Naturally, we are interested in reducing the probability of a type II error as much as possible, that is, increasing the sensitivity of the criterion. To do this, you need to know what it depends on. In principle, this problem is similar to the one that was solved in relation to type I errors, but with one important exception.

To evaluate the sensitivity of a test, you need to specify the amount of difference that it should detect. This value is determined by the objectives of the study. In the diuretic example, the sensitivity was low - 55%. But, perhaps, the researcher simply did not consider it necessary to detect an increase in diuresis from 1200 to 1400 ml / day, that is, by only 17%?

As the data scatter increases, the probability of both types of errors increases. As we will see shortly, it is more convenient to account for the magnitude of the differences and the spread of the data together by calculating the ratio of the magnitude of the differences to the standard deviation.

The sensitivity of a diagnostic test can be increased by reducing its specificity - a similar relationship exists between the level of significance and the sensitivity of the test. The higher the significance level (that is, the smaller a), the lower the sensitivity.

As we have already said, the most important factor that affects the probability of both type I and type II errors is the sample size. As the sample size increases, the probability of error decreases. In practice, this is very important, since it is directly related to the design of the experiment.

Before proceeding to a detailed consideration of the factors affecting the sensitivity of the criterion, we list them again.

Significance level a. The smaller a, the lower the sensitivity.

The ratio of the size of the differences to the standard deviation. The larger this ratio, the more sensitive the criterion.

Sample size. The larger the volume, the higher the sensitivity of the criterion.

Significance level

To get a visual representation of the relationship between the sensitivity of the criterion and the level of significance, let's return to Fig. 6.3. By choosing the significance level a, we thereby set the critical value of t. We choose this value so that the proportion of values ​​that exceed it - provided that the drug has no effect - is equal to a (Fig. 6.3A). The sensitivity of the criterion is the proportion of those values ​​of the criterion that exceed the critical one, provided that the treatment has an effect (Fig. 6.3B). As can be seen from the figure, if the critical value is changed, this share will also change.

Let's take a closer look at how this happens.

On fig. 6.4A shows the distribution of Student's t-test values. Difference from fig. 6.3 is that this is now the distribution obtained for all 1027 possible pairs of samples. The top graph is the distribution of t values ​​for the case when the drug does not have a diuretic effect. Suppose we chose a significance level of 0.05, that is, we took a = 0.05. In this case, the critical value is 2.101, which means we reject the null hypothesis and accept the differences as statistically significant at t > +2.101 or t. Now look at Fig. 6.4B. It shows the same distributions of t values. The difference in the chosen significance level is a = 0.01. The critical value of t has increased to 2.878, the dotted line has shifted to the right and cuts off only 45% of the lower plot. Thus, when moving from 5% to 1% significance level, the sensitivity decreased from 55 to 45%. Accordingly, the probability of a type II error increased to 1 - 0.45 = 0.55.

So, by reducing a, we reduce the risk of rejecting the correct null hypothesis, that is, finding differences (effect) where there are none. But by doing so, we also reduce sensitivity - the probability of detecting differences that actually exist.

Size of difference

Considering the influence of the significance level, we took the magnitude of the differences constant: our drug increased the daily diuresis from 1200 to 1400 ml, that is, by 200 ml. Now let's accept

constant significance level a = 0.05 and see how the sensitivity of the test depends on the magnitude of the differences. It is clear that large differences are easier to identify than small ones. Consider the following examples. On fig. 6.5A shows the distribution of t values ​​for the case when the study drug does not have a diuretic effect. Hatched are 5% of the largest absolute values ​​of t located to the left - 2.101 or to the right +2.101. On fig. 6.5B shows the distribution of t values ​​for the case when the drug increases the daily

Increase in daily diuresis, ml

diuresis by an average of 200 ml (we have already considered this situation). Above the right critical value lies 55% of the possible values ​​of t: the sensitivity is 0.55. Next, in fig. 6.5B shows the distribution of t values ​​for the case when the drug increases diuresis by an average of 100 ml. Now only 17% of t values ​​exceed 2.101. Thus, the sensitivity of the test is only 0.17. In other words, the effect will be found in less than one out of every five comparisons between the control and experimental groups. Finally, fig. 6.5D represents a case of increased diuresis by 400 ml. 99% of the values ​​of t fell into the critical region. The sensitivity of the test is 0.99: differences will almost certainly be detected.

Repeating this thought experiment, you can define the sensitivity of the test for all possible effect values, from zero to "infinite". Plotting the results on a graph, we get Fig. 6.6, where the sensitivity of the test is shown as a function of the magnitude of the differences. From this graph, you can determine what the sensitivity will be for a particular effect size. So far, the graph is not very convenient to use, because it is only suitable for this group size, standard deviation, and significance level. We will build another chart soon, more suitable for research planning, but first we need to understand more about the role of dispersion and group size.

