Infant smiling to nonsocial stimuli and the recognition hypothesis.
D000161:Acoustic Stimulation; D001307:Auditory Perception; D002652:Child Behavior; D002657:Child Development; D003071:Cognition; D005149:Facial Expression; D006801:Humans; D007223:Infant; D008297:Male; D012919:Social Behavior; D014796:Visual Perception