Thresholds of sensations thresholds of sensations- the main characteristics of any analyzer. There are: absolute, differential and operational threshold of sensations.

• The absolute lower threshold of sensation is the minimum value of the stimulus that causes a barely noticeable sensation.
• The absolute upper threshold of sensations is the maximum permissible value of an external stimulus.
• differential sensation threshold - the minimum difference between 2 stimuli or between 2 states of 1 stimulus, causing a barely noticeable difference in sensations.
• The operational threshold of sensations is the smallest difference between signals, at which the accuracy and speed of discrimination reach their maximum.

Editor's addition: What is in growing. literature is called the “absolute lower threshold”, in foreign literature called simply - "absolute threshold" (or "detection threshold"); in this case, it is more convenient to call the “absolute upper threshold” the “terminal threshold” (see Terminal threshold), however, it should be remembered that the latter is a theoretical fiction that no reasonable psychophysicist will measure using psychophysical methods; Neither does any of the existing threshold theories relate to it. (B.M.)

Psychological Dictionary. I. Kondakov

Thresholds of sensations

• Category - qualitative indicators of the sensitivity of the analyzer.
• Kinds:
  - absolute threshold (upper and lower),
  - differential threshold,
  - operational threshold.

encyclopedic Dictionary. Dushkov B.A., Korolev A.V., Smirnov B.A.

Thresholds of sensations- the main characteristics of any analyzer. There are absolute, differential (or distinctive) and operational P. o.

1. The absolute lower threshold is the minimum value of the stimulus that causes a barely noticeable sensation.
2. Absolute upper P. o. - the maximum permissible value of the external stimulus. The difference between the upper and lower absolute thresholds determines the operating range of the analyzer. However, its sensitivity within this range is not the same: it is greatest in the middle part of the range and decreases at its edges. This circumstance must be taken into account when determining the length of the code alphabet (see Coding), choosing the parameters of signals of a particular modality addressed to the operator, and in other cases.
3. Differential P. o. - a minimal difference between two stimuli or between two states of one stimulus, causing a barely noticeable difference in sensations.
4. Operational P. o. - the smallest amount of difference between signals at which the speed and accuracy of the difference reach a maximum.

Measurement of absolute and differential P. o. have now led to the idea of ​​the existence of a more or less wide “threshold zone”, within which the probability of a response varies from 0 to 1. The values ​​of all considered P. o. change in the process of adaptation and are influenced large number factors - from the spatiotemporal conditions of stimulation to the individual characteristics of the functional state of the observer P. o. are inversely proportional to the indicator of the corresponding type of sensitivity.

Thresholds define the boundaries within which sensations can occur, allowing one to identify the minimum and maximum strength of the stimulus under which sensations are noticeable. The threshold value depends on the type of analyzer, the characteristics of the receptors and the individual characteristics of the person.

The minimum amount of stimulation that begins to cause a noticeable sensation is called absolute lower threshold Feel. Upper absolute threshold sensation - such a magnitude of irritation, a further increase in which causes the disappearance of sensation or the appearance of pain. Stimuli whose strength is below or above absolute thresholds cause unconscious sensations. Sensations of this type are called subthreshold or subsensory.

The magnitude of the thresholds varies among different people. Some people are able to distinguish very quiet sounds, while others are unable to hear even loud noises. However, there are some average threshold values. Thus, on average, a person is able to perceive a light source in the dark at a distance of fifty to several hundred meters from himself. A person is able to perceive the sound of a clock ticking at a distance of about six meters from it. The average indicator of olfactory sensations is the ability to perceive the smell of perfume in a multi-room apartment.

Based on the experimental data of Ernst Heinrich Weber (1795-1878), mathematician Gustav Theodor Fechner (1801-1887) derived a relationship called the “Weber-Fechner law”: the magnitude of the sensation is directly proportional to the logarithm of the intensity of the stimulus.

