The sensitivity of analyzers, determined by the value of 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. Optimizing spectrum analyzer settings

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 within very 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 becomes sharper, 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 the sensation of pain 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 lengthens, visual perception decreases, twilight vision weakens, coordination of movements and functions of the vestibular apparatus are disrupted, and premature fatigue occurs.

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 medicinal drugs 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 the Traffic Rules prohibit driving a vehicle while intoxicated, in our country, unfortunately, there are strong traditions of doubting the correctness of the actions and/or results of the 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 discovered significant dysfunctions of the nervous system even 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 accidents.

Bob Nelson

Spectrum analyzers are most often used to measure very low level 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 techniques for increasing the sensitivity of a 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 the analyzer's noise reduction features to maximize instrument sensitivity.

Average self-noise level and noise figure

The sensitivity of a spectrum analyzer can be determined from its technical specifications. This parameter can be either the average noise level ( DANL), or noise figure ( NF). The average noise floor represents 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. Typically this parameter is expressed in dBm/Hz. In most cases, averaging is performed on a logarithmic scale. This results in a 2.51 dB reduction in the displayed average noise level. As we will learn in the following discussion, it is this reduction in noise floor that distinguishes the average noise floor from the noise figure. For example, if the analyzer's technical specifications indicate an average self-noise level of 151 dBm/Hz at 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. By the way, a CW signal that has the same amplitude as the spectrum analyzer noise will measure 2.1 dB higher than the noise level 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 own noise consists of two components. The first of them is determined by the noise figure ( NF ac), and the second represents thermal noise. The amplitude of thermal noise is described by the equation:

NF = kTB,

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

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

As a result, the average noise level 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 If root mean square power averaging is used, then term 2.51 can be omitted.

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

Settings that affect spectrum analyzer sensitivity

The spectrum analyzer gain is equal to unity. This means that the screen is calibrated to 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 error. This must be taken into account when using an input attenuator or amplifier in a spectrum analyzer. Turning on the input attenuator causes the analyzer to increase the equivalent gain of the IF stage to maintain a calibrated level on the screen. This, in turn, increases the noise level by the same amount, thereby maintaining the same signal-to-noise ratio. This is also true for the external attenuator. In addition, you need to convert to the IF filter bandwidth ( RBW), greater than 1 Hz, adding the term 10log( RBW/1). These two terms allow you to determine the noise floor of the spectrum analyzer at different values of attenuation and resolution bandwidth.

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

Adding a Preamp

You can use an internal or external preamplifier to reduce the spectrum analyzer's noise floor. Typically the specifications will give a second value for the average noise floor based on the built-in preamp, and all of the equations above can be used. When using an external preamplifier, a new value for the average noise floor can be calculated by cascading the noise figure equations and setting the spectrum analyzer gain to unity. If we consider a system consisting of a spectrum analyzer and an amplifier, we get the equation:

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

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

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

Equation (1) can now be used to determine a new average noise floor with an external preamp by simply replacing NF ac on NF system, calculated in equation (5). In our example, the preamplifier significantly reduces DANL from –151 to –168 dBm/Hz. However, this does not come for free. Preamplifiers typically have high nonlinearity and low compression points, which limits the ability to measure high-level signals. In such cases, the built-in preamplifier is more useful since it can be turned on and off as needed. This is especially true for automated instrumentation 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 provide methods for measuring their own noise and adjusting the measurement results based on the data obtained. 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 consists of the sum kTB, NF ac and the TU input signal. If you turn off the DUT and connect a 50 Ohm load 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 involves measuring the spectrum analyzer's self-noise with a large average and storing this value as a "correction trace." You then connect the device under test to a spectrum analyzer, measure the spectrum, and record the results in a “measured trace.” The correction is made by subtracting the “correction trace” from the “measured trace” and displaying the results as the “resulting trace”. This trace represents the “TU signal” without additional noise:

Resulting trace = measured trace – correction trace = [TC signal + kTB + NF ac]–[kTB + NF ac] = TU signal. (6)

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

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

In Fig. Figure 1 shows a relatively simple method of noise correction by applying mathematical processing of the trace. First, the noise floor of the spectrum analyzer with the load at the input is averaged, 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 mathematical processing - subtracting the two traces and recording the results in trace 3. How You see, noise correction is especially effective when the input signal is close to the noise floor of the spectrum analyzer. High-level signals contain a significantly smaller proportion of 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 disconnect the device under test and connect a 50 ohm load. A method of obtaining a “correction trace” without turning off the DUT is to increase the attenuation of the input signal (for example, by 70 dB) so that the spectrum analyzer noise significantly exceeds the input signal, and store the results in a “correction trace”. In this case, the “correction route” is determined by the equation:

Correction route = TU signal + kTB + NF ac+ attenuator. (7)

kTB + NF ac+ attenuator >> TU signal,

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

Correction route = kTB + NF ac+ attenuator. (8)

By subtracting the known attenuator attenuation value from formula (8), we can obtain the original “correction trace” that was used in the manual method:

Correction route = 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 use of a “correction path” for any settings.

