Weber Fechner's law establishes the connection between electrical. §4
In 1760, the French scientist and creator of photometry P. Bouguer studied his ability to distinguish a shadow cast by a candle if the screen on which the shadow falls was simultaneously illuminated by another candle. His measurements are quite
but they definitely established that the ratio l K/K (where l K is the minimum perceived increase in illumination, K is the initial illumination) is a relatively constant value.
In 1834, the German psychophysicist E. Weber repeated and confirmed the experiments of P. Bouguer. E. Weber, studying weight discrimination, showed that the minimum perceived difference in weight is a constant value equal to approximately 1/30. A load of 31 g differs from a load of 30, a load of 62 g differs from a load of 60 g; 124 g from 120 g.
This relationship has entered the history of research in the psychophysics of sensations under the name of the Bouguer-Weber law: the differential threshold of sensations for different sense organs is different, but for the same analyzer it is a constant value, i.e. l R/R = const.
This ratio shows what part of the original stimulus value must be added to this stimulus in order to obtain a barely noticeable change in sensation.
Further research showed that Béber's law is valid only for stimuli average size: when approaching absolute thresholds, the amount of increase ceases to be constant. Weber's law applies not only to subtle differences, but also to all differences in sensations. The differences between pairs of sensations seem equal to us if the geometric relationships of the corresponding stimuli are equal. Thus, increasing the lighting intensity from 25 to 50 candles gives subjectively the same effect as an increase from 50 to 100.
Based on the Bouguer-Weber law, Fechner made the assumption that barely noticeable differences (s.p.) in sensations can be considered equal, since they are all infinitesimal quantities. If the increment of sensation corresponding to a barely noticeable difference between stimuli is denoted as l E, then Fechner's postulate can be written as l E = const.
Fechner accepted the e.z.r. (lE) as a unit of measure, with the help of which one can numerically express the intensity of sensations as a sum (or integral) of barely noticeable (infinitesimal) increases, counting from the threshold of absolute sensitivity. As a result, he received two series of variable quantities - the magnitudes of the stimuli and the corresponding magnitudes of sensations. Feelings grow in arithmetic progression, when stimuli grow exponentially.
What does it mean? We take, for example, such stimuli as 10 candles, increase their number: 10 - 100 - 1000 -10000, etc. This is a geometric progression. When there were 10 candles, we had a corresponding feeling. When the stimuli were increased to 100 candles, the sensation doubled; the appearance of 1000 candles caused the sensation to increase threefold, etc. The increase in sensations occurs in an arithmetic progression, i.e. much slower than the increase in the stimuli themselves. The ratio of these two variables can be expressed in logarithmic formula: E = K log R + C, where E is the strength of sensation, R is the magnitude of the acting stimulus, K is the coefficient of proportionality, C is a constant that is different for sensations of different modalities.
This formula is called the basic psychophysical law, which is essentially the Weber-Fechner law. According to this law, the change in the strength of sensation is proportional to the decimal logarithm of the change in the strength of the influencing stimulus (Fig. 8).
Rice. 8. Logarithmic curve of the dependence of the magnitude of sensation on the strength of the stimulus, illustrating the Weber-Fechner law
A number of phenomena revealed by sensitivity studies do not fit into the framework of the Weber-Fechner law. For example, sensations in the area of protopathic sensitivity do not show a gradual increase as irritation increases, but upon reaching a certain threshold they immediately appear to the maximum extent. They approach the “all or nothing” type of reactions.
About half a century after the discovery of the basic psychophysical law, it again attracted attention and, on the basis of new experimental data, gave rise to a discussion about the true nature of the relationship between the strength of sensation and the magnitude of the stimulus, precisely expressed by a mathematical formula. The American scientist S. Stevens reasoned as follows: what happens when the illumination of a spot of light and, on the other hand, the strength of the current (frequency 60 Hz) passed through the finger are doubled? Doubling the illumination of a spot against a dark background has surprisingly little effect on its apparent brightness. The typical observer estimates the apparent increase to be only 25%. When the current strength doubles, the sensation of impact increases tenfold. S. Stevens rejects Fechner's postulate (lE = const.) and states that another quantity is constant, namely the ratio l E/E. Extending the Bouguer-Weber law to sensory quantities (lE/E = const), S. Stevens, through a series of mathematical transformations, obtains a power-law relationship between sensation and stimulation: E = kRD where k is a constant determined by the chosen unit of measurement, E is the strength of sensation, R - the value of the influencing stimulus, n - an indicator depending on the modality of sensation. The n index takes a value of 0.33 for brightness and 3.5 for electrical shock. This pattern is called Stevens' law.
