<P> One kind of environmental guidance of development has been described as experience - dependent plasticity, in which behavior is altered as a result of learning from the environment . Plasticity of this type can occur throughout the lifespan and may involve many kinds of behavior, including some emotional reactions . A second type of plasticity, experience - expectant plasticity, involves the strong effect of specific experiences during limited sensitive periods of development . For example, the coordinated use of the two eyes, and the experience of a single three - dimensional image rather than the two - dimensional images created by light in each eye, depend on experiences with vision during the second half of the first year of life . Experience - expectant plasticity works to fine - tune aspects of development that cannot proceed to optimum outcomes as a result of genetic factors working alone . </P> <P> In addition to the existence of plasticity in some aspects of development, genetic - environmental correlations may function in several ways to determine the mature characteristics of the individual . Genetic - environmental correlations are circumstances in which genetic factors make certain experiences more likely to occur . For example, in passive genetic - environmental correlation, a child is likely to experience a particular environment because his or her parents' genetic make - up makes them likely to choose or create such an environment . In evocative genetic - environmental correlation, the child's genetically - caused characteristics cause other people to respond in certain ways, providing a different environment than might occur for a genetically - different child; for instance, a child with Down syndrome may be treated more protectively and less challengingly than a non-Down child . Finally, an active genetic - environmental correlation is one in which the child chooses experiences that in turn have their effect; for instance, a muscular, active child may choose after - school sports experiences that create increased athletic skills, but perhaps preclude music lessons . In all of these cases, it becomes difficult to know whether child characteristics were shaped by genetic factors, by experiences, or by a combination of the two . </P> <Ol> <Li> What develops? What relevant aspects of the individual change over a period of time? </Li> <Li> What are the rate and speed of development? </Li> <Li> What are the mechanisms of development--what aspects of experience and heredity cause developmental change? </Li> <Li> Are there typical individual differences in the relevant developmental changes? </Li> <Li> Are there population differences in this aspect of development (for example, differences in the development of boys and of girls)? </Li> </Ol> <Li> What develops? What relevant aspects of the individual change over a period of time? </Li>

Who said infancy is the ideal period of learning