Through his concept of affect attunement, Stern describes the intersubjective relatedness of an infant with his caregiver. When the infant is still preverbal, the caregiver must communicate, in some fashion, the fact that she is attuned to the subjective emotional state of her infant. Early on this usually takes the form of mimicking. However, at around the age of nine months, Stern describes how the caregiver inherently shifts her behavior to incorporate the infant as an “intersubjective partner.” The affective state of the infant becomes joined by the mother in a manner that the infant is able to perceive and feel a part of.
From an early age, infants have the ability to perceive amodally. With affect attunement they are related with the caregiver not through just one of the five senses. Attunement involves something of a ‘sixth sense’. Through this amodal perception, the caregiver and infant share affective experiences such as joy, sadness, excitement, etc. Vitality affects account for affect that is not so categorical. Stern posits that discrete displays of affect occur only sporadically, every thirty to ninety seconds. Attunement does not have to wait for these discreet displays. Rather, attunement is continuous and, as Stern says, ‘almost omnipresent’, through a variety of behaviors and affective states. Vitality affects account for the presence of attunement and relatedness between infant and caregiver in the period between discreet categorical affect.