Scatter of values

The sensitivity of the test increases with the observed differences; as the spread of values ​​increases, the sensitivity, on the contrary, decreases.

Recall that Student's t-test is defined as follows:

where X1 and X2 are averages, s is the combined score of the standard

deviations a, n1 and n2 are sample sizes. Note that x1 and

X2 are estimates of two (different) means - p and p2. For simplicity, we assume that the volumes of both samples are equal, that is, n1 = n2. Then the computed value of t is an estimate of the quantity P1-P2 P-P

Thus, t depends on the ratio of the effect size to the standard deviation.

Let's look at a few examples. The standard deviation in our study population is 200 ml (see Fig. 6.1). In this case, an increase in daily diuresis by 200 or 400 ml is equal to one or two standard deviations, respectively. These are very noticeable changes. If the standard deviation were 50 ml, then the same changes in diuresis would be even more significant, amounting to 4 and 8 standard deviations, respectively. Conversely, if the standard deviation were, for example, 500 ml, then the change in urine output in 200 ml would be 0.4 standard deviation. Finding such an effect would be difficult and hardly worth it at all.

So, the sensitivity of the test is affected not by the absolute magnitude of the effect, but by its ratio to the standard deviation. Let's denote it f (Greek "phi"); this ratio φ = 5/a is called the noncentrality parameter.

Sample size

We have learned about two factors that affect the sensitivity of a test: the significance level a and the non-centrality parameter φ. The more a and the more f, the more feeling
validity. Unfortunately, we cannot influence at all, and as for a, its increase increases the risk of rejecting the correct null hypothesis, that is, finding differences where there are none. However, there is one more factor that we can, within certain limits, change at our discretion without sacrificing the level of significance. We are talking about the sample size (number of groups). With an increase in the sample size, the sensitivity of the test increases.

There are two reasons why increasing the sample size increases the sensitivity of the test. First, increasing the sample size increases the number of degrees of freedom, which in turn reduces the critical value. Secondly, as can be seen from the formula just obtained

the value of t grows with the sample size n (this is also true for many other criteria).

Figure 6.7A reproduces the distributions from fig. 6.4A. The upper graph corresponds to the case when the drug does not have a diuretic effect, the lower one - when the drug increases daily diuresis by 200 ml. The number of each group is 10 people. Figure 6.7B shows similar distributions. The difference is that now each group included not 10, but 20 people. Since the size of each of the groups is 20, the number of degrees of freedom is V = 2(20 - 1) = 38. From Table 4.1, we find that the critical value of t at the 5% significance level is 2.024 (in the case of samples of size 10, it was 2.101). On the other hand, an increase in the sample size led to an increase in the values ​​of the criterion. As a result, not 55, but 87% of the values ​​of t exceed the critical value. So, increasing the size of the groups from 10 to 20 people led to an increase in sensitivity from 0.55 to 0.87.

Going through all possible sample sizes, you can plot the sensitivity of the test as a function of the size of the groups (Fig. 6.8). With increasing volume sensitivity

is growing. At first, it grows rapidly, then, starting from a certain sample size, the growth slows down.

Sensitivity calculation is the most important component medical research planning. Now, having become acquainted with the most important factor that determines sensitivity, we are ready to solve this problem.

How to determine the sensitivity of a criterion?

On fig. 6.9 the sensitivity of the Student's test is presented as a function of the non-centrality parameter f = 5/s at a significance level a = 0.05. The four curves correspond to the four sample sizes.

The samples are assumed to be of equal size. What if it's not? If you refer to Fig. 6.9 when planning a study (which is very reasonable), then you need to consider the following. For a given total number of patients, it is precisely the equal number of groups that ensures maximum sensitivity. So, an equal number of groups should be planned. If, however, you decide to calculate sensitivity after the study, when, having found no statistically significant difference, you want to determine the extent to which this can be considered evidence of no effect, then you should take the size of both groups equal to the smaller of them. This calculation will give a somewhat underestimated sensitivity, but will save you from being overly optimistic.

Let's apply curves from fig. 6.9 for example with a diuretic (see fig. 6.1). We want to calculate the sensitivity of Student's t-test at a significance level of a = 0.05. The standard deviation is 200 ml. What is the probability of detecting an increase in daily diuresis by 200 ml?

The number of control and experimental groups is ten. We choose in Fig. 6.9 the corresponding curve and find that the sensitivity of the criterion is 0.55.

So far, we have been talking about the sensitivity of the Stew test.

Sample size

Halothane and morphine in open heart surgery

In ch. In Table 4, we compared the cardiac index during halothane and morphine anesthesia (see Table 4.2) and did not find statistically significant differences. (Recall that the cardiac index is the ratio of the minute volume of the heart to the surface area of ​​the body.) However, the groups were small - 9 and 16 people. The mean CI in the halothane group was 2.08 L/min/m2; in the morphine group 1.75 l/min/m2, i.e. 16% less. Even if the differences were statistically significant, such a small difference would hardly be of any practical interest.

