There are two main forms of changes 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 both increasing and decreasing sensitivity. So, for example, after 30-40 minutes of being in the dark, the sensitivity of the eye increases by 20,000 times, and later by 200,000 times. The eye adapts (adapts) to the dark 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 the action of constant stimuli, they begin to feel weaker and disappear. For example, it is a common fact for us to notice a distinct loss of olfactory sensations shortly 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 the described is the phenomenon of dulling sensation under the influence of a strong stimulus. For example, if you go out of the dark into bright light, then after "blinding" the sensitivity of the eye drops sharply and we begin to see normally.

The phenomenon of adaptation is explained by the action of both peripheral and central mechanisms. Under the action of mechanisms that regulate sensitivity 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, the mechanisms of central regulation at the level of the reticular formation come into action, which blocks the transmission of impulses so that they do not "clutter up" consciousness with excessive 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 the interaction of analyzers. According to I.P. Pavlov, a weak stimulus causes an excitation process in the cerebral cortex, which spreads easily (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 action 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 sounding a quiet tone of the same intensity and with the simultaneous rhythmic effect of light on the eye, it will seem that the tone also changes its intensity. Another example of the interaction of analyzers is the known fact of an increase in visual sensitivity with a weak taste sensation of sour in the mouth. Knowing the patterns of changes in the sensitivity of the sense organs, it is possible, by using specially selected side stimuli, to sensitize one or another analyzer. Sensitization can also be achieved through exercise. These data have an important practical application, for example, in cases where it is necessary 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 sense organs is called the interaction of sensations. The interaction of sensations, like adaptation, appears in two opposite processes: increase and 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. In synesthesia, sensation arises under the influence of irritation characteristic of another analyzer. Most often, visual-auditory synesthesia occurs when visual images appear under the influence of auditory stimuli ("color hearing"). Many composers had this ability - N.A. Rimsky-Korsakov, A.P. Scriabin and others. Although auditory-gustatory and visual-gustatory synesthesias are much less common, we are not surprised by the use of expressions such as "sharp taste", "sweet sounds", "screaming color" and others in speech.

Adaptation, or adaptation, is a change in the sensitivity of the sense organs under the influence of the action of a stimulus.

Three varieties of this phenomenon can be distinguished.

1. Adaptation as the complete disappearance of sensation in the process of prolonged action of the stimulus. In the case of constant stimuli, the sensation tends to fade. For example, a light load resting on the skin soon ceases to be felt. The distinct disappearance of olfactory sensations shortly after we enter an atmosphere with an unpleasant odor is also a common fact. The intensity of the taste sensation weakens if the corresponding substance is kept in the mouth for some time and, finally, the sensation may die out altogether.

Full adaptation of the visual analyzer under the action of a constant and immobile stimulus does not occur. This is due to compensation for the immobility of the stimulus due to the movements of the receptor apparatus itself. Constant voluntary and involuntary eye movements ensure the continuity of the visual sensation. Experiments in which the conditions for image stabilization1 relative to the retina were artificially created showed that in this case, the visual sensation disappears 2-3 seconds after its occurrence, i.e. complete adaptation.

2. Adaptation is also called another phenomenon, close to the one described, which is expressed in the dulling of sensation under the influence of a strong stimulus. For example, when a hand is immersed in cold water, the intensity of sensation caused by a temperature stimulus decreases. When we move from a semi-dark room into a brightly lit space, we are at first blinded and unable to distinguish any details around. After some time, the sensitivity of the visual analyzer decreases sharply, and we begin to see normally. This decrease in the sensitivity of the eye to intense light stimulation is called light adaptation.

The described two types of adaptation can be combined with the term negative adaptation, since as a result of them the sensitivity of the analyzers decreases.

3. Adaptation is called an increase in sensitivity under the influence of a weak stimulus. This kind of adaptation, which is characteristic of certain types of sensations, can be defined as positive adaptation.

In the visual analyzer, this is dark adaptation, when the sensitivity of the eye increases under the influence of being in the dark. A similar form of auditory adaptation is silence adaptation.

Adaptive regulation of the level of sensitivity, depending on which stimuli (weak or strong) affect the receptors, is of great biological importance. Adaptation helps to catch weak stimuli through the sense organs and protects the sense organs from excessive irritation in case of unusually strong influences.