According to S. Stevens, the power function has the advantage that when using a logarithmic scale on both axes, it is expressed by a straight line, the slope of which corresponds to the value of the exponent (n). This can be seen in Fig. 9: Slowly increasing brightness contrast and quickly increasing the electric shock sensation.
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Rice. 9. Power curve of the dependence of the magnitude of sensation on the strength of the stimulus, illustrating Stevens' law. 1.Electric shock. 2. Brightness.
For more than a hundred years, disputes between supporters of the logarithmic dependence of the strength of sensation on the magnitude of the stimulus (Fechner's law) and the power law (Stevens' law) have not ceased. If we neglect the purely psychophysical subtleties of this dispute, then both laws in their psychological meaning will turn out to be very close: both assert, firstly, that sensations change disproportionately to the strength of physical stimuli acting on the sense organs, and, secondly, that the strength of sensation grows much more slowly than the magnitude of physical stimuli.
Self-test questions
1. Prove insolvency to date methodological basis Fechner's research.
2.What is the difference between psychophysics-I and psychophysics-P, classical and modern psychophysics?
3.What are the measurement methods mental process ov (sensations) received the honorary name of classical?
4. What is the threshold for the disappearance of a sensation and the threshold for the appearance of a sensation?
H. Give examples of the influence of subthreshold signals on a person.
6.What is the essence of the central problem of psychophysics-1?
U. How does the magnitude of sensation depend on the strength of the stimulus (according to Fechner and Stevens)?
Weber-Fechner Law
In the second half of the 19th century. individual questions and problems lying on the border of physiology and psychology become the subject of special and systematic research, which is then isolated and formalized into relatively independent scientific directions. One of the first such areas was psychophysics, created by the German physiologist G. Fechner (1801-1887).
Psychophysics was conceived by Fechner as the science of the universal connection between the physical and spiritual world. The researcher came up with the doctrine of the identity of the mental and physical, and put forward the principle of the universal animation of nature. According to Fechner, a special science should be created that, with the help of experiment and mathematics, could prove the philosophical concept he put forward. Psychophysics was such a science, which he defined as an exact doctrine of the functional relationships between body and soul.
According to Fechner, psychophysics should engage in the experimental and mathematical study of various mental processes in their relation, on the one hand, to physical factors, which should constitute the subject of external psychophysics, on the other hand, in relation to anatomical and physiological foundations, which should represent the subject of internal psychophysics.
A special role in the study of this issue was played by E. Weber’s work on the study of touch and sensitivity thresholds. It was Weber's experiments that showed that there is a certain relationship between the physical and the mental, in particular, between irritation and sensation, and that the discovered relationships between them are amenable to experimental measurement. Considerable importance for determining the specifics new science Herbart's ideas played a role, in particular, his doctrine of the thresholds of consciousness and the rationale for the possibility of using mathematics in psychology.
Psychophysics became the science of the connection between stimuli and sensations. The provisions established by Fechner about the measurability of psychophysical relations and the possibility of applying a mathematical law to them brought to the fore the problem of developing special methods psychophysical measurement and methods of mathematical analysis and description of psychophysical relationships. General program the construction of psychophysics included three main tasks:
1) establish what law the relationship between mental and physical world, using the example of the connection between irritations and sensations;
2) give a mathematical formulation of this law;
3) develop psychophysical measurement methods.
The law, discovered by E. G. Weber (1834) and developed by G. T. Fechner, is the fundamental law of psychophysics.
Fechner believed that the material and the ideal are two sides of a single whole. Therefore, he set out to find out where the border between the material and the ideal lies. Fechner approached this problem as a natural scientist. In his opinion, the process of creating a mental image can be represented by the following diagram:
Irritation --> Excitement --> Sensation --> Judgment (physics) (physiology) (psychology) (logic)
The most important thing in Fechner's idea was that he was the first to include elementary sensations in the range of interests of psychology. Before Fechner, it was believed that the study of sensations, if anyone was interested in it, should be carried out by physiologists, doctors, even physicists, but not psychologists. This is too primitive for psychologists.
