Image.3.1. Analyzer adaptation (changed Sl).
Differential limit characterizes the amount to which the already caused irritant has to be changed for a person to notice its change. Differential limit is expressed as a percentage. For the same body it has become:
where I – the initial value of the irritant;
ΔI – growth caused by the feeling of change.
Irritant stimulates the receptor under increasing its strength to a certain level. The limit of 50% of cases of sensations summarizes the lower absolute limit. The next increase of the irritation strength begins when the analyzer stops to operate in the right way. Then the pain feelings appear that can completely disrupt the analyzer activity.
Psychophysiological experiments revealed that the magnitude of the sensitivity varies slower than the irritant’s strength.
According to Fechner’s law:
,
where E - intensity of feeling,
I – intensity of irritant,
K and C - constants.
Fechner’s Law explained in Image.3.2.
Human has many physiological analyzers. The main analyzers include:
1. Visual Analyzer.
2. Hearing analyzer.
3. Tactile analyzer.
4. Motor analyzer.
5. Smell and taste.
6. Temperature sensitivity.
7. Vibration sensitivity.
8. Organic sensitivity.
1. Visual Analyzer. The human eye responds directly to the brightness of the object, which is the ratio of luminous flux to the surface area that is lit.
Measured in candela per square meter (cd/m2).
The maximum limit of brightness is set by hygiene standards. When the brightness of over 30,000 nT blinding effect occurs.
The eye's range of sensitivity – 10-6 -106 nT.
Visual Analyzer has the greatest amount of adaptation. Light adaptation takes 8-10 min. In dark adaptation sensitivity of the eye reaches the optimum level for 30-50 min. Sensitivity, which is caused by light signals over time remains constant despite the disappearance of the signal. Persistence of Vision causes stroboscopic effect. Critical flicker frequency when the signal is perceived as continuous is within 12 ... 25 Hz.
While percepting the objects in two-dimensional and three-dimensional space field of view and depth vision is distinguished. Horizontal binocular field of view - 120...160 °, vertically up - 55...60 °, down - 65...72 °. Visual field narrows due to the perception of color. Zone optimum visibility is: up - 25 °, down - 35 °, left and right - to 32 °. Deep vision associated with the perception of space. Error estimation of the distance of objects (up to 30 m) is 12% of the distance. Time spent on information search operator desired object can be calculated as:
where n - number of fixations during the search,
tc - commit time,
tm – time of view moving.
The average duration of such visual fixations for solving the most common problems are: reading letters - 0.31 sec, search for symbols - 0.3 sec, the fixation status indicators (light or not) - 0.28 sec, the perception of symbols - 0, 04 sec. The average duration of search movements of the eye - 0.025 sec. It should be emphasized that the main characteristics of human visual analyzer are significantly changed in learning and training.
2. Hearing analyzer consists of external, middle and inner ear, auditory nerve and communication system to the brain. The range of sound vibrations that we hear is between 16 ... 20 Hz to 20 kHz ... 25 kHz. The absolute limit of sensitivity is the minimum pressure 2 105 Pa at 1 kHz (sound power 109 erg/cm2). Hearing analyzer differently perceives sounds of different frequencies. Low frequency sounds he perceives as not very loud, compared to higher frequency sounds of the same intensity.
Duration of sound stimulation, which is necessary for the emergence of feelings, also depends on the frequency and intensity of sound. Within the middle of the frequency and intensity of the sounds that we hear, the value differential limit is about 10% of the sound intensity. For frequencies above 1 kHz signal having a sense of presence in its length about 0.001 sec.
Verbal communication is perceived at a pace of speech to 160 words per minute. Optimal rate - 120 words/min in excess intensity noise words over 6 dB.
Limit the pain sensation is 130-140 dB and less dependent on frequency.
3. Tactile analyzer perceives sensations that arise in the action of various mechanical stimuli on the skin surface.
An example of the limits of sensitivity:
- For all fingers - 3 h/mm2;
- For surface brush - 12 h/mm2;
- For heel - 250 h/mm2.
Tactile analyzer has a high capacity for localization in space. Time limit of the tactile sensation is less than 0.1 seconds. Feature tactile analyzer is the rapid decrease in pressure or sense of touch. Time adaptation is within 2 ... 20 sec.
