Space Perception (Volume 4) (Paperback)

Book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1875. Excerpt: ... the other becomes visibly brighter. Hence, also these brightening and darkening after-images, as they might suitably be called, are, ?ocal retinal phenomena and cannot stem solely from pupillary change s. If, in this experiment, the virtual image is again consulted, it will be seen that the pupil moves spasmodically every time the slit is opened. Although the spirab are so chosen, that the intensity of the total light which penetrates through both slits remains constant, nevertheless, every new distribution of light seems to act as a stimulus on the iris. The brightening and the darkening after-image seemed to appear somewhat stronger in experiments with one slit than with two. It must remain undecided whether, and what share changes in the pupillary width have on the phenomenon. 6. In the two last mentioned cases investigated by Plateau and Dvorak, the after-image may indeed be designated the negative contrast of the original stimulation. But the course of the secondary condition is not one that oscillates. I have already expressed this hypothesis and so far I have seen no need to abandon it. According to this hypothesis, so many physical processes must be as*umed DEGREESin a sensory process, as sensory qualities may be distinguished psychologically in the latter.41 For similar perceptions, similar processes will have to be assumed, for dissimilar perceptions, dissimilar processes. Correspondingly, we shall have to bear in mind, that a special process is stimulated with the movement of the retinal image, which does not exist in repose and that in contrary movements quite similar processes in similar organs are * llachs Concerning the effect of the spatial distribution of light stimulation on the retina' (liber die Fiirxung der raumlichen Vertheilung des Lichtreizes auf die Netshaut.) S