So let's put the question this way: what was the probability of detecting a difference of 25%? The combined variance estimate is s2 = 0.89, so the standard deviation is 0.94 l/min/m2. Twenty five percent of 2.08 l/min/m2 is 0.52 l/min/m2.

Thereby,

5 _ 0.52 o ~ 0.94

Since the sizes of the groups do not match, we will choose the smallest of them - 9 - to estimate the sensitivity. 6.9 it follows that in this case the sensitivity of the criterion is 0.16.

The chances of detecting even a 25% difference were very small. Let's summarize.

The sensitivity of a test is the probability of rejecting the false hypothesis of no difference.

The sensitivity of the test is affected by the significance level: the smaller a, the lower the sensitivity.

The larger the effect size, the greater the sensitivity.

The larger the sample size, the greater the sensitivity.

Sensitivity is calculated differently for different criteria.

When the words " hypersensitivity», « sensitive person", and even the term that has already become commonplace sounds - HSP (highly sensitive people), it becomes immediately clear that we are talking about something that goes beyond the average, a certain statistical majority.

Many, having heard hypersensitivity" and " sensitive person", imagine a kind of muslin young lady, regardless of her real gender, who just faints" from an excess of feelings.

Someone thinks that all this is whims, and it is enough to “get together”, “stop winding yourself up”, and immediately this sensitivity will pass. All this, they say, from spoiled.

Still others, who are in the minority, believe that hypersensitivity- a gift, sensitive person, most likely talented and prone to creativity.

Let's try to figure out what HSP actually is, and, most importantly, how to live with it among those whose level of sensitivity is mostly lower.

Obviously, if there is an increased sensitivity, there is also a certain average, one might say - a statistical majority, something that many are accustomed to starting from as a norm.

Sensitivity in general is the ability nervous system a person to perceive various stimuli coming from outside, and respond to them. If you do not delve into the structure of the nervous system and physics, then in general we can say that human sensitivity exists within certain limits.

For example, human hearing recognizes sounds in the range of 20 - 20,000 hertz, or light human sensitivity is in the range of 380 - 760 nm, but everything that is inside these frames has very individual shades.

For example, to one person, the conversation of neighbors behind the wall will seem like a light, barely noticeable noise. Others won't hear anything at all. Third, every word will be heard. So it can be with color and with other sensations - taste, smells, touch. So it can be with the sensation of pain - any physician will tell you that the pain threshold in a person is individual.

At the same time, the researchers note that the population of the earth by about 10% - hsf highly sensitive people. The rest have the same average sensitivity, which is usually perceived as the norm. Rarely, there are cases of complete or partial loss of sensitivity, which are mainly associated with diseases of the central nervous system or with severe psychological shocks.

Why is that? Here, scientists so far agree that hypersensitivity is an innate characteristic. It is difficult to say to what extent it is determined by hereditary factors, because in some cases it is possible to observe the appearance of children with high sensitivity in the family of parents with average indicators.

True, no one will say for sure whether at least one of the child's parents really did not have hypersensitivity, or whether he simply actively suppressed it and skillfully hid it. There is not much research on this topic yet, but so far there are a few obvious signs of HHL.

HSP signs

Physical

This is the very case when the conversation of the neighbors behind the wall seems loud and distinct to you, unlike the others. You are annoyed by pungent odors, too bright light, you are susceptible to light touches, distinguish the slightest shades of taste, temperature, your body reacts quite noticeably to many interventions - drugs, caffeine, other psychoactive and stimulant substances, you have a lower pain threshold (pain comes earlier , from less visible stimuli than for most).

emotional

You have a heightened sense of empathy, you are quite easily imbued with the situation of another person and easily "pick up" his emotions, it is easy for you to feel the state of the people around you, sometimes - regardless of your desire, you easily feel the atmosphere of some place, you are more receptive to art, you are able to experience strong emotions from “little things”.

intellectual

You carefully consider and weigh your words, any incoming information, you tend to reflect on it, you have increased attention to details, nuances (for example, you notice grammatical errors and typos, are susceptible to all sorts of carelessness, negligence in the surrounding space, which others may not notice at all for a long time), you are able to see many meanings in any external object.

This division, of course, is conditional - it is impossible to disassemble a person, like a mechanism, into parts, therefore, of course, everything is connected. But a sensitive person is not necessarily one who has all the senses "at the limit."

For example, he may have very high auditory and visual sensitivity, while he may show a normal pain threshold, or, say, not be highly sensitive to drugs. Or, let's say a person has high empathy, but he is not inclined to go deep into intellectual meanings.

Therefore, now we will talk about what are the nuances of high sensitivity, touch on common myths about sensitivity, talk about how this relates to other aspects psychological characteristics person - for example, introversion / extraversion, psychotype, temperament, degree of neuroticism, and whether this can be a symptom of some other condition, illness.

