DESIGN FOR A BRAIN 



5/12 



to follow the dotted lines with a pen. The left- and right-hand 

 curves were drawn with the respective hands. The tracing shows 

 clearly that the co-ordination is poorer in the left hand. What 

 criterion reveals the fact ? The essential 

 distinction is that the deviations of the 

 lines from the dots are larger on the left 

 than on the right. 



The degree of motor co-ordination 

 achieved may therefore be measured by 

 the smallness of the deviations from some 

 standard line. Later it will be suggested 

 that there are mechanisms which act to 

 maintain variables within narrow limits. 

 If the identification of this section is 

 accepted, such mechanisms could be 

 regarded as appropriate for the co-ordina- 

 tion of motor activity. 



Figure 5/11/2 : Record 

 of the attempts of a 

 patient to follow the 

 dotted lines with the left 

 and right hands. (By 

 the courtesy of Dr.W.T. 

 Grant of Los Angeles.) 



5/12. So far we have noticed in stable 

 systems only their property of keeping 

 variables within limits. But such sys- 

 tems have other properties of which we shall notice two. They 

 are also shown by animals, and are then sometimes considered 

 to provide evidence that the organism has some power of 

 4 intelligence ' not shared by non-living systems. In these two 

 instances the assumption is unnecessary. 



The first property is shown by a stable system when the lines 

 of behaviour do not return directly, by a straight line, to the state 

 of equilibrium (e.g. Figure 4/5/3). 

 When this occurs, variables may be 

 observed to move away from their 

 values in the state of equilibrium, only 

 to return to them later. Thus, sup- 

 pose in Figure 5/12/1 that the field 

 is stable and that at the equilibrial 

 state R x and y have the values X 

 and Y. For clarity, only one line of 

 behaviour is drawn. Let the system be displaced to A and 

 its subsequent behaviour observed. At first, while the repre- 

 sentative point moves towards B, y hardly alters; but x t which 



68 



Figure 5/12/1. 



