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ADAPTATION OF SENSORY ORGANS.
Although our senses are limited in their ability to perceive signals, they are nevertheless constantly exposed to stimuli. The brain, which must process the signals it receives, is often in danger of being overloaded with information, and it would not have time to “sort and organize” it if there were no regulatory mechanisms that maintain the number of perceived stimuli at a more or less constant acceptable level.
This mechanism, called sensory adaptation, operates in the receptors themselves. Sensory adaptation, or adaptation is a change in the sensitivity of the senses under the influence of a stimulus. It reduces their sensitivity to repeated or long-term (weak, strong) stimuli. There are three types of this phenomenon.
1. Adaptation as the complete disappearance of sensation during the prolonged action of a stimulus.
In the case of constant stimuli, the sensation tends to fade. For example, a light weight lying on the skin soon ceases to be felt. A common fact is the distinct disappearance of olfactory sensations soon after we enter an atmosphere with an unpleasant odor. The intensity of the taste sensation weakens if the corresponding substance is kept in the mouth for some time, and finally the sensation may fade away completely.
Full adaptation of the visual analyzer does not occur under the influence of a constant and motionless stimulus. This is explained by compensation for the immobility of the stimulus due to movements of the receptor apparatus itself. Constant voluntary and involuntary eye movements ensure continuity of visual sensation. Experiments in which conditions were artificially created to stabilize the image relative to the retina showed that the visual sensation disappears 2-3 seconds after its occurrence, i.e. complete adaptation occurs (stabilization in the experiment was achieved using a special suction cup on which an image was placed that moved with the eye).
2. Adaptation is also called another phenomenon, close to the one described, which is expressed in a dulling of sensation under the influence of a strong stimulus. For example, when immersing your hand in cold water the intensity of the sensation caused by the cold stimulus decreases. When we find ourselves from a dimly lit room into a brightly lit space (for example, leaving a cinema on the street), we are first blinded and unable to discern any details around us. After some time, the sensitivity of the visual analyzer decreases sharply, and we begin to see normally. This decrease in eye sensitivity under intense light stimulation is called light adaptation.
The two types of adaptation described can be called negative adaptation, since as a result they reduce the sensitivity of the analyzers. Negative adaptation- a type of sensory adaptation, expressed in the complete disappearance of sensation during the prolonged action of a stimulus, as well as in the dulling of sensation under the influence of a strong stimulus.
3. Finally, adaptation is an increase in sensitivity under the influence of a weak stimulus. This type of adaptation, characteristic of certain types of sensations, can be defined as positive adaptation. Positive adaptation– a type of increased sensitivity under the influence of a weak stimulus.
In the visual analyzer, this is adaptation to darkness, when the sensitivity of the eye increases under the influence of being in the dark. A similar form of auditory adaptation is adaptation to silence. In temperature sensations, positive adaptation is detected when a pre-cooled hand feels warm, and a pre-heated hand feels cold when immersed in water of the same temperature. The existence of negative pain adaptation has long been controversial. It is known that repeated application of a painful stimulus does not reveal negative adaptation, but, on the contrary, acts more and more powerfully over time. However, new facts indicate the presence of complete negative adaptation to needle pricks and intense hot irradiation.
Studies have shown that some analyzers detect fast adaptation, while others detect slow adaptation. For example, tactile receptors adapt very quickly. When exposed to any prolonged irritation, their sensory nerve runs through only a small “volley” of impulses at the beginning of the stimulus. The visual receptor adapts relatively slowly (tempo adaptation time reaches several tens of minutes), olfactory and gustatory receptors.
Adaptive regulation of the level of sensitivity depending on what stimuli (weak or strong) affects the receptors is of great biological importance. Adaptation helps (through the senses) to detect weak stimuli and protects the senses from being overstimulated by unusually strong stimuli.
The phenomenon of adaptation can be explained by those peripheral changes that occur in the functioning of the receptor during prolonged exposure to a stimulus. Thus, it is known that under the influence of light, the visual purple located in the rods of the retina decomposes (fades). In the dark, on the contrary, visual purple is restored, which leads to increased sensitivity.
