© The Author(s) 2013

er.sagepub.com We conceptualize approach and avoidance, much as Lewin (1936) did, in terms of movements toward or away from stimuli in the environment. Such movements, however, are often inhib-ited by human beings (Lang, Bradley, & Cuthbert, 1997). Accordingly, it is useful to understand approach and avoidance in terms of operations of underlying systems. Gray (1981, 1982) theorized a behavioral activation system (BAS) that is sensitive to potential rewards and motivated to seek them, and a behavio-ral inhibition system (BIS) that is sensitive to potential threats and motivated to avoid them. Such systems are understood in terms of real-time interactions with the environment, yet consist of multiple subcomponents and tendencies. Individual differ-ences in BAS, for example, should bias perceptions of appeti-tive stimuli, trigger other approach-related thoughts, an