Under localization In acoustics, the recognition of the direction from which a sound comes in three-dimensional space and the recognition of the distance from the sound source is understood. Localization is based on directional hearing with both ears (binaural) and on distance hearing, which is also possible by hearing with one ear (monaural). Localization is a passive process in which only the sound received is localized through the ears, without the involvement of other sensory organs.
What is the localization?
In medicine, the term localization is used by several specialist areas with different content. For example, the term is used in neurology to assign motor and psychological functions to certain areas of the brain.
Mostly, localization is understood to mean the ability to hear directional and distance without involving other senses. Recognizing the direction from which the sound is coming in three-dimensional space usually requires hearing from both sides (binaural) because, among other things, the slight difference in travel time of the sound between the two ears is used by the brain to recognize the direction. The shape of the auricles also plays a role.
In principle, distance hearing also works with only one ear (monaural), since distance hearing can only take place indirectly. The brain evaluates certain qualities of the sound such as volume, frequency spectrum and sound reflections, compares them with empirical values and uses them to “estimate” the distance from the sound source.
Direct distance hearing is not possible, as this would only be possible in combination with directional hearing and with sound sources further away it would require a significantly greater distance between the left and right ear. The unconscious comparison of the parameters of the received sound with empirical values plays the greatest role when hearing a sound source from a distance.
Function & task
The localization of a sound source only through the auditory impression, without the involvement of other senses such as sight, is of great importance to humans.The localization ability is used to localize sound sources according to the classification as dangerous or non-dangerous in order to derive an action decision from the classification and the localization.
What is special is that localization is possible even with restricted vision or with complete loss of vision. For example, the localization and the additional estimation of the speed of a vehicle via the auditory perception provide a decision-making aid for safely crossing a busy road - even with severely restricted visibility.
In addition, the localization of a sound source also allows rough navigational orientation in some cases. In a forest area without foresight and without other possibilities for orientation, the localization of a sound source, in particular the determination of the direction from which the sound comes, can offer an orientation possibility.
For directional hearing, bilateral (binaural) listening is usually necessary. In the case of lateral sound sources, the brain can "calculate" the position of the sound source from the difference in transit time between the left and right ear, which is only a few milliseconds, and from the level differences resulting from the shadowing effects of the head.
If sound sources have to be located centrally in front of or behind the body or above, binaural hearing does not provide clear results for physical reasons. Here the outer ear with the special shape of the auricles and the auditory canal plays a special role.
The brain can evaluate resonances, sound reflections and minor frequency distortions on the auricles in such a way that the sound source can be localized, for example, from the front or the rear. A simple verification is possible by turning the head so that the sound source is to the side, as the localization then achieves the highest accuracy.
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Unrestricted directional and distance hearing are the prerequisites for being able to clearly localize a sound source. This means that localization limitations are usually associated with hearing loss in one or both ears.
If there is a one-sided hearing impairment, directional hearing is particularly impaired. However, it is astonishing that even with a one-sided total loss of hearing, directional hearing is not completely lost, since the loss of hearing in one ear can be compensated to a small extent via the effects of the auricle.
A central hearing disorder that affects both ears equally can be conductive or sensorineural hearing loss. The latter also includes hearing loss, in which the problems either lie in the conversion of the physical sound vibrations into nerve impulses in the cochlea or there are limitations in the neuronal transmission and / or the processing of signals in the hearing centers in the CNS.
This means that the localization ability is also impaired, since insufficient or incorrectly processed auditory signals arrive in the hearing centers or the incoming signals cannot be processed further correctly.
The restricted assets can be temporary or permanent. For example, neurotoxic poisons cause a temporarily limited ability to localize. This also includes excessive alcohol or other drug use.
Directional hearing requires particularly sensitive hearing, so that every central hearing disorder has a direct effect on directional hearing and thus on the ability to localize.
Tinnitus and other central hearing disorders also have a reducing effect on directional hearing. Often the beginning of hearing loss is only recognized due to a symptomatic functional disorder in directional hearing.