In general, hypersensitivity is not an innate characteristic of a person, but a consequence of certain conditions of the body. For example, sensitivity can increase in the presence of chronic lack of sleep, constant fatigue, severe stress (as, however, a partial decrease in sensitivity can also be a reaction to stress, as if “freezing” in the presence of very strong and indigestible feelings).

Hypersensitivity may accompany some mental disorders and somatic diseases especially related to the CNS. But this mention is only so that you can decide for yourself whether your characteristic is permanent or temporary. Here we will talk mainly about those whose hypersensitivity is constant, you yourself remember yourself like this all your life, and you have not observed any other serious deviations in the field of health.

So far, I have not come across studies in which it would be clearly possible to trace which psychotypes are more often associated with increased sensitivity. However, own practice gives enough reason to assert that hypersensitivity is neither the fifth type of temperament, nor any special psychotype, HSPs are found among representatives of different temperaments and psychotypes.

It can be said that some psychotypes appear among HSPs more often than others, but a clear correlation has not yet been traced. That is, a sensitive person can be born like that with any other character traits.

Many people assume that HSPs tend to be more introverted. This is logically understandable: a sensitive person needs more time to recover from contact with the outside world, because external stimuli act on him more than others, and he needs to disconnect from strong stimulation more often.

But I have also met extroverts among HSPs. Yes, such a person also needed to retire from time to time, to have time to recover, but the focus of such a person’s attention was still directed to the outside world, and not to the inner one, like introverts.

With temperament, too, it is not possible to establish a clear connection. It would be logical to assume that HSPs are more suited to people with fast arousal and slow deceleration, in other words, they are easy to turn on but difficult to calm down (which are melancholics), but this is more like speculation about what a sensitive person should be, or could be in the opinion of the middle majority, not on reality.

And the logic can be completely different. Sometimes heightened sensitivity fits, say, into a phlegmatic person who does not look like a sensitive person at all. However, the phlegmatic temperament creates good protection for the carrier of subtle sensitivity, and it even blossoms inside him in a lush color, since outwardly she is little threatened.

In general, here we can say that hypersensitivity is not directly related to specific features of the psychotype, temperament or focus of attention, it exists as a separate psychophysiological characteristic that is built into other personality parameters.

But a person not only experiences feelings, he also interprets them. For example, the fact that he is more responsive to the people around him and their condition, needs more rest from this stimulation, he can interpret in different ways.

He can calmly say to himself: “Yes, it’s already too much for me today, I want to be in silence” - and calmly retire. Or he can start to wind himself up in the spirit of “all people are like people, but I’m not like that, probably something is wrong with me, since everything starts to annoy me so quickly ....”

Often, HSPs are confused with people who are prone to anxiety, suspiciousness and thinking out on this basis for others. But heightened sensitivity and anxiety reinforced by fantasies are two different things.

A sensitive person will be able to capture the real state of another person - for example, he will be able to feel that his boss has already entered the office irritated and tense, and further scatter of employees only followed from his initial state. Therefore, a sensitive person is unlikely to take it personally. However, he may be hurt for another reason - too loud, too bright, too hard.

But an anxious person just may not feel the real state of the authorities, he is mainly occupied with his experiences, and therefore he will easily attribute the dressing to himself alone, and then he will worry for days about his alleged worthlessness and failure.

It is also easy to confuse people who are able to loudly and vividly demonstrate their feelings (it is not at all necessary that the feelings are sincere, and that they generally exist) with HSP. But demonstration and real feeling are very different things. HSPs are just not in a hurry to share their feelings so quickly, much less so loudly: the demonstration attracts attention even more, makes them digest a lot more external stimuli, and further exacerbates the fatigue from their own reactions.

And here it is very logical to mention a few common myths about sensitivity.

HSP: myths and reality

In fact, rather the opposite. Among them there are many generally strong people who control their feelings sometimes much better than representatives of the average majority.

Why? Yes, because from childhood, such a child understands that he is different from others, that his feelings are sometimes not taken seriously by others. Parents and other adults are not always ready to take feelings (and even more so - so subtle!) into account and sometimes even declare them abnormal.

Naturally, in response to this, the child develops defenses. And one of them is the formation of the skill of tracking and controlling your emotions. Yes, sometimes this leads to sad options - a habit is formed to suppress their feelings, low self-esteem, a feeling of constant misunderstanding and rejection.

But increased sensitivity also gives its bonus, especially in the presence of high intelligence: after all, the mass of feelings inaccessible to others is a mass of information, this is a more complete and rich knowledge of the world, this is a more subtle insight into the essence of human motives and relationships, and as a result - a more effective strategy of action, and in the long run - a more comfortable place in life.

In general, HSPs are less likely to act rashly “on emotions”, they are more likely to think about the nuances of their reactions and behavior, they can more effectively cope with difficult situations. life situations if only simply because life taught them very early to deal with their feelings in a world of the less sensitive.

Myth: A sensitive person is open, kind, and therefore very vulnerable.