In a series of experiments since 1834, E. Weber determined the existence of patterns between the influence of stimuli and the sensations they caused. The study proved that the new stimulus should differ from the earlier one by an amount proportional to the original stimulus. In one of his experiments, Weber increased the weight that a blindfolded person held. Weber found that the difference in weight that a person begins to notice largely depends on the initial weight of the object. So, a person will not feel the difference if you add a few grams to a kilogram weight. It has been experimentally determined that the average person will notice a difference with a three percent increase in weight. For example, when starting weight In 1 kg, a person will feel an increase of 33 g. With an increase or decrease in weight, the proportion remains the same: with a weight of 2 kg, a person will feel a difference with an increase in weight of 66 g. In a number of studies, it has been revealed that a similar pattern is characteristic of other types of sensations.

Based on these studies by Weber, the German scientist Gustav Fechner formulated the “fundamental psychophysical law” in 1860:

Where p- strength of feeling,

k- constant,

S- initial stimulus

S 0 is the minimum stimulus required for the sensation to appear.

The law, which at first glance seems complex, is quite consistent with everyday observations. For example, if during a concert one plays musical instrument, then the entry of the second into the party will be immediately heard by the audience. Against the background of a large orchestra and dozens of instruments, the addition of another instrument to the part will not be so noticeable.

Differential (difference) threshold- this is the minimum difference between signals that allows a person to perceive the difference between them.

This indicator allows you to determine what part of the initial strength of the stimulus must be changed in order to obtain a noticeable sensation of change in the strength of these stimuli.

The relative threshold for distinguishing light brightness is 1/100, sound intensity is 1/10, and taste effects are 1/5.

Sensations are characterized by the fact that a person is able to adapt to them. Over time or with the help of training, the intensity of the sensations can decrease or increase.

Sensory adaptation-- a change in sensation thresholds that occurs as a result of the adaptation of a sensory organ to the stimuli acting on it.

An example of a negative adaptation effect is the temporary or complete loss of one of the sensations. After spending long time in the dark, a person has difficulty adapting to bright light. Being in an enclosed space with a strong odor can cause a person to lose sensitivity to other odors. Long-term exposure to extreme noise causes hearing loss.

Adaptation also has a positive effect - people with musical ear are able to distinguish sounds of different heights, trained vision allows them to see well both in daylight and at night, a developed sense of smell allows them to perceive even the most subtle odors. It is worth noting that adaptation varies depending on the type of sensation. Visual adaptation requires much more time than auditory adaptation. If we leave a dark, soundproofed room, our hearing will first be restored, and only then our vision will be restored.

Qualitative indicators of analyzer sensitivity.

Absolute threshold (upper and lower),

Differential threshold,

Operational threshold.

Psychological Dictionary. THEM. Kondakov. 2000.

THRESHOLDS OF SENSATIONS

(English) thresholds of sensations) - the main characteristics of any analyzer. There are: absolute, differential and operational P. o. Absolute bottom By. - the minimum amount of stimulus that causes a barely noticeable sensation. Absolute top By. - the maximum permissible value of the external stimulus. Differential By. - a minimal difference between 2 stimuli or between 2 states of 1 stimulus, causing a barely noticeable difference in sensations. Operational By. - the smallest difference between signals at which the accuracy and speed of discrimination reach a maximum. Cm. , , . (K.V. Bardin.)

Editor's addition: What in growing up. literature is called the “absolute lower threshold”, in foreign literature it is called more simply - "absolute threshold"(or "detection threshold"); in this case, it is more convenient to call the “absolute upper threshold” the “terminal threshold” (see. ), however, it should be remembered that the latter is a theoretical fiction that no reasonable psychophysicist will measure psychophysical methods; none of the existing threshold theories. (B.M.)

Large psychological dictionary. - M.: Prime-EVROZNAK. Ed. B.G. Meshcheryakova, acad. V.P. Zinchenko. 2003 .

See what “thresholds of sensations” are in other dictionaries:

Thresholds of Sensation- qualitative indicators of the sensitivity of the analyzer. There are absolute (upper and lower), differential and operational thresholds of sensations... Psychological Dictionary

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.... ...

