A person produces speech by the coordinated movement of their articulatory system. The listener hears the sound (black line) and sees the mouth of the speaker open and close (represented by blue line). Some of the information in the sound is contained within the speech envelope (green line). The auditory regions of the brain (green circle) track the speech envelope, while the visual system (blue circle) tracks the visual movements of the mouth. The motor system (red circle) then decodes the intended mouth movement and integrates this with the response of the auditory regions to the incoming sounds.