Gustatory sensitivity. Gustatory sensory system. See what "gustatory sensitivity" is in other dictionaries
In the course of evolution, taste was formed as a mechanism for choosing or rejecting food. Food choices are based in part on congenital mechanisms, but largely depends on the connections developed in ontogeny.
Taste, like smell, is based on chemoreception and provides information about the nature and concentration of substances entering the mouth. As a result, reactions are triggered that alter the work of the digestive organs or lead to the removal of harmful substances that have entered the mouth.
Taste buds are concentrated in the taste buds located on the tongue, back of the pharynx, soft palate, tonsil and epiglottis. Most of them are on the tip of the tongue. Each of the approximately 10,000 human taste buds consists of several receptor and supporting cells. The gustatory bud is connected to the oral cavity through the gustatory pore. The taste receptor cell has a length of 10–20 µm and a width of 3–4 µm and is equipped at the end facing the pore lumen with 30–40 finest microvilli. They are believed to play an important role in reception chemical substances adsorbed in the kidney canal. Many steps in the conversion of the chemical energy of flavoring substances into the energy of nervous excitation of taste buds are still unknown.
Electrical potentials taste system... The total potential of receptor cells occurs when the tongue is irritated with sugar, salt and acid. It develops slowly: the maximum potential falls on the 10-15th s after exposure, although the electrical activity in the fibers of the taste nerve begins earlier.
Pathways and centers of taste. The so-called string drum and glossopharyngeal nerve, the nuclei of which are located in the medulla oblongata, serve as conductors for all types of gustatory sensitivity. Many of the fibers are specific because they only respond to salt, acid, quinine, or sugar. The most convincing hypothesis is that the four basic taste sensations - bitter, sweet, sour and salty - are encoded not by impulses in single fibers, but by the distribution of the frequency of discharges in a large group of fibers, which are differently excited by the flavoring agent.
Afferent signals caused by gustatory stimulation enter the nucleus of a single bundle of the brainstem. From this nucleus, the axons of the second neurons ascend in the medial loop to the thalamus, where the third neurons are located, the axons of which are directed to the cortical center of taste.
Taste and perception
For different people, the absolute thresholds of taste sensitivity differ significantly, up to "taste blindness" to individual agents. The absolute thresholds of gustatory sensitivity are highly dependent on the state of the body, changing, for example, during fasting and pregnancy. The absolute threshold of taste sensitivity is assessed by the occurrence of an indeterminate taste sensation, which differs from the taste of distilled water. Differential thresholds for gustatory discrimination are minimal at medium concentrations of substances, but with the transition to high concentrations they increase sharply. Thus, a 20% sugar solution is perceived as the sweetest possible, a 10% sodium chloride solution as the most salty, a 0.2% hydrochloric acid solution as the most acidic, and a 0.1% quinine sulfate solution as as bitter as possible. The threshold contrast (dI / I) for different substances varies considerably.
Taste adaptation. With prolonged action of the flavoring agent, adaptation to it develops, which is proportional to the concentration of the solution. Adaptation to sweet and salty develops faster than to bitter and sour. Cross-adaptation was also found, i.e. change in sensitivity to one substance under the action of another. Sequential application of several gustatory stimuli produces gustatory contrast effects. For example, adaptation to bitter increases sensitivity to sour and salty, while adaptation to sweet sharpens the perception of all other taste sensations. When several flavors are mixed, a new taste sensation arises that is different from the taste of the components that make up the mixture.
The ability to recognize the main types of taste. Testing of sensory sensitivity by recognizing the main types of taste is carried out on model solutions of chemically pure substances:
For the preparation of solutions, distilled water treated with active carbon is used. The solutions are stored in flasks with a ground stopper at a temperature of 18-20 ° C. For testing, 35 ml of solution is poured into tasting glasses. A total of nine samples are prepared: 2 glasses with any three solutions and 3 glasses with the fourth solution. The test subject does not need to know the order in which the samples are submitted. Take a 1-2-minute break between samples, rinsing your mouth with clean water. With seven or more correct answers, the candidate tasters recommend the following test problems to be completed.
Determination of the individual taste detection threshold.
In order to determine the threshold sensitivity to the main gustatory sensations, the expert is offered to try a series of solutions of increasing concentration (table). Each batch consists of 12 solutions.
