Spatially Determined Reactions 185 



mentioned in Chapter IV. If the effect of light is merely 

 " kinetic," causing no orientation, but movement about until 

 the animal chances to come into the shadow, vague restless- 

 ness or uneasiness is the human experience most closely 

 resembling its possible conscious accompaniment. In none 

 of these cases does spatial perception appear to be concerned. 

 Where, however, the response to light depends upon the eyes, 

 the accompanying psychic process may have a spatial char- 

 acter. Even though the eyes do not give clear images, if the 

 reaction is determined by the greater intensity of illumination 

 on one eye than on the other, it is possible that the visual field 

 present to the animal's consciousness may contain gradations 

 of intensity arranged side by side in a spatial pattern. An 

 important advance from mere phototropism to visual space 

 perception is made, according to Ra"dl, when an animal's eyes 

 are oriented by "a dark point in light space" rather than by 

 " a bright point in dark space," but the conditions that render 

 such orientation possible he does not attempt to define, other 

 than by suggesting that they are connected with the structure 

 of the eye itself (358). 



73. Orientation to Other Forces 



One force, which, as was noted in Chapter III, produces 

 orientation, namely, the electric current, we shall leave out 

 of account. It is not a stimulus to which animals are nor- 

 mally subject, and though its action on living matter is of 

 great interest to the physiologist, the comparative psycholo- 

 gist's difficulty in finding a psychic interpretation for the facts 

 may justify setting them aside. Similar considerations apply 

 to orientation to centrifugal force. There remain the orien- 

 tations that have been termed respectively " rheotropism " 

 and " anemotropism," responses to currents of water and to 

 currents of air. 