Their patterns show how perception thresholds change with the simultaneous action of several stimuli. Dictionary practical psychologist. M.: AST, Harvest. S. Yu. Golovin. 1998 ...

Feeling- This article is about reflecting sensory signals. For reflection of emotional processes, see Experience (psychology). Sensation, sensory experience is the simplest mental process, which is a mental reflection... ... Wikipedia

PSYCHOLOGY- 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

- (from Latin sensus feeling, sensation) an adaptive change in sensitivity to the intensity of the stimulus acting on the sense organ; can also manifest itself in a variety of subjective effects (see consistent about ... Great psychological encyclopedia

The magnitude of the stimulus, upon reaching which a sensation appears or other reactions occur (somatic, vegetative, encephalographic). Accordingly, the following are distinguished: 1) the threshold of perception of the lower sensory system; 2) response threshold... ... Great psychological encyclopedia

General designation various types research psychic phenomena through experimental methods. The use of experiment played a crucial role in the transformation of psychological knowledge, in the transformation of psychology from a branch of philosophy into... ... Great psychological encyclopedia

Coding- 1. the process of changing an incoming message from its original form to some other form (for example, the transformation of nerve impulses emanating from a receptor into a sensation, a mental phenomenon); 2. transformation of certain data from one form to another; 3.… … Encyclopedic Dictionary of Psychology and Pedagogy

Psychophysical functions- interaction of physiological and mental processes, which determines the level of sensitivity (thresholds of sensations) of the sensory system... Human psychology: dictionary of terms

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 magnitude of absolute thresholds, both lower and upper, varies depending on different conditions: the age of the person, the functional state of the receptor, the strength and duration of the irritation, 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 necessary 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.

Physiological mechanism The phenomenon of adaptation 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 acting in this moment to other senses. 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”.

Psychophysics

The absolute upper threshold of sensations

The absolute upper threshold of sensations- the maximum permissible value of an external stimulus, the excess of which leads to the appearance of painful sensations indicating a violation of the normal functioning of the body.

The absolute lower threshold of sensations

The absolute lower threshold of sensations- the minimum amount of stimulus that causes a barely recognizable sensation.

Absolute threshold

Absolute threshold- a type of sensory threshold described by G. Fechner. Characterizes the sensitivity of the sensory system. It is expressed by the magnitude of the stimulus, the excess of which gives a response from the body, primarily in the form of awareness of the sensation. To determine the absolute threshold, the methods of constant stimuli, minimal changes, and average error are used.

Differential threshold of sensations

Differential threshold of sensations- the minimum difference between two quantities of a stimulus, causing a barely recognizable difference in sensations.

Differential threshold

Differential threshold- a sensory threshold characterized by a minimal difference between two stimuli that are perceived as different or to which two different reactions can be formed. It is customary to quantitatively express the differential threshold as the ratio of the difference between the value of a constant stimulus, serving as a standard, and a variable one, which, depending on the value, is perceived as equal or different from the standard, to the value of a constant stimulus, since this ratio is constant in a fairly wide range of the stimulus, the usual for the observer.

Bouguer–Weber law

Bouguer–Weber law- one of the basic laws of psychophysics, discovered by the French scientist P. Bouguer, according to which a barely noticeable change in sensation when the intensity of the stimulus changes occurs when the original stimulus increases by a certain constant fraction of it. Thus, examining a person’s ability to recognize a shadow on a screen that was simultaneously illuminated by another light source, Bouguer showed that the minimum increase in illumination of an object & required to cause the sensation of a barely noticeable difference between the shadow and the illuminated screen depends on the illumination level of the screen I, but the ratio &/I is a constant value. The German scientist E. Weber came to the identification of the same pattern somewhat later, but independently of Bouguer. He conducted experiments on distinguishing weights, line lengths and sound pitches, in which he also showed the constancy of the ratio of a barely noticeable change in the stimulus to its original value. This ratio (&/I), which characterizes the value of the differential threshold, depends on the modality of sensation: for vision it is 1/100, for hearing - 1/10, for touch - 1/30. Subsequently, it was shown that the identified law does not have a universal distribution, but is valid only for the middle part of the range of the sensory system, in which differential sensitivity has a maximum value. Beyond this part of the range, the differential threshold increases, especially in the absolute lower and upper threshold ranges.

