104 TITCHENER AND PYLE— JUDGMENT OF DISTANCE. [April i8. 



Experiment IV. — H's results were, from the first, radically dif- 

 ferent from those of F. Whereas F showed an initial illusion-efifect 

 of about 35 mm., //'s first two series, with the shadows strong, gave 

 a variable line of 



Illusion long 248 mm. 



Illusion short 255 mm. 



and later series yielded results of the same order. That is to say, 



the shadows, in both sets of experiments, were practically ignored. 



H explained in the vernacular that " we couldn't fool him with 



those shadows " ; and the event proves him right. 



These particular shadows, it will be rernembered, lay upon the 



line of sewing thread, which was itself relatively narrow, and which 



had no vertical markers. If the shadows might be ignored, or 



abstracted from, under conditions thus favorable to their influence, 



it seemed to us that they might still more easily be ignored under 



the conditions of the earlier experiments, in which the horizontal 



line was relatively wide, and the three vertical markers stood out 



clearly upon the white background as the limits of the compared 



distances. To test this theory, we restored the apparatus to its 



original form, and made a series of experiments with one of our 



practised observers, Mr. Sailor. The instructions were that no 



attention should be paid to the shadows, but that judgment should 



be passed upon the lengths of the lines simply by reference to the 



position of the vertical markers. The results were as follows : 



Setting ot Variable Line with 

 Shadows Weak. Shadows Strong. 



Illusion long 250.5 mm. 251 mm. 



248 247 



Illusion short 251 248 



252 249 



The moral is clear. The observer is here able, by direction of 

 attention, to resist the solicitation of a strong illusion motive, clearly 

 presented. So much the more then will he, under the conditions 

 of our first experiments, resist the solicitation of an illusion motive 

 which he cannot see, of whose presence in the particular series he 

 is entirely ignorant, and which is left out of account in the instruc- 

 tions given him by the experimenter.^ 



^ H's tendency spontaneously to ignore the illusion-motive from the out- 

 set is an interesting fact. One of the writers (T) has come across other 



