 The motor theory of speech perception postulates that perception is somewhat like covered articulation, where the input is compared with one's own articulatory knowledge. Central to this active theory of speech perception is a recognition device in the brain, which coordinates the processing of the incoming signal on the basis of a set of internal articulatory patterns with which the incoming signal is compared and matched. And this is how it works. At the first stage, the ear amplifies the incoming signal and transmits it to the auditory nerve. During a primary auditory analysis, the signal is filtered, that is, non-speech components are separated from speech. Then, from the cleaned signal, auditory patterns such as formant frequencies are extracted and matched with the internal patterns. At the end of the recognition process, phonological units, that is phonemes or phonetic features, are extracted from the signal and are combined to form larger units.