MOTOR COORDINATIONS. 



151 



satisfactory is the evidence obtained by direct observation of another's 

 eyes. If the observer is careful not to look directly at the moving eye, 

 but rather at some point on the eyelid, the alternation of movement and 

 stops, as the subject attempts to move his eye slowly, will be clearly 

 distinguished. Photographic records show that these pauses are of 

 varying length, the shortest being of slightly less than 0.2". 



TECHNIQUE FOR MEASURING THE VELOCITY OF EYE-MOVEMENTS. 



It is unnecessary to repeat here a critical resume of the earlier 

 attempts to measure the duration of the eye-movements by optical 

 methods. 



The first measurements of the eye-movements from photographic 

 records are reprinted in table 24 from the paper by Dodge and Cline. 1 



TABLE 24. Duration of eye-movements. 

 [Values given in thousandths of a second.] 



Table 24 shows the mean duration of the eye-movements of three 

 subjects, A, B, and C, through angles varying from 5 to 40. The two 

 columns at the left give the angular lateral displacement of the line of 

 regard, together with an indication of the orientation of the lateral 

 displacement with relation to the preliminary line of regard. For 

 example, eye-movements of 40 were between two points which were 

 20 to either side of the primary line of regard. M. signifies the mean 

 value in terms of thousandths of a second, M. V. the mean variation, and 

 No. the number of records from which the mean is reckoned. At the 

 extreme right is given the general average for all three subjects for the 

 various angles of displacement. 



The results given in the table indicate that the duration of the move- 

 ments of any individual eye through a given angle tends to remain 

 constant within the limits of a relatively small variation from the mean. 

 The larger mean variation for the angular movements above 15 is due 

 in part to the differences which were found to exist between the adduc- 

 tive and the abductive movements of the eye. 



The table shows further that the duration of eye-movement increases 

 in direct ratio with the angle. Taking the general average of all three 



'Dodge and Cline, Psychol. Review, 1901, 8, p. 145. 



