“…Research during the past 20 years has shown that responsiveness to, and for, many kinds of stimulation, besides the traditional examples of food and water, does indeed change with the degree of prior availability of the stimulation. Lengthening the interval between successive stimulus exposures has been found in rats, monkeys, and other species to increase the probability of such behaviors as visual exploration of novel stimuli (Butler, 1957;Rabedeau & Miles, 1959), locomotor exploration of novel stimuli (Berlyne, 1955;Fowler, 1965Fowler, , 1967Myers & Miller, 1954;Schneider & Gross, 1965), unrewarded manipulation (Forgays & Levin, 1961;Premack & Bahwell, 1959), and light-contingent responding (Forgays & Levin, 1961;Fox, 1962;Premack & Collier, 1962;Stewart, 1960, p. 319 188). Decrements in responding during sessions that follow deprivation have been reported for each of the above stimuli: visual exploration (Butler & Harlow, 1954;Rabedeau & Miles, 1959), locomotor exploration (Adlerstein & Fehrer, 1955;Berlyne, 1955;Glanzer, 1961;Montgomery, 1951Montgomery, , 1952bMontgomery & Monkman, 1955;Montgomery & Zimbardo, 1957;Welker, 1957;Williams & Kuchka, 1957), unrewarded manipulation (Forgays & Levin, 1961;Harlow, 1950;Kling, Horowitz, & Delhagen, 1956;McCall, 1965;Premack & Bahwell, 1959;Schoenfeld, Antonitis, & Bersh, 1950;Welker, 1956), light-contingent responding (Forgays & Levin, 1961;Fox, 1962;…”