The Philosophical Review/Volume 1/Summary: Lipps - Die Raumanschauung und die Augenbewegungen
Wundt explains the overestimation of certain forms of linear and angular magnitude by reference to feelings of relative exertion in the motions of the eye. Besides failing to show how we get ideas of distance out of feelings of exertion, the theory rests on the unproved assumption that in measuring form and size the eye fixes in rapid succession a series of points. Given the consciousness of space, feelings of exertion might serve as signs for spatial determinations. It is doubtless true that we measure off space with the muscles of the eye, as with other muscles, especially of the neck; but this is only the determination of the position of a certain visual field in the series of possible fields, and has nothing to do with measurements within a given field. Phenomena of displacement of the visual field arising from paralysis of the eye muscles do not concern measurements within the field. James says we see depth directly, but as a matter of fact the visual field has neither depth nor form except what we ascribe to it by way of inference. On the basis of experience, the sensations arising from convergence of the eyes become signs of depth. Wundt holds that the original form of the monocular visual field is spherical, but there is no proof the monocular field was ever spherical; we formed the binocular field of vision first, and the monocular field may be only a reproduction of the binocular. Moreover, why not take the plane surface of the earth up to the horizon line as the original field, instead of the curved form of the sky? The oblique position of vertical lines seen in indirect fixed vision Wundt regards as a direct proof of his theory of motions of the eye. Wherein it is a proof is not easy to see. The sensations of convergence which serve as signs for consciousness of depth exist for points seen in indirect vision only in representative form, i.e. in a form so weak as not to overcome the immediate impression of a bidimensional visual field. In short, the actual position of the visual field is not taken into account. But this explanation, which is also substantially Wundt's, is really in opposition to his theory of measurements by motion of the eyes. The real problem lies deeper than this; the oblique appearance of the indirectly seen vertical line, as well as the curved appearance of the lines in Helmholtz's "chessboard" figure, is a question of the plane field of visual space, as this again is included in the question of the straight line. The straight line, which Wundt treats as if "given," implies consciousness of depth; and this straight line will seem to us to change its direction, when our consciousness of difference in depth, out of which together with the perception we construct the line, undergoes modifications. The point of reference from which we measure off the position and form of objects is not fixed, so that the same line viewed from the same standpoint will change the direction of the apparent curve as the point of reference changes. The phenomena of the apparent rising of the earth's surface to the horizon line, the overestimation of vertical lines as compared with horizontal, etc., find no sufficient explanation from motor sensations of the eye; they result from false estimates of depth. Here the principle of customary mean estimation plays an important part. We estimate falsely the dimensional value of a perception, partly through lack of experience and partly through applying to it norms which interpret analogous but more elaborated perceptions.