Reducing self-noise

The Agilent N9030A PXA Signal Analyzer (Figure 2) has a unique Noise Emissions (NFE) feature. The PXA signal analyzer's noise figure over the instrument's entire frequency range is measured during instrument manufacturing and calibration. These data are then stored in the device's memory. When the user turns on NFE, the meter calculates a “correction trace” for the current settings and stores the noise figure values. This eliminates the need to measure the PXA's noise floor as was done in the manual procedure, greatly simplifying noise correction and saving time spent 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 obtain results below the value kTB. These results may be reliable in many cases, but not in all. Confidence may be reduced when measured values are very close to or equal to the instrument's intrinsic noise. In fact, the result will be an infinite dB value. Practical implementation of noise correction typically involves introducing a threshold or graduated subtraction level near the instrument's noise floor.

Conclusion

We've looked at some techniques for measuring low-level signals using a spectrum analyzer. At the same time, we found that the sensitivity of the measuring device is influenced by the bandwidth of the IF filter, attenuator attenuation and the presence of a preamplifier. To further increase the sensitivity of the device, you can use methods such as mathematical noise correction and the noise reduction function. In practice, a significant increase in sensitivity can be achieved by eliminating losses in external circuits.

We learn about the world around us, its beauty, sounds, colors, smells, temperature, size and much more thanks to our senses. With the help of the senses, the human body receives in the form of sensations a variety of information about the state of the external and internal environment.

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

The sense organs are affected by stimuli. It is necessary to distinguish between stimuli that are adequate for a particular sensory organ and those that are inadequate for it. Sensation is the primary process from which 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 knowledge of reality is very important, since they constitute the only source of our knowledge about the external world and about ourselves.

Physiological basis of sensations. The sensation arises 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 is reflexive in nature; physiologically it provides the analytical system. An 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 highlight in it certain types of psychoenergy.

The concept of an 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, transmitting excitation that arose in the receptor in the higher centers of the nervous system, and efferent (centrifugal), through which impulses from higher centers are transmitted to lower levels;

Subcortical and cortical projective zones, where the processing of nerve impulses from peripheral parts occurs.

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

Reflex arc = analyzer + effector,

The effector is a motor organ (a specific muscle) that receives a nerve impulse from the central nervous system (brain). The interconnection 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 sensation to arise, the entire analyzer as a whole must work. The action of an irritant on a receptor causes irritation.

Classification and types of sensations. There are various classifications of the sense organs and the body’s sensitivity to stimuli entering the analyzers from the outside world or from inside the body.

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

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

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

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

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

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

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

The 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 the function of a special temperature analyzer that carries out thermoregulation and heat exchange between the body and 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 degree of equality and relief of the surface of objects, which can be felt while touching them.

Painful sensations signal a violation of the integrity of the tissue, which, of course, causes a defensive reaction in a person.

Temperature sensation - a feeling of cold, warmth, 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 vibration sensations, signaling the vibration of an object. The vibration sense organ has not yet been found.

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

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

Static or gravitational sensations reflect the position of our body in space - lying, standing, sitting, balance, 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 types of sensations can be considered externally internal. These include temperature, pain, taste, vibration, muscle-articular, sexual and static di and ammic.

General properties of sensations. Sensation is a form of reflection of adequate stimuli. However, different types of sensations are characterized not only by specificity, but also by common properties. These properties include quality, intensity, duration and spatial location.

Quality is the main feature of a certain sensation, which distinguishes it from other types of sensations and varies within a given type. Thus, auditory sensations differ in pitch, timbre, and volume; 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 sensory organ, but mainly by the time of action of the stimulus and its intensity. During the action of a stimulus on a sense organ, sensation does not arise immediately, but after some time, which is called the latent (hidden) period of sensation.

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

Sensitivity. The sensitivity of a sense organ is determined by the minimum stimulus, which, 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.

Stimuli of lesser strength, so-called subthreshold, 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 also by the upper threshold of sensation.

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

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

Adaptation. The sensitivity of analyzers, determined by the value of 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 adjustment, is a change in the sensitivity of the senses under the influence of a stimulus.

There are three types of this phenomenon:

Adaptation as a complete disappearance of sensation during the prolonged action of a stimulus.

