216 The Animal Mind 



(802). Special vigor and speed generally characterize 

 reactions to contact with moving objects. In eliciting the 

 scratch-reflex of dogs, an object drawn along the skin is 

 decidedly more effective than one pressed against the skin 

 for the same length of time (681, p. 184). The physio- 

 logical effect is probably, Sherrington says, the same as 

 that involved in the "summation" of successive slight 

 stimuli applied at the same point. As is well known, the 

 latter will bring about a response of considerable violence, 

 though each stimulus acting alone would apparently be 

 without effect. 



Is it likely that these responses to moving stimuli in 

 contact with the skin involve the perception of movement 

 as a form of space perception ; that is, a perception of the 

 successive positions occupied by the stimulus and their 

 relative direction? I think we may say that they prob- 

 ably do not, in the lower animal forms at least. And a 

 chief reason for saying so lies in the fact that the reactions 

 are so rapid. To perceive the spatial relations of stimuli, 

 or any other relations, is a process not favored by great 

 speed of response. The quicker the reaction, the less clear 

 the perception of its cause : such seems to be the general 

 law. The sensation accompanying contact with a moving 

 object may differ in intensity from that accompanying 

 a resting stimulus ; it may, in the lower forms, differ quali- 

 tatively in some way not represented in our own experi- 

 ence, but it can hardly be connected with the more complex 

 psychic processes involved in any form of space perception. 



In vision, also, there are special arrangements for react- 

 ing to moving stimulation. The sensitiveness of many 

 animals to changes of light intensity, although not a direct 

 adaptation to the spatial characteristics of a stimulus, serves 

 the same purpose, for changes in light intensity are oftenest 



