The proposed research has two major objectives: (1) the identification and further confirmation of a major developmental shift in emotional expression in the human infant, and (2) the study of several correlated developments which could be serving as determinants of this developmental shift. Consequently, six studies are proposed. The first study will attempt to confirm, via both longitudinal and cross-sectional testing methods, that a developmental shift is taking place in the manner in which infants cross to the mother on the two sides of the visual cliff. A second study deals with the age at which infant reactions to direct placement atop the two sides of the visual cliff first leads to evidence of fear, as evidenced by heart rate and behavior. Other studies are planned on fear of heights using apparatus other than the visual cliff, as well as on the relationship between falling experiences and fear of heights. The infant's ability to possess shape constancy will be investigated, to see whether developments on the visual cliff reflect certain perceptual developments. Still other studies will focus on the infant's reactions to stereoscopic projections of approaching and receding stimuli. The above studies are intended to focus on perceptual and affective developments between two and nine months of age.