Adaptation as a dulling of sensation under the influence of a strong stimulus. The two types of adaptation described 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 a stimulus under the influence of attentiveness, focus, and attitude is called sensitization. This phenomenon of the senses 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 analyzing 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 irritations that affect other sense organs at that moment. Change in the sensitivity of the analyzer under the influence of irritation of other sense organs. name for the interaction of sensations.

In this case, the interaction of sensations, as well as adaptation, will result in two opposite processes: an increase and decrease in sensitivity. The general rule here is that weak stimuli increase, and strong ones decrease, the sensitivity of sex analyzers through their interaction.

A change in the sensitivity of the analyzers can cause the action of other signal stimuli.

If you carefully, attentively peer, listen, savor, then 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.

When two stimuli are applied simultaneously, a simultaneous contrast occurs. This contrast can be clearly seen in visual sensations. The figure itself will seem lighter on a black background, and darker on a white background. A green object on a red background is perceived as more saturated. Therefore, military objects are often camouflaged so that there is no contrast. This includes the phenomenon of sequential contrast. After a cold one, a weak warm stimulus will seem hot. The feeling of sour increases sensitivity to sweets.

Synesthesia of feelings is the occurrence of sex through the outpouring of a stimulus from one analyzer. which are typical for another analyzer. In particular, during the action of sound stimuli, such as airplanes, rockets, etc., visual images of them arise in a person. Or someone who sees a wounded person also feels pain in a certain way.

The activities of the analyzers will interact. This interaction is not isolated. It has been proven that light increases auditory sensitivity, and faint sounds increase visual sensitivity, cold washing of the head increases sensitivity to the color red, and the like.

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

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

Sensitivity and sensation thresholds. 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, and does not see the light of stars of the sixth, seventh, etc. magnitude with his naked eyes. The minimum magnitude of the stimulus at which a barely noticeable sensation occurs is called the lower or absolute threshold of sensation. Stimuli 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 magnitude of the stimulus.

Determination of sensitivity.

Sensitivity- This is a person’s ability 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 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.).

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 perceives 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 increased through exercise.

Increased sensitivity.

There are absolute thresholds of sensations not only in intensity, but also in the quality of sensations. Thus, 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 of light do not cause sensations. Auditory sensations in humans are possible only when sound waves oscillate 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, discriminative 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 weighing 500 g by 10 g or even 15 g will go unnoticed. To feel a barely noticeable difference in body weight, you need to increase (or decrease) the weight by one-half 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, causing a barely noticeable change in sensations. Distinctive sensitivity is usually understood as the ability to respond to changes in stimuli.

Sensitivity threshold.

The threshold value depends not 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 the threshold have some deviations from it.

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

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

The absolute and discriminative 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 (hearing acuity increases in silence, and decreases in noise); b) from the receptor (when it becomes tired, it decreases); c) on the state of the central sections 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. X. Kekcheev, etc.). There are two types of visual adaptation: adaptation to darkness and adaptation to light. When moving from a lighted room to darkness, a person sees nothing for the first minutes, then the sensitivity of vision first slowly, then quickly increases. After 45-50 minutes we clearly see the outlines of objects. It has been proven that eye sensitivity can increase 200,000 times or more in the dark. The described phenomenon is called dark adaptation. When moving from darkness to light, a person also does not see clearly enough for the first minute, but then the visual analyzer adapts to the light. If in the 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: in loud noise, hearing sensitivity 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 especially long-term) stimuli, the sensitivity of the analyzers decreases, and under the action of weak stimuli it increases.

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

Adaptation is also very weakly expressed in kinesthetic sensations, which is again biologically justified: if we did not feel the position of our arms and legs and 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 adaptation mechanisms are processes occurring both in the peripheral organs of the analyzers (receptors) and in the cerebral cortex. For example, the photosensitive substance of the retinas of the eyes (visual purple) disintegrates under the influence 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 occur according to the laws.

Interaction of sensations. There is interaction in sensations of different types. Sensations of a certain type are enhanced or weakened by sensations of other types, and the nature of the interaction depends on the strength of the side sensations. Let us give an example of the interaction of auditory and visual sensations. If you alternately light and darken a room while a relatively loud sound is playing continuously, the sound will seem louder in the light than in the dark. There will be an impression of a “beating” sound. In this case, the visual sensation increased the sensitivity of hearing. At the same time, blinding light reduces auditory sensitivity.

Melodious quiet sounds increase the sensitivity of vision, deafening noise reduces 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 mild taste irritations.

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

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

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

Processes of interaction between sensations take place in. An increase in the sensitivity of the analyzer under the influence of weak stimuli from other analyzers is called sensitization. During sensitization, a summation of excitations in the cortex occurs, strengthening the focus of optimal excitability of the main analyzer under given conditions due to weak excitations from other analyzers (dominant phenomenon). The decrease in the sensitivity of the leading analyzer under the influence of strong stimulation of other analyzers is explained by the well-known law of simultaneous negative induction.

