378 HARVEY CARR 



does the slight decrease in efficiency resulting from the altered 

 conditions prove that the rats are relying upon these stimuli in 

 part, for any alteration of the subordinate and supplementary 

 sensory environment may produce disturbances as readily as 

 those aspects which are utilized as guides and controls. In 

 other words, these altered conditions may have operated merely 

 as sensory distractions. There are several considerations which 

 indicate the truth of this hypothesis. The rapid adjustment to 

 these changes is readily interpreted on this basis. The relatively 

 poor records secured by the second experimenter were evidently 

 due to fear. This emotional reaction was quite evident in the 

 animal's behavior. The hypothesis is further supported by the 

 fact that these changes did not materially effect the rate of 

 progress in the final perfection of the habits. 



The animals usually did assume and maintain a bodily orien- 

 tation during feeding resulting from and characteristic of their 

 direction of approach to the food box. However constancy of 

 motor attitude was not the invariable rule. No attempt was 

 made to control this factor nor were systematic records of bodily 

 orientation taken. We are thus forced to the conclusion that 

 the controlling and guiding stimulus to each choice consists 

 either of the sensory aspects of the alternate act or of a motor 

 attitude resulting from that act. 



EFFECT OF INCREASING THE TIME INTERVAL 



During the mastery of the problem, a period of 16.5 seconds 

 was devoted to feeding and handling between runs. After the 

 perfection of the association, this time interval between the 

 two acts was gradually increased in order to determine whether 

 the ability of the animals to make correct choices was dependent 

 upon the length of this interval. 



The results of this experiment are graphically represented by 

 curve 1 of fig. 8. The percentages of correct choices are repre- 

 sented by the ordinate values while the various time intervals 

 in seconds are distributed along the abscissa. The first four 

 percentage values were secured for the normal time interval of 

 16.5 sec. All percentage values for the periods of 16.5 and 44 

 seconds inclusive are based upon a total of 224 trials. As the 

 time interval is increased, the animals are given a greater oppor- 

 tunity for feeding, and necessarily fewer trials per day can be 



