The Experimental Analysis of Behavior
The 1957 American Scientist article, reproduced in full
The consequences of behavior, whether positive or negative, and the control acquired by various stimuli related to them do not exhaust the variables of which behavior is a function. Others lie in the field commonly called motivation. Food is a reinforcement only to a hungry organism. In practice this means an organism whose body weight has been reduced substantially below its value under free feeding. Reinforcing stimuli are found in other motivational areas. Responding to a key can be reinforced with water when the organism is deprived of water, with sexual contact when the organism has been sexually deprived, etc. The level of deprivation is in each case an important condition to be investigated. How does food deprivation increase the rate of eating or of engaging in behavior reinforced with food? How does satiation have the opposite effect? The first step toward answering such questions is an empirical study of rate of responding as a function of deprivation. An analysis of the internal mechanisms responsible for the relations thus discovered may require techniques more appropriately employed in other scientific disciplines.
An example of how the present method may be applied to a problem in motivation is an experiment by Anliker and Mayer  on the familiar and important problem of obesity. Obese animals eat more than normal, but just how is their ingestive behavior disrupted? Anliker and Mayer have studied several types of normal and obese mice. There are strains of mice in which the abnormality is hereditary: some members of a litter simply grow fat. A normal mouse may be made obese by poisoning it with goldthioglucose or by damaging the hypothalamus. The food getting behavior of all these types of obese mice can be observed in the apparatus shown in Figure 12. A fat mouse is shown depressing a horizontal lever which projects from the partition in the box. On a fixed-ratio schedule, every 25th response produces a small pellet of food, delivered by the dispenser seen behind the partition. A supply of water is available in a bottle.
Each mouse was studied continuously for several days. The resulting cumulative curves (Figure 13) show striking differences among the patterns of ingestion. Curve C shows normal cyclic changes in rate. The nonobese mouse eats a substantial part of its daily ration in a single period (as at a and 6), and for the rest of each day responds only at a low over-all rate. The result is a wave-like cumulative curve with 24 hour cycles. A mouse of the same strain made obese by goldthioglucose poisoning does not show this daily rhythm but continues to respond at a fairly steady rate (Curve A). The slope is no higher than parts of Curve C, but the mechanism which turns off ingestive behavior in a normal mouse appears to be inoperative. Curve B is a fairly similar record produced by a mouse of the same strain made obese by a hypothalamic lesion. Curves D and E are for litter mates from a strain containing an, hereditary-obese factor. E is the performance of the normal member. Curve D, showing the performance of the obese member, differs markedly from Curves A and B. The hereditary obese mouse eats at a very high rate for brief periods, which are separated by pauses of the order of one or two hours. A different kind of disturbance in the physiological mechanism seems to be indicated.
Williams and Teitelbaum  have recently produced a fourth kind of obese animal, with an apparatus in which a rat must eat a small amount of liquid food to avoid a shock. The avoidance contingencies specified by Sidman and illustrated in Figure 11 are used to induce the rat to ingest unusually large amounts of even unpalatable food. A condition which may be called “behavioral obesity” quickly develops.