According to Fechner, the desired boundary passes where sensation begins, that is, the first mental process arises. Fechner called the magnitude of the stimulus at which sensation begins the lower absolute threshold. To determine this threshold, Fechner developed methods that are actively used in our time. Fechner based his research methodology on two statements, called the first and second paradigms of classical psychophysics. 1. The human sensory system is a measuring device that responds appropriately to physical stimuli. 2. Psychophysical characteristics in people are distributed according to a normal law, that is, they randomly differ from some average value, similar to anthropometric characteristics. Today there is no doubt that both of these paradigms are already outdated and, to a certain extent, contradict modern principles of psychic research. In particular, we can note the contradiction to the principle of activity and integrity of the psyche, since today we understand that it is impossible to isolate and experimentally study one, even the most primitive, mental system from the entire structure of the human psyche. In turn, the activation in the experiment of all mental systems from the lowest to the highest leads to a very wide variety of reactions of the subjects, which requires an individual approach to each subject. However, Fechner's research was innovative in nature. He believed that a person cannot directly evaluate his sensations quantitatively, so he developed “indirect” methods with which one can quantitatively represent the relationship between the magnitude of the irritant (stimulus) and the intensity of the sensation caused by it. Suppose we are interested in at what minimum value of a sound signal the subject can hear this signal, i.e. we must determine the lower absolute loudness threshold. The measurement by the minimum change method is carried out as follows. The subject is given instructions to say “yes” if he hears the signal, and “no” if he does not hear it. First, the subject is presented with a stimulus that he can clearly hear. Then, with each presentation, the stimulus magnitude decreases. This procedure is carried out until the subject’s answers change. For example, instead of “yes,” he may say “no” or “apparently not,” etc.
The magnitude of the stimulus at which the subject's responses change corresponds to the threshold for the disappearance of the sensation. At the second stage of measurement, in the first presentation the subject is presented with a stimulus that he cannot hear in any way. Then, at each step, the stimulus magnitude increases until the subject's responses move from “no” to “yes” or “maybe yes.” This stimulus value corresponds to the threshold for the onset of sensation. But the threshold for the disappearance of a sensation is rarely equal to the threshold for its appearance. Accordingly, the absolute threshold will be equal to the arithmetic mean of the thresholds for appearance and disappearance. In a similar way, the upper absolute threshold is determined - the value of the stimulus at which it ceases to be perceived adequately. The upper absolute threshold is sometimes called the pain threshold, because at the corresponding stimulus magnitudes we experience pain - pain in the eyes when the light is too bright, pain in the ears when the sound is too loud.
Absolute thresholds - upper and lower - determine the boundaries of the surrounding world accessible to our perception. By analogy with a measuring device, absolute thresholds determine the range over which the sensory system can measure stimuli, but beyond this range, the performance of the device is characterized by its accuracy, or sensitivity. The absolute threshold value characterizes absolute sensitivity. For example, the sensitivity of two people will be higher in the one who experiences sensations when exposed to a weak stimulus, when the other person has not yet experienced sensations (i.e., who has a lower absolute threshold value). Consequently, the weaker the stimulus that causes the sensation, the higher the sensitivity. Thus, absolute sensitivity is numerically equal to a value inversely proportional to the absolute threshold of sensations. Different analyzers have different sensitivities. We have already talked about the sensitivity of the eye. The sensitivity of our sense of smell is also very high. The threshold of one human olfactory cell for the corresponding odorous substances does not exceed eight molecules. To call taste sensation, requires at least 25,000 times more molecules than to produce the olfactory sensation. The absolute sensitivity of the analyzer depends equally on both the lower and the upper threshold of sensation. The magnitude of absolute thresholds, both lower and upper, varies depending on different conditions: the nature of the person’s activity and age, the functional state of the receptor, the strength and duration of the stimulus, etc. Another characteristic of sensitivity is sensitivity to difference. It is also called relative, or difference, since it is sensitivity to changes in the stimulus. If we put a load weighing 100 grams on our hand, and then add another gram to this weight, then not a single person will be able to feel this increase. In order to feel an increase in weight, you need to add three to five grams. Thus, in order to feel the minimal difference in the characteristics of the influencing stimulus, it is necessary to change the strength of its influence by a certain amount, and that minimal difference between the stimuli, which gives a barely noticeable difference in sensations, is called the discrimination threshold.
