Faces as reinforcers: effects of pairing condition and facial expression.

The reinforcing properties of faces were investigated in two experiments in which tones were first paired with an adult female face and subsequently tested for their ability to potentiate visual fixation when compounded with a checkerboard pattern. In Experiment 1, infants who had been presented six pairings of a 65-dB, 1000-Hz tone with a smiling face later fixated a checkerboard pattern significantly more when it was compounded with the tone than when it was tested alone. Infants in random and backward controls fixated the checkerboard pattern roughly equal amounts in the presence absence of the tone, and infants in a no tone control did not exhibit a novelty response when shifted from the face to the checkerboard pattern. In Experiment 2, facial expression was varied across groups and the effects on conditioning of a 65-dB tone that immediately preceded the face were studied. On test trials, greater fixation in the presence of the tone than in its absence was observed when a smiling or a surprised expression was presented, but not when a neutral expression was presented. Differences scores (fixation on tone minus no tone test trials) were significantly greater than zero in the smiling and surprised conditions, and significantly greater in the surprised condition than in the neural condition. These findings demonstrate the feasibility of a conditioned visual fixation paradigm for the study of the reinforcing properties of faces and of infant associative learning in general, and suggest that the expression portrayed by a face contributes to its effectiveness as a reinforcer.