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. So, it is known that under the influence of light, visual purple, located in the rods of the retina, decomposes. In the dark, on the contrary, visual purple is restored, which leads to an increase in sensitivity. The phenomenon of adaptation is also explained by the processes taking place in the central sections of the analyzers. With prolonged stimulation, the cerebral cortex responds with internal protective inhibition, which reduces sensitivity. The development of inhibition causes increased excitation of other foci, which contributes to an increase in sensitivity in new conditions.

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 affecting other sense organs. A change in the sensitivity of the analyzer under the influence of irritation of other sense organs is called the interaction of sensations.

The literature describes numerous facts of sensitivity changes caused by the interaction of sensations. Thus, the sensitivity of the visual analyzer changes under the influence of auditory stimulation.

Weak sound stimuli increase the color sensitivity of the visual analyzer. At the same time, a sharp deterioration in the distinctive sensitivity of the eye is observed when, for example, the loud noise of an aircraft engine is used as an auditory stimulus.

Visual sensitivity also increases under the influence of certain olfactory stimuli. However, with a pronounced negative emotional coloring of the smell, a decrease in visual sensitivity is observed. Similarly, with weak light stimuli, auditory sensations are enhanced, and exposure to intense light stimuli worsens auditory sensitivity. There are known facts of increasing visual, auditory, tactile and olfactory sensitivity under the influence of weak pain stimuli.

A change in the sensitivity of any analyzer is also observed with subthreshold stimulation of other analyzers. So, P.P. Lazarev (1878-1942) obtained evidence of a decrease in visual sensitivity under the influence of skin irradiation with ultraviolet rays.

Thus, all our analyzer systems are capable of influencing each other to a greater or lesser extent. At the same time, the interaction of sensations, like adaptation, manifests itself in two opposite processes: an increase and a decrease in sensitivity. The general pattern here is that weak stimuli increase and strong ones decrease the sensitivity of the analyzers during their interaction.

The interaction of sensations is manifested in another kind of phenomena called synesthesia. Synesthesia is the occurrence under the influence of irritation of one analyzer of a sensation characteristic of another analyzer. Synesthesia is seen in a wide variety of sensations. The most common visual-auditory synesthesia, when, under the influence of sound stimuli, the subject has visual images. There is no overlap between different people in these synesthesias, however, they are quite constant for each individual.

The phenomenon of synesthesia is the basis for the creation in recent years of color-musical devices that turn sound images into color ones. Less common are cases of auditory sensations when exposed to visual stimuli, taste sensations in response to auditory stimuli, etc. Not all people have synesthesia, although it is quite widespread. The phenomenon of synesthesia is another evidence of the constant interconnection of the analyzer systems of the human body, the integrity of the sensory reflection of the objective world.

An increase in sensitivity as a result of the interaction of analyzers and exercise is called sensitization.

The physiological mechanism for the interaction of sensations is the processes of irradiation and concentration of excitation in the cerebral cortex, where the central sections of the analyzers are represented. According to I.P. Pavlov, a weak stimulus causes an excitation process in the cerebral cortex, which easily irradiates (spreads). As a result of the irradiation of the excitation process, the sensitivity of another analyzer increases. Under the action of a strong stimulus, a process of excitation occurs, which, on the contrary, has a tendency to concentration. According to the law of mutual induction, this leads to inhibition in the central sections of other analyzers and a decrease in the sensitivity of the latter.

Bob Nelson

Most often, spectrum analyzers are used to measure very small signals. These may be known signals that need to be measured, or unknown signals that need to be detected. In any case, to improve this process, you should be aware of methods for increasing the sensitivity of the spectrum analyzer. In this article, we will discuss the optimal settings for measuring low level signals. In addition, we will discuss the use of noise correction and analyzer noise reduction functions to maximize instrument sensitivity.

Average self-noise and noise figure

The sensitivity of the spectrum analyzer can be found in its specifications. This parameter can be either the average level of intrinsic noise ( DANL), or noise factor ( NF). The average noise floor is the amplitude of the spectrum analyzer's noise floor over a given frequency range with a 50 ohm input load and 0 dB input attenuation. This parameter is usually expressed in dBm/Hz. In most cases, averaging is performed on a logarithmic scale. This reduces the displayed average noise level by 2.51 dB. As we will learn from the discussion below, it is this noise reduction that distinguishes the average noise floor from the noise figure. For example, if the analyzer specification specifies an average noise floor of 151 dBm/Hz with an IF filter bandwidth ( RBW) 1 Hz, then using the analyzer settings you can reduce the device's own noise level to at least this value. Incidentally, a CW signal that has the same amplitude as the spectrum analyzer noise will be measured 2.1 dB above the noise floor due to the summation of the two signals. Similarly, the observed amplitude of noise-like signals will be 3 dB higher than the noise floor.