Sensations arise as a result of the transformation of the specific energy of stimuli into the energy of the nervous processes of the body. The physiological basis of sensation is a nervous process stimulated by the action of a particular stimulus on an adequate analyzer. The sensation is reflexive in nature.
Weber-Fechner law, basic psychophysical law, determines the relationship between the intensity of sensation and the strength of irritation acting on any sensory organ. Based on the observation of the German physiologist E. Weber, who established (1830-34) that not an absolute, but a relative increase in the strength of a stimulus (light, sound, weight pressing on the skin, etc.) is perceived:
where?I is the difference threshold, I is the original stimulus.
The ratio of the difference threshold to the value of the original stimulus is a constant value and is called the relative difference or differential threshold. The reciprocal of the differential threshold is called differential sensitivity. Studies have shown that the magnitude of differential sensitivity is not the same for different modalities.
So, a chandelier with 8 bulbs seems to us just as brighter than a chandelier of 4 light bulbs, how much brighter is a chandelier made of 4 light bulbs than a chandelier made of 2 light bulbs. That is, the number of light bulbs must increase several times so that it seems to us that the increase in brightness is constant. Conversely, if the increase in brightness is constant, it will seem to us that it is decreasing. For example, if we add one light bulb to a chandelier of 12 light bulbs, we will hardly notice an increase in brightness. At the same time, one bulb added to a chandelier of two bulbs gives a significant apparent increase in brightness.
It is curious that Fechner did not derive his equation based on general considerations, like Bernoulli (although, in principle, he could have). He analyzed the results obtained by another German physiologist, Ernst Weber. In the mid-19th century, this scientist studied the characteristics of human perception of weight various cargoes, and discovered an interesting pattern. Disregarding Weber's specific figures, it is as follows: if a subject held a load weighing 100 grams in his hand, he did not notice an increase of 5 grams, but noticed an increase of 10 grams. However, if the subject held a load weighing 200 grams in his hand, he did not notice an increase of 10 grams, but only an increase of 20 grams. In other words, the minimum noticeable increase in the weight of the load turned out to be directly proportional to its original weight. Weber found that this pattern operates over a fairly wide range in the perception of weight, sound intensity, brightness, etc. Serious deviations from it were observed only at very weak and very strong stimulus intensities. Mathematical analysis Weber's results and led Fechner to an expression one-to-one similar to Bernoulli's equation.
Let us note that Weber did not ask his subjects to somehow subjectively evaluate the weight of the loads; he only asked them to note the moment when they recorded a change in weight. This means that the identified pattern does not relate to some high-level psychological characteristics perception and thinking - as can be considered based on Bernoulli's law - but characterizes rather low-level, primary processes of perception. Moreover, the Weber-Fechner law operates even where our perception seems to have nothing to do with it. In particular, if a hormone injection is used as a stimulus, then the intensity of the body's physiological response to the injection also obeys this law. That is, it is possible that the Weber-Fechner law does not relate to the peculiarities of perception by the senses, but generally describes the reaction of a person and his body to any kind of external influences.
But the Weber-Fechner law does not only apply to humans. Back in the 20s of the last century, evidence was obtained that insects also obey it. In particular, the locomotor activity of Popillia Japonica beetles increases with increasing light stimulus intensity in accordance with the Weber-Fechner law.
We have enough grounds to put forward a rather bold hypothesis: the pattern of the Weber-Fechner law describes the intensity of the reaction of any complex cognitive system to external stimuli - be it the human body or any other organic or social system.