This is also from the realm of fantasy. HSPs tend to keep their feelings away from others most of the time, or at least that's what experience teaches them. Not every closed person belongs to the HSP category, but we can say that among the HSPs there are many who are considered to be closed. And, especially having the experience of different perceptions of themselves, HSPs are very selective in communication.

The capacity for empathy, which HSPs certainly have to a large extent, is not a reason for kindness, let alone naivete. The experience of subtle feeling can be applied in many ways, but think about it: subtle sensitivity involves feeling all spectrums.

And this means that a sensitive person feels not only the wonderful feelings of people filled with positive. In principle, there are not enough of them in the world, to put it mildly. And it turns out that the main content of empathy is a very different, and far from always positive state of people.

What conclusions can HSPs draw from this? - yes, whatever. You can find yourself in a helping profession in order to attach this empathy, to give it a place. And you can hate the whole human race for the constant violation of boundaries and for that very joyless inner content. And for example, to become a charming villain like Hannibal Lecter, who, in addition to killing, enjoys delicate dishes from their liver or brain, decorates the house with exquisite paintings and listens to rare performances of the opera.

Therefore, in terms of moral guidelines, HSPs can be at any pole of society, and sensitivity will only impart certain shades to their actions, but it in no way limits their choice in terms of their own ethics.

Myth: Sensitive people are talented and smart

This is partly true, of course, because hypersensitivity itself is an indication for certain types of activities in which it is needed - many areas of art and science (especially where intuition matters), in general, a creative environment that helps professions - psychologists, doctors, social workers.

But at the same time, increased sensitivity also imposes certain restrictions - for example, a sensitive person cannot always work in the conditions in which the majority can work. And sometimes it becomes an obstacle to career development in the standard way accepted in society and a particular profession.

I have known people who have a high sensitivity combined with low intelligence. This is perhaps the most difficult of all HSPs, because they do not have enough resources to realize their uniqueness, while they also do not always succeed in fully integrating into the world of ordinary people.

In summary, HSPs are simply people with a distinct characteristic that goes along with different personality traits. Of course, increased sensitivity to one degree or another leaves an imprint on the formation of a psychotype, and on interaction with temperament, and on behavioral habits.

And this is certainly a variant of the norm, which, however, differs from the majority and creates certain problems for such people. And in the next part of the article, we will dwell in more detail on the development of a sensitive child and talk about what parents should do, whose child is just like that: “ Sensitive child: features of the development of a sensitive person».

Various sense organs that give us information about the state of the external world around us can be more or less sensitive to the phenomena they display, i.e. may reflect these phenomena with greater or lesser accuracy. Sensitivity of the sense organs It is determined by the minimum stimulus that, under given conditions, is capable of causing a sensation.

The minimum strength of the stimulus that causes a barely noticeable sensation is called lower absolute threshold sensitivity. Irritants of lesser strength, the so-called subthreshold, do not evoke feelings. The lower threshold of sensation determines the level absolute sensitivity this analyzer. There is an inverse relationship between absolute sensitivity and the threshold value: the lower the threshold value, the higher the sensitivity of this analyzer. This relationship can be expressed by the formula E- 1 / R, where ^-sensitivity, R- threshold value.

Analyzers have different sensitivities. In humans, visual and auditory analyzers have very high sensitivity. As the experiments of S. I. Vavilov (1891-1951) showed, the human eye is able to see light when only 2-8 quanta of radiant energy hit. This allows you to see dark night a burning candle at a distance of up to 27 km from the eye.

The auditory cells of the inner ear detect movements whose amplitude is less than 1% of the diameter of a hydrogen molecule. That allows us to hear the ticking of the clock in complete silence at a distance of up to 6 m. The threshold of one human olfactory cell for the corresponding odorous substances does not exceed eight molecules. That allows you to feel the presence of perfume with only one drop of it in a room consisting of six rooms. It takes at least 25,000 times more molecules to produce a taste sensation than it does to create an olfactory sensation.

The absolute sensitivity of the analyzer is limited not only by the lower, but also by upper threshold sensitivity. This is the maximum strength of the stimulus, at which a sensation adequate to the acting stimulus still arises. Further increase the forces of stimuli acting on the receptors cause them only pain sensations, for example, an ultra-loud sound or blinding brightness.

The value of absolute thresholds depends on the nature of the activity, age, functional state of the organism, strength and duration of irritation.

In addition to the magnitude of the absolute threshold, sensations are characterized by a relative, or differential, threshold. The smallest difference between two stimuli that causes a barely perceptible difference in sensations is called discrimination threshold, or difference threshold. German physiologist E. Weber (1795-1878), testing a person's ability to determine the heavier of the two objects in the right and left hand, found that differential sensitivity is relative, not absolute. This means that the ratio of a barely perceptible difference to the magnitude of the initial stimulus is a constant value. The stronger the intensity of the initial stimulus, the more it should be increased in order to notice the difference, i.e. the greater the barely perceptible difference.

