DRIVE AND MOTIVATION 



[ 5'3 



Obstruction Method 



Because even the simplest expression of motivation 

 involves work, fatigue and other competing motives, 

 it is possible to look at the consummatory response 

 and other measures of motivated behavior as the 

 strength of the tendency to overcome some inter- 

 ference in reaching a goal. This principle is put di- 

 rectly to work in the obstruction method. Here the 

 motivated animal is required to cross some barrier to 

 reach its goal. In the case of the rat, the barrier might 

 be a physical obstruction, such as a tunnel filled with 

 sand, a doorway blocked with many thicknesses of 

 paper or an electrified grid which the animal must 

 traverse. In the first two cases, the animal must work 

 to reach its goal; in the last, it must take punishment. 

 In all of these methods, the frequency with which the 

 barrier is crossed in unit time, the speed of response 

 and the size of the barrier necessary to inhibit goal- 

 directed behavior completely are all measures of the 

 strength of drive. 



The obstruction box with an electrified grid was 

 developed by the Columbia workers under Warden 

 (164) and used as a standardized test for (he measure- 

 ment of many kinds of motivation in the rat. The pro- 

 cedure was to use rats 185 days old, presumably sati- 

 ated in all drives except the one being tested. First, 

 the animals were familiarized with the goal object 

 and a standard electric shock; then they were placed 

 in the starting chamber, and the number of ap- 

 proaches, contacts and crossings of the grid were re- 

 corded in a 20-min. period. After each crossing, the 

 animal was allowed brief exposure to the goal object 

 and was returned to the starting chamber before any 

 significant amount of consummation. In different 

 experiments, the goal objects were food, water, a 

 receptive female, a male, another rat of the same sex, 

 a litter of infant rats, a new area to be explored or, 

 as a control, an empty, familiar goal box. Thus, it was 

 possible to measure the relative strength of different 

 drives against the standard of the electrified grid as a 

 function of such things as amount of deprivation, de- 

 gree of deficit or hormonal change in the internal en- 

 vironment, and the type of goal object. 



A summary of the major results obtained with this 

 method is shown in figure 3. In terms of the number of 

 crossings of the grid in a 20-min. period, the rank 

 order of drives from the strongest to the weakest is: 

 maternal, thirst, hunger, sex and exploratory. This 

 ordering may only be taken as suggestive, however, 



1 2 3 4 5 6 7 8 "28 

 DAYS OF DEPRIVATION 



fig. 3. A summary of obstruction-box data from the rat 

 showing the mean number of crossings of an electrified grid in 

 a 20-min. period to reach different goal-objects. The abscissa 

 shows the periods of deprivation of food and water for both 

 sexes and of sexual experience for male rats. Points at the 

 extreme right show the mem number of crossings made bj 

 estrous and diestrous female rats and by multiparous females 

 as well as by rats of both sexes when the t;oal object was a new 

 compartment that could be explored. [From Warden ul>|> 



since there was considerable variability in the scores 

 of individual animals, and there is some question as 

 id whether .ill the conditions of lestiiiL; were truly com- 

 parable. 



In addition to this rank ordering, several other 

 findings are worth) of note. In sexual behavior of the 

 emale rat, there is a clear association between the 

 frequency of grid crossing and the estrous cycle, the 

 maximum occurring during estrus and the minimum 

 in diestrus, just as in the case of the activity measure. 

 In contrast, the male shows a constant daily rate of 

 crossing, even after varying amounts of sexual dep- 

 rivation from 12 hr. to 28 days. In the cases of hungei 

 and thirst, on the other hand, as deprivation proceeds, 

 there is a surprisingly early point when the amount of 

 drive decreases. After 1 to 2 days of thirst and 2 to 4 

 days of hunger, grid crossing decreases in frequency. 

 Perhaps this decrease actually represents a true meas- 

 ure of one aspect of motivation, different from that 

 in the activity and ingestion measures. While we have 

 no experimental evidence illuminating these differ- 

 ences, the obstruction method, nevertheless, is a 

 valuable standard test for the measurement of motiva- 

 tion. 



