Manifestations of tactile disorders are disorders in the ability to identify internal sources of irritation, sensations of temperature, pain, pressure, humidity, erroneous differentiation of external signs of familiar objects and objects, illusory sensations and tactile (tactile) hallucinations, imaginary perception of the body scheme.
One of the oldest examples of tactile illusion known to all psychologists was presented by Aristotle ("Aristotle's illusion"). If you cross two fingers and roll a pea or some small object between them, then to a person it will seem double.
The most successful and anatomically correct explanation of this phenomenon was given by Robertson. He explained this effect by the fact that when an object touches in turn with the index and middle fingers, the points of contact are in different levels of space.
Therefore, there is an imaginary sensation (tactile illusion) that the point of contact with the index finger is higher, although the finger is actually lower, and vice versa - the point of contact with the middle finger is lower, while in fact, the finger is higher.
The sides of the fingers involved in this experience, in their normal position, are not located next to each other in space, and usually do not touch the same object, therefore, consciousness perceives one object to which they are unusually touching, located simultaneously in two places, that is, consciousness "interprets" him as two different subjects.
Not every distortion of the process of sensation and perception is considered by specialists to be a sign of a mental disorder. Tactile illusions can arise in a healthy person under the influence of certain ("wrong") conditions - with temporary functional disturbances in the activity of the central nervous system (deep fatigue, absent-mindedness and, against its background, lack of concentration of perception).
Doctors consider only disorders of sensation and perception as pathological disorders, leading to a sharp and long-term violation of the recognition of the environment and to the persistent formation of severe mental disorders.
Psychologists distinguish in a person the presence of a tactile channel, which is responsible for his bodily and tactile sensations - an increase or decrease in temperature and pressure, pain effects.
It is natural for a person to fix his unusual and unpleasant mental state on the basis of changes in his sensations in the physical sense. In other words, a person recognizes ("registers") his fear by "coldness in the back" and "trembling in the knees", excitement and delight is determined by a rapid heartbeat.
In general cases, manifestations of tactile illusions and hallucinations are expressed in the form of erroneous sensations of cold or warmth (thermal illusions), touching the body, pinching (haptic illusions), the appearance of "goose bumps", crawling insects.
More recently, scientists from three scientific institutions - Massachusetts Institute of Technology, Harvard and McGill University - made an amazing discovery. They have proven that it is quite possible to create tactile illusions similar to visual illusionary effects.
According to one of the discoverers Christopher Moore, the brain (consciousness) interprets what it sees or tasted by touch, depending on the "context", for a very simple reason - because a person subconsciously wants this (tuned in to this "wave") and seeks to get an unknown sensation ...
He also explained the meaning of the work of a group of scientists, the desire to understand the general mechanisms of illusions (most of the imaginary perception is associated with vision), and to make sure that in the field of touch it is also possible to artificially create an illusion.
To confirm their theory about the possibility of creating a tactile illusion by analogy with visual distortion, scientists conducted an experiment. They created a version of the tactile illusion based on the illusion of vision well known to all specialists - the illusion of a moving quartet.
Two large black dots, located in opposite corners of an imaginary geometric figure - a square, move at high speed according to a certain pattern - "upper left + lower right corner - upper right + lower left".
During this movement, the person begins to think that the points are in horizontal or vertical movement (forward and backward, up and down). But, this is not the whole version of the illusion.
With long-term observation of movement, a person discovers that up and down movement replaces movement from right to left and vice versa. Sometimes consciousness "suggests" movement in a circle, in any direction. Scientists claim that with an effort of will, you can change the direction of movement.
Since this experiment confirms the possibility of creating an illusion - a deceptive perception of a real action by the consciousness, this means that the same illusion can be created in the field of tactile sensations. Scientists for their experiment used a device that was originally created as a Braille display (for people with impaired or impaired vision).
At the end of the experiment, each of the participants in the experiment said that he felt with his fingers the same movements that he had seen on the screen before, that is, the tactile perception turned out to be the same with the visual one, including the created illusion.
Scientists from the Center for Intelligent Machines at McGill University of Canada (headed by Vincent Hayward) created a special series of Braille displays that transmitted a visual image to the receptors of human skin. Such a product served as a tool for Moore and his colleagues to recreate tactile illusions.
Gradually complicating the conditions of the experiment by complicating the moving picture, scientists received an unexpected result - with an increase in the movement of points and their number, the power of the illusion increases. From what scientists have concluded that the brain somehow re-sorts the received signals, and changes the type of perception of what is happening, the perception mechanism is still unclear.
But, the main conclusion of the experimenters was that "games of consciousness" are also possible for tactile perception, which means that the mechanism of manifestation of illusions is common to all senses (and not only to visual perception), including the tactile sphere.
Another experiment based on a moving quartet was that all its participants, at the request of scientists, moved their eyes, repeating the perception of the movement of dots on the Braille display (horizontally, vertically).
And it turned out that the imaginary movements under the fingers coincided with the actual movement of the eyes, and when the participant's head tilted 90 degrees, the direction of movement of the points also changed in a tactile illusion. This proves that there is a direct connection between visual and tactile perception, as well as motor skills.
And quite recently, another group of scientists has identified and proved that the sense of touch sharpens vision, that is, the concept of "contact vision" actually exists, and the perception of an object by touch helps to see it better.
The mechanism of tactile illusions is the same as visual illusory phenomena, which means that the human brain "independently" is able to process the sensations of different senses, and combine it for itself into a general picture.