DELAYED REACTION 39 



mine whether the animals could form an association between the 

 lights and some constant marked differences in the external 

 environment. In order to test this, three backgrounds of widely 

 differing degrees of brightness were used as described above in 

 the section on method. The animals tested under these condi- 

 tions were: Rats Nos. 2, 4, 5 and 7 of Set A and Nos. 10, 12 

 and 16 of Set B; the dog Brownie; and the raccoon Jill. 



The results of this test were entirely negative. No case was 

 found where the animal made use of the different backgrounds 

 as cues for guiding its reactions. One or two of the animals 

 increased their interval of delay under the new conditions. 

 However, when the old conditions of similar backgrounds were 

 replaced, the long intervals of delay still continued. This ind - 

 cated that the improvement was due to practice. 



(d) Effect of number of boxes upon delay. — As stated above 

 in section (a), whenever an animal's reactions broke down upon 

 a particular box, that box was dropped from the tests and the 

 discrimination confined to the other two. The following ani- 

 mals were tested under these changed conditions: Rats 4, 11, 

 1 5 and 1 6 ; the dog Blackie ; and the raccoons Jack, Bob and 

 Betty. The results are given for convenience above under 

 section (a). Here it may be noted that all the animals delayed 

 longer with two than with three boxes. This can be readily 

 explained on the basis of the complexity of the problem. The 

 maximum delay for any animal is decided by the accuracy of 

 its response. With two boxes, this accuracy was increased and 

 hence the maximum delay recorded was greater. 



(e) Effect of other conditions upon delay. — The results do not 

 indicate certainly any effect of punishment or of the number 

 of trials upon the length of the interval of delay. 



The results of this section indicate that the following factors 

 influence the maximal amount of delay: (i) Different groups 

 of animals; (2) size of release, and (3) the number of light 

 boxes used. The following factors do not influence the amounts 

 of delay: (i) Punishment and reward; (2) number of trials 

 daily, and (3) backgrounds of different brightnesses. 



C. Methods of Reaction After Delay Used by the Animals. — 

 There are three different methods of delay which might have 

 appeared and in point of fact did appear in our delayed reac- 

 tion experiments: (i) The animal may maintain an orientation 