The analyzer's inherent noise has two components. The first of them is determined by the noise figure ( NF ac), and the second is thermal noise. The thermal noise amplitude is described by the equation:

NF=kTB,

Where k= 1.38×10–23 J/K - Boltzmann's constant; T- temperature (K); B is the bandwidth (Hz) in which the noise is measured.

This formula determines the thermal noise energy at the input of a spectrum analyzer with a 50 Ω load. In most cases, the bandwidth is reduced to 1 Hz, and at room temperature the calculated value of thermal noise is 10log( kTB)= -174 dBm/Hz.

As a result, the value of the average level of intrinsic noise in the 1 Hz band is described by the equation:

DANL = –174+NF ac= 2.51 dB. (1)

Besides,

NF ac = DANL+174+2,51. (2)

Note. If for the parameter DANL rms power averaging is used, the term 2.51 can be omitted.

Thus, the value of the average level of self-noise –151 dBm/Hz is equivalent to the value NF ac= 25.5 dB.

Settings affecting the sensitivity of the spectrum analyzer

The gain of the spectrum analyzer is equal to one. This means that the screen is calibrated against the analyzer's input port. Thus, if a signal with a level of 0 dBm is applied to the input, the measured signal will be equal to 0 dBm plus/minus the instrument's error. This must be taken into account when using an input attenuator or amplifier in the spectrum analyzer. Turning on the input attenuator causes the analyzer to increase the equivalent gain of the IF stage to maintain the calibrated level on the screen. This, in turn, raises the noise floor by the same amount, thus maintaining the same signal-to-noise ratio. This is also true for an external attenuator. In addition, it is necessary to recalculate to the passband of the IF filter ( RBW) greater than 1 Hz by adding the term 10log( RBW/1). These two terms allow you to determine the noise level of the spectrum analyzer at different values ​​of attenuation and resolution bandwidth.

Noise level = DANL+ attenuation + 10log( RBW). (3)

Adding a preamp

The built-in or external preamplifier can be used to reduce the spectrum analyzer's inherent noise. Typically, the data sheet will list a second value for the average noise floor, including the built-in preamp, and all of the above equations can be used. When using an external preamplifier, a new average noise floor can be calculated by cascading the noise figure equations and assuming the gain of the spectrum analyzer to be unity. If we consider a system consisting of a spectrum analyzer and an amplifier, we get the equation:

NF system = NF predus+(NF ac–1)/G predus. (4)

Using value NF ac= 25.5dB from the previous example, 20dB preamp gain and 5dB noise figure, we can determine the overall system noise figure. But first you need to convert the values ​​​​to a ratio of powers and take the logarithm of the result:

NF system= 10log(3.16+355/100) = 8.27 dB. (5)

Now you can use Equation (1) to find a new value for the average noise floor with an external preamplifier by simply replacing NF ac on NF system, calculated in equation (5). In our example, the preamp significantly reduces DANL-151 to -168 dBm/Hz. However, this is not given for free. Preamplifiers tend to have a lot of non-linearity and a low compression point, which limits the ability to measure high level signals. In such cases, the built-in preamp is more useful as it can be turned on and off as needed. This is especially true for automated control and measuring systems.

So far, we have discussed how the IF filter bandwidth, attenuator, and preamplifier affect the sensitivity of a spectrum analyzer. Most modern spectrum analyzers have methods for measuring their own noise and correcting the measurement results based on the acquired data. These methods have been used for many years.

