Differential effects of happy,neutral, and sad still‐faces on 2‐, 4‐ and 6‐month‐old infants

The role of facial expression in the determination of infants' reaction to the sudden still‐face of a social partner was investigated. In a within subject design, 2, 4 and 6‐month‐old infants were tested in periods of normal interaction interspersed with periods of prolonged still‐face episodes in which the female adult social partner adopted either a happy, neutral, or sad static facial expression while maintaining eye contact with the infant. Proportion of infants' smiling and gazing at the social partner as indices of reaction from the various still‐face episodes reveal that, in comparison with same age control groups, four and six‐month‐old infants did not demonstrate any differential responses depending on either happy, neutral, and sad still‐faced expression. In contrast, two‐month olds demonstrated some evidence of a reduced still‐face effect in the happy still‐face condition. These results point to early developmental changes in the mechanisms underlying the still‐face phenomenon. We propose that by 4 months, and not prior, the reaction to still‐face episodes are essentially based on the detection of social contingencies. Copyright © 2002 John Wiley & Sons, Ltd.     

Asymmetric interference in 3‐ to 4‐month‐olds' sequential category learning

Three‐ to 4‐month‐old infants show asymmetric exclusivity in the acquisition of cat and dog perceptual categories. The cat perceptual category excludes dog exemplars, but the dog perceptual category does not exclude cat exemplars. We describe a connectionist autoencoder model of perceptual categorization that shows the same asymmetries as infants. The model predicts the presence of asymmetric retroactive interference when infants acquire cat and dog categories sequentially. A subsequent experiment conducted with 3‐ to 4‐month‐olds verifies the predicted pattern of looking time behaviors. We argue that bottom‐up, associative learning systems with distributed representations are appropriate for modeling the operation of short‐term visual memory in early perceptual category learning.