This study found that the facial action of moderately or widely opening the mouth is accompanied by brow raising in infnats, thus producing “surprise” expressions in non-surprise situations. Infants (age = 5 months and 7 months) were videotaped as they were presented with toys that they often grasped and brought to their mouths. Episodes of mouth opening were identified and accompanying brow, nose, and eyelid movements were coded. Results indicated that mouth opening is selectively associated with raised brows rather than to other brow movements. Trace levels of eyelid raising also tended to accompany this facial configuration. The findings are discussed in terms of a dynamical systems theory of facial behavior and suggest that facial expression cannot be used as investigators' sole measure of “surprise” in infants.

This research was conducted as part of the second author's undergraduate honors program project and was supported in part by a grant from the NICHHD #1RO1 HD 22399-A3 awarded to G. F. Michel.