Stevens Law
Stevens' law is a variant of the basic psychophysical law, establishing a power-law rather than logarithmic (see Fechner's Law) relationship between a subjective series (a series of sensations, impressions) and a series of stimuli:
where Y is the subjective magnitude of the sensation, S is the magnitude of the stimulus (irritant), K is a constant depending on the unit of measurement. Indicator p power function different for different modalities-sensations. According to Stevens, this law is valid for any number of stimuli, both physical, which are easily subject to objective measurement (weight, intensity of sound and light, line length, temperature, etc.), and any others for which there are no objective measures ( a series of handwritings, drawings, etc.). With the help of 3.S., numerical or quantitative estimates the magnitude of sensations in the form of establishing a given relationship between two stimuli. Thanks to this, scales of quantities were created: subjective scales of loudness, lightness, heaviness, visually perceived length, area, distance, flickering speed; subjective scales of electric shock, taste, multiplicity, auditory beats, etc. It turned out that power series valid for all studied stimulus modalities. The l indicator ranges from 0.3 (for loudness) to 3.5 (for electric shock). The power function, being depicted on a logarithmic scale on both coordinate axes, has the form linear dependence with a slope determined by the exponent n. Along with Fechner’s law, which establishes a logarithmic relationship between the magnitude of the stimulus and the magnitude of the sensation, 3. S. is one of the most important psychophysical laws. However, the question of which one is more universal and which one should be preferred remains debatable.
The Weber-Fechner law is major discovery in the field of psychophysics, which allows us to characterize something that, it would seem, cannot be characterized by any kind, namely, human sensations.
Basic psychophysical law of Weber - Fechner
First of all, let's look at the most important components of this expression. The Weber-Fechner law states that the intensity of a person's sensation is proportional to the logarithm of the intensity of the stimulus. Needless to say, at first glance this formulation of the Weber-Fechner law sounds scary, but in fact, everything is quite simple.
Back in the 19th century, the scientist E. Weber was able to show with the help of several experiments that each new stimulus, in order for a person to be able to perceive it as different from the previous one, must have a difference with the previous version by an amount that is proportional to the original stimulus.
The simplest example of this statement is any two objects that have a certain mass. For a person to perceive them as different in weight, the second one must differ by 1/30.
Another example can be given in lighting. For a person to see the difference in the light of two chandeliers, their brightness must differ by 1/100. That is, a chandelier made of 12 light bulbs will be slightly different from one to which only one was added, and a chandelier made of one light bulb to which one more was added will give significantly more light. Despite the fact that in both cases only one light bulb is added, the difference in lighting will be perceived differently, since it is the ratio of the initial stimulus and the one that is subsequent that is important.
Weber–Fechner law: formulaThe formulation that we examined above is supported by a special formula that expresses the action of the Weber-Fechner psychophysical law. In 1860, Fechner was able to formulate a law that states that the strength of sensation p is proportional to the logarithm of the intensity of the stimulus S:
p=k*log(S)\(S_0)
where S_0 is a value reflecting the intensity of the stimulus: if S
To understand this law, the concept of the so-called threshold, established in the process of psychophysical research, is especially important.
Thresholds of sensations Weber-Fechner law
Subsequently, it was found that the existing intensity of irritation requires the achievement of a certain specific level in order for a person to be able to feel its impact. Such a weak impact, which gives a barely noticeable sensation, is called the lower threshold of sensation.
There is also such a level of influence, after which the sensations are no longer able to intensify. In this case we are talking about the upper threshold of sensation. A person feels any kind of impact exclusively in the interval between these two indicators, which are therefore called external thresholds of sensation.
It must also be said that there is no parallelism in the full sense of the word between the intensities of sensation and irritation. 
cannot even in the interthreshold interval. This is easy to prove with an example: imagine that you picked up a bag, and it, of course, has some weight. After this we will put a piece of paper in the bag. In fact, the weight of the bag is now increased, but a person will not feel such a difference, despite the fact that it lies in the area between the two thresholds.
In this case, we are talking about the fact that the increase in irritation is too weak. The amount by which the irritation increases is usually called the discrimination threshold. It follows that stimulation with too low a discriminative intensity is subthreshold, and with too strong a stimulus is beyond the threshold. Moreover, the level of these indicators also depends on sensitivity in relation to discrimination - if the sensitivity to discrimination is higher, then the discrimination threshold is correspondingly lower.
Question 17. Psychophysical problem (Weber-Fechner and Stevens laws). Types of thresholds and sensitivity.
Founder of psychophysics- German philosopher and physicist Fechner. Psychophysics is based on the idea that with a continuous increase in the intensity of the stimulus, the intensity of the sensation increases discretely.
Sensitivity- is the ability of living matter to respond to changes external environment or internal environment.
In psychology, sensitivity is understood as the ability of living systems to respond to changes in the external and internal environment by the manifestation of sensations (sensory sensitivity).
