FACTORS INFLUENCING THE RECALL OF COMPLETED AND OF INTERRUPTED ACTIVITIES
Behavior usually occurs, not as disconnected reactions to unrelated stimuli, but in the form of more or less coherent groups of reactions. Such a series of actions as perceiving an empty feeling in the stomach, looking at one's watch, walking into the kitchen and asking whether dinner will be ready soon cannot be described adequately as responses A, B, C, and D, evoked by stimuli A1, B1, C1, and D1. Rather, this is a sequence of actions in which each member must be understood as deriving from the individual's hunger and his need or his desire for food. The responses appear to be the product both of a continuing state of hunger and of other elements in the situation, presumably unrelated to each other, such as the watch, the kitchen door, and the mother at the stove. It is to the continuing state that we must look for an understanding of the organized character of the series of actions. The psychological definition of the basis on which responses are thus organized into groups has long been a subject of discussion and investigation. A variety of terms, such as drive, motive, set, and direction, has been suggested to designate the principle which underlies and unifies such sequences of behavior on different levels of complexity.
In certain instances, the organized character of a series of responses can be attributed to a persisting physiological state called a "drive" or "tissue need." These disturbed states of the organism include dryness of the mucous membranes of the throat (underlying the thirst drive), distention in the bladder or colon (the excretory drives), tensions in the genital organs (the sexual drive), and spasmodic contractions of the stomach wall (the hunger drive). As long as these tissue needs persist, they continue to arouse responses; the series of responses comes to an end only when the disturbance subsides.
At the present stage of our knowledge, however, it is not possible