“…The physical challenge tasks consisted of inhalations of carbon dioxide (CO 2 ) enriched air (for details, see Lejuez, Forsyth, & Eifert, 1998) and of a timed, breath-holding procedure (Hajek, Belcher, & Stapleton, 1987). The psychological challenge consisted of the modified Paced Auditory Serial Addition Task (PASAT; Diehr, Heaton, Miller, & Grant, 1998), a mental arithmetic challenge task requiring sustained attention despite aversive auditory feedback for incorrect responses that has been shown to produce elevated levels of stress (Holdwick & Wingenfeld, 1999). Participants were instructed to continue the tasks for as long as they liked but not to continue past the point at which they became uncomfortable.…”