i68 



BRAIN MECHANISMS AND LEARNING 



added incentive. This was accomplished by having the wrons; lever 

 terminate the series of stimulations, and the correct lever re-start the 

 series. Thus the animal making all correct responses would be stimulated 

 as before, i second on, 2^ seconds oft. But during learning, each day, the 

 sequence would be interrupted every time an error occurred, and restarted 

 only by the next correct response (Fig. 15). 



EFFECT OF STIMULUS AFTER LEARNING 



SELF STIMULATION POINTS 



NO SS 

 PTS 





MAXIMUM IMPAIRMENT 



MODERATE IMPAIRMENT 



MINIMUM IMPAIRMENT 



Fig. 14 

 Memory test for twenty-three points, all of which yielded impair- 

 ment on learning test. Seventeen cases were self-stimulators. Si-x were 

 non-self-stimulators. The figure shows that fifteen of the self-stimu- 

 lation points yielded maximum impairment when introduced after 

 learning; the other two self-stimulation points yielded moderate 

 impairment. Of the non-self-stimulation points, three yielded moder- 

 ate impairment, and 3 yielded almost no impairment. 



When this test was applied to the confused selt-stimulators, those with 

 very rapid rates of self-stimulation were no longer confused. Several of 

 the slower self-stimulators appeared, however, to be still confused 

 (Table I). The possibility remained that those still appearing confused were 

 in fact making errors to terminate negative reinforcement; i.e. they were 

 receiving both positive and negative reinforcement from the same 

 stimulus (Roberts, 195 8). To test for this in a very preliminary fashion 

 three of them were given tests for escape responding yielded by the 

 electric stimulus, and these three did give evidence of escape. Thus we 

 cannot find from these tests any support for the notion that the self-stimula- 

 tion points cause a bona-fide confusion. Rather, it appears that the large 

 reinforcing effect of the electric stimulation somehow overrides the 

 smaller positive reinforcing effect of the food. When food and electric 