Pain sensitivity. Above it was argued that any analyzer has pain, if the value exceeds the upper irritants absolute threshold. On this basis, the existence of specific receptors in pain sensitivityis denied. Later it was found free nerve endings in the epithelial layer of the skin, which are the specialized pain receptors. Between tactile and pain receptors there are complex relationships. They show that the lowest density of pain receptors falls on those areas of the skin that most rich tactile receptors, and vice versa. The tension caused by various receptor function in the life of the organism. Pain caused defensive reflexes, such as reflex distance from the stimulus. Tactile sensitivity associated with the reflexes of reference, in particular, is closer to the reflex stimulus.
Tactile sensitivity associated with the reflexes of reference, in particular, is closer to the reflex stimulus.
The biological significance of pain is that it is a danger signal, mobilizes the body to fight for survival. Under the influence of the pain signal tunable operation of all systems of the body and increases its reactivity.
The threshold of pain sensitivity abdominal skin - 20 h/mm2, all fingers -300 h/mm2. When feeling pain there is almost a direct correlation between the intensity of feeling and irritation in the range of the threshold sensitivity.
4. Motor analyzer allows a person to manage the security devices, pens, buttons, pedals and so on.
Best effort: for pens - 20...40 N, for buttons, toggle switches, switches - 1400...1600 N, for foot pedals - 20...50 N; levers for manual control - 120...160 N. Velocity range that developed through movements of hands is 0.01...8000 cm/sec, the most commonly used speed is 5..300 cm / sec. Vertical movement of arm exercises rather than horizontal. Movement to himself performed faster than from themselves. Motor analyzer can be greatly improved by training.
5. Smell and taste can be used by a human operator in finding various deviations in the technological process and in case of danger. The absolute limit of smell in humans (0.1-1.0) mg / liter of air (measured in milligrams of substance particles per liter of air). Differential limit is an average of 38%. In physiology and psychology prevalent four component theory of taste, according with which there are four kinds of taste: sweet, bitter, sour and salty. All other taste is their combination. Absolute limits of taste analyzer expressed in values of concentration of the solution, almost 10,000 times higher than olfactory.
Taste and olfactory sensations reflect not only the properties of substances, but also the state of the organism. Distinguished taste sensitivity analyzer is pretty rough, averaging 20%.
6. Temperature sensitivity is provided by two types of receptors. Some react only to cold, others - only heat. The absolute limit of temperature sensitivity for thermal receptors - 0,2 ° C for the cold - 0,4 ° C. Differential limit is about 1°C.
At work analyzers and signal perception in humans significantly influence the psychological characteristics of the individual: attention, memory and so on. (See below).
7. Vibration sensitivity. Intense vibration during prolonged exposure causes significant changes in the activity of all systems of the human body and can cause disease. Vibration low intensity may be useful, reduces fatigue, boosts metabolism, increases muscle strength. Special analyzers who perceive vibration is not yet discovered. Range feeling vibrations are from 1 to 10000 Hz. The highest sensitivity is found to frequencies 200 ... 250 Hz. Thresholds vibration sensitivity is different for different parts of the body. The greatest sensitivity with distal parts of the body, that is, those most distant from its median plane (e.g., hands).
8. Organic sensitivity. The brain receives information not only on the environment but also on the organism. In the internal organs under the influence of external conditions arise sensations which generate signals that are essential regulation of internal organs.
Human analyzers function in a complex interaction. For every person affected analyzer simultaneously several stimuli, which then affect the entire system analyzers. It is therefore necessary to consider not only the possibility of the analyzer, but also the conditions under which a person is. We know that loud noise alters the sensitivity of vision. The sensitivity of the visual apparatus is reduced under certain smells, temperature, and vibration. Determining the optimum operating conditions, to consider the whole system of stimuli acting on analyzers human comprehensively take into account environmental factors.
The final part.
Today we learned about the lecture with the following concepts:
-Environment (Atmosphere, Hydrosphere, Lithosphere, Biosphere, Noosphere)²;
-Living environment²;
-Working Environment, Domestic Environment²;
-Open Environment²;
-Hazards, noxious agent²;
-Potential factor, quality factor, the maximum allowable level of factor²;
-Active negative, passive and active, passive factors²;
-Noise and vibration²;
-Ionizing Radiation²;
-Maximum permissible concentration²;
-Physiological man’s analyzers²
It should again be emphasized that a person uses security measures to VrF due to the physiological analyzers. However, not all are active VrF can feel human. To do this, use measuring instruments. In the absence of measuring utensils, only knowledge of dangerous and harmful factors, especially their effects on man, security measures can help a person stay healthy in today's urban environment.