Behaviorism is primarily concerned with observable and measurable aspects of human behavior that are directed by stimuli. Behaviorist learning theories emphasize changes in behavior that result from stimulus-response associations made by the learner. Behaviorists seek scientific explanations that predict the occurrence of behavior as it relates to environmental factors. Examples of behavior contracts include agreements between teachers and students to complete homework assignments on time in exchange for extra help or to minimize classroom distractions by being punctual and not leaving one's seat without permission.