What data, problems, and concepts are most relevant in determining the role of stimulation in human development? A critical analysis of the relationships between long term stimulation, behavior, and cognitive functioning and development points up biases and gaps in past as well as contemporary approaches. Each of the four sections of this paper focuses upon a central topic and related issues. Theoretical and methodological background and a review of salient features of certain theories of infant and child development are the first topics considered. In the third section, a rough conceptual framework is constructed to aid in interpreting research studies and to furnish guideposts for further empirical exploration. The last section presents selectively reviewed studies on infant learning and cognition by first analyzing research on the early months of infancy and by surveying subsequent development in sensorimotor, perceptual, and symbolic modes. An extensive bibliography is included. (WY)