Psychologically considered, memory defects may occur either in the storing or retentive part of the nerve-cells, or they may involve the much more complicated and associated process of reproduction of the retained images. Both may be involved at the same time. In imbecility, idiocy, dementia, etc., a born or acquired loss of retentive power is present. In pianists — for example, Paderewski — or chess players — Morphy, Pillsbury, etc., a state of localized hyperamnesia is present. This group would include all such prodigies. Occasionally one sees these two groups represented in one individual, as in an imbecile who has great power for mathematical calculation, etc. A case of this kind proves that the old assump tion of closely localized memory-centres is false. Memory may be said to reside in all parts of the sensory nervous system. In another group the ordinary amnesias may be placed. These vary with each individual and depend largely on the healthy tone of the nervous sys tem. A third group' would include the paramnesias, or illusions of memory. In this condition (1) there is a loss of distinction be tween memory of things which really did hap pen and an imagination of things which never did or could. The so-called °constitutional liar" is an example of this inability to dis tinguish between real and imaginary, and many types of insane persons are similarly affected in an extreme degree. The reverse of taking an imagination for a real thing is (2) taking a real thing experienced for the first time as a memory of something experienced be fore— thought of having seen, heard or felt just that same thing before," also called (1/41eja vue." Such a feeling has nothing to do with
native retentiveness, but only with the °feel ing of familiarity," which is essentially the presence of an organic sensation which is absent in the simple paramnesia. In some in sanities this form of double memory is very prominent and leads to the belief on the part of the person so affected that he is prophesying when he is only recalling what he experienced before. (3) There is also an associated paramnesia in which 'things actually experienced suggest ideas falsely taken as memories of other things never experienced. This condition is seen in children and often leads to false testimony. It is also responsible for most °presentiments" or alleged antecedent knowl edge of what has happened. Examples of such memories of the actually non-existent are seen in the stories of faith cures, where all the heal ing is that of ills that never really existed, save as associated false memories. On these false memories is erected much of the corn plicated structure of spiritualism, second sight and other similar phenomena. See IDIOCY ; PERSONALITY AND ITS DISORDERS; SPEECH, De FECTS OF; and RETENTIVENESS.
Bibliography.— Baldwin, 'Dictionary of Psychology and Philosophy' ; Freud, 'Psycho pathology of Every Day Life' (chapter in pathology 1917); Ribot, 'Diseases of Mem ory' ; Gio11on, 'Les Maladies de la Memoires,' with full consideration of hyperamnesia (1897)• Sallier, 'Troubles de la Memoir& (1wn), and Pardo, disturbi della memoria' (1899).