Absolute Upper Threshold of Sensations The absolute upper threshold of sensations is the maximum permissible value of an external stimulus, the excess of which leads to the appearance of painful sensations, indicating a disruption of the normal functioning of the body.
Psychological Dictionary. 2000 .
See what “Absolute Upper Threshold of Sensations” is in other dictionaries:
absolute upper threshold of sensations- Etymology. Comes from Lat. absolutus unlimited. Category. A type of absolute threshold of sensations. Specificity. The maximum permissible value of an external stimulus, the excess of which leads to the appearance of painful sensations that... ...
absolute upper threshold of perception Great psychological encyclopedia
upper absolute threshold of perception- (absolute upper threshold of perception, absolute upper threshold of sensations) the maximum permissible value of an external stimulus, exceeding which leads to the appearance of painful sensations indicating a disruption of normal activity... ... Great psychological encyclopedia
terminal threshold- the stimulus reaches such a magnitude that the sensation usually associated with such a stimulus disappears or changes to another modality. For example, with very high light brightness, the sensation becomes painful. Dictionary of practical... ... Great psychological encyclopedia
sensation thresholds- Category. Qualitative indicators of analyzer sensitivity. Types: absolute threshold (upper and lower), differential threshold, operational threshold. Psychological Dictionary. THEM. Kondakov. 2000... Great psychological encyclopedia
THRESHOLDS OF SENSATIONS- the main characteristics of any analyzer. There are absolute, differential (or distinctive) and operational P. o. The absolute lower threshold is the minimum amount of stimulus that causes a barely noticeable sensation. Absolute upper P. o.... ...
The science of mental reality, how an individual perceives, perceives, feels, thinks and acts. For a deeper understanding of the human psyche, psychologists study the mental regulation of animal behavior and the functioning of such... ... Collier's Encyclopedia
HEART- HEART. Contents: I. Comparative anatomy........... 162 II. Anatomy and histology........... 167 III. Comparative Physiology......... 183 IV. Physiology................... 188 V. Pathophysiology................ 207 VI. Physiology, pat.... ... Great Medical Encyclopedia
This article is about the reflection of sensory signals. For reflection of emotional processes, see Experience (psychology). Sensation, sensory experience is the simplest mental process, which is a mental reflection... ... Wikipedia
HEARING ANALYZER- a set of somatic, receptor and nervous structures, the activity of which ensures the perception of sound vibrations. S. a. consists of a receptor (ear), an auditory nerve and a complex system of nerve connections and brain centers. S. a. person... ... Encyclopedic Dictionary of Psychology and Pedagogy
So far we have been talking about the qualitative difference in types of sensations. However, quantitative research, in other words, their measurement, is no less important. The human senses are amazingly delicate devices. Thus, the human eye can distinguish a light signal of 1/1000th of a candle at a distance of a kilometer. The energy of this irritation is so small that it would take 60,000 years to heat 1 cm3 of water by 1° with its help.
However, not every irritation causes a sensation. For a sensation to arise, the stimulus must reach a certain magnitude. The minimum magnitude of the stimulus at which sensation first occurs is called absolute threshold of sensation. Stimuli that do not reach it lie below the threshold of sensation. Thus, we do not feel individual specks of dust and small particles falling on our skin. Light stimuli below a certain brightness limit do not cause visual sensations.
The absolute threshold value characterizes absolute sensitivity sense organs. The weaker the stimuli that cause sensations (i.e., the lower the value of the absolute threshold), the higher the ability of the sensory organs to respond to these influences. Thus, absolute sensitivity is numerically equal to a value inversely proportional to the absolute threshold of sensations. If absolute sensitivity is denoted by the letter E, and the value of the absolute threshold by P, then the relationship between absolute sensitivity and absolute threshold can be expressed by the formula E=1/P.
Different analyzers have different sensitivities. The threshold of one human olfactory cell for the corresponding odorous substances does not exceed 8 molecules. It takes at least 25,000 times more molecules to produce the sensation of taste than to produce the sensation of smell. A person has a very high sensitivity of visual and auditory analyzers.
The absolute sensitivity of the analyzer is limited not only by the lower, but also by the upper threshold of sensation. The upper absolute threshold of sensitivity is the maximum strength of the stimulus at which a sensation adequate to the current stimulus still occurs. A further increase in the strength of stimuli acting on our receptors causes a painful sensation (extra-loud sound, blinding brightness). The value of absolute thresholds, both lower and upper, varies depending on various conditions: the nature of the person’s activity and age, the functional state of the receptor, the strength and duration of the stimulus, etc.
