To approach the mental processes used in purchasing decisions, some authors employ the concept of the black box, which represents the cognitive and affective processes used by a consumer during a purchase decision. The decision model situates the black box in a broader environment which shows the interaction of external and internal stimuli (e.g. consumer characteristics, situational factors, marketing influences and environmental factors) as well as consumer responses. The black box model is related to the black box theory of behaviourism, where the focus extends beyond processes occurring "inside" the consumer, and also includes the "relation" between the stimuli and the consumer's response.