Pieper's law

Pieper's law- empirical pattern according to which the threshold visual perception decreases proportionally square root stimulus area, provided that this area exceeds 1 angular degree.

Ricco's Law

Ricco's Law- a pattern discovered in 1877, according to which such characteristics of the threshold stimulus as its brightness and angular area are inversely proportional. This law is valid for light stimuli with small angular dimensions. Its mechanism is the nervous summation of stimuli, due to which the eye is adjusted to perceive light of low intensity.

Stevens Law

Stevens Law- a modification of the basic psychophysical law proposed by the American psychologist and psychophysiologist S. Stevens, according to which between a number of sensations and a number of physical stimuli there is not a logarithmic, as in Fechner, but a power dependence: Y = k * S to the power of n, where Y is subjective size, sensation; S - stimulus; n is the exponent of the function; k is a constant depending on the unit of measurement. Moreover, the exponent of the power function is different for different modalities of sensations: for loudness it has a value of 0.3, for an electric shock - 3.5.

Talbot's Law

Talbot's Law- a pattern according to which the visible brightness of a source of intermittent light, when the frequency of light flickering merges, becomes equal to the brightness of continuous light having the same luminous flux values.

Donders' Law

Donders' Law- the law of summation of the mental (cognitive) process, based on the postulate of additivity, or non-overlapping, of its individual stages. Based on the study of reaction time as a process that unfolds in the period between the appearance of a stimulus and the implementation of a response, F. Donders substantiated the “subtraction method”, designed to provide the ability to determine the duration of individual stages. Thus, after measuring the time of a simple reaction, this time must be subtracted from the time of a more complex reaction to obtain the time spent in the detection, stimulus discrimination and response selection stages. But later the possibility of parallel mental reactions was shown, which refuted the postulate of their additivity.

Fechner's law

Fechner's law- a law formulated in 1860 by G. Fechner in “Elements of Psychophysics”, according to which the magnitude of sensation is directly proportional to the logarithm of the intensity of the stimulus. Those. the increase in the strength of irritation in geometric progression corresponds to the increase in sensation in arithmetic progression. This formula for measuring sensations was derived from Weber's studies, which showed the constancy of the relative magnitude of the increment of the stimulus that causes the sensation of a barely noticeable difference. At the same time, his own postulate was introduced that a barely noticeable increase in sensation is a constant value and can be used as a unit of measurement of sensation.

Hick's law

Hick's law- the statement that the reaction time when choosing from a certain number of alternative signals depends on their number. This pattern was first obtained in 1885 by the German psychologist I. Merkel, and in 1952 it received experimental confirmation in the research of V.E. Hick, in which it took the form of a logarithmic function: VR = a*log(n+1), where VR is the average value of the reaction time for all alternative signals; n is the number of equally probable alternative signals; a is the proportionality coefficient. The unit was introduced into the formula to take into account one more alternative, in the form of missing a signal.

Visual camouflage

Visual camouflage- deterioration in recognition of signs of the object of actual perception upon presentation of another stimulus, which can act simultaneously with the main one (simultaneous visual masking), precede it (direct masking) or follow it (reverse masking).

Brightness contrast

Brightness contrast- the ratio of the brightness of visual stimuli located in the same field of perception when solving a discrimination task. The minimum value of brightness contrast for simultaneously perceived objects is 1–2%, for sequentially perceived objects - at least 4%. When solving practical problems related to stimulus recognition, the contrast value should be from 65 to 85%.

Classical theory of sensory continuity

Classical theory of sensory continuity- one of the two main theories of classical psychophysics, characterized by the rejection of the concept of a sensory threshold (J. Jastrow, F. Urban). The main postulate of this theory is the assumption that the sensory series is not discrete, structured by sensory thresholds, but is built according to the principle of continuity, representing a continuous series various degrees clarity. According to this theory, at any moment in time, the sensory system is affected by many different factors, favorable or unfavorable for the process of recognition of any particular stimulus. Under these conditions, the occurrence of sensation depends both on the intensity of the stimulus and on the ratio of side factors present at the moment of action of the stimulus.