Concentration of model solutions (in g / dm 3) to determine individual taste thresholds
The solutions are prepared in distilled water treated with active carbon. The concentration is considered detected if the test solution is identified in three triangular comparisons. In each triplet of solutions, two are the solvent, and one is the investigated one. They are served in an ascending sequence, within one triplet, of a random sequence unknown to the subject. For example:
The threshold sensitivity to the main types of taste in organoleptic-analytic candidates should be:
for sweet taste< 7,0 г/дм по сахарозе;
for a salty taste< 1,5 г/дм по NaCl;
for sour taste< 0,5 г/дм по винной кислоте;
for bitter taste< 5,0 г/дм по MgS0 4 ;
Determination of the individual threshold gradient of taste perception. Taste Threshold is the smallest difference in flavor concentration that an expert can detect. It is determined in solutions with a mild, but well-recognizable taste. The absolute value of the threshold difference depends on the concentration of the solution, therefore the sensitivity of the taste of an expert should be assessed on an individual basis.
threshold taste gradient on model solutions (table). For example, a 1% glucose solution is easy to distinguish from a 2% solution, and a 20% glucose solution from a 21% solution is almost impossible. In both solutions, the concentration difference is 1%, but in the first case the concentration gradient is 2.0, in the second - 1.05.
Concentration of model solutions (in g / dm 3) to determine the individual threshold taste gradient
To find the threshold taste gradient, the expert is offered the method of triangular comparisons to find an experimental sample against the background of reference solutions. The order of feeding the solutions is the same as when determining the detection thresholds for the main types of taste.
Zero solutions are solutions of sucrose, sodium chloride, tartaric acid and magnesium sulfate of background concentration. The threshold gradient of the subjects should be:
Individual threshold taste gradient (IPG) characterizes the ability to detect changes in the taste of the test product.
Assessment of taste memory. The stability of taste and smell (sensory memory) is one of the most valuable qualities of a taster. Taste memory is assessed by the ability to determine intensity and quality
taste sensations. An organoleptic analyst candidate is offered to try 6-7 solutions and are asked to arrange them in order of increasing concentration of the flavoring agent. A similar task is to determine two identical samples from seven solutions of different concentrations. The test solutions must differ more than the individual taste threshold of the evaluator. The concentration gradient of the test solutions is found by the formula 2IPG - 1. For example, if the individual threshold gradient of the evaluator is 1.3, the test gradient will be 2x1.3-1 = 1.6.
In order to determine the stability of taste sensations, the evaluator gets acquainted with the taste of solutions of 8-10 substances. Then give three samples of the previous series, which the subject must identify. The standard series consists of substances whose taste is related to wine (in%): tannin - 0.2, citric acid - 0.5, acetic acid - 0.2, glucose - 2, succinic acid - 0.1, tartaric acid -1, diethyl ester of tartaric acid - 0.2, lactic acid - 0.03, sodium sulfide - 0.1. When training taste memory, test problems can be complicated by a decrease in the concentration gradient of solutions and an increase in the number of substances offered for identification.
Determines the formation of taste sensations, is a reflexogenic zone. With the help of the taste analyzer, various qualities of taste sensations, the strength of sensations, which depends not only on the strength of irritation, but also on the functional state of the body, are assessed.
Structural and functional characteristics of the taste analyzer.
Peripheral department... Taste receptors (taste cells with microvilli) are secondary receptors; they are an element of taste buds, which also include supporting and basal cells. The taste buds contain cells containing serotonin and cells that form histamine. These and other substances play a role in shaping the sense of taste. Individual taste buds are polymodal formations, as they can perceive various types of taste stimuli. Taste buds in the form of separate inclusions are located on the back of the pharynx, soft palate, tonsils, larynx, epiglottis and are also part of the taste buds of the tongue as an organ of taste.
The peripheral section of the taste analyzer is represented by taste bulbs, which are located mainly in the papillae of the tongue. Taste cells are dotted at their end with microvilli, which are also called taste hairs. They come to the surface of the tongue through the gustatory pores.
The taste cell has a large number of synapses that form fibers drum string and glossopharyngeal nerve. The fibers of the tympanic string (a branch of the lingual nerve) fit all the mushroom papillae, and the fibers of the glossopharyngeal nerve - to the grooved and leaf-shaped. The cortical end of the gustatory analyzer is located in the hippocampus, parahippocampal gyrus, and in the lower part of the posterior central gyrus.
