8 Journal of Comparative Neurology. 



assume that the effect is the same as that of a false accommoda- 

 tion of the maculae and the instinct to correct it has potence to 

 make the new accommodation before an act of judgment can 

 adjudicate the question. ^ Whether this is an entirely satisfactory 

 solution or not there is little doubt that external attention is of 

 the nature of a reflex which may or may not retain a relation 

 of subordinated connection with conscious processes. If care- 

 ful attention is paid to what goes on during these involuntary 

 acts of accommodation one may notice a certain sensation in 

 the eyeball and muscles usually not felt at all. Now even 

 where these sensational elements do not enter consciousness as 

 such (or at all) they are stored up along with the retinal sensa- 

 tion and may be employed in the formation of a sense of posi- 

 tion — a concept of a spatial nature. However obscure the 

 mechanism of this process, there is no doubt that it takes place. 

 When we exercise ourselves in the effort to mentally estimate 

 the position of various objects in the field of vision seen by aid 

 of momentary illumination and discover that this too is possible, 

 it simply seems to mean that associations have been fixed be- 

 tween lateral cells in the retina and the muscle sensations pro- 

 duced in bringing an image on the macula lutea through the 

 necessary arc to impose it on that spot. 



Experitnent. — Using a screen at a fixed distance from the eye the subject 

 practices the estimation of distances until a degree of familiarity with the 

 measures is obtained. Then in the dark try the same by instantaneous electric 

 spark. Note accuracy. Tabulate results. Now try the same experiment vary- 

 ing the duration of the illumination and observe whether there is an optimum 

 period and, if possible, whether the eye is moved. Compare the two methods 

 of estimation, i. e., that where the eye motions are used directly and those 

 where they are used indirectly. 



It is, then, obvious that the same class of sensations, viz. 

 those derived from the act of accommodation, may be used in 

 one case to produce a sense of effort or may become, in another, 

 data for localization. 



' Compare the labored attempt of Ziehen to explain this point. Leitfaden, 

 p. 134 et seq. 