It is necessary to distinguish from absolute sensitivity relative, or difference, sensitivity, i.e. sensitivity to changes in stimulus. In the first half of the 19th century. The German scientist M. Weber, studying the feeling of heaviness, came to the conclusion that when comparing objects and observing the differences between them, we perceive not the differences between the objects, but the ratio of the differences to the size of the objects being compared. Likewise, we notice changes in the illumination of the room depending on the initial illumination level. If the initial illumination is 100 lux (lux), then the increase in illumination that we first notice should be at least 1 lux. If the illumination is 1000 lux, then the increase should be at least 10 lux. The same applies to auditory, motor, and other sensations.
The minimum difference between two stimuli that causes a barely noticeable difference in sensations is called the discrimination threshold, or difference threshold. As already mentioned, difference sensitivity is a relative value, not an absolute one. This means that the ratio of the additional stimulus to the main one must be a constant value. Moreover, the greater the value of the initial stimulus, the greater the increase should be to it.
The discrimination threshold is characterized by a relative value that is constant for a given analyzer. For a visual analyzer this ratio is approximately 1/1000, for an auditory analyzer - 1/10, for a tactile analyzer - 1/30.
Based on Weber's experimental data, another German scientist, G. Fechner, expressed the dependence of the intensity of sensations on the strength of the stimulus with the formula: Y = K log j + C, (where S is the intensity of the sensation; j is the strength of the stimulus; K and C are constants). According to this position, which is called the basic psychophysical law, the intensity of sensation is proportional to the logarithm of the strength of the stimulus. In other words, as the strength of the stimulus increases in geometric progression, the intensity of the sensation increases in arithmetic progression (Weber-Fechner law).
Difference sensitivity, or sensitivity to discrimination, is also inversely related to the value of the discrimination threshold: the greater the discrimination threshold, the lower the difference sensitivity.
The phenomenon of adaptation
It would be wrong to think that both the absolute and relative sensitivity of our sense organs remains unchanged and that its thresholds are expressed in constant numbers. Thus, it is known that in the dark our vision becomes sharper, and in strong light its sensitivity decreases. This can be observed when you move from a dark room to light or from a brightly lit room to darkness. As studies have shown, this change is very large and the sensitivity of the eye when moving from bright light to darkness increases 200,000 times.
The described changes in sensitivity, depending on environmental conditions and called adaptation sense organs to environmental conditions exist both in the auditory sphere and in the sphere of smell, touch, and taste. So, in order for vision in a dark room to acquire the required sensitivity, about 30 minutes should pass. Only after this does a person acquire the ability to navigate well in the dark. Adaptation of the auditory organs occurs much faster. Human hearing adapts to the surrounding background within 15 s. A change in sensitivity in the sense of touch also occurs quickly (a slight touch to the skin ceases to be perceived after just a few seconds).
The phenomena of thermal adaptation (getting used to temperature changes) are well known. However, these phenomena are clearly expressed only in the average range, and adaptation to extreme cold or extreme heat, as well as to painful stimuli, almost does not take place. The phenomena of adaptation to odors are also known.
The textbook edited by A.V. Petrovsky identifies three types of adaptation phenomena.- Adaptation is the complete disappearance of sensation during prolonged exposure to a stimulus.
- Adaptation as a dulling of sensation under the influence of a strong stimulus.
(These two types of adaptation are combined with the term “negative adaptation”, since as a result it reduces the sensitivity of the analyzers.) - Adaptation is also called an increase in sensitivity under the influence of a weak stimulus. This type of adaptation is defined as positive adaptation. In the visual analyzer, dark adaptation of the eye, when its sensitivity increases under the influence of darkness, is a positive adaptation. A similar form of auditory adaptation is adaptation to silence.
Interaction of sensations
The intensity of sensations depends not only on the strength of the stimulus and the level of receptor adaptation, but also on the stimuli currently affecting other sense organs. A change in the sensitivity of the analyzer under the influence of irritation of other sense organs is called interaction of sensations.
Research conducted by S.V. Kravkov showed that not a single sense organ can work without affecting the functioning of other organs. Thus, it turned out that sound stimulation (for example, a whistle) can sharpen the functioning of the visual sense, increasing its sensitivity to light stimuli. Some odors also influence in the same way, increasing or decreasing light and auditory sensitivity. The general pattern is that weak stimuli increase, and strong ones decrease, the sensitivity of analyzers during their interaction.