When sensations just appear - it's absolute sensitivity. and when sensations change - differential or difference. They correspond to two main types cognitive activity:
1) object detection
2) process of discrimination
The absolute sensitivity of the sensory system is based on its ability to detect weak, short or small stimuli. Differential sensory sensitivity is based on the ability of the sensory system to distinguish between signals.
In order to measure the level of absolute and differential sensitivity, the concept of sensation thresholds or sensory thresholds is introduced.
The main question of psychophysics– this is a question about thresholds.
Types of thresholds:
v absolute threshold (upper and lower),
v differential threshold,
v operational threshold.
Psychophysics research has shown that not every stimulus causes a sensation. The minimum intensity of stimulation required to produce a sensation is called lower absolute threshold . The lower threshold gives a quantitative expression for sensitivity: the sensitivity of the receptor is expressed by a value inversely proportional to the threshold: E = I/J, where E is sensitivity and J is the threshold value of the stimulus.
Along with this there is also upper absolute threshold , i.e. the maximum intensity possible for the sensation of a given quality. A further increase or decrease in the magnitude of the stimulus leads to pain or leads to destruction of the sensory organs.
Differential threshold - the difference between stimuli at which they become barely noticeable.
Operational threshold - the type of sensory threshold corresponding to the smallest difference between two stimulus values, at which the accuracy and speed of recognition have maximum values.
Thresholds for various types sensations are different. Within the same species they can be different different people, from the same person in different time, under various conditions.
Human sensitivity thresholds are not constant. Their change is influenced external conditions. The sensation threshold is related to one stimulus, and sensitivity is related to the entire sensory system as a whole. The relationship between the threshold of sensation and sensitivity is inversely proportional. The higher the threshold of sensation, the lower the level of sensitivity.
Conditions affecting the sensation threshold:
1) individual differences between people
2) a certain functional state of the subject
3) experimental conditions
4) the presence of internal sensory noise
5) experimental procedure
E. Weber established that a certain ratio between the intensities of two stimuli is required in order for them to give different sensations. This relationship is expressed in the law established by Weber: the ratio of the additional stimulus to the main one must be a constant value : ∆J/J = K, where J denotes irritation, ∆ J is its increase, K is a constant value depending on the receptor.
Based on Weber's law, Fechner made the assumption that barely noticeable differences in sensations can be considered equal, since they are all infinitesimal quantities, and taken as a unit of measure with which the intensity of sensations can be expressed numerically as the sum (or integral) of barely noticeable (infinitesimal) increases, counting from the threshold of absolute sensitivity. As a result, he received two series of variable quantities - the magnitudes of the stimuli and the corresponding magnitudes of sensations. Sensations grow in arithmetic progression when stimuli grow in geometric progression. The ratio of these two variables can be expressed in a logarithmic formula: E= K1gJ+ C, Where E- strength of feeling, J- the magnitude of the current stimulus, TO and C are some constants. This formula defining dependence of the intensity of sensations on the intensity of the corresponding stimuli, and represents Weber-Fechner psychophysical law . The change in the strength of sensation is proportional to the decimal logarithm of the change in the strength of the influencing stimulus.
Stevens Law : « The magnitude of the sensation is a power function of the magnitude of the stimulus ", i.e. between a number of sensations and a number of physical stimuli there is not a logarithmic, as in Fechner, but a power-law relationship: Y = k * Sn,
where Y is a subjective value, sensation;
S - stimulus;
n is the exponent of the function;
k is a constant depending on the unit of measurement.
Moreover, the index of the power function is different for different modalities of sensations.
Important characteristic each sensory system- the ability to notice differences in the properties of simultaneously or sequentially acting stimuli.
The sensory system has the ability to adapt its properties to environmental conditions and the needs of the body.
Sensory adaptation- This general property sensory system, which consists in adaptation to a long-acting stimulus.
There are 2 types of sensory adaptation:
ü general (or global)
ü local (or selective).
General adaptation manifests itself in a decrease in absolute and increase in differential sensitivity of the entire sensory system. Local adaptation manifests itself in addiction to the action of a constant stimulus. Local adaptation comes down to a decrease in the sensitivity not of the entire sensory system, but of some part of it subjected to prolonged exposure to a stimulus.