The differential sensation threshold for the same organ is constant value and is expressed by the following formula: dJ/J \u003d C, where Y is the initial value of the stimulus, adj- its increase, causing a barely noticeable sensation of a change in the magnitude of the stimulus, C is a constant. The value of the differential threshold for different modalities is different: for vision it is about 1/100, for hearing - 1/10, for tactile sensations - 1/30. This law is called the Weber-Bouguer law, and it is valid only for medium ranges.

Based on Weber's experimental data, the German physicist G. Fechner (1801-1887) expressed the dependence of the intensity of sensations on the strength of the stimulus by the following formula: E=klogJ+ C where E- the magnitude of sensations, / is the strength of the stimulus, ki C - constants defined by a given sensory system. According to the Weber-Fechner law, the magnitude of sensations is directly proportional to the logarithm of the intensity of the stimulus. In other words, the sensation changes much more slowly than the strength of the stimulus grows. An increase in the strength of irritation in a geometric progression corresponds to an increase in sensation in an arithmetic progression.

The sensitivity of the analyzers, determined by the magnitude of the absolute thresholds, is not constant and changes under the influence of physiological and psychological conditions. The change in the sensitivity of the sense organs under the influence of the action of the stimulus is called sensory adaptation. There are three types of this phenomenon.

• 1. Adaptation howcomplete loss of sensation during prolonged action of the stimulus. It is a common fact that the sense of smell disappears distinctly shortly after we enter a room with an unpleasant odor. However, complete visual adaptation up to the disappearance of sensations under the action of a constant and motionless stimulus does not occur. This is due to the compensation of the immobility of the stimulus due to the movement of the eye itself. Constant voluntary and involuntary movements of the receptor apparatus ensure the continuity and variability of sensations. Experiments in which conditions were artificially created to stabilize the image relative to the retina (the image was placed on a special suction cup and moved along with the eye) showed that the visual sensation disappeared after 2–3 s.
• 2. Dullness of sensations under the influence of a strong stimulus is called negative adaptation. For example, getting from a dimly lit room into a brightly lit space, we are first blinded and unable to distinguish any details around us. After some time, the sensitivity of the visual analyzer decreases sharply, and we begin to see normally. Another variant of negative adaptation can be observed when immersing a hand in cold water: the intensity of sensations caused by Kholodov once stimulant, soon decreases.
• 3. An increase in sensitivity under the influence of a weak stimulus is called 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.

Adaptation has a huge biological significance: it allows you to capture weak stimuli and protect the senses from excessive irritation in case of strong stimuli.

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 other senses is called interaction of sensations in this case, we can observe both an increase and a decrease in sensitivity. The general pattern is that weak stimuli affecting one analyzer increase the sensitivity of another, and vice versa - strong stimuli reduce the sensitivity of other analyzers when they interact. For example, accompanying the reading of a book with quiet, calm music, we increase the sensitivity and susceptibility of the visual analyzer, but if the music is too loud, the reaction will be the opposite.

We can observe the interaction of sensations in a phenomenon called synesthesia, in this case, the properties of various sensory systems merge, which allows a person to hear "color music", see "warm colors", etc.

The increase in sensitivity as a result of the interaction of analyzers and exercises is called sensitization. The possibilities for training the sense organs and their improvement are very great. There are two areas that determine the increase in the sensitivity of the senses:

sensitization, which spontaneously leads to the need to compensate for sensory defects: blindness, deafness. For example, some deaf people develop vibrational sensitivity so strongly that they can even listen to music;

sensitization caused by activity, specific requirements of the profession. For example, high degree perfection is achieved by olfactory and gustatory sensations in tasters of tea, cheese, wine, tobacco, etc.

Thus, sensations develop under the influence of living conditions and the requirements of practical activity.

Sensitivity is a measure of the ability of a radio receiver to receive weak radio signals. It is quantitatively estimated by the minimum value of the EMF signal at the input of the radio receiver, at which the required signal-to-noise ratio at the output takes place in the absence of external interference.