Increased sensitivity as a result of the interaction of analyzers and exercise is called sensitization. A. R. Luria distinguishes two aspects of increased sensitivity according to the type of sensitization: the first is of a long-term, permanent nature and depends mainly on sustainable changes occurring in the body; the second is temporary in nature and depends on emergency effects on the subject’s condition - physiological and psychological. The age of the subject is clearly associated with changes in sensitivity. Studies have shown that the sensitivity of the sensory organs increases with age, reaching a maximum by 20-30 years in order to gradually decrease thereafter.
In another experiment, facts were obtained, changes in the electrical sensitivity of the eyes and tongue in response to the presentation of the words “sour as lemon” to the subjects. These changes were similar to those observed when the tongue was actually irritated by lemon juice. Knowing the patterns and changes in the sensitivity of the sensory organs, it is possible, by selecting side stimuli, to sensitize one or another receptor.
The interaction of sensations is also manifested in a phenomenon called synesthesia- the emergence, under the influence of irritation of one analyzer, of a sensation characteristic of other analyzers. In psychology, the facts of “colored hearing” are well known, which occurs in many people, and especially in many musicians (for example, Scriabin). Thus, it is widely known that we evaluate high sounds as “light”, and low sounds as “dark”.
It is characteristic that the phenomenon of synesthesia is not distributed equally in all people. One of these subjects with exceptional severity of synesthesia, the famous mnemonist Shch., was studied in detail by A. R. Luria. This person perceived all voices as colored and often said that the voice of the person addressing him, for example, was “yellow and crumbly.” The tones he heard gave him visual sensations of various shades (from bright yellow to purple). The perceived colors were felt by him as “ringing” or “dull”, as “salty” or “crispy”. Similar phenomena in more erased forms occur quite often in the form of an immediate tendency to “color” numbers, days of the week, names of months in different colors.
Improving sensations during exercise
We have already mentioned that sensitization of the senses is possible through exercise. Such sensitization usually leads to two ways: firstly, the need to compensate for sensory defects (blindness, deafness); secondly, the specific requirements of some professions. Thus, the loss of vision or hearing is to a certain extent compensated by the development of other types of sensitivity. There are cases where people deprived of vision engaged in sculpture, which indicates a highly developed sense of touch. The development of vibration sensations in the deaf also belongs to this group of phenomena. Some people who are deaf develop vibrational Sensitivity so strongly that they can even hear music. To do this, they place their hand on the instrument or turn their back to the orchestra. Deaf-blind O. Skorokhodova, holding her hand at the throat of the speaking interlocutor, could thus recognize him by his voice and understand what he was talking about. Many deaf-blind and blind people have well-developed olfactory sensitivity. They can recognize people they know by smell.
The phenomena of sensitization of the sense organs are observed in people who have been engaged in certain special professions for a long time. Thus, it has been established that dyers can distinguish up to 50-60 shades of black; steelworkers distinguish the subtlest shades of a red-hot flow of metal, indicating the presence of foreign impurities. It is known what subtlety can be achieved in the determination of taste nuances by tasters, or the ability of musicians to capture differences in tones that are completely imperceptible to the average listener.
All these facts show that in the conditions of the development of complex forms of conscious activity, the acuity of absolute and difference sensitivity can change significantly and that the inclusion of one or another feature in a person’s conscious activity can significantly change the acuity of this sensitivity.
Sensitivity thresholds. Types of thresholds. Psychometric curve. Methods for measuring thresholds. Statistical nature of sensory phenomena. Direct and indirect measurements and scaling of sensations. Basic psychophysiological law.
Response plan
Sensitivity thresholds.
Types of thresholds
Psychometric curve.
Methods for measuring thresholds.
Direct and indirect measurements and scaling of sensations.
Answer:
Sensitivity thresholds.
The operation of each analyzer has its own specific patterns. Along with this, all types of sensations are subordinated to general psychophysiological patterns.
PSYCHOPHYSICS a branch of psychology that studies the quantitative relationship between the strength of a stimulus and the magnitude of the resulting sensation. Founded by G. Fechner in the 2nd half. 19th century Covers two groups of problems: measurement of the threshold of sensations, i.e. the limit of sensitivity of the human sensory system (Weber-Fechner law, etc.), construction of psychophysical scales (S. Stevens, etc.).
For any sensation to occur, the stimulus must have a certain amount of intensity. The minimum amount of stimulation that causes a barely noticeable sensation is called the absolute lower threshold of sensation. The ability to sense these weakest stimuli is called absolute sensitivity. It is always expressed in absolute numbers. For example, to create a sensation of pressure, an effect of 2 mg per 1 sq. mm of skin surface is sufficient.
Along with absolute sensitivity, one should distinguish between relative sensitivity - sensitivity to distinguishing the intensity of one effect from another. Relative sensitivity is characterized by the discrimination threshold.
