RESPONSES TO MONOCHROMATIC LIGHT 13 



show that we are working with the stimuli at the point where 

 they possess approximately equal stimulating power. We get 

 one of two reactions without being able to predict which will 

 occur, viz., a break down in habit or a complete reversal with 

 respect to choice of light. Possibly our inability to predict the 

 response may be due to slight fluctuations in the current sup- 

 plying the arc, which would alter the intensity of the two lights 

 unequally (the distribution of energy in the spectrum of any 

 source varies greatly, depending upon the temperature at which 

 the source is burned). 



Similar tests upon Rat II (reacting positively to yellow) 



Table IV shows that this animal never learned to discrimi- 

 nate between the yellow and blue at anything like equal energies. 

 This gave us an opportunity to test the question of reversal in 

 choice of positive light. The tests show without discussion that 

 his discrimination had been based upon the difference in intensity. 



April 26th. Gave series of 15 trials with yellow as only stim- 

 ulus, 93% correct. This was done to bring animal back to 

 normal habit of reacting to one stimulus. Then for 7 trials 

 full intensity blue was substituted for the yellow. Went to blue 

 on every trial. 



April 2/th. Yellow and blue full intensity, 10 trials. Chose 

 blue on every test. Then blue was cut out and yellow given alone. 

 10 trials, 80% correct. 



April joth. Yellow alone, full intensity, 15 trials, 100% 

 correct. 



May 1st. Yellow and blue full intensity, 20 trials. Went to 

 blue on every trial. This shows the same results as tests on 

 April 27th. 



Another series of tests was undertaken where white light 

 (from Nernst filament projected direct upon plaster surface) 

 was substituted for blue or yellow at will. 10 



May 1 6th. Yellow (animal's positive color) at full intensity. 

 Nernst in place of blue. 9 trials. Animal went to white light 

 on every trial. Immediately following this test one was given 

 in which white light was substituted for yellow. 10 trials. Went 

 to white light on every trial. 



May iyth. Another series was given with identical results. 



10 It will be remembered that Washburn suggested this type of test at the Boston 

 meeting of the American Psychological Association (1910). 