Operational sensation threshold

Operational sensation threshold- the smallest difference between two stimulus values, at which the accuracy and speed of recognition have maximum values.

Extinction threshold

Extinction threshold- a concept used in psychophysics to designate the degree of stimulus intensity, with a decrease in which the stimulus no longer causes a sensation (for an absolute threshold), or differences between stimuli are not detected (for a differential threshold).

Threshold of appearance in psychophysics

Threshold of appearance in psychophysics- the magnitude of the stimulus, upon reaching which a sensation begins to arise.

Thresholds of sensations

Thresholds of sensations- qualitative indicators of the sensitivity of the analyzer. There are absolute (upper and lower), differential and operational thresholds of sensations.

Fechner's threshold theory

Fechner's threshold theory- a model created by G. Fechner, designed to explain the principle of operation of sensory systems. It identifies four stages in the process of sensory reflection: irritation ( physical process), excitement (physiological), sensation (mental), judgment (logical). Sensory threshold is understood as the transition from arousal to sensation. When considering quantitative relationships, Fechner, excluding the physiological stage from consideration, tried to identify the relationship directly between irritation and sensation. Thanks to this, the basic psychophysical law was derived.

Threshold theories

Threshold theories- theoretical models designed to explain the principle of operation of sensory systems. The main problem that is solved is the existence and essence of sensory thresholds. Some theories believe that sensory systems operate on a discrete, or threshold, principle, while others believe that they operate on a continuous basis. The main threshold theories include classical theory Fechner, classical theory of sensory continuity, neuroquantum theory, high-threshold theory, psychophysical model of signal detection, two-state theory.

Constant irritant

Constant irritant- one of two stimuli, remaining constant in magnitude and acting as a sample in determining differential thresholds.

Psychometric curve

Psychometric curve- a graph of the dependence of the probability of detecting (or distinguishing) a stimulus on its magnitude, usually obtained in a psychophysical experiment using the method of constant stimuli. The ordinate axis represents the relative frequency of positive responses, the abscissa axis when determining the absolute threshold is the intensity of the stimulus, and when determining the differential threshold, as a rule, the absolute value of the difference between constant and variable stimuli.

Psychophysics

Psychophysics- a section of psychology founded by G. Fechner, devoted to the measurement of sensations depending on the magnitude of physical stimuli. There are two branches of psychophysics: measurement of sensory sensitivity and the study of psychophysical functions.

Sensory threshold

Sensory threshold- the magnitude of the stimulus, upon reaching which a sensation or other reactions begin to occur (somatic, vegetative, electroencephalographic). In accordance with this, a distinction is made between the lower sensitivity threshold of the sensory system and the response threshold of the effector, which indicates the body’s response to the stimulus.

Terminal threshold

Terminal threshold- the stimulus reaches such a magnitude that the sensation usually associated with this stimulus disappears or changes to another modality. For example, when the brightness of the light stimulus is very high, the sensation of light becomes painful.

Broca-Sulzer phenomenon

Broca–Sulzer phenomenon- the effect of violating Bloch's law. It is characterized by the fact that when the duration of the light stimulus increases beyond a certain critical point, the sensation of brightness, passing the maximum, begins to fall: several short light flashes are more noticeable compared to flashes of equal intensity and total time, but longer flashes. The duration of the light stimulus, at which the visible brightness is maximum, depends on the intensity of the stimulus and on its color: the critical point is reached more slowly at blue color, faster - when red.

Sensitivity

Sensitivity- the ability of a living organism to actively respond to stimuli. It is customary to distinguish between absolute and differential sensitivity.

Styles-Crawford effect

Stiles–Crawford effect- the difference in the subjective brightness of light having the same intensity, depending on the angle at which it enters the central fovea of ​​the retina. Light is perceived as brighter if it passes through the center of the pupil, and as less bright when passing through its peripheral parts.