Discrimination threshold, or differential threshold, is a barely perceptible minimum difference in the strength of two stimuli of the same type.
The discrimination threshold is the minimum difference between two different stimuli that already causes early sensations in 75% of cases.
Types of thresholds
There are 2 types of thresholds: 1. Absolute (minimal stimulus that causes sensation). The lower absolute threshold is characterized by the criterion “I see - I don’t see” - this is an irritant that already causes sensations in 75% of cases, the upper absolute threshold is an irritant that still causes sensations in 75% of cases. These are painful sensations. 2. Differential - the minimum difference in stimuli that we feel (when comparing 2 stimuli).
Let us assume that we present the individual results of measuring the absolute auditory threshold, noting the probability values of the subject’s responses that he hears the sound on the ordinate axis, and the corresponding values of sound intensity on the abscissa axis. If there were an absolute threshold in the literal sense, then we would get the graph presented in Fig. 1. There would be a range of sound intensities to which the subject would never respond, and at a certain threshold intensity there would be a sharp transition to constant responses, when all presented stimuli are perceived. However, in real experiments this does not happen. As the intensity of the sound increases, the probability of the subject's response that he hears the sound gradually increases (Fig. 2). In this case, the absolute threshold is defined as the stimulation level at which detection occurs 50% of the time. If we assume that the signals are sent against a background of noise, then it follows that 0 on the x-axis indicates the level of background noise.
Lower threshold of sensations- minimum stimulus value, causing a barely noticeable sensation (designated J 0). If the intensity of the stimulus is less than J0, then it is not felt by the body.
Upper threshold of sensations- maximum value, which the analyzer can adequately perceive (J m m).
Sensitivity range the range between J 0 and J mm is called.
Differential, difference threshold - the smallest magnitude (*J) of differences between stimuli when they are still perceived as different.
The value of *J is proportional to the intensity of the signal J, the size of the step, that is, the threshold difference, depends on the size of the original stimulus. The units on the stimulus intensity scale will not be equal, but will increase as the stimulus increases. obeying Weber's law:*J/J = K. For the visual analyzer, the coefficient K = 0.01, for the auditory analyzer K = 0.1.
Operational threshold for signal intelligibility - that magnitude of difference between signals at which the speed and accuracy of discrimination reaches a maximum. The operational threshold is 10 - 15 times higher than the differential, or difference, threshold.
Intensity of sensation determined by law Weber-Fechner: the intensity of sensation (E) is directly proportional to the logarithm of the stimulus strength (J): E = k log J + c
Time threshold of sensations - This is the minimum duration of action of the stimulus, which is necessary for the occurrence of sensations.
Spatial threshold - the minimum size of the stimulus, barely perceptible by the organ of perception.
Latent period of reaction- this is the period of time from the moment the signal is given until the moment when the sensation occurs.
Psychometric curve.
Methods for measuring thresholds.
Installation method. The subject himself changes the intensity of the stimulus, either increasing or decreasing it, until he receives a barely noticeable sensation (when determining the absolute threshold) or a sensation equal in strength to the given one (when determining the difference threshold). At the same time, sensitivity increases and thresholds decrease.
Boundary (minimum change) method. The subject is presented with a sequential series of stimuli, in minimal and equal steps, of increasing and decreasing intensity. When determining the absolute threshold, the following is determined: 1. The magnitude of the stimulus first felt by the subject (with increasing intensity); 2. The magnitude of the stimulus that is not felt by the subject for the first time (with decreasing intensity). The arithmetic mean of these 2 values is the absolute threshold. When determining the differential threshold, 4 values are found. If we take the descending series as an example, we first find the value of the stimulus at which it ceases to appear large compared to the given one, and then bring it to the level at which it first begins to appear smaller than the given one. The same is determined with the ascending series.
Method of constant stimuli (constants). This method is based on statistical processing of a large number of test responses. The subject is presented with stimuli in a random order. When determining the absolute threshold, the subject must say whether he feels something or not. When determining the difference threshold, the stimuli alternate with the normal one. The threshold value is determined by counting the “correct” and “incorrect” responses of the subject.
Statistical nature of sensory phenomena.
Statistical decision theory (signal detection theory) is based on the idea that sensory systems always operate in a background of noise and that there are different thresholds for different levels of noise. Thus, we have 2 distribution curves: 1. When there is only noise, 2. When there is a signal against a background of noise. In signal detection experiments, the subject had to indicate whether he heard the signal. With such tests, 4 outcomes are possible:
There is a signal and the subject says yes.
