Spatially Determined Reactions 203 



/' Again, the power of getting true spatial images seems to 

 be bound up closely with the power of moving the sensitive 

 surface. We get our best tactile space perceptions through 

 active touch, involving movement of the hands and fingers; 

 our visual space perceptions are profoundly influenced by eye 

 movements. Where the movements of an animal's body as a 

 whole are very rapid, as in the case of winged insects, this 

 fact may compensate for the immovability of its eyes. 

 Forel, as we have seen, thinks that insects which can explore 

 objects by moving the antennae, bearing the organs of smell, 

 over them, may have smell space perceptions, such as are un- 

 known to our experience ; they may perceive the shape and 

 size of odorous patches as we could do if our organs of smell 

 were on our hands (132). Now, movement of a sense organ 

 brings about the same result that movement of a stimulus 

 across a resting sense organ does ; that is, the stimulus affects 

 different points of the sensitive surface in succession. But 

 the vital significance of the two is quite different ; movement 

 of an object across a resting sense organ means very likely 

 that the object is alive ; it must be instantly reacted to, and the 

 speed of the reaction is unfavorable to the formation of a true 

 space perception. Movement of the sense organ, however, 

 gives a series of impressions on successive points of the sensi- 

 tive surface, from a resting object. While the sense organ is 

 being moved, it is probable that other reactions of the animal 

 will be suspended. Whether any part in the formation of 

 that complex conscious content which we call a spatial 

 image, consisting of different sensations simultaneously 

 apprehended, is played by the "lasting over" of the impres- 

 sions on one sensitive point after the stimulus has passed on to 

 the next, a phenomenon which we find both in touch and in 

 sight sensations, it is impossible to say. (^We are, however, 

 apparently justified in the statements that the essence of 