Taste cells continually divide and die continuously. The replacement of cells located in the front of the tongue, where they lie more superficially, occurs especially quickly. Replacement of taste bud cells is accompanied by the formation of new synaptic structures
Conductor department... Inside the taste bud are nerve fibers that form receptor-afferent synapses. Taste buds of different areas of the oral cavity receive nerve fibers from different nerves: taste buds of the anterior two-thirds of the tongue - from the drum string, which is part of the facial nerve; the kidneys of the posterior third of the tongue, as well as the soft and hard palate, tonsils - from the glossoglossal nerve; taste buds located in the region of the pharynx, epiglottis and larynx - from the superior peglottic nerve, which is part of the vagus nerve.
These nerve fibers are the peripheral processes of bipolar neurons located in the corresponding sensory ganglia, representing the first neuron of the conduction part of the gustatory analyzer. The central processes of these cells are part of a single bundle of the medulla oblongata, the nuclei of which represent the second neuron. From here, the nerve fibers in the medial loop approach the optic hillock (third neuron).
Central department. The processes of neurons in the thalamus go to the cerebral cortex (fourth neuron). The central, or cortical, department of the taste analyzer is localized in the lower part of the somatosensory cortex in the region of the tongue. Most of the neurons in this area are multimodal, that is, they respond not only to gustatory, but also to temperature, mechanical, and nociceptive stimuli. The taste sensory system is characterized by the fact that each taste bud has not only afferent, but also efferent nerve fibers that approach taste cells from the central nervous system, thereby ensuring the inclusion of the taste analyzer in the integral activity of the body.
The mechanism of gustatory perception... For a gustatory sensation to arise, the irritant must be in a dissolved state. A sweet or bitter flavoring substance that dissolves into molecules in saliva, penetrates the pores of the taste buds, interacts with the glycocalyx and is adsorbed on the cell membrane of the microvilli, into which “sweet-feeling” or “bitter-sensitive” receptor proteins are embedded. When exposed to salty or sour flavors, the concentration of electrolytes around the taste cell changes. In all cases, permeability increases cell membrane microvilli, the movement of sodium ions into the cell occurs, the membrane depolarizes and the receptor potential is formed, which spreads both along the membrane and along the microtubular system of the taste cell to its base. At this time, a mediator is formed in the taste cell (acetylcholine, serotonin, and, possibly, hormone-like substances of a protein nature), which in the receptor-afferent synapse leads to the emergence of a generator potential, and then an action potential in the extrasynaptic parts of the afferent nerve fiber.
Perception of taste stimuli. The microvilli of taste cells are formations that directly perceive the taste stimulus. Membrane potential taste cells range from -30 to -50 mV. Under the action of gustatory stimuli, a receptor potential of 15 to 40 mV arises. It is a depolarization of the surface of the taste cell, which is the cause of the appearance of a generator potential in the fibers of the tympanic string and glossopharyngeal nerve, which is transferred upon reaching critical level into propagating impulses. From the receptor cell, excitation is transmitted through the synapse to the nerve fiber with the help of acetylcholine. Some substances, such as CaCl 2, quinine, heavy metal salts, cause not primary depolarization, but primary hyperpolarization. Its occurrence is associated with the implementation of negative rejected reactions. In this case, no propagating impulses arise.
Sensitivity of receptors to different types of gustatory stimuli.
Different taste cells have different sensitivity to different taste substances, which are divided into four groups: sour, salty, sweet, bitter. Each cell always responds to more than one flavoring agent, sometimes even to all four, but it has the greatest sensitivity to one of them. Accordingly, depending on the location of cells with a particularly high sensitivity to a particular taste stimulus, different parts of the tongue also have different sensitivity.
It has been established that the tip of the tongue and its anterior third are most sensitive to sweets, where mushroom-shaped papillae are located, the lateral surfaces to sour and salty (leaf-shaped papillae), and the root of the tongue to bitter (grooved papillae, or taste papillae surrounded by a shaft).
Gustatory cells are characterized by fluctuations in the threshold of irritation and a different nature of the response to the same stimuli under different conditions. Their excitability depends on constant influences on each other, as well as on the state of the receptors of the digestive tract, olfactory tract, etc. Normally, there is a certain "tuning" of taste receptors in accordance with the state of the body, in particular with the state of satiety.
