132 FLETCHER, COWAN AND ARLITT 



TABLE 10— Continued 



Trial No. 



of 



No. of Chick 25 26 27 28 29 30 errors 



2 9 " 20 " 18 " 57.5" 49 " 36 " 21 



4 24 " 39 " 1' 8 " 23 " 28 " 10 " 26 



10 28 " 43 " 26 " 1' 24 " 53 " 7 " 14 



14 11 * 5 " 27 " 15 " 9 " 12 " 19 



Average 18+" 26+" 34+" 44 + " 34 + " 16 + " 



20 7.5" 22 " 29 " 32 " 7 " 30.5" 13 



23 43 " 51 " 18 " 31 " 4 " 35 " 20 



25 5 " 36 " 24 " 6 " 6 " 21 " 20 



Average 18+" 36+" 23 + " 23 + " 5 + " 28+" 



41 5 " 7 " 6.5" 11 " 9.5" 6 " 8 



43 21 " 50 " 30 " 32 " 53 " 41 " 23 



46 12.5" 29 " 28 " 1' 3 " 23 " 9 " 21 



47 8 " 19 " 19 " 29 " 23 " 11 " 12 



48 5 " 6 " 4 " 4 " 10.5" 12.5" 16 



51 1'43.5" 1' 33 " 1' 13 " 2 " 36 " 2' 13 " 8 



Average 25+" 34+" 26 + " 23 + " 25+" 35 + " 



71 6 " 3 " 10.5" 2.5" 3 " 5.5" 14 



72 1' 21 " 47 " 1'38 " 55 " 45 " 1' 3.5" 29 



74 10 " 19 " 26 " 11.5" 23 " 8 " 14 



80 5 " 5 " 4.5" I'll " 14 " 24 " 11 



81 8 " 5 " 4 " 7 " 4 " 4 " 18 



Average 22 " 15+" 28+" 29+" 17+" 21 + " 



EXPERIMENTS WITH SENSORY DISCRIMINATION 



The apparatus used for testing the ability of the chicks to 

 make sensory discriminations was the Yerkes visual choice appa- 

 ratus. Only the two middle alleys were used, the other two 

 being shut off by wooden partitions. Stimulus screens with 

 openings in them large enough to permit the chick to pass 

 through were slipped into the grooves at each end of each 

 alley. The screens were made of photographic mounting card- 

 board and two of them were light grey and two dark grey in 

 color. The exit path in which the light grey screens were 

 placed was always open and the ' chick choosing that path pro- 

 gressed directly out of the apparatus to the chicken pen and 

 the society of the other chicks. The exit path characterized 

 by the dark screens was always closed at the far end and the 



