We are not talking supra-segmental-phonemes here, So what is the child doing motorically at 6 to 8 months--during the period of Lalling and Jargon?
This is not to imply that the 6 month old baby is using supra-segmental phonemes here.
Instead what we are underscoring is the fact that the basic rudiments of prosody for the language have been recognized, and are being practiced by the baby.
Later these well rehearsed patterns will be available for the more complicated supra-segmental phonemic function to occur.
In terms of motor development, babies at this point are actually able to stand by holding on to something.
When they grab an object, they will hold their thumb in opposition to the fingers.