Joint attention is typically defined as two individuals coordinating visual attention to an object of mutual interest. Some of the specifics of this definition are not important: for example, more than two individuals can be involved, it can be any type of attention (e.g., visual or auditory), and the attention need not be to an object – it can be to an event, a location, an idea, or anything else. The most crucial part of the definition is the “coordinating” part – the part that makes joint attention joint, rather than just parallel attention. Joint attention means more than just two individuals attending to the same thing; in addition, both individuals need to know together with each other that they are attending to the same thing (see Tomasello 1995). They need to be aware (in some sense) that they are sharing attention. This strict definition of joint attention is not always used in the literature, but as we will see below, it is important to keep in mind when comparing the joint attention skills of humans and animals.
In humans, joint attention plays an extremely important role in many social activities, including communication, cooperation, and education. For example, there is much research showing that infants and toddlers learn novel words more easily when the words are presented to them inside, as opposed to outside of, a joint attentional focus. Joint attention supports learning (and other cooperative activities) by providing a “meeting of minds” or shared base of understanding on which to build. The clearest signs of joint attention behaviors emerge developmentally in human infants around 9–12 months of age.
Nonhuman animals are often credited with the ability to engage in joint attention as well. For example, a wide variety of animals (e.g., monkeys, apes, dogs, dolphins, birds, and goats) can follow others’ gaze direction to end up looking at the same thing, and thus many researchers have claimed that they engage in joint attention. However, while gaze following sometimes results in joint attention, it does not always do so. For example, I can follow your gaze without you even being aware that I am present, much less looking at the same thing. What is needed for joint attention in this case is some indication that attention is shared. If each individual alternates gaze between the object and the other individual, resulting in eye contact, this is often taken as an indication of joint attention, both in gaze following situations and on its own, for example, when an infant looks back and forth between his mother’s face and a toy they are playing with. However, gaze alternation is also not necessarily evidence of joint attention, as there are many reasons why one might alternate gaze between an object and a social partner, for example, to see what the social partner is going to do with the object, or simply because both the object and the partner are interesting or salient. Gaze following and gaze alternation thus might involve parallel or alternating attention, rather than coordinated, shared, joint attention. Perhaps the most convincing evidence of joint attention is declarative gestures: communicative gestures such as showing and pointing that are performed with the goal of attracting someone else’s attention to an object so that attention and attitudes about it can be shared. However, lower-level, more egocentric explanations of these gestures are also possible, so research is needed to determine just how joint the joint attention of infants and animals really is.
This type of research has already been conducted with human infants. For example, after 1-year-old infants follow others’ gaze, they often look back to their partner with a smile, and/or point to the object themselves, to share attention to it with their partner. When they alternate gaze with adults while playing with toys, they often produce “sharing looks” expressing their attitude about the toy to the adult (see Hobson and Hobson 2007 for more on sharing versus other types of looks). The expressive, communicative quality of these looks to the adult indicates that infants are doing more than just unilaterally checking or monitoring the adult’s focus of attention or looking to see what she is going to do next. Direct tests of possible alternative explanations of 12-month-olds’ declarative pointing also show that infants point in order to share attention and interest with their partner about the object, rather than for lower-level, more egocentric reasons (Liszkowski et al. 2004). Finally, and more generally, studies show that 1-year-old infants keep track of what experiences they have shared with whom (Moll et al. 2008). Together these studies suggest that, at least by around 1 year of age, human infants engage in joint attention that is truly joint.
This type of evidence is not so easy to find for other animals, despite in-depth research on relevant behaviors like gaze following and communicative gestures. By far, the most such research has been done with chimpanzees, our closest nonhuman primate relatives. Chimpanzees have a quite sophisticated understanding of others’ attention (in the sense of what others can see or have seen in the immediate past). They are also motivated to follow others’ gaze, and they routinely gesture themselves to direct others’ attention to objects. However, there is little (if any) evidence that they do these things for the sole purpose of sharing attention about objects with others, as an end in itself, like humans do (Tomonaga et al. 2004). Researchers who credit chimpanzees and other animals with joint attention invariably use weaker definitions of joint attention that do not require attention truly to be shared (Leavens and Racine 2009).
One obvious and important question for future research is to see whether evidence of truly joint joint attention can be found in animals. The same question also applies to human infants younger than 9 to 12 months of age, who can follow gaze and who sometimes show gaze alternation between objects and social partners. Finally, it will be interesting to look for relations between joint attention and other theoretically related behaviors such as cooperation and some of the more social types of imitation (see Hobson and Hobson 2007), which all involve sharing or aligning attitudes, goals, or behavior with others, and which are also thought by many to be uniquely human skills.