J. OLDS AND M. E. OLDS 



159 



that the animal had stopped making errors. Every test consisted of 2 days, 

 one with the left lever correct (indicated by graph on left), the other with 

 the riglit lever correct (indicated by graph on right), to rule out position 



WIDE RED 

 PLASTIC LEVER 



LONG WHITE 

 METAL LEVER 



RED PLASTIC 

 FLOOR MARKER 



PHOTO 

 CELL 



11 



x:i. 



WHITE METAL 

 FLOOR MARKER 



^ LIGHT 



'source 



FOOD TRAY 



Fig. 6 

 Problem box. Response on correct lever causes food magazine 

 to operate. Animal must retrace steps and break photo-beam in 

 order for correct lever to work a second time. Correct lever 

 changes from side to side from day to day. After about a month 

 of preliminary training, each animal daily achieves criterion 

 (ten correct runs in a row) in about three to twenty-five trials. 



preference. In the six tests shown in Fig. 7, errors level off in all cases, 

 while correct responses continue to cumulate. 



In the first test, there was no stimulation. Then stimulation was intro- 

 duced in an effort to interfere with the learning mechanism. For this 

 purpose a series of i-second trains of sine wave current (60 o.p.s.) was 

 introduced at a constant rate of one for every three seconcis. A pair of 



