Between 9-14 months of age, the tendency for a young human infant to focus attention preferentially on the face - like stimuli in it's environment develops into an ability to follow the gaze of adults and to look where they are looking. At this point they begin to show a phenomenon known as joint attention whereby they use another individual's gaze direction to focus their own attention on the same object. They also begin to engage in shared joint attention, where they look from the object to another individual and back again, to check that they are both attending to the same object [...]. Michael Tomasello goes so far as to argue that shared attention is the key cognitive skill that distinguishes humans from the rest of the animal kingdom.