Auditory Process

Auditory process . Hearing is the psycho-physiological processes that provide man with the ability to hear.

Summary

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• 1 the sound
• 2 The human ear
• 3 Auditory System
  • 1 Sense of hearing in humans
  • 2 External ear
  • 3 Middle ear
  • 4 Internal Oído
• 4 thresholds of hearing
• 5 protection system
• 6 Some psychoacoustic phenomena
• 7 Other data of interest
• 8 curious facts
• 9 Fountains

Sound

Sound is not an object moving through the air, but a sensation created by the brain perceiving slight vibrations in the air . A sensation, in the organ of hearing , produced by wave motion in an elastic medium (normally air), due to very rapid changes in pressure, generated by the vibratory motion of a sound body.

The function of the transmitting medium is fundamental, since sound does not propagate in a vacuum. Therefore, for sound to exist, a source of mechanical vibration is necessary, as well as an elastic medium ([solid, liquid or gaseous) through which the disturbance propagates. Air is the most common transmitting medium for sound. The speed of sound propagation in air is approximately 343 meters per second at a temperature of 20°C (293 kelvin).

When an object (emitter) vibrates, it also vibrates the air around it. This vibration is transmitted in the distance and causes a membrane inside the ear, the eardrum, to vibrate (by resonance), which encodes (converts) that vibration into electrical information. This information is transmitted to the brain through neurons . The brain decodes that information and converts it into a sensation. This sensation is called “sound” .

The human voice (the various sounds that make up speech) are also considered sounds. These are studied in phonetics and in phonology .

the human ear

The ear is one of the five senses of the sensory system, which has the ability to perceive sound (sound perception).

Auditory System

In mammals , the ear or auditory system consists of three parts.

sense of hearing in humans

The auditory system consists of three basic sections, the outer ear , the middle ear, and the inner ear .

Its importance is radical when it comes to appreciating sounds. Each of these sections has a specific purpose in the difficult task of detecting and interpreting sounds. The outer ear picks up sounds from outside and serves as a channel to transmit these sounds to the middle ear. There, the energy of the sound waves is transformed into internal vibrations of the middle bone structure; then, these vibrations become compressed waves that pass into the internal fluids. In the inner ear, the energy of the compressed waves is transformed into nerve impulses, so that they can be transmitted to the brain.

external ear

It is made up of the ear and an ear canal approximately 2 cm long. The function of the ear is to provide protection to the middle ear in order to prevent any damage to the eardrum. In addition, it channels sound waves that, thanks to the length of the ear canal, can be amplified up to 3000 Hertz to reach the eardrum without any modification. When sound passes through the external ear, it still does so in the form of pressure or impulse waves, with regions where the pressure is altered. It is not until the sound reaches the eardrum that the energy of the mechanical waves is converted into internal vibrations of the bone.

Middle ear

It is an air-filled cavity that contains the eardrum and three small interconnected bones – the malleus, the incus, and the stirrup. The eardrum is a tightly stretched membrane that vibrates when the pressure of sound waves hits it. A compression forces the eardrum inwards, while a refraction pushes it outwards, in this way, the eardrum vibrates at the same frequency as the sound wave, producing the phenomenon of acoustics. Being connected to the malleus, the movements of the eardrum activate the three ossicles so that they move at the same frequency as the sound. In turn, the stapes is connected to the inner ear; and thus, the vibrations that reach it are transmitted to the fluid of the middle ear where the sound waves are compressed.

The three small bones act as levers to amplify the frequencies of the waves. Due to a mechanical advantage, the stirrup shape is more efficient than the hammer shape. It is even better than that of the eardrum since Since the pressure of the wave hits the flat surface of the eardrum, it is concentrated in the small curves of the stirrup, therefore the force of the stirrup when vibrating is 15 times greater than that of the eardrum. This feature enhances the ability of humans to hear those almost imperceptible sounds. The middle ear cavity is connected to the mouth by the Eustachian tube.. This connection allows equalizing the pressure within the different cavities of the ear. During a cold, this tube becomes blocked with mucous and is unable to balance pressure; This usually causes earaches and other discomforts.

Inner ear

It is made up of the cochlea, the semicircular canals or labyrinth, and the auditory nerve. The cochlea and semicircular canals are filled with a watery fluid. This fluid and the nerve cells of the labyrinth have no function at the time of hearing; they simply serve as accelerometers for the detection of accelerated movements and help maintain balance. The cochlea is a snail-shaped organ that should be able to stretch about 3 cm. In addition to being filled with fluid, the inner surface of the cochlea is lined with more than 20,000 nerve cells, as fine and thin as a hair , which serve one of the most critical roles within the auditory system.

