As adults we develop a complex set of emotional expressions and a perceptual understanding of our own and others' emotional states. Infants appear to have two innate rudimentary emotional arousal responses to stimuli, referred to as approach and avoidance. The infant's emotional life consists of little more than these two arousal states, an attraction to pleasant stimulation eliciting approach and a withdrawal or avoidance of unpleasant stimulation.

Given that this is the nature of emotional arousal the newborn arrives equipped with, the approach-avoidance response makes perfect evolutionary sense. It might also suggest that infants are born with an innate understanding of the meaning intended in the emotional facial expressions of others. Hence if the caregiver adopts a playful posture and conveys a happy facial expression, then the infant will be in an approach arousal state and will most likely respond positively by mirroring the expression portrayed.

The opposite also applies, where parents adopting a despondent posture are likely to initiate an avoidance arousal state in the infant. In an avoidance arousal state the infant will exhibit behaviours designed to provoke a change in the parent's behaviour, such as crying and pick-me-up gesturing, or sucking an object such as a pacifier or the edge of a blanket.

A continuation of parental despondency could have serious consequences for the infant's normal socio-emotional development. This could cause alterations to the infant's sleeping patterns and increase levels of irritability, anger and anxiousness. An infant's avoidance of aversive situations is limited due to their immature motor development, so they resort to simple avoidance tactics such as turning the head, gaze avoidance and crying.