There is no signal and the subject says yes
There is a signal and the subject says no
There is no signal and the subject says no
P 
When answering, the subject uses some criterion. For example, in the figure, criterion A1 is “decisive”, i.e. the subject does not miss signals, but also has a large number of false alarms. Criterion A3 is cautious: the subject does not give false alarms, but also misses almost half of the signals. It follows from this that criterion A2 is optimal; it allows you to give the largest number of correct answers with a minimum of errors. But this is true only on the assumption that the payment for correct answers and the penalty for incorrect ones are equivalent. However, if we assume that the subject is paid for correct answers but not penalized for incorrect ones, then the decision criterion will shift to the right (the subject will indicate that he hears the tone every time, and although this leads to a large number of false alarms, He won't pay for this.) Consider an experiment called payment matrix. According to this matrix, the subject receives 10 cents for each detected signal and 4 for each correct answer about the absence of a signal. At the same time, he himself must pay 2 cents for each error of any type. In this case, the most advantageous criterion will be shifted from A1 to A2. Thus, the subject places his criterion at the point where the expected payment is maximum.
The criterion is the point on the sensation scale that separates the subjects' yes and no answers to the question about the presence of a sensation.
Let us consider an experiment in which all trials were empty, and rewards and penalties were given in such a way that the dependence of the probability of a hit on the probability of false alarms is depicted by diagonal A. Then, if a signal is actually presented in the trials, the diagonal will shift higher (A1). This suggests that the shape of the curve reflects a person's sensitivity to the signal and can be used as a measure of it. This diagonal is called the receiver operating characteristic (ROC).
Direct and indirect measurements and scaling of sensations.
There are 3 ways to scale sensations:
Fractionation method. The subject is presented with a standard of a certain intensity, which he must compare with a number of other stimuli and choose the one that is equal to half the standard.
Attitude assessment. The subject is presented with 2 stimuli of different intensity and asked to evaluate the relationship between them. For example, is a weak sound 0.2 in volume; 0.5; or 0.7 strong sound.
The direct method is called "magnitude estimation". The subject is presented with a tone of moderate volume, for example, equal to 80 decibels, and is told that this tone should be rated 10 units. The subject must numerically estimate the relative loudness of all subsequent tones, assigning a numerical value less than 10 to the weaker ones, and a greater value to the stronger ones.
Basic psychophysiological law.
Basic psychophysical law. In 1834, Weber, repeating the experiments of Bouguer (1760), found that the minimum perceived difference in weight is a constant value of 1.30. Thus, Weber derived the formula
R = constant (where R is the minimum perceived weight gain and R is the weight of the original load). Having transformed this formula, Fechner derived the following - the magnitude of the sensation is proportional to the logarithm of the magnitude of irritation: S = k logR. The Bouguer-Weber law applies only to the average zone of stimulus intensity. In other words, relative thresholds lose significance for very weak and very strong stimuli. This was established by Fechner.
Fechner also established that if the intensity of the stimulus is increased in geometric progression, then the sensation will increase only in arithmetic progression. (Fechner's Law). At the same time, he admitted that the minimum increase in sensation is always the same. However, Stevens refuted this law. He argued that the sensations of all modalities do not increase equally with increasing intensity of stimulation. For example, if you double the illumination of a spot on a dark background, then its brightness will not increase very much (according to a typical observer - by 25%), but if you double the current passed through the finger, the sensation increases 10 times. Based on this, Stevens concluded that the psychological quantity S relates to the physical quantity R as follows: S= kR n. The exponent n takes the value of 0.33 for brightness and 3.5 for impact. The value of k depends on the units chosen
So far we have been talking about the qualitative difference in types of sensations. However, no less important is the quantitative analysis of the intensity of sensations.
Not every irritation causes a sensation. For a sensation to arise, the stimulus must reach a certain magnitude. The minimum magnitude of the stimulus at which sensation first occurs is called lower absolute threshold of sensation. Stimuli that do not reach it lie below the threshold of sensation. Thus, we do not feel individual specks of dust and small particles falling on our skin. Light stimuli below a certain brightness limit do not cause visual sensations.
The value of the lower absolute threshold characterizes absolute sensitivity sense organs. The weaker the stimuli that cause sensations (i.e., the lower the absolute threshold), the higher the absolute sensitivity of the senses. Different analyzers have different sensitivities. The threshold of one human olfactory cell for some odorous substances does not exceed 8 molecules. It takes at least 25,000 times more molecules to produce the sensation of taste than to produce the sensation of smell. A person has a very high sensitivity of visual and auditory analyzers.
