MOTOR COORDINATIONS. 153 



Cline. Bruckner found the relation reversed in his own case, i. e,, the 

 adductive movements were longer than the abductive. This led him 

 to conclude that the differences are mere personal peculiarities rather 

 than universal differences of the eye-movements in the two directions. 



All these various characteristics of the simple eye-movements have 

 since been confirmed by a wealth of photographic records. 1 They make 

 it clear that the reciprocal innervation of the antagonistic muscles of 

 the eye under normal conditions is a nice adjustment of great regularity 

 in ordinary vision. 



We know of no other voluntary action which is so completely with- 

 drawn from voluntary control as the eye-movements. There is scant 

 sensory data concerning them, so scant that ordinarily one is unable to 

 give any subjective account of these movements. Physiologically their 

 velocity is probably determined by visual considerations. Eye-move- 

 ments exist for the sake of unconfused vision. They should be of such 

 short duration that vision does not seem to be interrupted. They 

 must be rapid enough to prevent the confusion of an apparently moving 

 field. When satisfactorily executed, attention is abstracted from the 

 eye-movements to the clear vision that they condition. For our pur- 

 poses it is a further advantage of the eye-movements that they are 

 thoroughly habituated. 



Moreover, the technique is adequate. The records are photographic. 

 The time is given directly through regular interruption of the recording 

 beam of light by a vibrator in series with a tuning-fork. It should be 

 noted, however, that the photographic procedure is not without some 

 difficulties of its own. The eyelid may droop and interfere with the 

 recording light without parallel interference of vision. Excessive head- 

 movements may render a considerable portion of the plate illegible, or 

 take the subject out of focus of the recording-camera. However, the 

 demands on the subject's intelligence and cooperation are so small that 

 satisfactory sets of eye-movement records were obtained by Diefendorf 

 and Dodge from 40 inmates of the Connecticut Hospital for the Insane, 

 including manic, depressed, epileptic, paralytic, and prsecox patients. 



Our photographic arrangements for recording the movements of the eye 

 are similar to those for recording eye-reaction, except that instead of the 

 apparatus to expose peripheral objects, two constant fixation marks are 

 shown (F l and F 2 , fig. 14). These latter are so oriented that in looking 

 from one to the other the eye of the subject will move through an angle 

 of 40, i. e., 20 on either side of its primary position, as in the eye-move- 

 ments of 40 which were measured by Dodge and Cline. The subject 

 occupied position II, figure 1, exactly as in the eye-reaction measure- 

 ments. The physiological brilliancy of the arc light was stopped down 



Unfortunately the pretentious work of Koch (Archiv f. d. ges. Psychol., 1908, 13, p. 196) is 

 unreliable. In spite of apparently minute care in determining fixation, he can not prevent 

 inaccuracies of vertical displacement. All such inaccuracies, however, will appear on his records 

 as a modification of the apparent time of movement. The wide individual variation in the 

 velocity of the eye-movements which he found is an instrumental artifact. 



