PSYCHOLOGICAL PROGRAM AND TECHNIQUE. 173 



corresponded to the position of the test object, it was reasonable proof 

 that the subject had actually seen the lines and had not reacted to some 

 false impression, which, with many untrained subjects, would quite 

 naturally be the case, provided the subject knew in what axis the lines 

 were going to appear. The test object window was round so that a 

 shift in the axis would produce no observable difference in its shape or 

 position. Experience has shown, however, that an experimental diffi- 

 culty is encountered when the whole window and frame are exposed to 

 the subject. 



In figure 51 (see page 186), we reproduce a full-sized photograph of 

 the window of the test object. The bottom and right-hand edges of the 

 figure, as well as the lower right-hand portion, have been covered with 

 a black paper mat; the other portion shows the circular boundary of 

 the window. If the reader mil hold this illustration at arm's length it 

 will be seen that certain parts of the boundary for the light and dark 

 hnes have particular prominence, as, for example, positions 1 and 3, as 

 contrasted with 2 and 4. This phenomenon can not be seen in the 

 illustrations which have been shown by Ives,^ who figures only square 

 areas of such striae as are under consideration. \\'Tien looking at the 

 test field, surrounded by a definite black circular frame, it is possible, 

 after a httle practice, to sense the presence of lines and to give their 

 direction on the basis of this intersection phenomenon where the lines 

 form acute angles with the dark border. It is also possible to do 

 this with smaller Hnes than can be seen in the center of the field. 

 When using the test object in only one axis, as has apparently been the 

 custom at Nela Research Laboratory, where Ives, Cobb, Johnson, 

 Luckiesh, and others have used this test object in a number of re- 

 searches, it is doubtless possible with practised subjects to instruct 

 them to give attention only to the center of the field, and judge when 

 lines appear there. 



For the purpose of our investigation and other investigations at 

 the Nutrition Laboratory, it seemed highly desirable to eliminate this 

 criterion for judgment. The iris diaphragm (D, fig. 39) successfully 

 solved the problem. In the apparatus as used the test object is 

 located 170 cm. from the eye of the subject. The diaphragm D is 31 

 cm. from the subject's eye. Thus, when he accommodates for the dis- 

 tance of the test object, the edge of the diaphragm is very hazy and 

 indefinite. By reducing the opening in the diaphragm to a diameter of 

 12 mm. and properly placing the tube and the artificial pupil in relation 

 to the diaphragm and the test object, the subject was unable to see any 

 of the circular frame surrounding the test field and could not see the 

 entire field. The portion exposed to view was circular, with indefinite 

 edges and approximately 7.5 cm. in diameter. This reduced to a negli- 



1 Ives, Abstract Bulletin of the Physical Laboratory of the National Electric Lamp Asso., 1913, 

 1, opp. p. 36. 



