Ultra sensitive hands
The human fingertips can perceive protrusions that are only 5 microns high, which is about 1/1 5 of the diameter of a hair. The tongue and lips are more sensitive, and putting a hair in your mouth will immediately feel something big in your mouth.
When touching an object, human touch will show three abilities at the same time, namely, the "spatial resolution" of perceiving the pressure of the object, the "spatial resolution" that distinguishes the distance between the two points of the object, and the "time resolution" that captures the time change of the object's vibration.
These three abilities have a lot to do with fingerprints.
If the fingertips are as smooth as the rubber film, the skin of the fingertips will all sink when they touch the object, and the sense of touch is also very poor. However, if there are fingerprints, each fingerprint is separated by the "grooves" on both sides, and it is difficult to touch the adjacent "grooves", so there will be a very sensitive sense of touch. The resolution of the distance between the two points is different in different parts of the skin, and the finger has a higher resolution than the wrist.
So what does this structure that feels the sense of touch look like? In fact, the structure is very simple, and no matter which part of the body they are distributed in the skin, the structure is the same. Why is such a simple structure able to feel all kinds of stimuli? Some people think that this is related to the depth they are in the skin, the structures close to the surface of the skin are sensitive to stimuli that cause changes in the shape of the skin such as skewing, while the structures located in the deep layers are more sensitive to the time of compression and the intensity of pressure.
The human sense of touch is already very sensitive, and if it is trained, it will be more significantly improved. If you can touch ordinary people with 5 micron protrusions, they can touch 1 micron after training; ordinary people with a distance of 3 mm between two points can be improved to 1 mm through Braille (Braille) training, so that Braille makes the hand become an "eye". After further training, you can also turn your hand into an "ear". The American blind, deaf and mute female teacher and writer Helen Keller is a typical example. She became blind, deaf and mute when she was two years old due to scarlet fever, but she still finished college with tenacious perseverance and became a world-famous "goddess" who defeated the triple disability of blindness, deafness and mute. She also pioneered the method of "listening" with her hands: "When listening" to the other person," stretch out three fingers, put your thumb on the other person's throat to feel the vibration, use your index finger to feel the lip movement, and use the middle finger to feel the nasal sound.
"Atomic-level" hearing
You may not believe it, but it is a certain fact: the human ear can hear vibrations of very small magnitudes equivalent to the diameter of an atom (about 10-8 mm). This super-micro-vibrational structure can be heard hidden in the worm tube of the inner ear. It is a thin film with millions of neatly arranged cilia on the film, which can bend and deform with sound waves, and then have an electrical effect, forming nerve impulses that pass into the brain to make people hear. Although the gravitational wave tester can also measure very small gravitational waves, it can only work under very special environmental conditions, such as ultra-low temperature, no vibration and so on. However, the human ear can eliminate all kinds of interferences and maintain the "atomic level" perception of hearing in the human body full of vibrations, which is indeed remarkable. Even better, the human ear has the ability to recognize and selectively listen to the desired sound, which is unmatched by instruments. Some instruments have a very high degree of perception, but it simply judges the presence or absence of sound; the hearing aid, although subtle, amplifies unnecessary noise.
Some people may think that the dog's ear is more perceptible than the human ear, because the dog can hear a faint sound that people can't hear, but this is actually wrong.
In terms of perception, both humans and dogs are "atomic", the difference is only in the range of sound waves heard, people are 20 Hz to 20000 Hz, dogs are 20 Hz to 40000 Hz.
The ear has the function of gathering sound, but what is the function of the small protrusion (ear screen) located in front of the ear hole? One explanation is that this is an evolutionary remnant of the lid that was waterproof to the ear when living in the water. On land, it is an important structure for discerning the direction of sound. The sound coming from the front is reflected back by the ear screen, and it enters the ear hole after touching the ear screen, while the sound coming from the back of the side can be reflected by the ear screen and directly enter the ear hole. In this way, there will be a time difference between the sounds coming from all directions, so that the direction can be discerned. Bats mainly rely on hearing to move, so its part, which is equivalent to a human ear screen, grows particularly long and developed, so that it is easy to obtain a sense of direction.
The human ear is quite sensitive in discerning the direction of sound. According to research, people can distinguish two sound sources that are only 10 centimeters (that is, 3 degrees) apart at 2 meters in front of them; if the left and right distances are replaced by up and down distances, the resolution will decrease, and the same feeling as the original can only be obtained when the distance between the sound sources is increased to 15 degrees. This difference can be explained from the perspective of biological evolution: rabbits and other animals have food below, while natural enemies are above, so they are more sensitive to sounds coming from up and down, while horses, deer, etc. are only more sensitive to the left and right directions.
In addition, the human ear is also quite good at distinguishing the level of sound. Studies have shown that an average person can distinguish the level of 2,000 sounds.
5.0 vision
The average person's vision can reach 1.5 to 2.0, but what is the limit of vision? As far as is known, people with a visual acuity of 5.0 and 3.0 have been found in Taiwan Province of China and Kenya. As we all know, the quality of vision is based on the closest distance between two points that can be distinguished. The so-called 1.0 vision refers to the fact that when the angle formed by the straight line between the connecting eye and the two points is as small as 1 corner minute (1/60 degree), the two points can still be distinguished. If the angle is reduced by 1/2, it can also distinguish between the two points, which is called 2.0, the angle is reduced to 1/3 is 3.0, and after the reduction to 1/5, it is 5.0. In other words, a person with a vision of 5.0 sees something at 500 meters as clearly as a person with a vision of 1.0 sees something at 100 meters.
Why is it that people cannot see in the night when there is no moonlight, but those animals that are active at night can walk in the dark night? It turns out that the size of a person's pupil changes with brightness,
The pupil is only 50 times the adjustment range, and the rest depends on the retina to adjust, but 4/5 of the light that reaches our retina slips away from the retina. There is also a layer of reflection behind the retina of those animals that can "block" the light that passes through. When those rays of light are reflected back into the retina, the sensitivity of the retina increases. Some people think that the eyes of cats and dogs shine brightly at night and appear particularly bright, which may be related to this.
An olfactory sense full of unknown numbers
The olfactory function is also a feeling. On each side of the upper part of the human nostril is a 1.3 square centimeters of yellow-brown mucosa, distributed with about 50 million olfactory cells. When the molecules of the substance are adhered to the olfactory cells, the olfactory cells feel stimulated. Ordinary people can distinguish between 2,000 odors. So, how do olfactory cells separate them?
At present, there are more than 30 hypotheses, but among them are widely recognized the "key" and "key hole" theories. This theory holds that olfactory cells are "key holes", odorous material molecules are "bonds", and only when the shape of the "key" is completely consistent with the "key holes", the smell information can be transmitted to the brain through the nerves, producing a sense of smell. Judging from the current research results, the size and shape of the material molecules are definitely related to odor, but this alone is not enough to explain the whole truth. Therefore, the sense of smell is still a feeling full of unknowns.