In the fifth book of his De aspectibus, the medieval Latin version of Ibn al-Haythamb al-Manir, Alhacen undertakes to determine precisely where a given ray of light will reflect to a given center of sight from a variety of convex and concave mirrors based on circular sections. As applied specifically to convex and concave spherical mirrors, this problem exercised several seventeenth-century thinkers, Christiaan Huygens foremost among them, and in that context it soon became known as Alhazens solution (or solutions) (...) of this problem is deficient in comparison to that of Huygens and later mathematicians. It is my purpose in this paper to show by reconstruction that in fact, far from deficient in any absolute sense, Alhacen’s approach to this problem was remarkably ingenious and elegant in its conceptual simplicity. (shrink)

A comparison of the manuscripts has shown that De li aspecti, the Italian version of Alhacen's De aspectibus, Vat. lat. 4595 (I), was copied from London, British Library, Royal 12 G vii (L). The discovery of long omissions in L, not reproduced in I, disproves this conclusion. The error has two reasons: a sampling too small, the confusion between phenetic and cladistic approaches.

That the medieval Latin version of Ibn al-Haytham's Kitāb al-Manā[zdotu]ir was translated into Italian in the fourteenth century has been known for well over a century. Recent studies have shown that this translation, which is contained in Vat. Lat. 4595, was instrumental in the composition of Lorenzo Ghiberti's Commentario terzo on art. Some eight years ago, the author of the present article tentatively identified the actual manuscript-source of that translation as MS Royal 12.G.7, which is currently held in the British (...) Library. This study establishes beyond reasonable doubt that his tentative identification was correct: MS Royal 12.G.7 is indeed the Latin source for the Italian translation in Vat. Lat. 4595. (shrink)

Dans la première moitié du xii e siècle, les chartrains créent un lexique spécialisé pour l’optique en sélectionnant des termes sans connotation théologique et en leur ajoutant un sens géométrique. Grâce à Constantin l’Africain, ils y intègrent l’ophtalmologie. Alors que ce lexique est utilisé par les traducteurs gréco-latins, les traducteurs arabo-latins, à l’exception de l’Émir Eugène de Sicile, ignorent largement ces spécialisations sémantiques. L’hétérogénéité des choix des traducteurs réintroduit ainsi une incertitude lexicale qui nécessite une clarification des concepts et une (...) sélection des termes. Dépendant de l’évolution générale du lexique philosophique, la fixation du vocabulaire de l’optique est loin d’être achevée à la fin du siècle. (shrink)

Representation and content in some (actual) theories of perception -- Representation in perception and cognition : task analysis, psychological functions, and rule instantiation -- Perception as unconscious inference -- Representation and constraints : the inverse problem and the structure of visual space -- On perceptual constancy -- Getting objects for free (or not) : the philosophy and psychology of object perception -- Color perception and neural encoding : does metameric matching entail a loss of information? -- Objectivity and subjectivity revisited (...) : color as a psychobiological property -- Sense data and the mind body problem -- The reality of qualia -- The sensory core and the medieval foundations of early modern perceptual theory -- Postscript (2008) on Ibn al-Haytham's (Alhacen's) theory of vision -- Attention in early scientific psychology -- Psychology, philosophy, and cognitive science : reflections on the history and philosophy of experimental psychology -- What can the mind tell us about the brain? : psychology, neurophysiology, and constraint -- Introspective evidence in 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)

Perception of the external world is an essential part of the animal (including human) life, both as a source of knowledge and as a way to survive. Medieval authors accepted this view, and despite general concerns about the reliability of the senses in the acquisition of certain and objective knowledge, they thought that for the most part our perceptual system gets things right when it comes to the perceptual features of things—but not always. Our article focuses on thirteenth- and fourteenth-century (...) philosophical discussions of illusions and other types of perceptual errors. Reception of incorrect information, misjudgments concerning perceptual objects, the binding problem, and similar cases that explain perceptual errors will be analyzed. We discuss what might be called medieval Aristotelian/Avicennian theories of perception and the internal senses (drawing mainly from Albertus Magnus and Thomas Aquinas), as well as the so-called perspectivist accounts of perception, especially that by Alhacen. Finally, we take up a debate between Peter Auriol and his critics, which contains elements that can be seen as precursors of later skeptical worries. The concern here is that, just like in contemporary discussions leading to disjunctivism, the absence of a secure way to distinguish between veridical and non-veridical perception leads to a general worry about the reliability of our experience of the world. (shrink)

This article studies a fragment on the conic sections that appear in the Codex Atlanticus, fols. 611rb/915ra. Arguments are put forward to assemble these two folios. Their comparison with the Latin texts available before 1500 shows that they derive from the De speculis comburentibus of Alhacen and the De speculis comburentibus of Regiomontanus, joined together in his autograph manuscript. Having identified the sources, and discussed their mathematics, the issue of their transmission is targeted. It is shown that these notes (...) were written by Paolo dal Pozzo Toscanelli, through whom they reached the notebooks of Leonardo da Vinci. (shrink)