Deafness (deafness, surditas, anakusis) is the complete absence of hearing sensation. There are numerous reasons for this. Deafness can be congenital or acquired and can occur on one or both sides. The decisive factor for the prognosis in many cases is how early the hearing disorder is recognised and treated. Especially in children, undetected deafness can cause severe developmental delays, especially in speech. Here you can read everything you need to know about deafness.
Deafness or the often synonymous term deafness describes the complete loss of hearing sensation. The cause can lie along the entire path between the perception of sound in the ear and the processing of acoustic stimuli in the brain. There are also forms of deafness in which the affected person can pick up sounds with the ear, but cannot process and understand them.
Deafness can be unilateral or bilateral, congenital or acquired. In some cases, deafness is only temporary (e.g. due to infections of the ear), in other cases it is permanent.
Anatomy and physiology of the ear
The ear has three parts: Outer ear, middle ear and inner ear.
The outer ear consists of the auricle and the outer auditory canal through which the sound waves pass into the middle ear (air conduction).
The transition to the middle ear is formed by the eardrum, which is directly connected to the so-called hammer (malleus). Together with two other tiny bones (anvil = incus and stirrup = stapes), the hammer forms the so-called ossicles. They guide the sound from the eardrum via the middle ear into the inner ear, where the auditory perception is located.
The inner ear and the middle ear are mostly located in the petrous bone, a part of the bony skull. The sound is transmitted from the ossicles via the so-called oval window to the cochlea. However, sound can bypass this path via the eardrum and also reach the cochlea via the skull bone (bone conduction). The sound is registered in the cochlea and transmitted via the auditory nerves to the brain, first processed in the lateral brain and then sent to higher processing centres. Every stage of hearing perception and processing can be disturbed and lead to deafness.
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Differentiation between hearing loss and deafness
Hearing loss is a loss of hearing perception, deafness is the complete loss of hearing perception. The distinction can be determined objectively with a hearing test (sound threshold audiometry): The hearing loss is determined in the so-called main speech area. The main speech range is the frequency range in which human speech predominantly takes place. It lies between 250 and 4000 Hertz (Hz). Frequencies in the main speech range are particularly well perceived by the human ear, which is why hearing loss in this range has a particularly severe effect.
The extent of the hearing impairment is determined as hearing loss (expressed in decibels = dB) compared to normal hearing. A distinction is made between mild (20 to 40 dB), moderate (40 dB and above) and severe (60 dB and above) hearing losses. Residual hearing loss describes a hearing loss between 90 and 100 dB. From a hearing loss of 100 dB in the main speech range, the definition of deafness is fulfilled.
About two out of every thousand children are deaf in both ears from birth. Congenital unilateral deafness occurs in less than one child in a thousand. In newborns with risk factors (e.g. premature birth), the risk of deafness is about ten times higher. According to the Deaf Federation, about 80,000 people in Germany are deaf. About 140,000 people have such a severe hearing loss that they need a sign language interpreter.
A distinction is made between one-sided and two-sided deafness. Some people are deaf from birth. In other cases, deafness develops slowly or suddenly (e.g. due to an accident).
With the one-sided deafness, the hearing ability is not perfect indeed, however, as a rule considerably restricted nevertheless. Other people often notice that the affected person reacts late or not at all to sounds (such as a sudden loud bang).
Since hearing is severely impaired overall, people with one-sided deafness are more likely to ask questions during a conversation because they are often unable to fully absorb the information in the conversation. In addition, people who are deaf in one ear often speak very loudly (sometimes with poor articulation) and make the sound of radio and television remarkably loud. Such behaviour is usually the first indication of hearing loss or unilateral deafness.