Intentions make a difference: infant responses to still-face and modified still-face conditions.

In two studies, 3-, 6- and 9-month-old infants interacted with their mothers during natural, still-face, and modified still-face (i.e., mothers wearing a mask, or drinking from bottle) conditions. Infants were also presented with matching doll conditions to control for the possibility that their responses might be due to changes in superficial perceptual features. Regardless of age, infants displayed negative affect to the still-face, but, in contrast to recent reports, not to the modified still-face conditions. However, whereas infants' positive affect also depended on their mothers' communicative intentions, these responses changed with cognitive maturation. As expected, infant responses to their mothers were significantly different from those to the doll. The implications of these findings for theories of communication are discussed.