“…Following response acquisition under responsecontingent schedules of food presentation (e.g., Kelleher & Morse, 1968), shock postponement (e.g., McKearney, 1969), or response induction by periodic response-independent shock (e.g., Morse, Mead, & Kelleher, 1967; see Hutchinson, 1977, for a review), lever pressing of squirrel monkeys can be maintained by shock presentation under interval schedules, which present shock following the first response after a specified temporal interval (see Morse & Kelleher, 1977, for a review). But when shock is delivered under ratio schedules, that is, following a specified number of responses, pressing typically is suppressed, even when the number of responses per shock is matched to a preceding condition in which responding was maintained under an interval schedule (Branch & Dworkin, 1981). Current conceptualizations of "shock-maintained behavior hold that the schedule of shock presentation is fundamental in determining the consequent stimulus function of shock (Morse & Kelleher, 1977) -presented under interval schedules, shock functions to reinforce responding; under ratio schedules, it serves to punish responding.…”