Tonotopy

When listening to multiple levels of analysis processes the received acoustic signals are held, especially in the understanding of language. The theory of tonotopy (derived from Ancient Greek a) τόνος [ tonos ] = that which one stretches a bit, string, rope, belt; Voltage, emphasis, balance; Raising, tone of voice / b ) τόπος [ topos ] = place, location, tract of land, area, place, room ) tries the first acoustic analysis of these multi-level transformations in electrical potentials to describe and explain. This is about the exact location of the transformation of mechanical vibrations within the cochlea into electrical neural impulses, forwarding these pulses to the central nervous system and there held in spatially differentiated structures processing of original acoustic signals according to their pitch. It is a neurobiological explanation.

Illustration of frequency

While listening to the recorded from the outside sound waves are vestibuli through the motions of the stapes through the oval window to the Scala in the cochlea ( cochlear ) transmitted. By the propagation of the traveling wave, it comes to the deflection of the basilar membrane which divides the cochlea into two chambers filled with the perilymph that connect to each other have at helicotrema. On the basilar membrane is the organ of Corti with hair cells. These are very fine ' hair ' to be able to detect shearing of the membrane composite. Please note: the stronger the deflection ( a strong sound wave was the cause ), the stronger the shear, the more frequently the fire springing to the hair cells of neurons, the louder a stimulus or noise is detected. But exactly here lies the weak point of the system that can be damaged by excessive sound levels, especially at this point: the hairs can be sheared irreversible.

The most pronounced firing range of the basilar membrane is assigned as a frequency. The closer the location of the maximum deflection of the oval window (in this case, the mechanical vibrations are coupled into the hydraulic system ) is, the higher the pitch. The closer the maximum is the helicotrema, the lower the pitch. In other words, any place on the basilar membrane is associated with a particular frequency under certain conditions (quiet and pure tones ). The frequency - spatial transformation is carried out non-linear ( see Bark scale ). The picture registered by the basilar membrane frequencies in the brain takes place in strip form in the Heschl Querwindung of the superior temporal gyrus and the temporal gyri transverse processes. The center provides primary auditory cortex represents the high frequencies up to 20000 Hz back medially, the low frequencies up to 200 Hz represents forward lateral. According to the theory of tonotopy including any location associated with a particular frequency within the auditory cortex.

This theory is therefore also referred to as frequency - location mapping or Einortstheorie and therefore constitutes variant of Somatotopik dar.

Conceptual delimitation of Somatotopik

In tonotopy it is not a point- to-point imaging of " body regions " in narrow sense. Hence, we are not a somatotopy as it is encountered in the sensorimotor cortex, but to a very different sensory quality, which refers not to the perception of one's body and for the feedback on my own body ( proprioception ). Nevertheless, the speech must in a sense of " somatotoper illustration " from a sense organ also be similar so the skin must be construed as a sensory organ ( Exterozeption ). Shown is the case of the tonotopy not physical, but rather a physical continuum. It is in principle to the image of a specific acoustical spectrum or frequency group, which is received by the basilar membrane as " somatic " parameters on the level of the peripheral nervous system as the " prototype " - and modulated as a "copy" is transferred to the central nervous system. This is done, inter alia, also taking into account the relevant hearing range or the perceived pitch. The Frequenzansprechbarkeit the basilar membrane can thus vary.

Said modulation is also known as relative figure or as a package. If only the measurable physiological registering a specific pure frequency at a certain point of the basilar membrane meant and not topically structured type of forwarding to the CNS, it is not spoken of tonotopy but by Tonlokalisation on the basilar membrane.

This tonotopy should not be equated with somatotopy, but be advised of common principles of organization.

These general criteria of the picture have further led to the term " map ", see chap. Tonotopic maps. With the designation card, as is common in the language of networks, is rather the spatial- schematic -level presentation or representation of general characteristics meant in the sense of similarity, frequency and importance (relevance). In the case of tonotopy is primarily a tape-like representation continuously continuous frequencies. In the English language the general criteria of central nervous illustrations are referred to as "place theory".

Frequency and Pitch

One should be careful not to equate the perceived pitch with the detected by this method frequency position of a clay or clay mixture. Pitch is a perception of a higher order, which is to say that a number of preprocessing steps are needed to extract from the physical stimulus a sensation of pitch or to abstract. Because when correlated for simple sinusoidal tones on the basilar membrane of the Erregungsort well to the perceived pitch, there may be large deviations complex tones ( sounds, sound noise mixtures, etc. ). Thus, we are able to associate sounds a pitch whose frequency equivalence was not present in the physical stimulus. The Virtual pitch provides a relatively coherent and reliable approach for the extraction or determination of the perceived pitch ( tonality ).

Tonotopic maps

Tonotopic maps have been described due to different neuroscientific methods. These represent neurophysiological models represent ( self-organization ) within the meaning of Kohonennetzen. In animals, such cards have been proven. They have, for example, in the bat precisely in the region a strong extension to where the animal discharges tones to 61 kHz own orientation. The orientation of the bat when flying is done known about the analysis of the Doppler shift.

Understanding speech

Using the technical model tonotoper cards, it is explained and understood that pure frequencies are first divided in terms of a frequency band, and then further processed. Furthermore, According cards have been described, as they are essential for a mother tongue and characteristic for the specific language understanding of a native language. This touches on the fields of phonetics and phonology. Further steps in the understanding of language are the recognition of phonemes, word meaning (semantics ) and the contexts of action. For each of these levels, there is the ultimate meaning and context of action ( pragmatics ). Example of a "safe" identification of ambiguous situations: " At this fishing a small # depends ish. "