In order for the human eye to be able to fully adapt to darkness after daylight, i.e. it takes 40 minutes for its sensitivity to approach the absolute threshold. During this time, vision changes in its own way physiological mechanism: From cone vision, typical for daylight, within 10 minutes the eye moves to rod vision, typical for night. At the same time, the sensations of color disappear and are replaced by black and white tones characteristic of achromatic vision.
In relation to other sense organs, it has not yet been proven that their receptor apparatus contains any substances that chemically decompose when exposed to a stimulus and are restored in the absence of such exposure.
The phenomenon of adaptation is also explained by the processes occurring in the central sections of the analyzers. With prolonged stimulation, the cerebral cortex responds with internal protective inhibition, reducing sensitivity. The development of inhibition causes increased excitation of other foci, which contributes to increased sensitivity in new conditions (the phenomenon of sequential mutual induction).
Another regulatory mechanism is located at the base of the brain, in the reticular formation. It comes into effect in the case of more complex stimulation, which, although captured by receptors, is not so important for the survival of the organism or for the activity in which it is currently engaged. We are talking about habituation, when certain stimuli become so familiar that they cease to influence the activity of the higher parts of the brain: the reticular formation blocks the transmission of corresponding impulses so that they do not “clutter up” our consciousness. For example, the greenery of meadows and foliage after long winter At first it seems very bright to us, but after a few days we get so used to it that we simply stop noticing it. A similar phenomenon is observed among people living near an airfield or highway. They no longer “hear” the noise of planes taking off or trucks passing by. The same thing happens to a city dweller who stops feeling the chemical taste drinking water, and on the street he does not smell car exhaust fumes or hear car horns.
Thanks to this useful mechanism (the habituation mechanism), it is easier for a person to notice any change or new element in the environment, it is easier to concentrate his attention on it, and, if necessary, to resist it. This kind of mechanism allows us to focus all our attention on some important task, ignoring the usual noise and bustle around us.
Various sense organs that give us information about the state of the external world around us may be sensitive to the displayed phenomena with greater or less accuracy.
The sensitivity of our sense organs can vary greatly within wide limits. There are two main forms of sensitivity variability, one of which depends on environmental conditions and is called adaptation, and the other on the conditions of the body’s state and is called sensitization.
Adaptation– adaptation of the analyzer to the stimulus. It is known that in the dark our vision sharpens, and in strong light its sensitivity decreases. This can be observed during the transition from darkness to light: a person’s eye begins to experience pain, the person temporarily “goes blind.”
The most important factor influencing the level of sensitivity is the interaction of the analyzers. Sensitization– this is an increase in sensitivity as a result of the interaction of analyzers and exercise. This phenomenon must be used when driving a car. Thus, the weak effect of side irritants (for example, wiping the face, hands, back of the head with cold water or slowly chewing a sweet and sour tablet, for example, ascorbic acid) increases the sensitivity of night vision, which is very important when driving a car in the dark.
Different analyzers have different adaptability. There is practically no human adaptation to the sensation of pain, which has important biological significance, since painful sensation is a signal of trouble in the body.
Adaptation of the auditory organs occurs much faster. Human hearing adapts to the surrounding background within 15 seconds. A change in sensitivity in the sense of touch also occurs quickly (a slight touch to the skin ceases to be perceived after just a few seconds).
It is known that operating conditions associated with constant readaptation of analyzers cause rapid fatigue. For example, driving a car in the dark on a highway with changing road illumination.
Factors such as noise and vibration have a more significant and constant impact on the senses while driving a car.
Constant noise (and the noise that occurs when a car is moving is usually constant) has a negative effect on the hearing organs. In addition, under the influence of noise, the latent period of the motor reaction is prolonged, visual perception is reduced, twilight vision is weakened, coordination of movements and functions are impaired. vestibular apparatus, premature fatigue sets in.
