Historically, one of the most controversial forms of mental imagery is the so-called eidetic image. An eidetic image is one that, for the subject, reputedly bears remarkable stimulus-like properties. The subject claims to LITERALLY SEE, in exceptional detail, an image of some recently-seen object. Although the image is "mental" it appears to be in physical space. Although eidetic images share features with memory images and projected images, they are distinct in that they can, according to the reports of subjects, be
INSPECTED FOR NEW DETAIL IN THE MANNER
OF A PHYSICALLY-PRESENT STIMULUS OBJECT.
The investigation of eidetic images poses special problems for psychology. The principal problem is how to characterize the subjective reports of eidetic imagery. Both the reliability of subjective reports and the precise nature of the supposed "inspection" of the images present problems, particularly if psychology is understood to be a science with quantifiable parameters. These problems have led many physcologists to question the existence, in the strict sense required by science, of eidetic images. Descriptivists and strict behaviorists claim there is no way to differentiate performances consistent with so-called eidetic images from performances consistent with extraordinary descriptive memory. According to some, then, eidetic images are just memory images.
Eidetic images are distinct from after-images. Typically, after-images are an involuntary reaction brought about as a result of overstimulation of the retina. A flash of light, intent staring at a bright color patch, and similar events overload the retinal tissues, causing them to send signals to the brain after the source of the stimulation is removed. After- images often appear to be floating space before the eyes or to be on nearby surfaces. They do not appear to be in a fixed in a physical location. An after-image will appear to move when the eyes focus on a different location.
Eidetic images, on the other hand, can be triggered by what appears to be simple visual inspection of a physical object. No overloading of the retinal tissues appears to occur, since the visual study of the object usually lasts several minutes and eye movements are continuous during the process. When the object is removed, a person capable of forming an eidetic image will retain a detailed memory image that (according to the subject) appears to be relatively stable in physical space. Often, it appears to be in the same physical space independent of eye movements. If, for example, a figure or painting is shown on a wall or desk top and then removed, the eidetic subject will point to the appropriate surface area location when describing the details of the eidetic image "seen" in the vacated space. (See Stromeyer and Psotka, 1970, p. 346 and A. Richardson, 1969, pp. 29-44 for more on the distinction between eidetic images and after-images.)
Eidetic imagery is generally reputed to exist in a significant percentage of children between the ages of seven and fourteen. Eidetic imagery, particularly in children, has been studied at least since 1819 (Purkinje), and several other important studies were made near the turn of the century (Binet, 1899 and Jaensch 1909). The topic fell out of favor with the advent of behaviorism. The few contemporary studies made have tended to confirm (via subjective reports of children) the findings of older, traditional psychology. Haber and Haber (1964) found that 8% of children between the ages of 7 and 12 appeared to have eidetic imagery (Haber and Haber in A. Richardson, 1969, p. 37). Eidetic imagery tends to disappear with age and is very rare among adults.
Eidetic images are usually generated spontaneously in children and by choice in adults. Maintaining an eidetic image, in either case, requires both interest and effort on the part of the subject. Despite this, eidetic images appear to fade in most cases at rates that are not fully controllable by the subject. It is therefore a judgment call as to whether to list eidetic images as under conscious control or not. (In my work, I have indicated that they are not, because the greatest incidence of eidetic imagery is among children.)
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