Fixed-interval reinforcement of running in a wheel.

The notion of "rate of responding" in the study of operant behavior presupposes a unit of behavior of which instances can be counted. Such operants as pressing a lever (rat), pecking a key (pigeon), or pulling a plunger (man) are fairly complex sequences of events, with an identifiable beginning and end. The rat reaches toward and grasps the lever, depresses it, allows it to rise, and releases it; or if it keeps hold of the lever, the response begins with depressing the lever and ends with permitting it to rise. In either case the rat is in approximately the same position before and after responding. The response is "phasic"; it can be repeated without engaging in other behavior, and instances can be counted. Changes in rate of responding can be studied. A countable unit is not always easily identified. In reinforcing a rat for "holding down a lever" or for "standing motionless," for example, we may record time spent in a given position; but it is not clear that duration of not-moving corresponds to a rate of emission. A related problem is raised by continuous responding. Is the rate at which a rat runs down a straightaway equivalent to the rate of pressing a lever? In approaching this problem, we can begin by noting how a continuous response, such as running in a wheel, changes under certain conditions of reinforcement. A previous report (Skinner, 1938 pp. 355-357) described the behavior of rats reinforced with food for running a given distance in a wheel. In the present experiment, running was reinforced on a fixed-interval schedule. The problem of defining a "unit" must be met at once in deciding how the movement of the wheel is to operate the food magazine. When the magazine is operated upon completion of a given number of turns, running is reinforced on a "ratio" schedule. But how much of a turn, how much action, is to be called "running" on an interval schedule? In the present case, precision switches operated by a cam on the wheel shaft were arranged 180 degrees out of phase. After a reinforcement was set up by the programming circuit, both switches had to close (in succession) to operate the magazine. In one sense, this defines a unit of running, though it is not clear that such a unit is meaningful in describing behavior throughout the interval.