Noise Correction

When measuring the characteristics of a certain device under test (DUT) with a spectrum analyzer, the observed spectrum is the sum of ktb, NF ac and input signal TU. If the DUT is turned off and a 50 Ohm load is connected to the analyzer input, the spectrum will be the sum ktb And NF ac. This trace is the analyzer's own noise. In general, noise correction consists of measuring the intrinsic noise of the spectrum analyzer with a large average and storing this value as a "correction trace". You then connect the device under test to the spectrum analyzer, measure the spectrum, and record the results in the "measured trace". The correction is done by subtracting the "correction trace" from the "measured trace" and displaying the results as a "result trace". This trace is a "DOT signal" with no additional noise:

Resulting trace = measured trace - correction trace = [DOT signal + ktb + NF ac]–[ktb + NF ac] = TR signal. (6)

Note. All values ​​were converted from dBm to mW before subtraction. The resulting trace is in dBm.

This procedure improves the display of low-level signals and allows for more accurate amplitude measurements by eliminating the error associated with the spectrum analyzer's inherent noise.

On fig. 1 shows a relatively simple method for correcting noise by applying trace math. First, the spectrum analyzer noise floor is averaged with input loading, the result is stored in trace 1. Then the DUT is connected, the input signal is captured, and the result is stored in trace 2. Now you can use math - subtracting two traces and putting the results in trace 3. How You see, noise correction is especially effective when the input signal is close to the spectrum analyzer's noise floor. High-level signals contain much less noise, and the correction does not have a noticeable effect.

The main disadvantage of this approach is that each time you change the settings, you have to turn off the device under test and connect a 50 ohm load. The method to obtain a "correction trace" without turning off the DUT is to increase the attenuation of the input signal (eg by 70 dB) so that the noise of the spectrum analyzer significantly exceeds the input signal, and store the results in the "correction trace". In this case, the "correction trace" is given by the equation:

Correction trace = TR signal + ktb + NF ac+ attenuator. (7)

ktb + NF ac+ attenuator >> TU signal,

we can omit the "signal TR" term and state that:

Correction trace = ktb + NF ac+ attenuator. (8)

By subtracting the known value of the attenuator from formula (8), we can get the original "correction trace" that was used in the manual method:

Correction trace = ktb + NF ac. (9)

In this case, the problem is that the "correction trace" is only valid for the current instrument settings. Changing settings such as center frequency, span, or IF filter bandwidth makes the values ​​stored in the "correction trace" incorrect. The best approach is to know the values NF ac at all points of the frequency spectrum and the application of the "correction trace" at any setting.

Noise Reduction

The Agilent N9030A PXA signal analyzer (Figure 2) has a unique noise reduction (NFE) feature. The noise figure of the PXA signal analyzer over the entire frequency range of the instrument is measured during manufacture and calibration. This data is then stored in the instrument's memory. When the user turns on the NFE, the meter calculates a "correction trace" for the current settings and stores the noise figure values. This eliminates the need to measure the intrinsic noise of the PXA, as was done in the manual procedure, which greatly simplifies noise correction and saves time spent on measuring instrument noise when changing settings.

In any of the described methods, thermal noise is subtracted from the "measured trace" ktb And NF ac, which allows you to get results below the value ktb. These results may be reliable in many cases, but not in all. Confidence may decrease when the measured values ​​are very close to or equal to the instrument's inherent noise. In fact, the result will be an infinite value in dB. A practical implementation of noise correction typically involves introducing a threshold or graduated subtraction level near the instrument's own noise floor.

Conclusion

We looked at some methods for measuring low level signals with a spectrum analyzer. At the same time, we found that the sensitivity of the measuring device is affected by the bandwidth of the IF filter, the attenuation of the attenuator and the presence of a preamplifier. Techniques such as mathematical noise correction and self-noise reduction can be used to further increase the sensitivity of the instrument. In practice, a significant increase in sensitivity can be achieved by eliminating losses in external circuits.

The world around us, its beauty, sounds, colors, smells, temperature, size and much more we learn through the senses. With the help of the sense organs, the human body receives in the form of sensations a variety of information about the state of the external and internal environment.

SENSATION is a simple mental process, which consists in reflecting the individual properties of objects and phenomena of the surrounding world, as well as the internal states of the body with the direct action of stimuli on the corresponding receptors.

The sense organs are irritated. It is necessary to distinguish between stimuli that are adequate for a particular sense organ and inadequate for it. Sensation is the primary process from which the knowledge of the surrounding world begins.

SENSATION is a cognitive mental process of reflection in the human psyche of individual properties and qualities of objects and phenomena with their direct impact on his senses.

The role of sensations in life and cognition of reality is very important, since they constitute the only source of our knowledge about the external world and about ourselves.

