In semiotic terms, these are the physical embodiment (signifiers) of speech signs, which are gestural by nature (see below).
Use of the broadest definition of gesture (not restricted to hand movements) allows Hockett’s “rapid fading” design feature of human language to be accommodated as a type of sign in semiotic theory.
Sound and light are analogue signals, whereas mouth and hand gestures are discrete symbolic entities.
In speech, the sound of the contact of the tongue in the letter T can be distorted by surrounding mouth movements, as in the phrase “perfect memory”.
When pronounced at conversational speed, the sound of the tongue contact is completely obscured by surrounding consonants even though this T movement is fully carried out.