Illusions

ILLUSIONS (from Lat. illusio—mockery), represent a disorder of the process of perception and, together with hallucinations, belong to the so-called "deceptions of the senses." The precise definition of I. since the French psychiatrist Esquirol has been based on their opposition to hallucinations: the latter arise in the absence of external influence on the sense organs and are therefore imaginary perceptions; the basis of illusory perception, however, always lies in some sensory irritation, but reaching consciousness in a distorted, perverted form. Thus, illusions are incorrect, false perceptions of real reality, not adequate to the sensory irritation. When someone hears a voice without external auditory irritation or sees an object in its absence, he hallucinates; if, on the other hand, in the noise of footsteps a subject distinguishes abusive words or a bush is taken for a human figure, one is dealing with an illusion. Like hallucinations, illusions can relate to different spheres of perception, be one- or two-sided, individual or (under special conditions) collective. One should distinguish, according to their sources of origin, objectively conditioned I. from subjectively conditioned ones. The former are explained by the peculiarities of the perceived object. Thus, due to the unequal speed of propagation of sound and light waves, phenomena of thunder and lightning seem separated in time; due to the different refraction of light in different media, a straight stick immersed in water seems broken; two lines of equal size, of which one is intersected by additional dashes, are perceived contrary to reality as unequal. Of the same type, I. are experimentally caused by figures from the Muller-Lyer set. Recognition of the true nature of a falsely perceived object leads either to the disappearance of I. or to the realization of its discrepancy with the actual properties of the object. Subjectively conditioned illusions are linked to changes in the psycho-physiological properties of the perceiving organism. These changes, inadequate to external irritations, arise both in peripheral sense organs and in central divisions of the nervous system. Without the participation of the latter (chiefly the cerebral cortex), an illusory process is impossible. However, not always does the physiological change leading to I. arise primarily in the central nervous system. When the starting point of changes are the sense organs (e.g., upon pressure on the eyeballs), the corresponding illusions (in this case—sensation of sparks) are designated as peripheral, in contrast to central ones, the basis of which lies in the altered function of the central nervous system. Central I. are especially persistent in disorders of the analyzer divisions of the cerebral cortex. Damage to the left occipital lobe (chiefly fields 18 and 19 according to Brodmann, as well as posterior divisions of the parietal area) often leads, for example, to constant disturbances in the assessment of spatial relations; damage to the gyri hippocampi and the horn of Ammon is accompanied by olfactory I. Since the basis of I. can lie not only in morphological destructions but also in some neurodynamic changes, "central" I. often arise even in healthy subjects. Neurodynamic conditions favorable for the occurrence of I. are created in such states of the organism which are subjectively experienced as mental agitation, confusion of consciousness, emotional excitement, etc. In the norm, I. are usually episodic, elementary, and labile. In mentally ill persons, I., on the contrary, can take a sharply expressed character, are distinguished by abundance and constancy and sometimes exert a great influence on the condition and behavior of the patients. They easily arise in excited, with unstable attention manic patients, in superficially perceiving imbeciles, in states of confused consciousness. Melancholic despondent and fearful states, the distrust and suspicion of paranoiacs, as well as other emotional experiences, are also sources of I., often giving food for delusional interpretations. In alcoholics, not only in delirious states but also outside them, there exists a tendency to the appearance of illusory perceptions of sight and hearing already with weak sensory irritations. Acute infections and poisonings by certain poisons (meskalin, hashish) cause the appearance of abundant and diverse illusions. The distinction of I. from hallucinations in individual cases can be very difficult, especially when they exist simultaneously in a patient. Being distorted perceptions of reality, I. must, to a certain extent, obey the laws of this reality, on which is based, among other things, the distinction of visual I. from hallucinations; visual I. are doubled when viewed through a triangular prism, are colored with colored glasses, seem distant in an inverted binocular, which does not happen with hallucinations. From I. it is necessary to distinguish closely related phenomena of incorrect interpretation of perceptions, when a subject attributes to an object a meaning not corresponding to it (e.g., dust and pebbles are taken for gold, pieces of glass for diamonds, etc.). Such "judgment errors" are proposed (Liepmann) to be called "intellectual I." in contrast to genuine "sensory" I.

I. Vvedensky. I. of memory is a phenomenon, to a greater or lesser extent, common to all people. An impression that took place in the past is rarely reproduced exactly. Usually not only do individual details drop out, but the reproduced elements themselves are perverted in the direction indicated by the psychic attitude of the subject and various suggestive influences acting on him. K. and V. Stern, and with us A. P. Nechaev studied this phenomenon experimentally-psychologically. Chiefly they investigated how the content of the pictures shown is reproduced by the subjects. It turned out that the objects depicted on the latter changed in memory their color and place, and those that fell out of memory were replaced by such which were not on the pictures at all. In inquiries regarding details, incorrect answers grew. Especially subjective proved to be the testimony of children, as well as generally uncultured, easily suggestible and emotional persons. Weak memory favors the occurrence of false memories. The described phenomenon is important to have in mind when evaluating testimony at trial, into which one must always introduce a certain correction for the different inaccuracy of reproduction by different persons. Of various pathological forms of memory deceptions (paramnesias), one can speak of I. of memory in cases when patients, under the influence of the dominant affect in them, distort in one direction or another the events they experienced in the past; thus, paranoiacs always unconsciously process their memories in the sense of the delusion dominating their consciousness, depressive patients see their past in the light of self-accusation ideas, and many psychopaths (schizoids, hysterics, etc.) are completely devoid of the ability to give objective testimony about their impressions, as soon as these are touched by their interests and affects.