crying leads to a response from caregiver.
as long as caregiver provides correct response, crying is reinforced.
baby then directs crying for comfort towards caregiver who responds with comforting 'social suppressor' behaviour.
as baby is reinforced for crying, the caregiver receives negative reinforcement as crying stops - escaping from something unpleasant is reinforcing.
when infant is fed, drive is reduced and produces a feeling of pleasure, this is rewarding - positive reinforcement.