigible knowledge, of all its occurrent mental states. This chapter gives evidence to support these claims; elaborates the complex psychology of the subject found in Descartes and other early moderns; and notes some ways in which these early moderns contributed to the genesis of the modern subject. Finally, it compares McDowell’s conception of the Cartesian mind with the conceptions of mind found in the writings of Descartes, Berkeley, and Leibniz, finding that his characterization caricatures the positions of early modern philosophers. McDowell's characterization has four elements: consciousness as essence of mind; intentionality as exclusively mental; the veil of perception; and the transparency of mind. Only the second point, about intentionality, fully fits Descartes. As a consequence of his own misdirection, McDowell misses the actual basis of his difficulty in connecting mind with world, which arises from a point of agreement between him and Descartes: the removal of intentionality from material sensory systems. But whereas Descartes could relocate (nonconceptual) sensory intentionality in mental states, McDowell is left to account for it with his overly cognitivized scheme of perceptual content as exclusively conceptual. (Paper first given at the European Society for Early Modern Philosophy, 2007.). (shrink)

Descartes understood the subject matter of physics (or natural philosophy) to encompass the whole of nature, including living things. It therefore comprised not only nonvital phenomena, including those we would now denominate as physical, chemical, minerological, magnetic, and atmospheric; it also extended to the world of plants and animals, including the human animal (with the exception of those aspects of the human mind that Descartes assigned to solely to thinking substance: pure intellect and will). Descartes wrote extensively on physiology and (...) on the physiology and psychology of the senses. This chapter examines the notions of *physiology* and *psychology* in medical and natural philosophical works of Descartes' day; follows his efforts to bring physiology into his mechanistic idiom; considers the relation between physiology of the animal machine and psychological functions that yield functionally appropriate behavior; goes into his physiology and psychology of vision; and elaborates the tension in Descartes' works between his metaphysically supported micro-corpuscularism and his discussion of the animal machine as an organic unity comprising various functionally and teleologically characterized systems. The chapter draws on Descartes' works in both metaphysics and natural philosophy, including his Treatise on Man (originally published as L'Homme, 1664). (shrink)

Every perceptual experience has an objective and a subjective side. We see object size, independent of distance, but we also see that distant objects project smaller images. Early modern conceptions focused on local stimulation and thus on the subjective aspect. Helmholtz and Hering emphasized the objective aspect. Helmholtz split visual experience into two stages, with sensation representing the subjective side and perception, through cognitive processes, the objective side. Gestalt theory denied this dualism, rejecting both sensory and cognitive stages. Despite contrary (...) evidence, the sensation/perception dualism persists, in brightness models and past experience theories. That we can detect visual angle and luminance does not mean that these are raw sensations out of which perception of size and lightness is built. Size and color constancy are truly visual, not cognitive. Instructions to subjects in vision experiments must avoid the proximal mode on the one hand and cognitive judgments on the other. (shrink)

As the word “optics” was understood from antiquity into and beyond the early modern period, it did not mean simply the physics and geometry of light, but meant the “theory of vision” and included what we should now call physiological and psychological aspects. From antiquity, these aspects were subject to geometrical analysis. Accordingly, the geometry of visual experience has long been an object of investigation. This chapter examines accounts of size and distance perception in antiquity (Euclid and Ptolemy) and the (...) Middle Ages (Ibn al-Haytham), before turning to "natural geometry" in Kepler and Descartes. It finds a purely mechanical realization of natural geometry in Descartes (primarily in his L'Homme, 1664), in which he conceives states of the visual system as varying in accordance with distance, much as his geometrical compasses vary their spatial relations in accordance with geometrical proportions. This reading challenges the notion that a two-dimensional sensation (without three-dimensional phenomenality) was universally accepted prior to the nineteenth century by positing a direct psychophysiological account of the experience of distance in Descartes. It thereby challenges the interpretations of Descartes on natural geometry of George Berkeley, Nancy Maull, Margaret Wilson, Erwin Panofsky, and Jonathan Crary. (shrink)