Changes in the sensitivity of the senses also change with a person’s age. After 35 years, visual acuity and its adaptation generally decrease, and hearing deteriorates. And although many drivers attribute this to poor lighting and weak headlights, the indisputable fact remains that their eyes do not see equally well. With age, they not only see worse, but are also more easily blinded, and their field of vision narrows more often.
Let us now consider the influence of alcohol and other psychoactive and medicines on human mental activity.
When taking sleeping pills, sedatives, antidepressants, anticonvulsants (phenobarbital) and antiallergic drugs (pipolfen, tavegil, suprastin), drowsiness, dizziness, decreased attention and reaction time occur. Harmless cough or headache medications can have a depressant effect on the central nervous system, reducing attention and slowing reaction speed. First of all, these are drugs containing codeine (tramadol, tramalt, retard, pentalgin, spasmoveralgin, sedalgin).
Thus, you should carefully study the instructions for the drug that the driver is going to take before getting behind the wheel.
Let us now consider the effect of alcohol on driving. Although in the Rules traffic It is prohibited to drive a vehicle while intoxicated; in our country, unfortunately, there are strong traditions of doubting the correctness of actions and/or the result of an intoxication test. Believing that “I am normal,” the driver gets behind the wheel drunk and puts other people and himself in danger.
Thus, studies have found significant dysfunction nervous system already from fairly small doses of alcohol. Objectively, a noticeable weakening of the functions of all sensory organs from very small doses of alcohol, including beer, has been established.
Under the influence of an average dose, that is, one to one and a half glasses of vodka, motor acts at first accelerate and then slow down. Another feeling that is easily lost by a drunk person is the feeling of fear.
In addition, it should be borne in mind that when the temperature drops by 5°, the harmful effects of alcohol increase almost tenfold! But people are sure that alcohol has a warming effect, and they believe that for a frozen person a sip of something strong is the best medicine.
Thus, our ability to see, hear, and feel is influenced by many things that are familiar to us: light and darkness, medications, alcohol. When driving a car, you need to take this into account in order to avoid dangerous situations and road accidents.
Sensations have certain properties: adaptation, contrast, sensation thresholds, sensitization, consistent images. If you peer for a long time at some object located in the distance, its outlines blur.
1 . Adaptation. It is an increase or decrease in the sensitivity of analyzers as a result of continuous or prolonged exposure to stimuli. Adaptation can manifest itself as a complete disappearance of sensation as a result of prolonged exposure to the stimulus, and as a decrease or increase in sensitivity under the influence of the stimulus.
2 . Contrast, This phenomenon is that weak stimuli increase sensitivity to other simultaneously acting stimuli, and strong ones reduce this sensitivity.
3 . Thresholds of sensations . In order for sensitivity to a stimulus to appear, it must reach a certain intensity. The lower threshold of sensation is the minimum magnitude or strength of the stimulus that is capable of causing nervous excitation in the analyzer sufficient for the occurrence of sensation. The lower the value of this threshold, the higher the sensitivity of this analyzer.
Upper the threshold of sensation is the maximum value of the stimulus above which this irritation ceases to be felt. A person hears, for example, 20,000 vibrations in 1 second. The absolute threshold of sensation varies from person to person. The threshold of sensations changes with age. Thus, for old people, the absolute upper threshold of audibility of tones is about 15,000 vibrations per second. The value of the absolute threshold can be influenced by the nature of a person’s activity, his functional state, the strength and duration of irritation, etc.
Difference sensation threshold (threshold distinctions) represents the minimum difference in intensity of two homogeneous stimuli that a person is able to feel. In order to catch this difference, it is necessary that it reach a certain value. For example, sounds of 400-402 vibrations per 1 second. are perceived as sounds of the same height; 2 weights weighing 500 and 510 g seem equally heavy. The lower the difference threshold value, the higher the differentiation ability of this analyzer to distinguish between stimuli.