The absolute sensitivity of the analyzer is limited not only by the lower, but also by the upper threshold of sensation. The upper absolute threshold of sensation is called the maximum strength of the stimulus, at which a sensation adequate to the current stimulus still arises. A further increase in the strength of stimuli acting on our receptors causes a painful sensation (extra-loud sound, blinding brightness). The value of absolute thresholds, both lower and upper, varies depending on various conditions: the age of the person, the functional state of the receptor, the strength and duration of the stimulus, etc.
It is necessary to distinguish from absolute sensitivity relative, or difference, sensitivity, i.e. sensitivity to changes in stimulus, discovered by the German scientist M. Weber. Difference sensitivity is a relative value, not an absolute one. This means that the greater the magnitude of the initial stimulus, the greater must be the addition to it in order for a change in sensation to occur. For example, we notice changes in the illumination of a room depending on the initial illumination level. If the initial illumination is 100 lux (lux), then the increase in illumination that we first notice should be at least 1 lux. If the illumination is 1000 lux, then the increase should be at least 10 lux. The same applies to auditory, motor, and other sensations.
The minimum difference between two stimuli that causes a barely noticeable difference in sensation is called threshold of discrimination or difference threshold. The discrimination threshold is characterized by a relative value that is constant for a given analyzer. For a visual analyzer, this ratio is approximately 1/100 of the intensity of the initial stimulus, for an auditory one - 1/10, for a tactile one - 1/30.
The phenomenon of adaptation
Both the absolute and relative sensitivity of our sense organs can vary within very large limits. For example, in the dark our vision becomes sharper, and in strong light its sensitivity decreases. This can be observed when you move from a dark room into the light - a person’s eyes begin to experience pain, it takes some time for the eyes to adapt to the bright lighting. In the opposite case, when a person moves from a brightly lit room to a dark room, he also does not see anything at first (he temporarily “goes blind”) and it takes 20-30 minutes for him to be able to navigate well enough in the dark. Studies have shown that the sensitivity of the eye increases 200,000 times when moving from bright light to darkness.
The described changes in sensitivity are called adaptation sense organs to environmental conditions. Adaptation is a change in the absolute and relative sensitivity of the senses under the influence of external influences. Adaptation phenomena are characteristic of both the auditory sphere and the sense of smell, touch, and taste. The change in sensitivity that occurs according to the type of adaptation does not occur immediately; it has its own temporary characteristics. These temporal characteristics are different for different sense organs. So, in order for vision in a dark room to acquire the required sensitivity, about 30 minutes should pass. Adaptation of the auditory organs occurs much faster. Human hearing adapts to the surrounding background within 15 s. A change in sensitivity in the sense of touch also occurs quickly (a slight touch to the skin ceases to be perceived after just a few seconds). The phenomena of thermal adaptation (getting used to temperature changes) are well known. However, these phenomena are clearly expressed only in the average range, and adaptation to extreme cold or extreme heat, as well as to painful stimuli, almost does not take place. The phenomena of adaptation to odors are also known.
There are three types of adaptation phenomena:
1. Adaptation as the complete disappearance of sensation during prolonged exposure to the stimulus.
2. Adaptation as a dulling of sensation under the influence of a strong stimulus. (These two types of adaptation are classified as negative adaptation, since as a result it reduces the sensitivity of the analyzers.)
3. Adaptation is also called an increase in sensitivity under the influence of a weak stimulus. This type of adaptation is defined as positive adaptation. In the visual analyzer, dark adaptation of the eye, when its sensitivity increases under the influence of darkness, is a positive adaptation. A similar form of auditory adaptation is adaptation to silence.
The physiological mechanism of the adaptation phenomenon consists of changes in the functioning of receptors. For example, it is known that under the influence of light, visual purple, located in the rods of the retina, decomposes. In the dark, on the contrary, visual purple is restored, which leads to increased sensitivity.
The phenomenon of adaptation is also explained by the processes occurring in the central sections of the analyzers. With prolonged irritation, the cerebral cortex responds with internal protective inhibition, reducing sensitivity
Interaction of sensations
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. For example, sound stimulation (whistle) can sharpen the functioning of the visual sense, increasing its sensitivity to light stimuli. Some odors also influence in the same way, increasing or decreasing light and auditory sensitivity. A change in the sensitivity of the analyzer under the influence of irritation of other sense organs is called interaction of sensations.
All our analyzing systems are capable of influencing each other. In this case, the interaction of sensations, like adaptation, manifests itself in two opposite processes - an increase and decrease in sensitivity. The general pattern is that weak stimuli increase, and strong ones decrease, the sensitivity of analyzers during their interaction.