These nerve cells differ from others in their length by a few nanometers; They also have different degrees of elasticity to the fluid that passes over them. As the compressed waves move across the interface between the malleus and the oval window of the inner ear toward the cochlea, small nerve cells are activated. Each of them has a natural sensitivity to a particular frequency of vibration. When the frequency of the compressed waves matches the natural frequency of the nerve cells, they resonate with a long amplitude of vibration. This increase in amplitude induces the cells to release an electrical impulse that is transmitted to the brain through the auditory nerve. Through a process that is not fully understood,

hearing thresholds

The hearing thresholds or limits considered standard correspond to intensities from 0 dB (hearing threshold) to 120 dB (pain threshold) where there is already discomfort or physical pain.

The audible frequency range is from 20 to 20,000 Hz.

Throughout this spectrum of audio frequencies, the sensation of intensity or loudness varies. The unit of loudness is the fonio.

protection system

We have two muscles (stapedius and tensor tympani) that tense or relax the eardrum and the chain of ossicles automatically, depending on the intensity of the sound, limiting the amount of energy transmitted to the cochlea (whose hair cells are very sensitive). The only drawback of this system is the adaptation time, during which the ear can be seriously damaged.

In addition, the external auditory canal can secrete cerumen as a protective barrier against the arrival of loud sounds.

Some psychoacoustic phenomena

• Frequency discrimination:In sounds of close frequencies, if one of them has more intensity, it masks the other (this is precisely called masking). At frequencies close to the same level, we perceive an intermediate frequency called an intertone.
• Binaural hearing:The localization of sounds in space is achieved thanks to the separate processing of information from each ear and the subsequent comparison of phase and level between both signals. We have more developed the horizontal sense than the vertical sense of hearing.
• Haas effect:We do not differentiate sounds separated in time by less than 40-50 milliseconds. In this case the first sound that is produced is the one that is perceived, and the second is heard as part of it. Starting at 50 ms, they are already processed as separate sounds.
• Presbycusis:It is hearing loss with age.

Other data of interest

• The range of hearing, like that of vision, varies from person to person. The maximum range of hearing in man includes sound frequencies from 16 to 28 thousand cycles per second. The smallest pitch change that can be picked up by the ear varies with Pitch and Volume. The most sensitive human ears are able to detect changes in the vibration frequency (pitch) that corresponds to 0.03% of the original frequency, in the range between 500 and 8000 vibrations per second. The ear is less sensitive to changes in frequency if it involves sounds of low frequency or intensity.
• The ear’s sensitivity to sound intensity (loudness) also varies with frequency. The sensitivity to changes in volume is greater between 1000 and 3000 cycles, so that changes in a Decibel can be detected. This sensitivity is lower when sound intensity levels are reduced.
• Differences in the sensitivity of the ear to loud sounds cause several important phenomena. Very high tones produce different tones in the ear, which are not present in the original tone. These subjective tones are likely to be caused by imperfections in the natural function of the middle ear. Discordances in tonality that produce large increases in sound intensity are a consequence of the subjective tones that are produced in the ear. This occurs, for example, when the volume control on a radiois adjusted.
• The intensity of a pure tone also affects its intonation. High tones can increase up to a note of the musical scale; low tones tend to get lower and lower as the intensity of the sound increases. This effect is only noticeable in pure tones. Since most musical tones are complex, hearing is generally not affected by this phenomenon to any appreciable extent. When sounds are masked, the production of lower pitched harmonies in the ear can dampen the perception of higher pitches. Masking is what makes it necessary to raise one’s voice in order to be heard in noisy places.
• The human ear is not capable of picking up sounds of any frequency; the lower and upper limits are approximately 16 and 45,000 hertz, respectively.
• The timbre allows us to distinguish, between 2 sounds of equal intensity and height, which is the source of each one.
• The human ear can only perceive sounds between certain frequency limits, outside of this, the ear remains deaf, the lower limit is between 1.6 and 20 vibrations per second, the upper limit is very variable from one person to another, it can be set to 20,000 oscillations per second, beyond that frequency no sound is perceived. However, sounds of a frequency higher than that which the human ear is capable of perceiving have been captured in animals such as dogs.
• It is very curious what happens with bats, it has been proven that these mammals are capable of flying in absolutely dark rooms. Thus it was discovered that these animals had extremely fine hearing. They also found out that the mechanism of these night pilots was that they emitted very high-pitched screams that were inaudible to the human ear, since they reached 500,000 vibrations per second. These ultrasounds spread about 340 meters per second around the animal. Upon reaching any obstacle, the waves are reflected and return to the bat, which is thus informed of the obstacles ahead.

Fun facts

• Cockroaches– Cockroaches pick up sound with their body hairs. These hairs are sensitive enough to detect the slightest movement of air produced by sound waves.
• Worms– Worms do not have hearing, but they can detect vibrations in the ground and react consecutively.
• Grasshopper– The ears of grasshoppers are located in the central section of the body. Crickets have ears on their knees.