4. Sensitization. Represents an increase in the sensitivity of analyzers due to increased excitability of the cerebral cortex
brain under the influence of the simultaneous activity of other analyzers. The sensitivity of the analyzer can be increased using pharmacological agents, as well as during the activity of other analyzers (for example, sensations of rhythm contribute to increased muscle-motor sensitivity). It can also be developed with the help of exercises (for example, musicians develop high auditory sensitivity, tasting specialists develop olfactory and gustatory sensations).
5 . Sequential images. Expressed in the continuation of sensations when the effect of the stimulus has already ceased. When sensing, the receptor of a particular sense organ is in a state of excitation for some time. After the cessation of exposure to the stimulus, excitation in the receptor does not disappear immediately. For example, after leaving a subway car, for a few seconds it seems to us that we are still moving on the train.
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General understanding of sensory processes. Classification of types of sensations and their characteristics. The problem of measuring sensations.
Sensory processes are processes associated with the formation and change of human sensations; processes associated with the work of human senses, as a result of which sensations appear.
Sensation is a reflection of the properties of objects in the objective world, arising from their direct impact on receptors. Sensation is a reflection in a person’s consciousness of individual properties and qualities of objects and phenomena that directly affect his senses.
Sensation is not only a component of a sensory image, but also an activity or a component of it. Sensitivity is formed in the action that it afferents and regulates, and its development - differentiation, subtlety and accuracy of sensations - significantly depends on the action. In humans, the development of ever more subtle sensations is inextricably linked with the development of social practice: giving rise to new objects with new qualities, it also gives rise to new sensations. From a physiological point of view, sensations represent the activity of: receptors that perceive irritations; conducting centripetal nerve pathways along which excitation arising in the receptors is transmitted to the corresponding areas of the cortex hemispheres; the central cortical sections of the analyzers, where the processing of nerve signals coming from receptors occurs.
Constant orientation of a person in environment carried out according to the physiological mechanism of the “reflex ring”, which ensures constant feedback a person with the world around him. The sensation arises in phylogeny on the basis of elementary irritability as sensitivity to stimuli that do not have direct environmental significance, thereby reflecting an objective connection between biotic and abiotic environmental factors. Unlike the sensations of animals, human sensations are mediated by his practical activities, the whole process historical development society.
The presence of a dependence of sensations on external stimuli forces us to raise the question of the nature of this dependence. Research has established that not every stimulus causes a sensation. A minimum intensity of stimulus is required to produce a sensation. This minimum intensity is called the lower absolute threshold.
Along with the lower one, there is an upper absolute threshold, i.e. the maximum intensity possible for the sensation of a given quality.
There is also a difference threshold of sensation - this is the minimum difference in the intensity of two homogeneous stimuli that a person is able to feel. E. Weber established that a certain ratio between the intensities of two stimuli is required in order for them to give different sensations. This ratio is expressed in the law he established: the ratio of the additional stimulus to the main one must be a constant value. Further studies showed that this law is valid only for stimuli of average magnitude: when approaching absolute thresholds, this value ceases to be constant.
Sensitivity thresholds shift depending on a person’s attitude to the problem that he solves, differentiating certain sensory data. The same physical stimulus of the same intensity can be both lower and higher than the threshold of sensitivity, depending on what significance it acquires for a person.
The characteristics of sensitivity are not limited to psychophysical laws. For the sensitivity of an organ, its physiological state is also important. The significance of physiological aspects is reflected, first of all, in the phenomena of adaptation, in the adaptation of an organ to a long-term stimulus.
A.V. Petrovsky distinguishes three types of adaptation phenomena.
1. Adaptation as the complete disappearance of sensation during prolonged exposure to the stimulus.
2. Adaptation as a dulling of sensation under the influence of a strong stimulus.
3. Adaptation is also called an increase in sensitivity under the influence of a weak stimulus. This type of adaptation is defined as positive adaptation. In the visual analyzer, dark adaptation of the eye, when its sensitivity increases under the influence of darkness, is a positive adaptation. A similar form of auditory adaptation is adaptation to silence. The phenomenon of contrast is closely related to adaptation, which manifests itself in a change in sensitivity under the influence of previous irritation (increased sensation of cold after hot).
