From Big Medical Encyclopedia

VISUAL ILLUSIONS — the false, distorted images of reality arising in the course of vision. Emergence 3. and. it is connected with features of emergence of visual feelings. Visual feelings are not identical to visual objects on a retina of an eye; any subject is projected on a retina of an eye in the turned look, the size of this projection is limited to the sizes of a retina, and the visual object continuously changes the position in space owing to the constant movement of an eye. Nevertheless the person perceives the world around not in a wrong way, its display in our consciousness is true what vital practice convinces of. The life experience of the person imprinted in the highest departments of a brain brings correction in visual feelings, providing the correct orientation in surrounding space. At the same time also wrong judgments are possible. So, if to arrange one of two identical circles among big, and another — among small circles, the first will seem less than the second. The same piece of a straight line is perceived big, smaller in size, depending on in what parallelogram in size it joins as diagonal.

The person got used whole to allocate the size of any part inherent in this whole with characteristics and properties. Therefore in a big parallelogram the piece of a straight line will seem big, than in a smaller parallelogram. Parallel lines during the crossing by their short multidirectional lines seem non-parallel. Pieces, identical on length, seem big having been in vertical position. 3. and. such actually come down to mistakes in assessment of the pieces compared in size, corners, distances between objects, to mistakes at perception of a form etc. Some 3. and. physical speak. conditions of vision, napr, mirages, the seeming change of the stick which is partially shipped in water, etc. 3. and. can be a consequence of strong emotions, in particular if they arise at the person captured by some preconception idea, the idea which seized consciousness. So, the person in a condition of strong fear in the dark if he trusts in a possibility of attack on it of robbers, sees them in each bush, in each dark subject. Understanding of origins 3. and. creates a possibility of their use in practice. E.g., if necessary to make an impression of equality top and bottom parts of letters or figures their upper part is done a little smaller, than lower. The vertical arrangement of strips on fabric visually extends a figure and does it less full, and the horizontal arrangement of strips creates opposite effect. In painting 3. and. create effect of visual perspective, impression of a raznoudalennost of the objects represented on a flat cloth of a picture. The phenomenon 3 is widely used. and. in architecture.

In some types of activity of the person 3. and. gain extremely important value. In particular, in flight practice 3. and., arising in flight, can be a cause of infringement of the mode of flight, accidents and even accidents. Characteristic example 3. and. in flight — the seeming movement of objectively motionless lonely shining point on a homogeneous background, napr, weeds behind a lonely star in a rupture of clouds (autokinetichesky illusion). Origin 3. and. perception of the movement of own eye as the movements of any shining point recorded by it in conditions when its situation cannot be compared with the provision of other objects is such. Illusion of the moving point is supplemented in consciousness with contours of the airplane or fires of the airplane flying ahead. In some conditions emergence of the illusion of «swelling» of bodies arising at rapprochement with a certain speed with any subject is possible. Origin of this look 3. and. is that the speed of convergence of visual axes is less, than the speed of rapprochement with a subject. Thereof it seems that rapprochement with a subject stopped, and the subject quickly increases in sizes — as if inflates. During the flight over a plain surface of clouds an impression of the fact that the airplane is as if over the center of a huge saucer that is explained by the visual «underestimation» of distance which is progressively increasing with removal of the perceived objects can be made. At recognition of light sources fires on the earth can sometimes be perceived as fires in air and vice versa. The light source can seem split on several sources etc. In still, heated air at position of the Sun in a zenith at the pilot coming in the land an impression of doubling of a landing strip down can be made. Accepting a false strip for true, the pilot appears in a heavy emergency. This look 3. and. received the name «delibab» (a midday mirage). Quantity of types 3. and., arising in flight, it is very big, they hardly give in to classification. But practically in it there is no big need since it is important to mean that they arise at all pilots, is more often in night flights, at limited visibility, at insufficient trust to indications of onboard devices, at exhaustion etc. Any kind 3. and. it can be suppressed by a special training, in particular by education of absolute trust to aviation devices.

3. and., as well as any other disturbances perceptions (see), arise in certain conditions at one and all people. However 3. and. can be a symptom of a number of mental diseases (see. Illusions ).

B. S. Alyakrinsky.