igoS.] 



OF SUBLIMINALLY COLORED STIMULI. 



381 



Fernald has been good enough to send us an account of the condi- 

 tions under which her observers found the after-image, and to make 

 a special series of observations, with Mr. C. E. Ferree as observer. 

 " The head," she says, " must be held firm (my method is the bit, 

 with the impression of the teeth). The background must be light, 

 and the illumination good. The observer must hold the fixation 

 steadily after the stimulus is removed. The after-image screen 

 must be white to obtain Y or B after-images and black to obtain 

 R after-images. A very slight change in conditions makes a great 

 difference in results, which seem to me to depend wholly on bright- 

 ness." Professor Baird was acquainted with these conditions be- 

 fore he undertook his perimetrical observations. 

 The new set of observations is as follows. 



Observer: C. E. Ferree. Full illumination on bright day (May 17, 1908). 

 Nasal meridian, right. White ground. Projection field white, except in obs. 

 14-17, when it was black. Stimulus, 13 sq. mm. Distance from eye to 

 stimulus, 25 cm. 



Positive results occur in the two first and two last observations 

 of the series. The former may be explained in terms of chromatic 

 adaptation. If, as the illumination suggests, the observer began the 



PROC. AMER. PHIL. SOC, XLVII. I89 Y, PRINTED OCTOBER 3, I908. 