Another property of sensations is sensitization - an increase in the sensitivity of analyzers due to an increase in the cerebral cortex under the influence of the simultaneous activity of other analyzers (for example, increased rhythm helps to increase muscle-motor sensitivity).
Many perceptual tasks require the joint work of several perceptual systems, so intermodal or transitional forms of sensitivity are possible, occupying an intermediate position between traditional modalities. A typical intermodal sensation is the sensation of vibration. Another example is the “sixth sense” of the blind. It is known that people who are blind from birth or from childhood are able to detect obstacles at a distance and successfully avoid them. The development of intermodal sensations, which make it possible to compensate for certain sensory deficiencies, emphasizes the importance that the presence of a specific perceptual task has for the development of perceptual systems.
Let's consider the classification of sensations. The first and simplest classification distinguishes sensations by modality:
1.visual; 2. auditory; 3. taste; 4.olfactory; 5. tactile.
The following classification: by the nature of energy: 1.photoperception; 2. chemoperception; 3. mechanical perception.
A.R. Luria believes that the classification of sensations can be carried out according to at least two basic principles - systematic and genetic (in other words, according to the principle of modality, on the one hand, and according to the principle of complexity or level of their construction, on the other).
Systematic classification of sensations. By identifying the largest and most significant groups of sensations, they can be divided into three main types: 1. interoceptive (combine signals that reach us from the internal environment of the body);
2.proprioceptive (provide information about the position of the body in space and the position of the musculoskeletal system, provide regulation of our movements);
3. exteroceptive sensations (provide signals from the outside world and create the basis for our conscious behavior):
a) contact perception - the perceived object is localized on the surface of the body;
b) distant perception - the experience of the absence of physical contact with the perceived object.
Genetic classification allows us to distinguish two types of sensitivity:
a) protopathic (more primitive, affective, less differentiated and localized), which includes organic feelings (hunger, thirst, etc.); b) epicritic (more subtly differentiating, objectified and rational), which includes the main human senses. Epicritic sensitivity is younger in genetic terms, and it controls protopathic sensitivity. Every sensation includes polarity, two-sidedness. It, on the one hand, reflects some aspect of reality acting on the receptor as a stimulus, on the other hand, it to some extent reflects the state of the body. Connected with this is the presence in sensitivity, on the one hand, of affective, and on the other hand, perceptual, contemplative moments. Both of these sides are represented in sensations in unity.
Let's consider the question of measuring sensations. Weber derived a law according to which the ratio of the additional stimulus to the main one must be a constant value. Fechner said that psychological quantities cannot be measured directly, only thresholds can be measured. Sensation is a function of the energy of influence. According to Fechner, the unit of measurement of psychological quantities can be a barely noticeable difference. Thus, the intensity of the sensation can be calculated from the intensity of the stimulus. Fechner derived a law, which was later called the basic psychophysical law, according to which the change in the strength of sensation is proportional to the decimal logarithm of the change in the force of influence. Sensations grow in arithmetic progression when stimuli grow in geometric progression. Fechner's view is called objective psychophysics.
Stevens further revised Fechner's law. He derived two postulates: any person can compare his sensations by intensity, and everything that can be called an adjective in the comparative degree can be measured. Stevens came to the conclusion that the basic psychophysical law is expressed not by a logarithmic curve, but by a power curve. This pattern is called Stevens' law.
Different types of sensations are characterized not only by specificity, but also by properties common to them. These properties include: quality, intensity, duration and spatial localization. Quality is the main feature of a given sensation, distinguishing it from other types of sensations and varying within a given type of sensation. The qualitative diversity of sensations reflects the infinite variety of forms of matter movement. The intensity of the sensation is its quantitative characteristics and is determined by the strength of the current stimulus and functional state receptor. The duration of a sensation is its temporal characteristic. It is also determined by the functional state of the sensory organ, but mainly by the time of action of the stimulus and its intensity. When a stimulus acts on a sense organ, the sensation does not arise immediately, but after some time - the so-called latent (hidden) period of sensation. Latent period various types sensations are not the same. And finally, sensations are characterized by the spatial localization of the stimulus. Analysis carried out by spatial receptors gives us information about the localization of the stimulus in space. Contact sensations correspond to the part of the body that is affected by the stimulus.
