366 



HARVEY CARR 



ing from this enclosure are two exits, |R" and L, each 4" x 4" 

 in dimensions. These exits are separated from each other by a 

 distance of 6", and they open into two runways, A and B, both 

 of which lead to the food box F. These paths to the food box 

 can be closed by means of two sliding doors situated at C and D. 

 A group of eight white rats was tested upon a simple alter- 

 nation between two positions habits. On each trial the animal 

 was taken from the food box and placed by hand at the posi- 

 tion marked by an arrow in the figure. Both position and 



Figure 1. — Plan of apparatus. R and L, two exits; A and B, two pathways; 

 C and D, sliding doors; F, food; Arrow, position in which rats are placed in 

 apparatus; X and Y, two positions at which rats were placed in control tests. 



body orientation were kept constant from trial to trial, the 

 head of the animal being placed at the position of the arrow 

 head equidistant from the two exits. On the first trial of each 

 day the path leading from the exit R was left open, while the 

 path from L was blocked. On the next trial L was opened and 

 R blocked, and this procedure was repeated for each day" so that 

 the order of presentation may be represented by the schema 

 of R-L-R-L-R-L, etc. The number of trials per day was varied 

 from two to eighteen according to the condition of the animal 

 and the stage of learning. Progress in mastery was measured 

 in terms of the percentage of correct choices, and a choice was 

 termed correct whenever the proper door was entered sufficiently 

 to secure a body orientation along the length of the passage 



