Work in this field has focused on a stimulus-organism-response (S[arrow right]O[arrow right]R) approach, which was adopted by Mehrabian & Russell (1974), who suggested that the outcome of the influence of various environmental stimuli was revealed in approach or avoidance behavior. Mehrabian and Russell (1974) also proposed that intervening between the environmental stimuli and approach or avoidance are three emotional states: pleasure, arousal and dominance (PAD). The combination of these determines whether or not a person wishes to remain in a particular environment-i.e., approach or avoid.