There are two main forms of change in the sensitivity of the analyzer - adaptation and sensitization.
Adaptation is a change in the sensitivity of the analyzer under the influence of its adaptation to the current stimulus. It can be aimed at either increasing or decreasing sensitivity. For example, after 30-40 minutes of being in the dark, the sensitivity of the eye increases 20,000 times, and subsequently 200,000 times. The eye adjusts (adapts) to darkness within 4-5 minutes - partially, 40 minutes - enough and 80 minutes - completely. Such an adaptation, which leads to an increase in the sensitivity of the analyzer, is called positive.
Negative adaptation is accompanied by a decrease in the sensitivity of the analyzer. So, in the case of constant stimuli, they begin to be felt weaker and disappear. For example, it is a common fact for us that the olfactory sensations noticeably disappear soon after we enter an atmosphere with an unpleasant odor. The intensity of the taste sensation also weakens if the corresponding substance is kept in the mouth for a long time. Close to what is described is the phenomenon of dulling of sensation under the influence of a strong stimulus. For example, if you come out of the darkness into bright light, then after “blinding” the sensitivity of the eye sharply decreases and we begin to see normally.
The phenomenon of adaptation is explained by the action of both peripheral and central mechanisms. When mechanisms regulating sensitivity act on the receptors themselves, they speak of sensory adaptation. In the case of more complex stimulation, which, although captured by receptors, is not so important for activity, central regulation mechanisms come into play at the level of the reticular formation, which blocks the transmission of impulses so that they do not “clutter” consciousness with excess information. These mechanisms underlie adaptation by the type of habituation to stimuli (habituation).
Sensitization is an increase in sensitivity to the effects of a number of stimuli; physiologically explained by an increase in the excitability of the cerebral cortex to certain stimuli as a result of exercise or interaction of analyzers. According to I.P. Pavlov, a weak stimulus causes an excitation process in the cerebral cortex, which easily spreads (ir-
radiates) along the cortex. As a result of the irradiation of the excitation process, the sensitivity of other analyzers increases. On the contrary, under the influence of a strong stimulus, an excitation process occurs, which tends to concentrate, and according to the law of mutual induction, this leads to inhibition in the central sections of other analyzers and a decrease in their sensitivity. For example, when a quiet tone of equal intensity is sounded and at the same time the rhythmic effect of light on the eye will appear that the tone also changes its intensity. Another example of the interaction of analyzers is the well-known fact of increased visual sensitivity with a weak taste sensation of sour in the mouth. Knowing the patterns of changes in the sensitivity of the sensory organs, it is possible to sensitize a particular analyzer by using specially selected side stimuli. Sensitization can also be achieved as a result of exercise. These data have important practical applications, for example, in cases of need to compensate for sensory defects (blindness, deafness) at the expense of other, intact analyzers or in the development of pitch hearing in children involved in music.
Thus, the intensity of sensations depends not only on the strength of the stimulus and the level of adaptation of the receptor, but also on the stimuli currently acting on other sense organs. A change in the sensitivity of the analyzer under the influence of irritation of other senses is called the interaction of sensations. The interaction of sensations, like adaptation, appears in two opposite processes: an increase and a decrease in sensitivity. Weak stimuli, as a rule, increase, and strong ones decrease, the sensitivity of the analyzers.
The interaction of analyzers is also manifested in the so-called synesthesia. With synesthesia, the sensation occurs under the influence of irritation characteristic of another analyzer. Visual-auditory synesthesia most often occurs when visual images (“color hearing”) appear under the influence of auditory stimuli. Many composers possessed this ability - N.A. Rimsky-Korsakov, A.P. Scriabin et al. Auditory-gustatory and visual-gustatory synesthesia, although they are much less common, we are not surprised by the use in speech of expressions like: “sharp taste”, “sweet sounds”, “screaming color” and others.
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