Ibn al-Haytham on Binocular Vision
Early modern physiological optics introduced the concept of correspondence to the study of the conditions for the fusion of binocular images. The formulation of this concept has traditionally been ascribed to Christiaan Huygens (in a work published posthu
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Ibn al-Haytham on Binocular Vision
Abstract Early modern physiological optics introduced the concept of correspondence to the study of the conditions for the fusion of binocular images. The formulation of this concept has traditionally been ascribed to Christiaan Huygens (in a work published posthumously in 1704) and to an experiment often attributed to Christoph Scheiner (1619). Here it will be shown that Scheiner’s experiment in fact had already been conceptualized, first in antiquity by Ptolemy (90–168 AD), then in the Middle Ages by Ibn al-Haytham (Latinized as Alhacen) (d. after 1040), and the extent of the latter’s knowledge of the mechanisms of binocular vision will be analyzed. It will then be explained why Ibn al-Haytham, who was a mathematician but addressed this problem as an experimentalist, succeeded in discovering the theoretical horopter (the locus of points in space that yields single vision) and yet failed to recognize that the horizontal line of the horopter could be described as a circular plane around the viewer’s head, credit for which must instead go to Vieth (1818) and Müller (1826). Nevertheless, through his experimental studies Ibn al-Haytham established the notion of corresponding points, explored what the cases of homonymous (direct) and heteronymous (crossed) diplopias could reveal about the mechanisms of vision, and prepared the ground for the discovery by Panum of the fusional area. The influence on Western science of al-Haytham’s pioneering treatise Kitāb al-manāẓir (Book of Optics) is examined, beginning with his successors in the Latin-speaking world, and in particular Italy.
A key chapter in the physiology of optics considers the conditions for the fusion of the quasi- or displaced images generated by the two eyes. Interestingly, the ancient Greeks did not explore the questions raised by binocular vision in any depth. Euclid only devotes three propositions to this problem (Optica, prop. 26–28)1 and limits his analysis to what is seen of a sphere in binocular vision. If the diameter of the sphere is less than, equal to, or greater than the inter-pupillary distance, then the two eyes will perceive a spherical cap that is greater than, equal to, or less than the
1
Elaheh Kheirandish, The Arabic Version of Euclid’s Optics, New York, 1999, pp. 80–90; Wilfred R. Theisen, “Liber de visu,” Mediaeval Studies 41 (1979), pp. 78–80.
© Springer International Publishing Switzerland 2016 D. Raynaud, Studies on Binocular Vision, Archimedes 47, DOI 10.1007/978-3-319-42721-8_5
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hemisphere, respectively. Nowhere does Euclid address the question as to how disparate visual stimuli are integrated. Galen attempted to rectify this lacuna by deriving a definition of the disparity between the quasi-images produced by the two eyes from one of Euclid’s propositions (Optica, prop. 30). Unfortunately, Galen’s exposition on binocular vision is extremely brief2 and its primary aim is to provide an anatomical description of the ocular paths. Ptolemy’s treatment of
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