a procedure in which brief, inescapable aversive stimuli are presented at fixed intervals (shock–shock intervals) in the absence of a specified response. If the response is made, the aversive stimulus is postponed by a fixed amount of time (the response–shock interval) from that response. Also called avoidance without warning signal; continuous avoidance; free-operant avoidance. [Murray Sidman (1923– ), U.S. psychologist]