DRIVE AND MOTIVATION 



l 5 l 



The value of the learning technique in the studv of 

 motivation, then, lies primarily in the fact that it of- 

 fers a large variety of ways of measuring performance 

 as a function of motivation where investigations may 

 be made of such variables as the amount of work re- 

 quired, the amount of ingestion or consummation, 

 the nature of the punishment or reward used as in- 

 centive or reinforcement, and the strength of drive 

 varied by deprivation, hormonal changes, etc. Thus, 

 an animal learns to press a lever to get food and its 

 rate of pressing or performance, once it has learned, 

 is a function of its hunger, what kind of reinforcement 

 or reward it gets from pressing, and the amount of 

 work required for each reinforcement (143). For 

 example, the marmoset will perform at a high rate of 

 responding when 10 per cent glucose is given as a 

 reinforcement for every lever-pressing and will hardly 

 work at all for a 40 per cent reward. On the 

 other hand, when 80 lever-pressings are required for 

 each reinforcement, the animal will not work for 10 

 per cent glucose but will give the highest rate of 

 responding for 40 per cent (unpublished observa- 

 tions). Similar measures of motivation may be ob- 

 tained from the latency, strength and frequency oi 

 response in such learned performances as running 

 down a runway to reach a goal box containing an 

 incentive, lifting the lid of a food cup, jumping from 

 a platform through a window to a goal platform, 

 turning a wheel to get food or getting off a grid that 

 is electrified or can be electrified, etc. 



Summai v 



It is possible, then, to define many of the concepts 

 in motivation operationally and to measure drive, 

 goal-directed behavior and satiation quantitatively. 

 Gross bodily activity yields a measure of undirected 

 drive. Directed drive is measured by strength of con- 

 summatory behavior, preference or choice and learned 

 performance (including the obstruction method) as 

 shown by the latency, frequency, speed and magni- 

 tude of response. Where goal-directed behavior is 

 involved, it is possible, furthermore, to assess the in- 

 centive value of goals, their role in orienting and 

 directing the execution of motivated behavior and 

 their function as rewards and punishments. In all of 

 these cases, satiation may be measured as drive re- 

 duction and the competitive interference of other 

 motivation with the expression of the motive being 

 measured. 



Drive can be produced by deprivation, deficit, 

 hormonal changes and certain other fluctuations in 



the internal environment as well as by goal stimuli 

 functioning as incentives. The greater the drive, the 

 greater the activity, the greater the consummatory 

 response, the greater the energy expended and the 

 work done, the greater the barrier that will be over- 

 come to reach a goal, the greater the preference, and 

 the greater the level of learning reached. Increasing 

 drive beyond a certain point, however, may result 

 in a decrement in motivated behavior, in some cases, 

 presumably as a result of physical impairment of the 

 animal. But whether the decrement shows up or not, 

 and at what intensity of drive, will depend upon the 

 measure of motivation used. 



THE NEUROPHYSIOLOGY OF MOTIVATION 



In reviewing the literature on the physiological 

 mechanisms underlying motivated behavior, we 

 shall use as a framework the general multifactor 

 mechanism schematically described earlier in this 

 chapter. While this approach loses some of the ad- 

 vantage of discussing each kind of motivation sepa- 

 rately, it allows us in focus directly upon the physio- 

 logical problem, to make useful comparisons among 

 the various kinds of motivated behavior and to point 

 up sharply the gaps in our knowledge of physiological 

 mechanisms. [For a separate discussion of the major 

 kinds of biological motivation sec Morgan & Stellar 

 (109).] To be sure, we shall eventually learn that each 

 kind of motivation lias its own, unique physiological 

 mechanism, but at this stage of knowledge, the simi- 

 larities brought out by a unified approach are more 

 important than the differences, for what we can 

 learn about one kind of motivation can be most 

 helpful in our understanding of other kinds. 



Diencephalic Mechanisms 



The evidence to date strongly points to a major 

 focus of the physiological mechanism in control of 

 motivated behavior in the dicncephalon, primarily 

 the hypothalamus. (This is considered in Chapter 

 XXXYII of this work by Ingram.) Physiological 

 studies of this region of the brain implicate it as an 

 important integrating mechanism in the control of 

 autonomic and somatic adjustments of the kind that 

 are important in motivation. For example, Hess (70; 

 cf. 61), in his extensive stimulations of the diencepha- 

 lon of waking cats with chronically implanted elec- 

 trodes, was able to produce: changes in arterial 

 pressure, respiration and pupil size; salivation, vomit- 