Introduction
The laboratory workshop is intended for undergraduates studying in the direction 260100 "Food from vegetable raw materials".
Tasks for laboratory exercises and methodological instructions for their implementation are drawn up in accordance with the current program and meet the requirements of the Federal educational standard higher professional education in the direction of training 260100 "Food from vegetable raw materials" (qualification (degree) "master"). The purpose of laboratory studies is to acquire special knowledge on the synthesis and isolation of substances from natural raw materials used as enhancers of taste, color and aroma in the food industry, familiarity with the features of standardization and analysis of these compounds. When performing laboratory work, students must use the knowledge gained in the study of disciplines such as "Food Chemistry", "Analytical Chemistry. Physicochemical methods of analysis "," Organic chemistry "," Physical chemistry ".
Laboratory work is performed by each student independently. At the end of the work, the student must draw up a report.
Work requiring the use of highly volatile and flammable liquids (petroleum ether, ethanol, chloroform, etc.) must be carried out under traction in polished dishes.
Taste is the body's response to molecular stimuli. All higher animals have separate responses to taste and smell. In less highly organized animals, such as invertebrates, the separation of taste and smell is less distinct.
There are four main types of taste : sour, sweet, salty and bitter.
To these four main types of taste, which were described in the 19th century by the German physiologist Adolph Fick, a fifth was recently officially added - the taste of umami. This taste is typical for protein products: meat, fish and broths based on them; it is created by monosodium glutamate. Other flavors include metallic, tart, and others.
Flavoring substances of food conventionally divided into the following groups:
1... Glucophoric (sweet) substances- mono- and disaccharides, saccharin, glycerin and glycine.
According to the glucophoric theory of sensation, the carriers of sweetness are the glucophoric groups —CH 2 (OH); -CH (OH), and regulators - auxogluconic groups -CH-.
2. Acidic substances- mineral and organic acids, sour salts - cause sour taste due to the presence of hydrogen ions. The exceptions are amino acids such as glycine, which has a sweet taste, butyric and nitrosulfonic acids, which have a bitter taste.
3. Salty substances- low molecular weight chlorine salts. The salty taste is determined by the presence of free chlorine ions. The exception is salts with a salty-sour taste (KBr, etc.) and bitter (KI, CaCl 2, MgCl 2, etc.). Admixing them in table salt impairs the salty taste, imparting unpleasant nuances.
4. Bitter substances- the above salts, glycosides, essential oils, for example, onion vegetables, citrus fruits (naringin, hespyridin); alkaloids (theobromine, caffeine). Thus, a bitter taste, just like a sweet one, arises when substances of various structures are exposed to receptors. The bitter taste of some substances appears only in combination with other substances. An example is limonin, which takes on a bitter taste when combined with citric acid, which is observed when citrus fruits freeze and rot.
To act on the nerve endings that cause taste sensations, a certain minimum concentration of the substance molecules is required, called gustatory threshold.
The thresholds of gustatory sensitivity are revealed by alternately applying solutions of substances with different gustatory qualities to the surface of the tongue (Table 1). The absolute threshold of sensitivity is the appearance of a certain taste sensation that differs from the taste of distilled water. The taste of the same substance can be perceived differently depending on its concentration in solution; for example, at low concentrations of sodium chloride, it tastes sweet, and at higher concentrations, salty. The maximum ability to distinguish the concentration of solutions of the same substance and, accordingly, the lowest differential threshold of taste sensitivity is characteristic for the middle range of concentrations, and at high concentrations of the substance, the differential threshold increases.
The absolute thresholds for gustatory sensitivity differ individually, but the overwhelming majority of people have the lowest threshold for detecting substances with a bitter taste. This peculiarity of perception arose in the process of evolution, it contributes to the rejection of the use of substances of bitter taste in food, to which the alkaloids of many poisonous plants belong. Taste thresholds differ for one and the same person depending on his need for certain substances; they increase due to prolonged use of substances with a characteristic taste (for example, sweets or salinity) or smoking, alcohol consumption, burning drinks.
