36 



HAROLD C. BINGHAM 



thin plate of glass across each compartment at a point just 

 beyond the exit, the chicks were stopped near the exit and yet 

 were not prevented from seeing the regular stimulus. As soon 

 as they had learned the way of escape and had ceased trying to 

 reach the stimulus, the glass plates were removed. 



After a perfect habit had been acquired, the amount of dif- 

 ference between the two stimuli was decreased. When the 



o 28 H o 7 + discrimination became perfect, the situation 



was changed to o 28 M o 9 +. The large circle was thus the 



standard which remained constant. The smaller circle was the 

 variable which was successively increased in size until the ani- 

 mal could no longer choose correctly. This limit of correct 

 choices was accepted as the chick's threshold of difference. 

 The changes in diameter of the variable, it was found, could be 



TEST SHEET 



Title of investigation, Form: o28H A 28+ 



Experimented on, 9 



Harvard Psychological Laboratory, December 25, 1912 



Record Sheet, 1; Series, 15 



6-4-29.5 

 Remarks: Tendency to choose by position, i.e., to go where it last escaped. 

 Usually goes immediately to other compartment when it has been shocked for wrong 

 choice. 



as great as 5 mm. between o 7 + and o 12+ when presented 

 with a standard © 28 + . Above ©12+ the diameter of the 

 variable was successivel}^ increased only by 1 mm. 



For tabulating results, a record sheet which had formerly 

 been used in the laboratory was well suited to my needs. It 



