EIDETIC IMAGES are subjective visual phenomena which assume a perceptual character and which resemble negative or positive after-images in that they are "seen" in the literal sense of the word. An eidetic individual is not only able to imagine an absent object but also to see it, either when he closes his eyes or looks at some surface which serves as convenient background for his eidetic image. An object may be eidetically seen either imme diately after it has been removed from sight or after a considerable period of time (minutes, days, years) has elapsed since the re moval; there are also spontaneous eidetic images. As regards form, colour, size, position in space, richness of details and other characteristics, the eidetic image may, in various ways, differ from the object which it represents. The individual who possesses eidetic images, i.e., "images of hallucinatory clearness," is in gen eral a "normal and healthy" person ; in other words, most hallu cinations, pseudo-hallucinations and related phenomena are not to be referred to as eidetic images, although clinically it may be difficult to distinguish between the two. Urbantschitsch's investi gations (1907) suggested a pathological basis for eidetic phenom ena. O. Kroh (191 7) discovered that eidetic images were fre quently found in normal children. E. R. Jaensch's experiments brought out the fact that eidetic images are distinctly different from negative after-images and memory-images although their behaviour is in many respects similar. In fact, E. R. Jaensch asserts that eidetic images represent two extremes; they are either pronounced after-images or visible memory-images. Jaensch also maintains that most individuals during childhood pass through an eidetic "phase." The frequency of the eidetic disposition, how ever, varies considerably in different geographic regions. In cer tain regions 8o–i00% of the children are reported eidetic. The experimental work as done by the Marburg school has led to the conclusion that the presence of eidetic imagery in an eidetic indi vidual implies the existence of closely correlated "typical" char acteristics in his physical make-up in the perceptions, of ter-images and memory-images of this individual, and in his intellectual and emotional life. Thus the eidetic type is a biotype, i.e., a definite "psychophysical reaction system." W. Jaensch assumes two eidetic subtypes : the T-type (referring to tetany) and the B-type (re ferring to Basedow's syndrome) .
Eidetic images exist in many individuals and they can be sub jected to laboratory methods. Aside from Germany, experimental work on the eidetic disposition has been done in England (G. W. Allport), France (Quercy), Italy (Kiesow) and in different re gions of the United States (Kluver). Phenomena corresponding to eidetic images in the visual field are supposed to exist in other sense-fields as well. H. Henning maintains that images do not exist at all in the field of the lower senses. Here all past sensory experiences are revived eidetically.
See E. R. Jaensch: Die Eidetik (Leipzig, 1925) ; E. R. Jaensch and others, Ueber den Aufbau der Wahrnehmungswelt (Leipzig, 1927) ; H. Kliiver, "Studies on the Eidetic Type and on Eidetic Imagery," Psychol. Bull., No. 25 (1928). (H. KL.)