Synonyms
Hearing, ear, hearing organ, sense of hearing, sense of hearing, acoustic perception, auditory perception,
Definition
Hearing/human hearing is our best trained sense. This means that we are able to distinguish, for example, twice as much as we can with visual impressions: From more than 24 frames per second on, we no longer recognize individual images, but a flowing film. Our eyes are overstrained, so to speak.
But even at a rate of 50 auditory impressions per second, our ears are still able to make distinctions and convert these auditory impressions into information that can be used by our brain for further processing. We are even able to distinguish and divide sounds in their different qualities pitch (up to 7000 different), volume, distance and directional hearing (up to 2° accurate). In addition, our hearing is very important: It serves us as a warning and protection system, for communication and for the pleasurable beautification of our everyday life.
History
Ever since humans have existed, hearing has been as much as a life insurance policy. Only those who could hear well were able to hunt animals, avoid predators or communicate adequately with neighbors. But even then, just like today, there was a decline in hearing.
For example, clay tablets with inscriptions were found during excavations of ancient Egyptian tombs, in which the deities were asked to restore hearing to the deceased in the afterlife. Greek scholars also frequently took up the topic of “hearing”, resulting in what are probably the oldest writings on sound and vibration. In the centuries that followed, numerous attempts were made to fathom this miracle of divine creation.
However, much knowledge from that early time was forgotten again over the centuries. It was not until the advanced 19th century, however, that a medical specialty on this topic was developed. The otorhinolaryngology was born, but physically speaking our ear can hear everything?
unfortunately, or fortunately no! We only hear acoustic events in a range of 0 dB, which corresponds to a sound pressure of about 20 μPa (= 2-10-5 Pa), up to over 130 dB (~ 10. 000 kPa) – still a quite respectable range.
The unit decibel (dB) is a quantity that rises first slowly and then faster and faster (logarithmic) and compares all values with the sound pressure at 0 dB. 0 dB represents the hearing threshold, i.e. the quietest perceptible noise (e.g. a very light breeze).
At 130 dB we speak of the pain threshold, i.e. the sound pressure level at which a sound is perceived as pain. The normal speech range is approximately between 40 dB and 80 dB at a pitch of around 2000 Hz. This is where the sensation of our hearing organ is greatest.
We hear sounds that are higher or lower than this frequency much quieter and therefore not as good. Some kind of mechanical effect produces a noise, a vibration of the air, which moves as a sound wave. Depending on the source of the noise, different sound waves are generated.
This sound wave hits the ear (auris externa) from the outside and is first of all captured by the auricles and bundled and conducted through the external auditory canal to the approximately pea-sized eardrum (membrana tympani, myrinx). This flexible round membrane can be used to make initial adjustments to our hearing when we are startled or expect a loud noise: With the help of a small muscle (musculus tensor tympani), the membrane can be stiffened, thereby reducing the normally occurring vibration; we hear more quietly. The eardrum also seals the next cavity, the tympanic cavity in the air-filled middle ear (auris media), against the auditory canal.
Like a drum, it is clamped into the bony ear frame (sulcus tympanicus) by a tendon ring (anulus fibrosus). For the eardrum to vibrate optimally, the pressure in front of and behind it must be equal. The ear trumpet (tuba auditiva) is used to ensure this.
If the ears are covered and swallowing is taking place, or if the nose is covered and pressure is built up inside, pressure can be deliberately equalized. Anyone who has ever flown in an airplane can certainly confirm this. On the inside there is a small bone, the hammer (maleus) with its handle attached to the eardrum.When the eardrum is vibrated, it is also set into oscillation and directs the movement with the aim of mechanical sound amplification (by about 22 times) via a chain of ossicles – the anvil (incus) and the stapes (stapes) – to the oval window, the wall of the inner ear (auris interna).
Here, too, a “braking muscle” at the stapes (musculus stapedius) can be used to attenuate sound transmission, especially when you are speaking loudly. In the fluid-filled cochlea that now follows, the migrating sound waves trigger vibrations of a special membrane at certain locations depending on their pitch. You can imagine this as a strip of paper that you hold between your index finger and thumb.
If you now blow the paper strip from the direction of your thumb, it begins to make waves. These waves become bigger towards the unfixed end of the paper, because there less holding resistance has to be overcome. However, to make the paper vibrate strongly near the fingers, it must be blown extremely hard, i.e. a high sound pressure must be built up.
In the same way, the hearing of different sound frequencies works. High tones have a lot of energy and make the membrane vibrate near its anchorage. Low tones with low energy, on the other hand, only manage to cause a vibration towards the free end of the membrane.
This splitting of the different sound frequencies is called dispersion. Strengthened by easily activated “additional springs” on the membrane (process of fine dispersion), some of the approximately 20,000 hair cells are then bent at the point of maximum membrane vibration, causing them to emit electrical signals. These signals can then finally be conducted via a nerve (nervus cochlearis) to the brain, to a special hearing center, where they are sent through various filters and evaluated.
These filters make up our actual hearing: They select related sounds from unrelated sounds, remove unnecessary background noise and give us the opportunity to listen to a person in a concentrated way. So it can happen that in the middle of a party with many conversations and therefore a high noise level our name is suddenly mentioned. Although the volume and pitch may not differ from the other conversations, we are able to filter out this familiar listening impression and let us become clear without background noise.
In further filters, the information from both ears is offset against each other. The same auditory impression arrives at both ears with a time delay because they are located on the right and left side of our head. This enables our brain to calculate from this time shift where the heard sound comes from.
This is how our perception of direction comes about. Some acoustic signals are also assigned to optical sensory impressions, which makes it possible for us to name things or recognize a great speaker as such! In short: Only through the extensive filter system in our brain can noise become meaningful hearing!
Our hearing cannot rest. It is constantly active, even if we do not notice it. For example, parents sleep despite the heavy traffic in the nearby street, but the bright sound of the child’s voice triggers an alarm and the body’s “wake-up program” sets in.
The inner ear is the first sensory organ that develops in us humans. Its development begins in the 4th week of pregnancy and is completed with the 24th week of pregnancy. Nevertheless, it still takes until the 26th week of pregnancy before we can finally hear the parental voices in a muffled way.
From the 6th month of pregnancy onwards, a fetus should react to sound stimuli. If hearing disorders are suspected, this should be checked as early as possible. By the 8th month of pregnancy, the outer ear and middle ear are also relatively well developed for hearing.
However, our hearing system is far from being fully developed and fully functional. To achieve this, the nerve pathways to the brain and the manifold interconnections that make sorting and filtering possible have to be developed by the end of the 5th year of life through “diligent hearing training”. However, what has not been formed by then in terms of connections and interconnections is irretrievably lost.
Listening exercises in these first years of life are therefore an absolute MUST!So we are able to recognize different sounds and noises, to filter out certain sounds from a multitude of others, to make ourselves noticeable in the dark and to connect our different senses. This wonder machine – our human hearing/hearing, our most differentiated sense – is very important for human life and at the same time our first opportunity to participate in the outside world. Therefore it is important to contribute as early as possible to its good education with our small fellow men and to help our big ones to keep it functional as long as possible!