Sensitization of the senses is possible not only through the use of side stimuli, but also through exercise. The possibilities for training the senses and improving them are endless. There are two areas that determine increased sensitivity of the senses:

1) sensitization, which spontaneously results from the need to compensate for sensory defects (blindness, deafness);

2) sensitization caused by the activity and specific requirements of the subject’s profession.

The loss of vision or hearing is to a certain extent compensated by the development of other types of sensitivity. There are cases when people deprived of vision engage in sculpture; they have a well-developed sense of touch. The development of vibration sensations in the deaf also belongs to this group of phenomena.

Some people who are deaf develop vibration sensitivity so strongly that they can even listen to music. To do this, they place their hand on the instrument or turn their back to the orchestra. Some deaf-blind people, holding their hand at the throat of the speaking interlocutor, can thus recognize him by his voice and understand what he is talking about. Due to their highly developed olfactory sensitivity, they can associate many close people and acquaintances with the smells emanating from them.

Of particular interest is the emergence in humans of sensitivity to stimuli for which there is no adequate receptor. This is, for example, remote sensitivity to obstacles in the blind.

The phenomena of sensitization of the sense organs are observed in persons with certain special professions. Grinders are known to have extraordinary visual acuity. They see gaps from 0.0005 millimeters, while untrained people see only up to 0.1 millimeters. Fabric dyeing specialists distinguish between 40 and 60 shades of black. To the untrained eye they appear exactly the same. Experienced steelmakers are able to quite accurately determine its temperature and the amount of impurities in it by the faint color shades of molten steel.

The olfactory and gustatory sensations of tasters of tea, cheese, wine, and tobacco reach a high degree of perfection. Tasters can accurately tell not only what type of grape the wine is made from, but also name the place where these grapes grew.

Painting places special demands on the perception of shapes, proportions and color relationships when depicting objects. Experiments show that the artist's eye is extremely sensitive to assessing proportions. It distinguishes changes equal to 1/60-1/150 of the size of the object. The subtlety of color sensations can be judged by the mosaic workshop in Rome - it contains more than 20,000 shades of primary colors created by man.

The possibilities for developing auditory sensitivity are also quite large. Thus, playing the violin requires special development of pitch hearing, and violinists have it more developed than pianists. For people who have difficulty distinguishing the pitch of sounds, it is possible, through special training, to improve their pitch hearing. Experienced pilots can easily determine the number of engine revolutions by ear. They freely distinguish 1300 from 1340 rpm. Untrained people only notice the difference between 1300 and 1400 rpm.

All this is proof that our sensations develop under the influence of living conditions and the requirements of practical work activity.

Sensory adaptation is a change in sensitivity that occurs as a result of the adaptation of a sensory organ to the stimuli acting on it. As a rule, adaptation is expressed in the fact that when the sense organs are exposed to sufficiently strong stimuli, sensitivity decreases, and when exposed to weak stimuli or in the absence of a stimulus, sensitivity increases.

Sensitization(Latin sensibilis - sensitive)– this is an increase in the sensitivity of analyzers under the influence of internal (mental) factors. Sensitization, i.e. exacerbation of sensitivity may be caused by:

· interaction, systemic work of analyzers, when weak sensations of one modality can cause an increase in the strength of sensations of another modality. For example, visual sensitivity increases with weak cooling of the skin or a low sound;

· the physiological state of the body, the introduction of certain substances into the body. Thus, vitamin A is essential for increasing visual sensitivity.;

· the expectation of a particular influence, its significance, the determination to distinguish between certain stimuli. For example, waiting in the dentist's office can encourage more toothache;

· experience acquired in the process of performing any activity. It is known that good tasters can determine the type of wine or tea by subtle nuances..

In the absence of any type of sensitivity, this deficiency is compensated by increasing the sensitivity of other analyzers. This phenomenon is called compensation for sensations , or compensatory sensitization .

If sensitization - this is an increase in sensitivity, then the opposite process - a decrease in the sensitivity of some analyzers as a result of strong excitation of others - is called desensitization . For example, increased noise levels in " loud» workshops reduces visual sensitivity, i.e. desensitization of visual sensations occurs.

Synesthesia(Greek synaisthesis – joint, simultaneous sensation)- a phenomenon in which sensations of one modality arise under the influence of a stimulus of another modality.

Contrast of sensations (French contraste - sharp contrast)- this is an increase in sensitivity to one stimulus when it is compared with a previous stimulus of the opposite type. Thus, the same white figure appears gray against a light background, but perfectly white against a black background.. A gray circle on a green background appears reddish, while on a red background it appears greenish.