Increased sensitivity as a result of interaction between analyzers is called sensitization. A.R. Luria distinguishes two types of sensitization: the first is long-term, permanent and depends primarily on sustainable changes occurring in the body; the second is temporary in nature and depends on emergency effects on the subject’s condition - physiological and psychological. The age of the subject is clearly associated with changes in sensitivity. Studies have shown that the sensitivity of the sensory organs increases with age, reaching a maximum by 20-30 years in order to gradually decrease thereafter.
The interaction of sensations is also manifested in a phenomenon called synesthesia- the occurrence, under the influence of irritation of one analyzer, of a sensation characteristic of other analyzers. In psychology, the facts of “colored hearing” are well known, which occurs in many people, and especially in many musicians (for example, Scriabin). Thus, it is widely known that we evaluate high sounds as “light” and low sounds as “dark”.
100 RUR bonus for first order
Select the type of work Diploma work Course work Abstract Master's thesis Practice report Article Report Review Test work Monograph Problem solving Business plan Answers to questions Creative work Essay Drawing Essays Translation Presentations Typing Other Increasing the uniqueness of the text Master's thesis Laboratory work On-line help
Find out the price
In order for a sensation to arise as a result of the action of a stimulus on the sense organs, it is necessary that the stimulus causing it reaches a certain value or threshold of sensitivity. There are two types of sensitivity thresholds: absolute And differential (or discrimination sensitivity threshold).
The minimum strength of the stimulus at which a barely noticeable sensation occurs is called lower absolute threshold of sensation.
Opposes the lower threshold of sensations upper threshold . The greatest strength of the stimulus, at which a sensation of this type still occurs, is called the upper absolute threshold of sensation . The upper threshold limits sensitivity on the greater side, and up to a certain limit, above which pain occurs or there is no change in the intensity of sensations.
Taking into account the above, we note that the larger the stimulus value, the higher the probability of its detection. According to psychologists (A.A. Krylov et al., etc.), in the near-threshold region this probability obeys the normal distribution law. Figure 12 shows a graph of the dependence of the probability of detection on the magnitude of the stimulus in the near-threshold region.
Rice. 12. Detection Probability Dependence
on the magnitude of the stimulus in the near-threshold
The abscissa axis shows the values of the stimuli used, and the axis ordinates – corresponding probabilities
To estimate the value of the absolute threshold, it is necessary to set the required probability of positive responses from subjects. Most often, 50 and 75% thresholds are used, i.e. stimulus values at which subjects detect it in 50% or 75% of cases, respectively.
Thresholds of sensations are individual for each person and change throughout his life.
Sensations, in addition to the magnitude of the absolute threshold, are also characterized by a threshold for discrimination, which is called the differential threshold.
Differential threshold - the smallest amount of differences between stimuli, when the difference between them is still discernible.
For example, if you put a load weighing 100 grams on your hand, and then add another gram to this weight, then a person will not be able to feel this increase. In order to feel an increase in weight, you need to add three to five grams. The German psychophysicist E. G. Weber, studying the sensation of heaviness, came to the conclusion that when comparing objects and observing the differences between them, we perceive not the differences between the objects, but the relationship of the differences to the size of the compared objects. So, if you need to add three grams to a load of 100 grams in order to feel the difference, then you need to add six grams to a load of 200 grams in order to feel the difference.
The differential threshold of sensations for different sense organs is different, but for the same analyzer it is a constant value. For example, the relative threshold for distinguishing light brightness is 1/100, sound volume is 1/10, and taste effects are 1/5.
These patterns are psychophysiological dependencies. They were opened in the first half of the 19th century. French physicist P. Bouguer, then confirmed and refined by the German psychophysicist E. G. Weber and received the name Bouguer's law –Weber .
Bouguer–Weber law states: the differential threshold of sensation is different for different sense organs, but for the same analyzer it is a constant value.
The constant quantity itself is called Weber's constants.
The values of Weber's constant for various senses are given in Table 2.
The lower and upper absolute thresholds of sensations (absolute sensitivity) and differential thresholds of discrimination (relative sensitivity) characterize limits of human sensitivity .
table 2
The meaning of Weber's constant for various senses
|
Feel |
Constant value |
|
Changing pitch |
|
|
Changing the brightness of the light |
|
|
Change in pressure on the surface of the skin |
|
|
Changing the weight of an item |
|
|
Changing the sound volume |
Along with this, they differ operational thresholds sensations - the magnitude of the signal at which the accuracy and speed of its discrimination reaches a maximum. This value is an order of magnitude larger than the discrimination threshold and is used in various practical calculations.
