1) The complex of real circumstances in which the organism or referenced part of the organism exists. This includes any physical event or complex of events that is not part of a behaviour and may include other aspects of the organism. Experiment. A series of actions that result in a set of special observations that would not otherwise have been possible. Usually involves manipulating certain variables (independent) in order to determine their effects on other variables (dependent.)

2) All of the events and stimuli that affect the behaviour of an organism. The environment includes events "inside the skin" like thinking, hormonal changes, and pain stimulation.