Adaptation processes begin at the receptor level, covering all neural layers of the sensory system. By speed this process all receptors are divided into fast And slowly adapting, when the effect of the constant stimulus ceases, the absolute sensitivity of the sensory system is restored.
Sensitization - increasing the sensitivity of the senses when exposed to adequate and inadequate stimuli.
Psychophysics- a science that studies the relationship between the magnitude of stimuli of a particular modality and the intensity of the sensations they cause.
The main question of psychophysics is the question of thresholds.
Absolute threshold (lower) - the minimum strength of the stimulus that causes a barely noticeable sensation - minimal sensitivity.
The absolute threshold (upper) is the maximum strength of the stimulus, a further increase causes pain - maximum sensitivity.
Absolute thresholds define the measurement range of the sensor system.
The difference threshold is the minimum amount of increase in the strength of the stimulus, which causes a barely noticeable change (weakening/increasing) of sensation (depending on the modality). Shows the accuracy (sensitivity) of the sensor system.
Weber's law: the ratio of a barely noticeable change in a stimulus (ΔI) to its original value(I) constantly: ΔI= const
This ratio characterizes the value of the differential threshold; the value of this threshold depends on the modality; however, this law is valid only for stimuli of average strength; in the region of threshold values it is violated.
Fechner's law: for each modality there is a certain relative value an increase in stimulation which always produces an observable change in the intensity of the sensation. S=K·logR+С
(S – magnitude of sensation, K and C – experimentally established constants, R – magnitude of irritation)
Irritation increases in geometric progression, and sensations increase in arithmetic progression, and the ratio of stimulus to sensation can be represented as a logarithmic curve. The intensity of the sensation is proportional to the logarithm of the intensity of the stimulus.
This law became a kind of addition to Weber's law.
Stevens Law: a variant of the basic psychophysical law, establishes a power-law relationship between a subjective series (a series of sensations, impressions) and a series of stimuli. Ψ=k*Sⁿ
(Ψ – sensation, S – stimulus, n – exponent of the function, depends on the modality, k – constant, depends on the unit of measurement)
Threshold research methods:
Installation method (method average error) - a person himself changes the intensity of the stimulus until he receives a barely noticeable sensation (absolute threshold) or a sensation equal in strength to a given one (difference). Several measurements are taken, then the arithmetic mean is determined.
Boundary method - a successive series of stimuli is gradually presented in minimal equal steps (once with decreasing intensity, the other time with increasing intensity). The arithmetic mean when decreasing is the “disappearance threshold”, when increasing – the “appearance threshold” (absolute thresholds); the amount by which the stimulus value must be changed for a person to notice a change in their sensations - the difference threshold.
Method of constant stimuli (irritations) – threshold values are determined based on statistical processing large number testimonials of the subject. Stimuli are presented in random order, the subject must say whether he feels the stimulus or not (absolute threshold); it seems to him to be greater than, less than, or equal to a constant (difference).
The research revealed:
Waiting error- the subject, guessing about the upcoming appearance (disappearance) of the sensation, changes the answer without waiting for the true sensation.
Accustoming error– a person gets used to giving a certain answer and does not change it even if the sensation changes.
Adaptation– an adaptive change in sensitivity to the intensity of the stimulus due to peripheral changes in the receptor and protective inhibition in the cortex. Highlight:
Disappearance of negative sensation
Dulling of sensation adaptation
Increased sensitivity - positive adaptation
Sensitization- increased sensitivity as a result of exercises and interaction of analyzers. Sensitization can be caused by the need to compensate for sensory defects (blindness) or by activity (dyers can distinguish 40 shades of black).
Synesthesia – the occurrence, under the influence of a stimulus on one analyzer, of a sensation that is characteristic of another analyzer.
The phenomenon of contrast– change in sensitivity under the influence of a previous stimulus (or accompanying one).
Changes in sensations can occur under the influence of second-signal stimuli (sour as lemon).
Associations of sensations:
Intermodal - by contiguity in space
Intramodal - by contiguity about time
The Weber-Fechner law is an empirical psychophysiological law, which states that the intensity of a sensation is proportional to the logarithm of the intensity of the stimulus. BASIC PSYCHOPHYSICAL LAW - a function of the dependence of the magnitude of sensation on the magnitude of the stimulus. For example, if you add one light bulb to a chandelier of two light bulbs, the apparent increase in brightness will be significant. The question of what is the relationship between sensation and irritation is answered by the so-called psychophysical Weber-Fechner law.
