I907,] TITCHENER AND PYLE— JUDGMENT OF DISTANCE. 105 



Summary and Criticism. 

 We have now shown : 



1. That imperceptible shadows, raised ahnost to the Hmit of 

 perceptibiHty, exert no influence upon the judgments of distance 

 passed by five observers ; 



2. That shadows, so weak as barely to hold their form distinct, 

 exert an influence upon judgment comparable with the influence 

 exerted by strong and clear shadows ; 



3. That it is possible, by voluntary direction of attention, to free 

 the judgment from the influence of a clear and strong illusion- 

 motive. 



In other words, we can find no experimental confirmation of 

 Dunlap's results, and we believe that a more exact analysis of the 

 conditions of his experiment shows these results to be illusory. We 

 suggest, further, that imperceptible shadows, if they affect judg- 



instances of it; but it does not appear to be common. Judd remarks {op. cit., 

 38) that " early in the practice series both observers noted the feeling of hav- 

 ing succeeded in abstracting from the oblique lines. That they had not done 

 so appears in the fact that the illusion continued in almost its full original 

 strength." There are, evidently, individual exceptions to the general mode of 

 apprehension of the regular Miiller-Lyer figure by unpractised or little prac- 

 tised observers. 



We could not, then, generalise from 5's results, if the figure employed 

 had been the regular Miiller-Lyer figure. But, as is stated in the text, the 

 figure employed was in so far different that the three vertical markers on 

 the front of the screen afforded definite resting-places for the eye. The 

 shadows were not, so to say, integral parts of the total figure shown; that 

 figure was, first of all, a black line, with a long thin vertical at its centre, and 

 short thick verticals at its two ends : the shadows were secondary. Under 

 these conditions, abstraction from the shadows, with definite instructions 

 from the experimenter to that effect, offers no special difficulty : 6"'s results 

 were, as a matter of fact, confirmed by unsystematic experiments made with 

 two other practised observers. 



H evidently represents a case of self-suggested A-Rcaktion (in Benussi's 

 terminology), that is, of the reaction in which "die Versuchsperson . . . die 

 Hauptlinie der Figur als einen selbstiindig und isoliert vorliegenden Gegen- 

 stand erfassen muss" {op. cit., 310). He would not be 'fooled' by the 

 shadows ; he directed his attention to the horizontal line. His and ^'s results 

 agree with those of Benussi's prescribed ^-reactions : " in der Tat hat Judd 

 ungefahr 1500 Einstellungen gebraucht, um die Tiiuschung auf einen Wert 

 zu bringen, der sich bei vorgeschriebener A-Reaktion nach einigen Einstel- 

 lungen erreichen lasst " {op. cit., 332). 



