Response Decrement

We can recognize at the outset two major types of response decrement : (1) decrement resulting from exercise or performance and (2) decrement resulting from lack of exercise. The first class is traditionally associated with fatigue, the second class with forgetting. There are many points of relation between the two classes. While our major attention will be given to decrement resulting from exercise, it is well to bear in mind that, from the standpoint of efficient performance, use and disuse operate in the same way; that is, there is an optimal rate at which performance may be repeated without decrement. Too much use as well as too much disuse is deleterious.

For each response there exists an optimal rate at which that response may be repeated without decrement. The amount of decrement exhibited in a given performance is relative, therefore, to the frequency with which response is made, the highest efficiency value lying at some median frequency. High frequency values are associated with the usual type of work decrement. Low frequency values are associated with habit disintegration and forgetting. An especially clear instance of response decrement from prolonged activity is found in experimental work on negative adaptation. When some simple reaction, such as the protective eyelid reflex, is elicited repeatedly, the amplitude of response falls progressively until a stage is reached where the stimulus (a loud noise) is no longer effective in producing response.

The principle of response frequency is directly related to the factor of task homogeneity or complexity, that is, the extent to which successive repetitions call for an identical response. Some individuals report that they accomplish more if they organize their work so that they can turn from one performance to another at will.


Response is rarely made to a single isolated stimulus; rather, there are available at any given time a variety ,of stimuli and reinforcing agents which may occasion one and the same response. Stimulus conditions change markedly in the course of prolonged activity; therefore, decrement is relative to the intensity of the stimulus complex. If the stimulus intensity decreases in a series of repetitions of one act, or even if it is held constant, response will also tend to decrease. But if a progressively stronger group of stimuli and reinforcing agents is applied during the series of repetitions, response may be unaffected and may even be augmented. This latter condition often obtains in the more complicated types of performance, where individuals may work for longer periods without noticeable decrement.

By increments in the amount of reinforcement of the task at hand in the interest of work constancy, irrelevant stimuli are rendered progressively less effective. Thus an individual who makes a long automobile journey is first able to attend to many other stimuli besides those associated with his driving. He looks at the scenery, converses with his companions, and calculates his mileage. As time passes, however, his preoccupation with the driving becomes more pronounced. The number of objects to which he attends is limited. He looks at the instrument panel and watches his oil and gasoline gauges, but he disregards the scenery and ceases to converse. Hours later he will still be driving, but now he is becoming more and more careless; he resents any obstruction to his activity, such as a stop light, and is apparently unable to stop driving. This suggests that the individual has passed beyond effective reinforcement and is actually suffering physiological impairment.

Not all the stimuli operating at a given time facilitate and reinforce the performance under examination. Those stimuli which would lead to rival response tendencies are in competition with the acting stimuli for control of the behavior flux. The amount of decrement exhibited is relative to the effectiveness of neural competition; that is, the stronger the rival impulses, the greater the decrement. Neuromuscular action patterns differ in their ability to resist decrement. Competition frequently results in the displacement of recently acquired reactions by reactions which are stronger and more deeply ingrained. After prolonged work delicate motor coordinations are often displaced, and there is clumsiness in speech and manners. Enunciation is slovenly and halting, the vocabularly shrinks, and the field of effective stimuli becomes narrowed. Unimportant intellectual problems are approached with emotional fervor, and peevish behavior is unusually prominent.

If the performance under survey is functionally related to another performance which has recently been exercised, there is an apparent transfer of decrement from one to the other. The amount of decrement developed in the second performance will be relative to the amount of decrement developed in the first. Assuming addition and subtraction to be
related performances, more decrement in subtraction will be exhibited when it follows addition than when it follows an unrelated performance, such as finger oscillation. This principle is generally referred to as transfer of fatigue; and while practically nothing is known about the exact conditions which determine it, the principle itself expresses an established fact. Of the several theories which have been proposed to account for this transfer, that which assumes that the related performances have common elements has the most adherents.