radio sensitivity, ability radio receiver receive radio signals weak in intensity and a quantitative criterion for this ability. The latter is in many cases defined as the minimum level of the radio signal in the receiving antenna (the emf induced by the signal in the antenna and is usually expressed in terms of mv or mkv, or the field strength near the antenna, expressed in mv/m), at which contained in the radio signal useful information can still be reproduced with the required quality (with sufficient sound volume, image contrast, etc.). In the simplest radio receivers, the sensitivity depends mainly on the degree of amplification of the signals in them: with an increase in the gain, normal reproduction of information is achieved with a weaker radio signal (it is considered higher). However, in complex radio receivers (for example, communications), such a way to increase Radio sensitivity loses its meaning, since in them the intensity of useful radio signals can be comparable to the intensity of external signals acting on the antenna simultaneously with these signals. radio interference that distort the received information. Limiting Radio sensitivity in this case is called interference-limited sensitivity; it is a parameter not only of the receiver, but also depends on external factors. Under the most favorable conditions (mainly when receiving in the meter and shorter wavelengths, and especially in space radio communications), external interference is weak and the main factor limiting Radio sensitivity, become the internal fluctuation noise of the radio receiver (see Fig. fluctuations electrical ). The latter, under normal operating conditions of the radio receiver, have a constant level, therefore Radio sensitivity, limited by internal noises, is a well-defined parameter; for measure Radio sensitivity in this case, one often takes directly the level of internal noise, characterized by noise figure or noise temperature (see also Threshold signal ). The sensitivity of the receiver is one of its main characteristics, which determines the possibility of long-range reception of transmissions. The lower the sensitivity, the more "long-range" the receiver. Therefore, in relation to sensitivity, they usually use the expressions better-worse instead of more-less, understanding the best sensitivity as one that is expressed by its lower value. There are several definitions of sensitivity, and to avoid confusion it is always important to know what sensitivity is being referred to. The following definitions are adopted: gain-limited sensitivity; sensitivity limited by synchronization; noise limited sensitivity.

Sensitivity radio receiver is a parameter that allows you to evaluate the ability of the receiver to receive weak signals from radio stations. Distinguish between the maximum and real sensitivity of the receiver.

Real Sensitivity defines the minimum input signal level at which standard (test) output power is provided at a given ratio of input signal voltage to noise voltage. For domestic receivers, the test output power is assumed to be 50 or 5 mW, depending on the class of the receiver. The specified signal-to-noise ratio when measuring the real sensitivity of the receiver in the LW, MW, HF bands is at least 20 dB, on VHF - at least 26 dB.

The voltage sensitivity of the receiver (for outdoor antennas) is measured in microvolts. The sensitivity of the receiver is the higher, the lower this voltage is. When working with an internal (built-in) antenna, the sensitivity is expressed by the minimum tension electric field and is measured in microvolts or millivolts per meter (µV/m or mV/m).

Maximum sensitivity is the gain limited sensitivity. It determines the minimum signal level at which the standard (test) output power is provided when all receiver controls are set to the positions corresponding to the maximum gain. The sensitivity of a radio receiver depends on many factors: the amplifying properties of all stages of the receiver path, the level of intrinsic noise, bandwidth, etc.

Modern receivers have very high sensitivity. For example, high-end receivers in the VHF range have a sensitivity of 1 ... 2 μV, and in the KB range - 5 ... 10 μV.

The sensitivity of a radio receiver is usually expressed in millivolts per meter (mV/m) or microvolts (µV). Superheterodyne radio receivers (superheterodynes) have the highest sensitivity, in which, with the help of special devices - a local oscillator and a mixer - before detection, the frequency of the radio signal is converted (lowered), which does not change the modulation law. The signal obtained as a result of the conversion is the so-called. intermediate frequency is additionally amplified by it, after which it is detected and amplified again (by the audio frequency).

The property of a radio receiver that makes it possible to distinguish a useful radio signal from radio interference by certain features characteristic of a radio signal is called selectivity. Otherwise, this is the ability of the radio receiver to select the desired radio signal from the spectrum electromagnetic oscillations at the receiving location, reducing interfering radio signals.

Distinguish between spatial and frequency selectivity. Spatial selectivity It is achieved by using an antenna that provides reception of the desired radio signals from one direction and attenuation of radio signals from other directions from extraneous sources. Frequency selectivity quantitatively characterizes the ability of a radio receiver to select from all radio frequency signals and radio interference acting at its input, a signal corresponding to the tuning frequency of the radio receiver.

Selectivity is a parameter that characterizes the ability of a radio receiver to receive and amplify a signal of an operating frequency against the background of "interfering" signals from other transmitters operating on adjacent channels (frequencies). This parameter is often confused or confused with the concept of "noise immunity". Noise immunity is a broader concept than selectivity. After all, interference can be considered as a signal from another transmitter, which constantly emits at an adjacent frequency, as well as a short-term lightning discharge, in which a very wide spectrum of frequencies is emitted. But if a relatively narrow-band signal of a neighboring transmitter can be neutralized by circuitry solutions (frequency selection or filtering), then it is almost impossible to filter out a broadband short-term interference signal, and interference has to be dealt with in other ways, in particular, using special methods of encoding and subsequent processing of the information component of the signal. It is on this principle that PCM devices are built.

