The temporal dynamics of infants' joint attention: Effects of others' gaze cues and manual actions.

Infants' development of joint attention shows significant advances between 9 and 12 months of age, but we still need to learn much more about how infants coordinate their attention with others during this process. The objective of this study was to use eye tracking to systematically investigate how 8- and 12-month-old infants as well as adults dynamically select their focus of attention while observing a social partner demonstrate infant-directed actions. Participants were presented with 16 videos of actors performing simple infant-directed actions from a first-person perspective. Looking times to faces as well as hands-and-objects were calculated for participants at each age, and developmental differences were observed, although all three groups looked more at hands-and-objects than at faces. In order to assess whether visual attention was coordinated with the actors' behaviors, we compared participants looking at faces and objects in response to gaze direction as well as infant-directed actions vs. object-directed actions. By presenting video stimuli that involved continuously changing actions, we were able to document that the likelihood of joint attention changes in both real and developmental time. Overall, adults and 12-month-old infants' visual attention was modulated by gaze cues as well as actions, whereas this was only partially true for 8-month-old infants. Our results reveal that joint attention is not a monolithic process nor does it develop all at once.