Basic psychophysical law
Based on the principle of the equality of minimal differences between sensations and Weber’s relation, the German scientist G. T. Fechner derived a psychophysical pattern, which was called basic psychophysical law. Based on this law, the strength of sensation is proportional to the logarithm of the magnitude of the active stimulus:
R = C (log S – log So),
Where:R – intensity of sensation; WITH– constant associated with Weber’s relation;S – intensity of the current stimulus;So – absolute threshold.
About a hundred years after this, the American scientist S. Stevens put forward the idea of the possibility of a person directly quantifying his feelings. He clarified the basic psychophysical law and established that the relationship between sensation and physical stimulus has no logarithmic , A sedate character , and derived the following formula:
R = C (S – So) 2.
Later, other clarifications of the basic psychophysical law were proposed, in particular by the domestic psychologist Yu. M. Zabrodin, who introduced an additional constant that takes into account the observation conditions and the tasks facing the subject.
Concept and main characteristics
sensory range
The range of our sensations forms sensory range . Although absolute and differential thresholds are clearly different characteristics, they share a common principle or assumption.
This assumption is as follows. It is assumed that the sensory array is discrete (i.e., discontinuous). This means: up to certain limits the sensation is there, and then it disappears.
The idea that our sensory system is organized according to a threshold, intermittent principle is called the concept discreteness sensory series, and its author is G. T. Fechner. Moreover, this point of view applies to both absolute and differentiated thresholds.
Psychophysicists, inspired by the idea of “absolute pitch,” or the vanishing point of sensation, conducted hundreds of experiments to determine the thresholds of sensitivity. They were surprised to find that the threshold seemed to be floating. In other words, even for very weak stimuli there is some probability of their detection, and for relatively strong ones there is a possibility of their non-detection.
The dependence of the probability of detecting (distinguishing) stimuli on their intensity is called psychometric function.
If the sensory system operates on a discrete basis, the psychometric function will look like this. Up to a certain level of stimulus intensity, the probability of detection is zero, then it is one (Fig. 13).
Subsequently, based on the results of psychophysical research, I. Muller proposed the idea of continuity of the sensory series. Its essence is that there is no threshold as such: any stimulus, in principle, can cause sensations. The actual psychometric function in this case is shown in Fig. 14.
Continuity theory explains why some weak signals are not detected. It consists in the fact that the ability to detect a stimulus is influenced not only by its physical intensity, but also by the disposition of the sensory system to sensation. This location depends on many random, poorly controlled factors: a person’s fatigue, the degree of his attentiveness, motivation, experience, etc.
In this case, some factors have a favorable effect on the observer’s ability to detect a signal (for example, extensive experience), while others have an unfavorable effect (for example, fatigue). Accordingly, unfavorable factors reduce detection ability, and favorable factors increase it. Hence there is no reason to talk about the existence of some special point on the axis of sensations where they are interrupted and disappear. The sensory range is continuous, and if we could create ideal observation conditions, the sensory system would perceive as small a signal as desired.
The psychometric curve can be obtained for various senses and all types of sensations, and each type of sensation has its own thresholds.
More than a hundred years have passed since the scientific discussion that took place between G. T. Fechner and I. Müller, but the problem of discreteness - continuity of the sensory series is still in the field of view of psychologists. The initial psychophysical ideas inspired many researchers and allowed them to create a lot of psychophysical concepts that are interesting both for theory and useful in practice.
Modern concepts of sensitivity thresholds are characterized by two features. The first of these is that discrimination and detection are treated as a process, an integral part of which is uncertainty and randomness. The second is that non-sensory mechanisms are being studied more and more deeply, in a broad sense - decision-making mechanisms that “come to the aid” of the sensory system and allow solving sensory problems in various ways.
Adaptation
The sensitivity of the analyzer is unstable and varies depending on different conditions. For example, if we are in a room with some odors, after a while we stop noticing these odors, because the sensitivity of the analyzer gradually decreases. A change in the sensitivity of the analyzer as a result of its adaptation to the strength and duration of the current stimulus is called adaptation.
In the visual analyzer, adaptations are distinguished dark And light For example, when entering a poorly lit room, we initially do not distinguish objects, but gradually the sensitivity of the analyzer increases. The example given concerns dark adaptation. If dark adaptation is associated with increased sensitivity, then light adaptation is associated with a decrease in light sensitivity.
Different analyzers have different speeds and adaptation ranges. Olfactory and tactile analyzers adapt more quickly.
The following main types of adaptation are distinguished:
o dulling of sensitivity under the influence of a strong stimulus;
o dulling of sensitivity under the influence of a monotonous stimulus;
o exacerbation of sensitivity under the influence of a weak stimulus.