Some preliminary experiments on vision without inversion of the retinal image.

Two important theories of upright vision hold that the inversion of the retinal image is necessary for the perception of things as upright. According to the first, which we may call the projection theory, objects are projected back into space in the directions in which the rays of light fall upon the retina. And the crossing of these lines of direction within the eye requires that if the object is to be projected right side up the retinal image must be inverted. The second theory, which may be termed the eye-movement theory, holds that the movements of the eye and our perception of the direction of such movements are the means by which we judge of the spatial relation of objects in the visual field. Upper and lower, according to this theory, mean positions which require an upward or downward movement of the eye to bring them into clear vision. But an upward movement of the eye brings into clear vision only what lies below the fovea on the retina. So that here too the perception of objects as upright requires that their retinal images be inverted. The purpose of the experiments, of which only the preliminary ones are here reported, was to throw some light, if possible, on the correctness of this assumption. Is the inverted image a necessary condition of our seeing things in an upright position? The method of approaching the problem was to substitute an upright retinal image for the normal inverted one and watch the result. This was done by binding on the eyes a simple optical con-