The physiological basis of sensations. Sensation occurs as a reaction of the nervous system to a particular stimulus. The physiological basis of sensation is a nervous process that occurs when a stimulus acts on an analyzer adequate to it.

The sensation has a reflex character; physiologically it provides the analyzer systems. The analyzer is a nervous apparatus that performs the function of analyzing and synthesizing stimuli that come from the external and internal environment of the body.

ANALYZERS- these are the organs of the human body that analyze the surrounding reality and single out certain or other types of psycho-energy in it.

The concept of analyzer was introduced by I.P. Pavlov. The analyzer consists of three parts:

The peripheral section is a receptor that converts a certain type of energy into a nervous process;

Afferent (centripetal) pathways that transmit the excitation that has arisen in the receptor in the higher centers of the nervous system, and efferent (centrifugal), along which impulses from the higher centers are transmitted to lower levels;

Subcortical and cortical projective zones, where the processing of nerve impulses from the peripheral regions takes place.

The analyzer constitutes the initial and most important part of the entire path of nervous processes, or the reflex arc.

Reflex arc = analyzer + effector,

An effector is a motor organ (a certain muscle) that receives a nerve impulse from the central nervous system (brain). The relationship of the elements of the reflex arc provides the basis for the orientation of a complex organism in the environment, the activity of the organism, depending on the conditions of its existence.

For a sensation to arise, the work of the entire analyzer as a whole is necessary. The action of the stimulus on the receptor causes the appearance of irritation.

Classification and varieties of sensations. There are various classifications of the sense organs and the sensitivity of the body to stimuli entering the analyzers from the outside world or from within the body.

Depending on the degree of contact of the sense organs with stimuli, contact (tangential, gustatory, pain) and distant (visual, auditory, olfactory) sensitivity are distinguished. Contact receptors transmit irritation through direct contact with objects that affect them; such are the tactile, taste buds. Distant receptors respond to irritation * that comes from a distant object; distantreceptors are visual, auditory, olfactory.

Since sensations arise as a result of the action of a certain stimulus on the corresponding receptor, the classification of sensations takes into account the properties of both the stimuli that cause them and the receptors that are affected by these stimuli.

Behind the placement of receptors in the body - on the surface, inside the body, in muscles and tendons - sensations are emitted:

Exteroceptive, reflecting the properties of objects and phenomena of the outside world (visual, auditory, olfactory, gustatory)

Interoceptive, containing information about the state of internal organs (hunger, thirst, fatigue)

Proprioceptive, reflecting the movements of the organs of the body and the state of the body (kinesthetic and static).

According to the system of analyzers, there are such types of sensations: visual, auditory, tactile, pain, temperature, taste, olfactory, hunger and thirst, sexual, kinesthetic and static.

Each of these varieties of sensation has its own organ (analyzer), its own patterns of occurrence and function.

A subclass of proprioception, which is sensitivity to movement, is also called kinesthesia, and the corresponding receptors are kinesthetic, or kinesthetic.

Independent sensations include temperature, which is a function of a special temperature analyzer that performs thermoregulation and heat exchange of the body with the environment.

For example, the organ of visual sensations is the eye. The ear is the organ of perception of auditory sensations. Tactile, temperature and pain sensitivity is a function of organs located in the skin.

Tactile sensations provide knowledge about the measure of equality and relief of the surface of objects, which can be felt during their palpation.

Pain signals a violation of the integrity of the tissue, which, of course, causes a protective reaction in a person.

Temperature sensation - a sensation of cold, heat, it is caused by contact with objects that have a temperature higher or lower than body temperature.

An intermediate position between tactile and auditory sensations is occupied by vibrational sensations, signaling the vibration of an object. The organ of vibrational sense has not yet been found.

Olfactory sensations signal the state of the food's suitability for consumption, clean or polluted air.

The organ of taste sensations is special cones sensitive to chemical irritants located on the tongue and palate.

Static or gravitational sensations reflect the position of our body in space - lying, standing, sitting, balancing, falling.

Kinesthetic sensations reflect the movements and states of individual parts of the body - arms, legs, head, body.

Organic sensations signal such states of the body as hunger, thirst, well-being, fatigue, pain.

Sexual sensations signal the body's need for sexual release, providing pleasure due to irritation of the so-called erogenous zones and sex in general.