In general, the dependence has the character of a general power function with different exponents for each type of condition (Stevens' Law). Conversely, if the increase in brightness is constant, it will seem to us that it is decreasing. What we said about visual sensations is also quite true regarding auditory sensations.
If we bring another candle, the light irritation will increase; At the same time, the strength or intensity of the light sensation will increase. Again we put a one-pound weight on the subject’s hand and, for comparison, we put a one-pound weight and four spools and ask the same question. For example, one third of a gram must be added to one gram for the subject to feel the difference in sensation, for thirty grams - ten grams, etc.
If we can measure the strength of stimulation, then based on Fechner’s formula just given, we can determine the strength of the corresponding sensations. We have seen that when sensations increase by the same amount, then irritations increase in such a way that their increment always maintains the same ratio to a given amount of irritation.
Consequently, we get a series of sensations that grows exponentially while irritation grows geometrically. Stevens' law - a variant of O. p. z. (S. Stevens, 1957) - power-law dependence of the magnitude of sensation on the magnitude of the stimulus.
Stevens's power law is widely used for the same reason as Fechner's logarithmic law: it describes many empirical data well. Fechner's law - a variant of O. p. z. (G. Fechner, 1860) - logarithmic dependence of the magnitude of sensation on the magnitude of the stimulus, expressed in threshold units. It was derived by the author theoretically on the basis of a number of a priori postulates (for the lack of evidence of which he has been criticized more than once) and Weber’s law.
Syn. psychophysical law, psychophysical function (not to be confused with the psychometric curve, or function). The dependence was derived by the German psychologist and physiologist G. T. Fechner on the basis of the Bouguer-Weber law and the additional assumption of the subjective equality of subtle differences in sensations. With the help of mathematics, Fechner theoretically substantiated that known fact that the sensation changes much more slowly than the strength of irritation increases.
Currently, numerous options for the latter have been proposed, but they do not have significant advantages compared to Z.F. See Stevens' Law, Psychophysics. This formula for measuring sensations was derived from Weber's research, which showed the constancy of the relative magnitude of the increment of the stimulus that causes the sensation of a barely noticeable difference.
Secondly, as a result of precise research, the law underlying the relationship between the intensities of irritation and sensation was found. To understand this law, the concept of the so-called threshold, established in the process of psychophysical research, is especially important. The level of irritation that gives such a barely noticeable sensation is called the lower threshold of sensation.
We can also say this: the ratio of the minimum increment in the strength of the stimulus that first evokes new sensations to the initial value of the stimulus is a constant value.
In this sense, the sensation of color is not a copy of an objective color that exists outside of us, as a naive realist thinks. The sensation of color and light occurs not only due to wave-like vibrations, but also due to other reasons.
Hardness”, “roughness”, “taste”, “smell” also depend on the stimulation of the corresponding sense organs, as well as on known objective reasons. They have a sense of color, but do not have terminal retinal apparatus. Consequently, their sense of color depends on some central apparatus. From this we can conclude that the difference between the functions of the sense organs is determined by both differences in the end apparatuses and the central ones.
If we're in dark room If we bring in a candle, you will get a feeling of light of a certain strength or intensity. Regarding the strength of irritation, we can say that in the second case it is twice as great as in the first. Therefore, triple stimulation does not produce a sensation of triple force, but less. But if the sensation does not grow in proportion to the irritation, then how does it grow? After this, we look at what this additional heaviness was, which produced a barely noticeable sensation of the difference in heaviness.
Psychophysical law of Weber-Fechner. Naive realism.
Then we place a two pound weight on his arm and do the same thing, i.e. We determine what additional heaviness is needed for the subject to notice the difference between the previous sensation and the present one. After this, we do the same with the third, fourth weight, until we determine for a sufficient number of weights the value of that additional weight, which creates a barely noticeable sensation of difference.
That is, the number of light bulbs must increase several times so that it seems to us that the increase in brightness is constant. WEBER-FECHNER LAW is a logarithmic dependence of the strength of sensation E on the physical intensity of the stimulus P: E = k log P + c, where k and c are certain constants determined by a given sensory system. The Weber-Fechner law is usually contrasted with the Stevens law, according to which this dependence is power-law and not logarithmic in nature.