Taste sensitivity depends on the following factors:
1. The chemical composition of saliva. Saliva that dissolves food is a complex mixture of chemical compounds containing both inorganic substances - chlorides, phosphates, sulfates, carbonates, thiocyanates, and organic compounds- proteins and digestive enzymes. After prolonged washing of the tongue with distilled water, as a result of which the taste buds are freed from saliva, the salt sensitivity threshold is significantly reduced;
2. Chemical nature taste-inducing compound and its concentration;
3. From what the person ate to the effects of this compound;
4. Temperatures of the consumed product: the lowest thresholds of sensitivity are obtained in the range of 22 - 32 ° C.
5. Places and areas of the stimulated area of the tongue, which is due to the peculiarities of the distribution of taste buds. The tip of the tongue is more sensitive to sweets than other areas, the sides of the tongue to sour and salty, and the root of the tongue to bitter.
6. Age: gustatory sensitivity in older people decreases, the tendency to decrease in sensitivity becomes noticeable by about 60 years;
7. Individual characteristics of a person.
Table 1. - Absolute thresholds of gustatory sensitivity of substances with a characteristic taste
Food products have either one taste (sugar - sweet, table salt - salty), or differ in a combination of basic types of taste. In this case, they speak of a harmonious and inharmonious combination of taste. So, harmoniously, as a whole, sweet or salty tastes are combined with sour or bitter ones. For example, sweet and sour taste of fruits, some confectionery products; bittersweet taste of chocolate; sour-salty taste of pickled vegetables; the salty and bitter taste of olives.
Combinations of salty-sweet, bitter-sour are considered inharmonious, these combinations are perceived as two different tastes, they are unusual for food products, are rare and occur, as a rule, due to spoilage.
Different flavors, when combined, can soften or enhance each other. So, sweet taste softens sour and bitter, sour enhances salty and bitter, astringent and pungent enhances sour and bitter, but softens sweet.
With the simultaneous influence of different tastes, the disappearance of the weakest of them can sometimes be observed, even if the substance that causes it is contained in quantities exceeding the threshold of sensation. Other factors that change or compensate for taste (pH of the medium, juiciness, fat content, etc.) can contribute to the disappearance of a weak taste. Salty, sweet and sour tastes disappear easily.
The taste of most substances has not yet been established. It is generally accepted that many proteins, polysaccharides, fats are devoid of taste. However, knowledge in this area is still incomplete. So, recently discovered specific proteins of plant origin, which have a high gustatory activity. Two of them (monellin, thaumatin) have an intensely sweet taste and can be considered as taste proteins.
In addition, substances have been found that are taste modifiers(substances that can change the taste), for example, the glycoprotein miraculin. After miraculin, acid is perceived as a sweet substance (this phenomenon is called taste illusion). It is assumed that miraculin is bound by the plasma membrane. The acid changes the conformation of the membrane, stimulating its sweet part. Modifiers are of particular interest to the food industry.
Usually, when sensory evaluation of food products, taste is understood as sensations arising from irritation of chemoreceptor cells, and tactile and olfactory sensations. The former are associated with the consistency of the product or the action of chemicals on the oral mucosa. In this regard, taste can be characterized by such a concept as astringency... It is caused by tannins that act on the inner surface of the oral cavity, as a result of which there is a feeling of contraction of the surface and its dryness. A sharp, pungent taste is felt due to a burn of the mucous membrane, for example, pepper capsaicin, mustard sinalbin.
To characterize the complex of impressions of taste, smell and touch during the distribution of the product in the oral cavity, determined quantitatively and qualitatively, the definition is used - deliciousness of food.
Flavoring substances are widely used in food production, their use is controlled by the bodies of the State Sanitary and Epidemiological Supervision of the Russian Federation.
Laboratory works
Evaluation of taste sensitivity
Testing of sensory sensitivity by recognizing the main types of taste is carried out on model solutions of chemically pure substances:
sweet - 1% sucrose solution
salty - 0.4% sodium chloride solution
acidic - 0.05% solution of tartaric acid
bitter - 0.5% magnesium sulfate solution
Distilled water treated with activated carbon is used to prepare the solution. The solutions are stored in flasks with ground-in stoppers at a temperature of 18-20 ° C. Pour 35 ml of solution into tasting glasses. A total of nine samples are prepared: two glasses with any three solutions and three glasses with the fourth solution. The test subject does not need to know the order in which the samples are submitted. Take a 1-2 minute break between samples, be sure to rinse your mouth with clean water. With seven or more correct answers, the tasters are recommended for the following test tasks.
