Attending and responding to eye gaze is crucial for human social interactions. Specifically, eye gaze plays an important role in directing and coordinating attention during triadic interactions between self, other and the environment. During a typical triadic interaction, a person may establish eye contact with another person and then direct that person's gaze to an object or event. The psychological process by which two people share attention towards the same object or event is called joint attention. Joint attention and the underlying triadic representations (self–other person–object) are thought to be unique to our species, supporting teaching, cooperation and language learning (Tomasello et al. 2005
; Saxe 2006
; Csibra & Gergely 2009
). Impairments in joint attention are one of the earliest signs of autism (Charman 2003
More than 30 years ago, Scaife & Bruner (1975)
first observed that infants follow a person's gaze and engage in joint attention. This seminal finding and the subsequent surge of behavioural research on the topic led to a rejection of the long-held Piagetian notion of infant egocentrism (Mundy & Newell 2007
). Moreover, research on joint attention suggests that infants' ability to share a common point of reference develops before spoken language (Baldwin 1995
), and that joint attention processes are important precursors of the later development of higher-level mental state attribution (Charman et al. 2001
Despite the progress that has been made in understanding the behavioural emergence of joint attention during infancy (e.g. Carpenter et al. 1998
), almost nothing is known about the brain substrate that supports joint attention in the developing child. Investigating the neural basis of joint attention in infants is important for several reasons, including the possibility that behavioural tasks are insufficiently sensitive to reveal early abilities in infants. In adults, joint attention relies on the recruitment of the medial prefrontal cortex (Williams et al. 2005
; Schilbach et al. in press
), a brain structure that has been more generally implicated in social cognition and theory of mind (Amodio & Frith 2006
). Here, we examined haemodynamic responses in five-month-old infants' prefrontal cortex during triadic social interactions using near-infrared spectroscopy (NIRS) (see Lloyd-Fox et al. (2010)
for a description of the method and its use with infants).
Infants were presented with three different experimental conditions. In all conditions, the infant watched an adult's face in the middle of the screen with an object either to the left or to the right side of the face. In the joint attention condition, the adult raised her eyebrows and smiled while holding eye contact with the infant, then shifted her eyes towards the object, then shifted her eyes back to the infant and finally turned her head towards the object. The ability to jointly attend with another person requires the infant to not only attend to the external object or event but also to monitor (i) the other person's attention towards the same object or event and (ii) the other person's attention in relation to the self. Our two control conditions thus disrupted these two critical aspects of joint attention. In the first control condition, the no referent condition, the person behaved exactly the same as in the joint attention condition, except that she looked and turned towards the side where there was no object. In the second control condition, the no eye contact condition, the person looked at the object without establishing any eye contact with the infant (the person looked down with her eyes closed before shifting her eyes towards the object). We predicted that the brain region that is specialized in dealing with triadic social interactions should be selectively engaged during the joint attention condition but not during the two control conditions, because they lack the triangular nature required to establish joint attention.