12 JOHN B. WATSON AND MARY I. WATSON 



Control tests on Rat I (reacting positively to blue) 



May 3rd. After normal series at equal energies 8 blue was 

 cut to 20 opening. Animal set up right position habit. Dis- 

 crimination lost. Normal series (5 trials) given again. Animal 

 went to blue as usual. The behavior of Rat II (yellow) had 

 prepared us for this type of result. The blue to them is high 

 in the scale of intensity; the yellow very low. When the blue 

 was brought down to one-eighteenth the energy of the yellow, 

 the two stimuli were too nearly equal in intensity to afford a 

 basis for a differential response. It may be argued that we had 

 reduced the intensity of the blue below the animal's threshold. 

 A long series of experiments shows that the blue still stimulates 

 the animals when the angular opening is between 1 and 2 de- 

 grees. The yellow threshold, on the other hand, lies much higher. 

 Our reason for not reporting upon this is due to the fact that 

 we have made the threshold tests throughout the spectrum a 

 separate study. It may be safely taken for granted that the 

 threshold for blue is below a 5 opening, whereas that for yellow 

 is probably not much below io° 9 (lower, somewhat, for the black 

 and white rat than for the white). 



May 4th. Normal series of 10 trials, all correct, blue cut 

 out. Animal was frightened at first (the change in condition 

 for him must have been large) and would hardly respond at 

 all. First trial went to blue side (darkness) ; then went to yellow 

 (light side) on every trial for 9 trials. Equal energy series of 5 

 trials then given. Went to blue on every trial. 



May 5th. Normal series, equal energies, 10 trials, 100% 

 correct. Then blue was cut to 10° yellow full intensity. 7 

 trials. Animal fell back on position habit. Went to right on 

 every trial. Then blue was cut out for 10 trials. Went to yellow 

 on every trial. Next blue was cut to io°. 6 trials. Went to 

 yellow on every trial. 



May 6th. Yellow full intensity, blue cut to io°. 10 trials 

 given. Went to yellow on every trial. 



The test upon these two days with io° opening upon blue 



8 By normal series, we mean in all cases about ten trials with both stimuli at 

 equal energy (unless otherwise stated). 



8 In most places in this paper the angular opening is given. This is for the 

 convenience of anyone desiring to repeat the work. If the relation in terms of 

 energy is desired, it will be remembered that the work of Brodhun and of Hyde 

 abundantly proves the Talbot-Plateau law. 