From the point of view of the data of modern science, the accepted division of sensations into external (exteroceptors) and internal (interoceptors) is insufficient. Some kinds of sensations can be considered externally internal. These include temperature, pain, taste, vibration, musculo-articular, sexual and static di and amich n and.

General properties of sensations. Sensation is a form of reflection of adequate stimuli. However, different types of sensations have not only specificity, but also common properties for them. These properties include quality, intensity, duration, and spatial localization.

Quality is the main feature of a certain sensation that distinguishes it from other types of sensations and varies within a given type. So, auditory sensations differ in pitch, timbre, loudness; visual - by saturation, color tone and the like.

The intensity of sensations is its quantitative characteristic and is determined by the strength of the stimulus and the functional state of the receptor.

The duration of a sensation is its temporal characteristic. it is also determined by the functional state of the sense organ, but mainly by the duration of the stimulus and its intensity. During the action of the stimulus on the sense organ, the sensation does not occur immediately, but after a while, which is called the latent (hidden) period of sensation.

General laws of sensations. General patterns of sensations are sensitivity thresholds, adaptation, interaction, sensitization, contrast, synesthesia.

Sensitivity. The sensitivity of the sense organ is determined by the minimum stimulus that, under specific conditions, becomes capable of causing a sensation. The minimum strength of the stimulus that causes a barely noticeable sensation is called the lower absolute threshold of sensitivity.

Irritants of lesser strength, the so-called subthreshold ones, do not cause sensations, and signals about them are not transmitted to the cerebral cortex.

The lower threshold of sensations determines the level of absolute sensitivity of this analyzer.

The absolute sensitivity of the analyzer is limited not only by the lower, but by the upper threshold of sensation.

The upper absolute threshold of sensitivity is called the maximum strength of the stimulus, at which there is still an adequate sensation for a certain stimulus. A further increase in the strength of stimuli acting on our receptors causes only a painful sensation in them (for example, a super-loud sound, dazzling brightness).

The difference in sensitivity, or sensitivity to discrimination, is also inversely related to the value of the discrimination threshold: the larger the discrimination threshold, the smaller the difference in sensitivity.

Adaptation. The sensitivity of analyzers, determined by the magnitude of the absolute thresholds, is not constant and changes under the influence of a number of physiological and psychological conditions, among which the phenomenon of adaptation occupies a special place.

Adaptation, or adaptation, is a change in the sensitivity of the sense organs under the influence of the action of a stimulus.

There are three types of this phenomenon:

Adaptation as a continuous disappearance of sensation in the process of prolonged action of the stimulus.

Adaptation as a dulling of sensation under the influence of a strong stimulus. The described two types of adaptation can be combined with the term negative adaptation, since it results in a decrease in the sensitivity of the analyzers.

Adaptation as an increase in sensitivity under the influence of a weak stimulus. This type of adaptation, inherent in some types of sensations, can be defined as positive adaptation.

The phenomenon of increasing the sensitivity of the analyzer to the stimulus under the influence of mindfulness, orientation, installation is called sensitization. This phenomenon of the sense organs is possible not only as a result of the use of indirect stimuli, but also through exercise.

The interaction of sensations is a change in the sensitivity of one analyzer system under the influence of another. 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 that affect other sense organs at that moment. Change in the sensitivity of the analyzer under the influence of irritation of other senses. the name of the interaction of sensations.

In this case, the interaction of sensations, as well as adaptations, will turn out to be in two opposite processes: an increase and a decrease in sensitivity. The main regularity here is that weak stimuli increase, and strong ones decrease, the sensitivity of the analyzers by their interaction.

A change in the sensitivity of the analyzers can cause the action of all-round signal stimuli.

If you carefully, carefully peer, listen, savor, then the sensitivity to the properties of objects and phenomena becomes clearer, brighter - objects and their properties are much better distinguished.

The contrast of sensations is a change in the intensity and quality of sensations under the influence of a previous or accompanying stimulus.

With the simultaneous action of two stimuli, a simultaneous contrast occurs. Such a contrast can be well traced in visual sensations. One and you yourself figure on a black background will seem lighter, on a white - darker. A green object on a red background is perceived as more saturated. Therefore, military objects are often masked so that there is no contrast. This should include the phenomenon of consistent contrast. After a cold, a weak warm stimulus will seem hot. The sensation of sour increases the sensitivity to sweet.

