COMPLEX NEURAL ARCS. 79 



On general principles, one might have expected that a reaction which 

 is at once so common and apparently so necessary to the individual 

 in the conduct of life would be short. But it should also be noted that 

 each ocular reaction to peripheral stimuli involves a considerable sen- 

 sory-motor elaboration of the stimulus. The adequate reacting eye- 

 movement is not only in a definite direction, but it is also of definite 

 extent. The accuracy of the eye-movement does not now concern us, 

 since we measure in reaction time only the beginning of the reactive 

 movement. But the beginning of every eye-movement is really only 

 the initial phase of a movement of definite direction and extent. 

 Before the eye starts to move, the elaboration of definite motor impulses 

 for that particular eye-movement must be complete. In a sense, then, 

 every ocular reaction to a peripheral stimulus is not a simple reaction 

 at all, but an individual's adaptation to a change in his environment. 

 In the past history of reaction, such a reaction would have borne the 

 misleading name of a " choice reaction." The length of the simple 

 ocular reaction consequently is not an anomaly. It corresponds 

 directly with a relatively complex but automatic elaboration of the 

 sensory-motor impulse. 



APPARATUS. 



RECORDING CAMERA. 



The general construction of the apparatus has not changed since it 

 was first described by Dodge and Cline, 1 though many of the details 

 have been improved. The eye-movements are photographed by means 

 of an enlarging camera of fixed length. In its present form it is sub- 

 stantially a wooden box, 4 feet long and 6.5 inches square, but tapering 

 at the lens end. The lens is a Bausch and Lomb convertible protar, 

 series vn, No. 8. Doubtless other lenses would answer the purpose, 

 but the above was specifically recommended by the manufacturer to 

 meet our demands, and proved satisfactory after some disappointing 

 experiences with other types. At the back end of the camera-box, in 

 place of the ordinary plate-holder, is a falling-plate recording-camera. 



The mechanism of the recording-camera 2 is exceedingly simple and 

 particularly adapted for psychological work, since it is noiseless, is 

 quickly changed in speed from 200 mm. per second to less than 1 mm. 

 per second, and reaches its maximum velocity in the first centimeter of 

 fall. It is daylight-loading with commercial plate-holders, and may 

 be used with either film, plate, or paper, according to the available 

 illumination. Finally, an image of the recording light, as it is reflected 

 from the cornea, may be seen on the focusing-glass up to the moment 

 of actual recording. This last is an absolutely essential feature in a 

 camera for recording the eye-movements of untrained subjects. 



arid Cline, Psychol. Review, 1901, 8, p. 145. 

 2 Now made by Spindler and Hoyer. 



