This experiment was designed to elucidate the function of adult facial and vocal behavior for infant perception and expression of affect. Nine infants were studied longitudinally at 2 months and at 3 1/2 months using a dynamic visual display that consisted of a videotape of a woman moving her face while expressing happiness or sadness. A second group of 10 infants were studied similarly ina version of this procedure that used a static videotaped display of the woman's face in which she showed fixed expressions of either emotion. Both types of visual displays were accompanied by a soundtrack playing either affectively matched or unmatched infant-directed (ID) speech. Infant visual fixations of the display area were determined during the experimental session by a trained observer who was kept unaware of the stimuli being presented. The sum of these fixations for infants in the Static condition was greater than that of infants in the Dynamic condition. A similar analysis of the average length of infants’ visual fixations revealed no significant results. Analyses of infant affect and "interactiveness" were also conducted by having trained raters score videotapes of each session using one of 4 rating scales. According to 2 of these measures, infant facial affect was more positive during displays that contained happy elements than during matched sad displays, and 3 1/2-month olds were more frequently rated as More Happy during matched happy displays. Thus, infants showed different affective responses to the 4 face-voice combinations, even though they did not attend differently to the displays. In addition, infant facial affect was more positive at 3 1/2 months because smiling at displays was more reliable at this age. The analysis of infant "interactiveness" revealed that 3 1/2-month olds in the Static condition were more "interactive" than those in the Dynamic condition. A supplementary analysis of a questionnaire that was designed to measure parents' perceptions of their infants showed that almost 1/5th of the attrition at 2 months could be accounted for by infants' tendencies to respond negatively to novel experiences. The results of this study are discussed in terms of their implications for future research in infant perception. / Ph. D.