Infants' Visual Processing of Faces and Objects: Age-Related Changes in Interest, and Stability of Individual Differences

Longitudinal measures of infant visual processing of faces and objects were collected from a sample of healthy infants (N-40) every month from 6 to 9 months of age. Infants performed two habituation tasks each month, one with novel female faces as stimuli, and another with novel complex objects. Different individual faces and objects served as habituation (i.e., visual learning) and dishabituation (i.e., novelty response) stimuli. Measures included overall looking time to the habituation stimuli, slope of habituation, and recovery to the dishabituation stimuli. Infants were more interested in faces than objects, but this was contextualized by task order. The order effect suggests a "habituation of habituation" effect. Infants showed an age-related decrease in interest in objects, but no decrease in interest in faces. This contradicts claims that infants shift around 6-7 months from interest in faces to interest in objects. The results showed modest between-month stability of interest in faces, but little stability in any other behavioral measures. This implies that habituation is driven more by unexplained subject x session x stimulus variance than by "infant IQ."