Motivation process that influences the direction, persistence, and vigor of goal directed behaviour. Homeostasis a state of internal physiological equilibrium that the body strives to maintain. Requires a sensory mechanism for detecting changes in internal environment, a response system that can restore equilibrium, and a control centre that receives information from sensors. Drive theory physiological disruptions to homeostasis produce drives, states of internal tension that motivate an organism that reduce this tension. Clark hull proposes that reducing drives is the ultimate goal of motivated behaviour. Flaws in theory found in certain behaviours, such as when people skip meals to diet (increases rather than decreases state of arousal) Modern incentive theorists emphasize the pull of external stimuli and how stimuli with high incentive value can motivate behaviour, even in the absence of biological need. Incentives environmental stimuli that pull an organism toward a goal. Increasing the external reward for a behaviour makes the behaviour less intrinsically rewarding.