In the first half of the 20th century, the basic paradigm guiding learning and instruction was behaviorism. Based upon this new behaviorist paradigm, design models emphasized the success of the instructor/teacher instead of the learner, in that given a certain stimuli; a particular response can be predicted. Cognitive psychology's reaction to the inability of behaviorism to account for much human activity. Constructivism is a theory of cognitive development and a philosophy of learning founded on the idea that the learner constructs knowledge in action, based on his/her pre-existing mental structures and mental activity. Social constructivism, as it has evolved, emphasizes the importance of culture and context in understanding what occurs in society and work and in constructing knowledge and developing competent professional behavior based on this understanding. Education and educational processes are determined by the interactions that take place between learners, educators, technologies and media, and the environment. This is the ecology of education.