The Positions of Retinal Images


PROF. KULPE, in his “Outlines of Psychology” (translation by Prof. Titchener), sets out with much effectiveness the argument in favour of believing that the visual perception of extended surface is an original datum of consciousness attached to the extended retinal surface (and no more to be explained than why the sensation red feels the way it does, and not otherwise); and he also shows conclusively that the peculiarity of nerve-excitation by which right- and left-ness and up- and down-ness are distinguished, is of peripheral (and not of central) origin; by adducing the facts of metamorphopsia, that is, the cases in which a portion of the retina has become detached by a wound, and has afterwards grown on again, and in which vision is correspondingly inverted—exactly as when a piece of the skin of the forehead has been grafted upon the nose, say, and upon touching it we seem, for a long time afterwards, to be touching the forehead. He thus attaches himself to the innate-space-sensation theory of James and Sumpf. But his effort to show that the out- and in-sensation is fundamentally dependent upon the different shape of the image cast upon the two retinas by an object, carries less conviction with it. This is, of course, an essential element of the sensation when the object looked at is so complex as to consist of two points at a given distance from each other. But when it consists of a single bright point only, we are still perfectly able to determine its position in depth (if it is looked at with two eyes), and the sensation-element which enables us to do this is plainly more fundamental than the other. To say the least, it is something which ought not to be overlooked.

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FRANKLIN, C. The Positions of Retinal Images. Nature 53, 341 (1896).

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