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EUPHA FOLEY TUGMAN 



which each sparrow was able to discriminate in the descending 

 series. The third column gives the least difference which each 

 sparrow was able to discriminate in the ascending order. The 

 last column gives the average of these two which is taken as 

 the threshold of discrimination for the standard .098 c.p. 



(a) Comparison with human threshold. The experimenter, 

 using the same apparatus and methods, investigated light dis- 

 crimination in three human subjects in order to compare the 

 results with those obtained with the birds. Two of the human 

 subjects were required to choose the darker and one the brighter 

 of the two stimulus areas. The subjects are spoken of as A, B, 



TABLE IV 



Comparison of brightness threshold for the four sparrows and the three human 

 subjects. 



and C. B gave very much better results all through the inves- 

 tigation than did either of the others and he responded to the 

 darker of the two lights. C did not give very good results. He 

 responded to the darker of the two lights. C was partially 

 color blind and yet he was always seeing yellow or red in the 

 lights. He said that the color in the lights confused him. This 

 fact may have caused his poor results. The experiment with 

 the human subjects was interrupted many times and often 

 several days would elapse between successive series. This un- 

 doubtedly had some effect on the judgments. As the observers' 

 time was limited, the work was not done as thoroughly or as 

 completely as in the case of the birds. The thresholds are not 

 absolute but are estimated from the limited data at hand. Table 

 IV gives the estimated thresholds for both the birds and the 



