igo8.] OF SUBLIMINALLY COLORED STIMULI. 379 



attention, may lead to a serious variation of numerical result. It 

 is, for instance, exceedingly doubtful if any but the most careful 

 and most highly practised observers can maintain their fixation so 

 accurately as to ensure a precise localisation of the retinal area 

 affected by a given stimulus. Moreover, we are here dealing with 

 a retinal function which tails off gradually from center to periph- 

 ery : so that a very slight shift of regard, or a momentary lapse 

 of attention, or a minimal change in adaptation or in illumination 

 may be enough to vitiate an observation. An illustration may be 

 taken from the records of the observer Bti., quoted above. The 

 outermost limit of B-vision, in the left eye, was determined as 48°. 

 Nevertheless, the observer reported, in the experiments proper, a 

 "trace of bluish, then gray " with the stimulus at 50°. There was 

 no colored after-image. But suppose a tinge of blue-adaptation : 

 then we might have had a perception of gray, and a yellow after- 

 image ; and we should still have been, apparently, beyond the limit 

 of B-Y vision. It was only the care taken to avoid chromatic 

 adaptation that prevented the positive result. 



It is, of course, precisely this crucial experiment which is de- 

 scribed affirmatively by Miss Fernald in 1905,^- and which came out 

 negatively in T's experiments of 1906. The question then arises 

 as to the accuracy of determination of the zonal limits. And on 

 this point we may quote specimen results from Miss Fernald's 

 tables. 



I. R stimulus on light gray background." 



io°-73° Stimulus imiformly seen as red. 



74.5° No color seen. 



76° Red seen in two observations. 



80° Red seen in four, no color seen in two observations. 



82.5° No color seen. 



84° No color seen. 



• 

 "We follow the phrasing of the Psychol. Review of 1905: "Exposure, 

 beyond the limits where any color is seen, is followed by a very clear after- 

 image." In the. Journ. Philos., Psychol. & Sci. Mcth., iii., 1906, 352 (Report 

 .of Sec. of N. Y. Acad, of Sciences), the report reads: "After-images were 

 perceived, almost without exception, as far out as any color could be dis- 

 tinguished, and in many cases were clearly seen though the stimulus color 

 was not recognised." 



^Psychol. Review, XII., 408. Italics ours. 