Synesthesia of feelings is the occurrence of a floor by an outpouring of an irritant of one analyzer of nidchutgiv. which are specific to another analyzer. In particular, during the action of sound stimuli, such as aircraft, rockets, etc., a person has visual images of them. Or whoever sees a wounded person also feels pain in a certain way.

The activities of the analyzers will be in interaction. This interaction is not isolated. It has been proven that light increases hearing sensitivity, and weak sounds increase visual sensitivity, cold washing of the head increases sensitivity to red, and the like.

Despite the variety of types of sensations, there are some patterns common to all sensations. These include:

• the relationship between sensitivity and sensation thresholds,
• phenomenon of adaptation
• interaction of sensations and some others.

Sensitivity and thresholds of sensations. The sensation arises as a result of the action of an external or internal stimulus. However, for the sensation to occur, a certain strength of the stimulus is necessary. If the stimulus is very weak, it will not cause sensation. It is known that he does not feel the touch of dust particles on his face, does not see with his naked eyes the light of stars of the sixth, seventh, etc. magnitude. The minimum value of the stimulus at which a barely noticeable occurs is called the lower or absolute threshold of sensation. Irritants that act on human analyzers, but do not cause sensations due to low intensity, are called subthreshold. Thus, absolute sensitivity is the ability of the analyzer to respond to the minimum amount of stimulus.

Definition of sensitivity.

Sensitivity is the ability of a person to have sensations. The lower threshold of sensations is opposed by the upper threshold. It limits sensitivity on the other hand. If we go from the lower threshold of sensations to the upper one, gradually increasing the strength of the stimulus, then we will get a series of sensations of greater and greater intensity. However, this will be observed only up to a certain limit (up to the upper threshold), after which a change in the strength of the stimulus will not cause a change in the intensity of the sensation. It will still be the same threshold value or it will turn into a painful sensation. Thus, the upper threshold of sensations is the greatest strength of the stimulus, up to which a change in the intensity of sensations is observed and sensations of this type are generally possible (visual, auditory, etc.).

Definition of sensitivity | Hypersensitivity | Sensitivity threshold | Pain sensitivity | Types of sensitivity | Absolute sensitivity

• High sensitivity

There is an inverse relationship between sensitivity and sensation thresholds. Special experiments have established that the absolute sensitivity of any analyzer is characterized by the value of the lower threshold: the lower the value of the lower threshold of sensations (the lower it is), the greater (higher) the absolute sensitivity to these stimuli. If a person smells very faint odors, this means that he has high sensitivity to them. The absolute sensitivity of the same analyzer varies among people. For some it is higher, for others it is lower. However, it can be improved through exercise.

• Increased sensitivity.

There are absolute thresholds of sensations not only in terms of intensity, but also in terms of quality of sensations. So, light sensations arise and change only under the influence of electromagnetic waves of a certain length - from 390 (violet) to 780 millimicrons (red). Shorter and longer wavelengths do not cause light sensations. Auditory sensations in humans are possible only when sound waves fluctuate in the range from 16 (the lowest sounds) to 20,000 hertz (the highest sounds).

In addition to the absolute thresholds of sensations and absolute sensitivity, there are also discrimination thresholds and, accordingly, distinctive sensitivity. The fact is that not every change in the magnitude of the stimulus causes a change in sensation. Within certain limits, we do not notice this change in the stimulus. Experiments have shown, for example, that when weighing a body by hand, an increase in a load of 500 g by 10 g and even 15 g will go unnoticed. To feel a barely noticeable difference in body weight, you need to increase (or decrease) the weight by 1/3 of its original value. This means that 3.3 g must be added to a load of 100 g and 33 g to a load of 1000 g. The discrimination threshold is the minimum increase (or decrease) in the magnitude of the stimulus that causes a barely noticeable change in sensations. Distinctive sensitivity is commonly understood as the ability to respond to changes in stimuli.

• Sensitivity threshold.

The value of the threshold does not depend on the absolute, but on the relative magnitude of the stimuli: the greater the intensity of the initial stimulus, the more it must be increased in order to obtain a barely noticeable difference in sensations. This pattern is clearly expressed for sensations of medium intensity; sensations close to threshold have some deviations from it.

