![]() ![]() The development of visual size constancy is therefore explained by supposing that the perceived visual object is a fusion of retinal image and memory “image,” which in ontogenesis was first an El Similar but more complex evolutionary considerations are put forward to explain the origin of color constancy and the laws of color contrast and transformation. In memory, of course, objects are constant in size. Jaensch thus supposed that El arise from the functioning of centers that are phylogenetically earlier and that they play a part in forming the memory of objects. While common afterimages (AI) are due to primitive retinal functions and obey Emmert’s law (their size is proportional to the distance at which they are projected), El do not obey this law but tend toward size constancy. Its opposite is the negative El, which appears in complementary colors. Its frequency is highest in young children. A positive El is a particularly strong visual afterimage, which has great clarity and which in its most pronounced form is reproduced in the colors of the stimulus object, often in very fine detail. Outside central Europe, Jaensch is best known through his work on eidetic images (El). Similarly, in experiments on space orientation, the first type of subject is less “stimulus bound” than is the second (cf. At one extreme, a briefly exposed mutilated word is “seen” by the subject as a meaningful one, even to the extent that on successive exposures it is reported as being much clearer, “in quite black print,” “standing out from the screen” subjects at the other extreme read letter by letter in an analytic rather than a synthetic way even when the word is long, meaningful, and well known to them. A simple example of the differential interpenetration of outer and inner is to be found in tachistoscopic experiments on reading. Memory has a stratified structure of primordial and later contents, with both phylogenetic and ontogenetic roots, and these two kinds of content emerge as such in various states of the person (e.g., in dark-adapted vision and under the influence of drugs such as alcohol). In Über den Aufbau der Wahrnehmungswelt (1923) Jaensch showed, anticipating Wittgenstein, that the world of perceptual experience is not a product or precipitate of external stimuli alone, or of inner (psychological) contents alone it is a product of both, in which inner and outer responses interpenetrate. ![]() His work on size and color constancies (1914), which later was integrated with his experiments on eidetic imagery (1925), was speculatively extended into a comprehensive theory of psychophysiological development, personality theory, and race psychology, as well as a theory of the structure and development of the world as perceived and known (1923). From the simpler visual phenomena he proceeded to experiments on the perception of space (1911) and extended his general discussion into the fields of aesthetics and epistemology. In this first book, for example, he moved from psychophysical experiments in visual acuity and the like to the pathology of vision. It is characteristic of Jaensch that in all his work, beginning with his earliest (1909), he moved beyond the particular problem with which he had started to the applications of his results. In 1913 he was appointed to a chair of philosophy at Marburg and founded the Psychological Institute there. Müller and Hermann Ebbinghaus, to whom he dedicated his first book (1909). After studying physics and mathematics at Göttingen he became a student of G. Erich Rudolf Jaensch, German psychologist, was born in Breslau in 1883 and died in Marburg an der Lahn in 1940. ![]()
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