PSYCHOLOGICAL PROGRAM AND TECHNIQUE. 



169 



(12) Sensory Threshold for Visual Efficiency. 



The general arrangement of the apparatus for the measurement of 

 visual ''acuity" is indicated by the schematic diagram in figure 39. 

 The subject occupied a position at the left end of the apparatus while 

 the operator was at the right, where he could manipulate the test ob- 

 ject and record the 

 readings, but be en- 

 tirely hidden from the 

 view of the subject. 

 When the subject is in 

 position against the 

 head-rest R the artifi- 

 cial pupil P is in con- 

 venient position for the 

 right eye. The line of 

 vision is from P through 

 a diaphragm opening, 

 Z>, through the hood 

 H, with its several 

 screens S which reduce 

 to a negligible quantity 

 the reflected Hght from 

 the four sides of the 

 hood, to the test object 

 0. In a suitable in- 

 closure LH a lamp is 

 arranged so that the 

 light is reflected at X 

 and thrown through 

 the test-object window. 

 The test object is man- 

 ipulated by the mi- ^. ,. ^ , j u r n a 



. ^ • + f Fig. 38. — The movement pattern which should be followed 



Crometer aajUStment ^yy the hand in pointing out the numbers in order. 



M. The head-rest was c . * ** * c a 



S, start of test; E, end. 



the same as that used m 



connection with the eye-reaction test (see fig. 32, p. 162). A in figure 

 32 represents the artificial pupil and its mounting, shown as P in figure 

 39. The dark blind B in figure 32 was in front of the subject's left 

 eye. The lens of the camera, which usually is directly in front of the 

 right eye (see fig. 35) was withdrawn and in its place a telescoping 

 tube 5 cm. in diameter and 28 cm. in length was put in position. 

 The end of the tube near the subject carried a small projection which 

 was suitable for adapting the apparatus to-the contour of the subject's 

 face. At the end of this projection the artificial pupil was located. 

 The whole telescoping tube (T in fig. 39) could be moved easily, so 