Each analyzer has its own discrimination threshold and its own degree of sensitivity. So, the threshold for distinguishing auditory sensations is 1/10, sensations of weight - 1/30, visual sensations - 1/100. From a comparison of the values, we can conclude that the visual analyzer has the greatest distinctive sensitivity.

The relationship between discrimination threshold and discrimination sensitivity can be expressed as follows: the lower the discrimination threshold, the greater (higher) distinctive sensitivity.

The absolute and differential sensitivity of analyzers to stimuli does not remain constant, but varies depending on a number of conditions:

a) from external conditions accompanying the main stimulus (in silence, hearing acuity increases, with noise it decreases); b) from the receptor (when it is tired, it decreases); c) on the state of the central departments of the analyzers; and d) on the interaction of the analyzers.

Adaptation of vision has been best studied experimentally (studies by S. V. Kravkov, K. Kh. Kekcheev, and others). There are two types of visual adaptation: dark adaptation and light adaptation. When moving from a lighted room into darkness, a person does not see anything for the first minutes, then the sensitivity of vision first slowly, then rapidly increases. After 45-50 minutes, we clearly see the outlines of objects. It has been proven that the sensitivity of the eyes can increase in the dark by 200,000 times or more. This phenomenon is called dark adaptation. When moving from darkness to light, a person also does not see clearly for the first minute, but then the visual analyzer adapts to the light. If at dark adaptation sensitivity vision increases, then with light adaptation it decreases. The brighter the light, the lower the sensitivity of vision.

The same thing happens with auditory adaptation: with strong noise, the sensitivity of hearing decreases, in silence it increases.

• Pain sensitivity.

A similar phenomenon is observed in the olfactory, skin and taste sensations. The general pattern can be expressed as follows: under the action of strong (and even more prolonged) stimuli, the sensitivity of the analyzers decreases, and under the action of weak stimuli it increases.

However, adaptation is poorly expressed in pain sensations, which has its own explanation. pain sensitivity arose in the process of evolutionary development as one of the forms of protective adaptation of the organism to the environment. Pain alerts the body to danger. Lack of pain sensitivity could lead to irreversible destruction and even death of the body.

Adaptation is also very weakly expressed in kinesthetic sensations, which again is biologically justified: if we did not feel the position of our arms and legs, we would get used to it, then control over body movements in these cases would have to be carried out mainly through vision, which is not economically.

Physiological mechanisms of adaptation are processes occurring both in the peripheral organs of the analyzers (in receptors) and in the cerebral cortex. For example, the light-sensitive substance of the retinas of the eyes (visual purple) disintegrates under the action of light, and is restored in the dark, which leads in the first case to a decrease in sensitivity, and in the second to its increase. At the same time, cortical nerve cells also occur according to the laws.

The interaction of sensations. There is an interaction in sensations of different kinds. Sensations of a certain type are intensified or weakened under the influence of sensations of other types, while the nature of the interaction depends on the strength of side sensations. Let us give an example of the interaction of auditory and visual sensations. If the room is alternately illuminated and darkened during continuous sounding of a relatively loud sound, the sound will appear louder in the light than in the dark. There will be an impression of "beating" of the sound. In this case, the visual sensation increased the sensitivity of hearing. However, blinding light lowers auditory sensitivity.

Melodious quiet sounds increase the sensitivity of vision, deafening noise lowers it.

Special studies have shown that the sensitivity of the eye in the dark increases under the influence of light muscular work (raising and lowering the arms), increased breathing, wiping the forehead and neck with cool water, and weak taste stimuli.

In the sitting position, the sensitivity of night vision is higher than in the standing and lying positions.

Hearing sensitivity is also higher in a sitting position than in a standing and lying position.

The general pattern of the interaction of sensations can be formulated as follows: weak stimuli increase sensitivity to other, simultaneously acting stimuli, while strong stimuli reduce it.

The processes of interaction sensation proceed in. An increase in the sensitivity of the analyzer under the influence of weak stimuli from other analyzers is called sensitization. During sensitization, excitations in the cortex are summed up, the focus of optimal excitability of the main analyzer under given conditions is strengthened due to weak excitations from other analyzers (dominant phenomenon). The decrease in the sensitivity of the leading analyzer under the influence of strong stimuli from other analyzers is explained by the well-known law of simultaneous negative induction.