VISION 191 



by which it may change the direction of its visual axis from one object 

 to another or may follow the movements of objects within the range 

 of vision. 



1. Monocular Fixation. Let two individuals work together, one 

 as subject and the other as observer. Let them sit on opposite sides 

 of the table. Let the subject close or screen one eye. 



(1) Hold any object directly in front of the subject; let the subject 

 keep his gaze continually fixed upon the object. Move the object 

 quickly toward the subject's left, and note the fixation anew of the 

 object in its new position. What muscle or muscles accomplished this 

 act of monocular fixation? 



(2) Move the object quickly in the opposite direction ; then upward,, 

 downward, diagonally, noting the instantaneous adaptation of the eye 

 to the new direction, recording also the muscle or muscles involved in 

 each act. Are all the movements apparently equally ready and exact ? 



(3) Bringing the object to a point directly in front, 1 m. distant, 

 note through how great a lateral movement it may be carried without 

 inducing any discernible change in the visual axis of the eye. 



(4) Bring the object to the central position and move it very slowly 

 outward in any direction, noting whether the changes in the direction 

 of the visual axis are equally slow and regular. 



2. Binocular Fixation. In the above experiments it was probably 

 noted by both subject and observer that the closed or screened eye 

 responded to every movement of the other eye. 



(5) With both eyes open and fixed upon an object held directly in 

 front at a distance of about 1 m., let the observer move the object 

 quickly; then slowly, right, left, up, down, and around, and observe 

 the continuous perfect fixation of the object with both eyes. 



(a) What muscles are involved in following an object from one's 

 right side to his left? In each other direction in turn? 



(b) Do all these muscles seem to act perfectly in all of the subjects 

 examined? If not, describe any variation. 



3. Convergence, (a) Let the subject direct his gaze at the tip of 

 the observer's ear, and without warning change his point of binocular 

 fixation to some distant object in the same line of vision. What change 

 in the eyes of the subject is noticeable by the observer? What 

 muscles were involved in producing the change? 



(6) Hold an object in front of the subject and 1 m. distant. Move 

 it directly toward the subject's eyes and note the convergence of the 

 lines of vision of the two eyes. What muscles perform the act? 



(c) Through how short a distance may the object be moved in 

 the direct line of vision without causing a discernible change of the 

 angle of convergence of the two eyes. 



(d) From the central, 1 m. position, carry the object to a point 

 about \ m. to the right and \ m. above the eyes of the subject. What 

 muscles are involved in the act of convergence? 