The term "selectivity" in the characteristic of a radio receiver is usually supplemented with the words "adjacent channel" and characterize it with the help of specific physical concepts and magnitudes. It usually goes something like this: "Adjacent channel receiver selectivity is -20 dB at +/- 10 kHz offset". physical meaning this clumsy phrase is as follows: if the frequency of the "interfering" signal differs from the "working" frequency by 10 kHz (higher or lower), then with equal levels of "useful" and "interfering" signals at the receiver input, the level of the "interfering" signal at the output of the receiver will be 20 dB (10 times) less than the level of the "useful" signal. And if this parameter is equal to -40 dB, then the "interfering" signal will weaken by 100 times, and so on. Sometimes this multi-story parameter is replaced by one of the components - the bandwidth. The bandwidth in the above example is 20 kHz, or +/- 10 kHz relative to the center frequency (which we have is determined by the channel number). We will explain this further with the help of a spectral diagram. But the "noise immunity" of the PPM receiver, unfortunately, cannot be unambiguously characterized.

In the VHF band, adjacent channel selectivity is measured at two values ​​of the interfering signal detuning - 120 and 180 kHz. This is because for a VHF broadcasting system, the nearest adjacent channel (interfering) is 120 kHz away from the desired signal frequency when both signals have the same in-phase modulation, and the nearest adjacent channel having a different modulation is away from the frequency useful signal at 180 kHz.

Adjacent channel selectivity is determined mainly by the intermediate frequency path and changes insignificantly within the range.

Image selectivity determines the attenuation by the radio receiver of the interfering signal, which is separated from the received signal by twice the value of the intermediate frequency. The selective (selective) properties of the radio receiver in the mirror channel are determined by the resonant properties of the selective circuits up to the frequency converter (input circuits, UHF).

Selectivity by intermediate frequency determines the attenuation by the receiver of the interfering signal, the frequency of which is equal to the intermediate frequency of the receiver. Operation of radio stations on these frequencies is prohibited. However, in some cases, the harmonics of radio stations may coincide with the intermediate frequency of the receiver. However, they can be a strong interference when receiving other radio stations.

The attenuation of interference with a frequency equal to the intermediate one is carried out by the resonant circuits of the input circuits and the high-frequency amplifier. To further attenuate this interference, a special filter is included at the receiver input, which is tuned to an intermediate frequency and thereby weakens the penetration of interference into the input circuits of the receiver.

reception- the ability of the body to perceive information from external and internal environment. The primary perception of all stimuli in the human body is carried out receptors- specific cells that perceive the effects of external and changes in the internal environment of the body.

Sensitivity- the ability of the body to perceive information (stimuli) from the external and internal environment and respond to it with differentiated forms of reactions.

Analyzer- a functional association of structures that performs the perception and analysis of information (receptor - pathways - cortical center).

2. Sensitivity classification:

Kinds sensitivity by modality:

1)Simple

- exteroception:distant- hearing, vision; contact- pain, tactile, temperature, feeling of pressure (pyesthesia), taste; mixed(?) – sense of smell

- interoception(chemo-, baro-, osmoreceptors),

- proprioception(joint-muscular feeling - kinesthesia, feeling of movement of the skin fold - dermatokinesthesia, vibrational - seismoesthesia, sense of weight - baroesthesia).

2)Complex

- localization(topesthesia),

- discriminatory,

- two-dimensional-spatial(graphesthesia, dermatolexia),

- three-dimensional-spatial(stereognosis).

Types of sensitivity according to the level of information processing:

1)protopathic(thalamic or vital) - perceives gross influences that threaten the life of the organism - fibers of type B and C.

2)epicritical(cortical, gnostic) - provides subtle recognition and differentiation of various influences - fibers of type A.

Gued-Scherer law(1905) - in the process of regeneration of the sensory nerve, first the restoration of protopathic, and then epicritical sensitivity occurs.

3. Peripheral components of the sensitivity system:

Types of contact exteroreceptors:

1)Painful: nociceptor - nociceptive system (see below).

2)Temperature: warm - Ruffini's ending and cold - Bulb Krause.

3)Tactile(1 type of receptors - with small, delineated fields) : Merkel disc (slowly adapting) and Meissner corpuscle (rapidly adapting).

4)pressures and weights(type 2 receptors - with extensive fields) : the body of Golgi-Mazzoni (slowly adapting) and the body of Vater-Pacchini (quickly adapting).

5) vibrations- periosteal receptors

Types proprioceptors (for details, see the topic "Reflex-motor sphere"):

1)muscle spindles 1 and 2 types.

2)tendon receptors(Golgi body).

Types sensitive fibers:

1)thick myelin type A-alpha(40-50 m/s) - proprioception;

2)thick myelin type A-beta(30-40 m/s) - tactile;

3)thick myelin type A-gamma(20-30 m/s) - pressure;

4)thin myelin type B(10-14 m/s) - pain and temperature;

5)unmyelinated type C(2 m/s) - pain (protopathic).

Sensitivity: morphophysiology

1. General features of the three-neuronal pathways of superficial and deep sensitivity

The first the neuron is located in the spinal (cranial) node.

axons second neurons cross over.

Third neuron located in the ventrolateral complex of the thalamus, its axon - thalamocortical path passes through the posterior third of the posterior leg of the internal capsule and the radiant crown, ends in the posterior central gyrus and the upper parietal region.