To determine the threshold sensitivity to basic gustatory sensations, the evaluator is suggested to try a series of solutions of increasing concentration. Each batch consists of 12 solutions. The concentration is considered detected if the test solution is identified in three triangular comparisons. In each triplet of solutions, two contain water, and one contains the test solution. They are served in a sequence unknown to the subject. The solutions are prepared in accordance with Table 2.
Table 2. - Solutions used in determining the threshold gustatory sensitivity
| Solution number | Substance (g / L) | |||
| sucrose | NaCl | wine acid | MgSO 4 | |
| 1.0 | 0.1 | 0.05 | 1.0 | |
| 1.3 | 0.2 | 0.07 | 1.3 | |
| 1.7 | 0.3 | 0.1 | 1.7 | |
| 2.0 | 0.4 | 0.15 | 2.1 | |
| 2.7 | 0.5 | 0.20 | 2.7 | |
| 3.5 | 0.7 | 0.27 | 3.5 | |
| 4.5 | 1.0 | 0.35 | 5.5 | |
| 5.7 | 1.5 | 0.45 | 5.7 | |
| 7.3 | 2.0 | 0.6 | 7.3 | |
| 9.4 | 2.8 | 0.8 | 9.4 | |
| 12.0 | 4.0 | 1.00 | 12.0 |
The threshold sensitivity to the main types of taste in candidates for tasters should be: for sweet taste - 7 g / l of sucrose; for salty taste - 1.5 g / l for sodium chloride; for sour taste - 0.5 g / l of tartaric acid; for a bitter taste - 5.0 g / l of magnesium sulfate.
TASTE SENSITIVITY
Taste irritations are perceived by the taste buds. The bulbs are located in the mucous membrane. They occupy almost the entire thickness of the stratified epithelium, but do not reach the free surface. Taste receptors are also found in the mucous membrane of the dorsum of the tongue, soft palate, the anterior surface of the epiglottis and vocal cords, the posterior pharyngeal wall and the upper part of the esophagus. In the mucous membrane of the oral cavity, taste buds are found as separate inclusions.
There are four types of basic taste sensations - sweet, salty, sour and bitter. With prolonged exposure to any flavoring agent, the sensitivity to it gradually decreases due to taste adaptation. However, adaptation to one flavoring agent does not affect sensitivity to other flavoring stimuli.
Complex taste sensations that arise when eating a variety of foods are caused by irritation not only of taste buds, but also of surface sensitivity receptors (tactile, temperature), as well as olfactory receptors.
Different parts of the mucous membrane of the tongue are unequally sensitive to the main stimuli. Sweet is perceived by all points of the tongue, but this feeling is more pronounced at its tip. Bitter is also perceived by all points of the tongue, but leaf-shaped and roller-shaped papillae are most sensitive to it. Salty tastes better with the tip of the tongue.
There are several methods for testing taste sensitivity. So, if it is necessary to find out whether there are disturbances in taste sensitivity to all or to some types of stimuli, the patient is offered to rinse his mouth with 10 ml of a certain solution (temperature 20-25 ° C) for 3-5 seconds with intervals for bitter 3 minutes, and for other stimuli 2 min. For research, you can use a 20% sugar solution, 10% sodium chloride solution, 0.2% hydrochloric acid solution and 0.1% quinine sulfate solution.
When studying the taste sensitivity of individual parts of the tongue, a drop of the corresponding solution is applied to them using a thin brush or glass rod. In order to avoid spreading of liquid over the entire surface of the tongue, the patient indicates on the plate with the designations of the four main stimuli the one that corresponds to his sensation. Before the examination and after each test, the patient must thoroughly rinse his mouth. According to some authors, the order of application of taste stimuli does not play a role, from the point of view of others, the taste sensitivity to sour should be assessed last, since sour reduces taste sensitivity in general.
There is also evidence that weak (subthreshold) solutions of quinine and sodium chloride increase sensitivity to sugar. If it is necessary to determine the threshold, use solutions of increasing concentration. The threshold is considered the concentration at which the patient first establishes the type of stimulus.
When studying threshold concentrations, individual fluctuations of the body must be taken into account.
Different types of gustatory sensitivity are characterized by a certain latent period of sensation, ie, the time interval between the application of a stimulus and the appearance of a particular sensation (Table 1).
