VISUAL PERCEPTION OF THE CHICK - 85 



introduced before the beginning of series 11, it is improbable 

 that the brightness factor served as a basis of discrimination 

 in more than two or three series after the third. The bright- 

 ness difference was rapidly reduced and in view of the bright- 

 ness threshold as determined by Lashley (reference 21 : Chapter 

 2), this factor would have been nil after series 5. The maximum 

 number of correct choices in a series is first reached by chick 

 27 in series 19. Additional comment upon the appearance of 

 discrimination evidence will be postponed for discussion in 

 connection with the shock as a motive in the learning. 



2. The number of correct choices offers a measurement of 

 progress in forming the discrimination habit or secondary task. 

 Tn the primary or maze task a more reliable unit of measurement 

 to denote progress is the elimination of useless movements. 

 Change in the number of trials at the outside corners offers 

 one means of determining improvement In the experiment 

 box. To indicate improvement, the number of trials at the 

 outside corners must begin relatively high and decrease with 

 ten as the minimal limit. The larger numbers in the early 

 series may be due either to the chick's failure to step upon the 

 proper portion of the tripping device, even though the approach 

 is the -f exit (outside corner), or to choices of the — compart- 

 ment and consequent trials at the — exit. 



Improvement with respect to outside corners Is generally 

 noticeable from the first. While each individual has "bad 

 days," the table Indicates a general tendency towards decrease. 

 The average for the three chicks suggests that the curve repre- 

 senting the number of outside corner trials would tend to 

 become a fairly straight line gradually descending towards the 

 limit If a sufficiently large number of individuals were tested. 

 This limit is reached by chick 27 for the first time in series 24 

 and maintained throughout three successive series. 



3. Similarly, the number of trials at the stimuli must be 

 relatively large at the beginning. As the chick learns Its task, 

 however, the unsuccessful attempts at the stimulus decrease 

 with considerable rapidity. Chick 25 first eliminates all 

 attempts at the stimulus In series 11. Chick 27 next reaches 

 the same stage in series 14. It Is Interesting to note that 

 perfection In this particular negative task is attained more 

 rapidly than In the positive task of outside corner trials. 



