128 PSYCHOBIOLOGY 



muscular activity. This does not imply that any fact of consciousness 

 is " produced ", or created, by physiological action. 



Whether a change (or process) in consciousness can modify neural 

 processes, is a separate question. No scientific reason can be assigned 

 against the postulation of such influence : but many persons have a strong 

 religious bias against the postulate, just as many have a religious bias 

 for it. 



If we should assume that conscious processes have a conditioning 

 function ("causal function") in the body, we would necessarily relate 

 this to the reflex-arc by assuming that the immediate or primary bodily 

 effect is a change in the dominance relations of the elementary arcs in the 

 total arc-system. The immediate conscious process (change of attention) 

 which may characteristically be conditioned by a change in the integration 

 of the nervous system may, conversely, condition a change in integration. 



" CENTERS " IN THE BRAIN AND CORD. 



In dealing with neural functions many physiologists and physiologizing 

 psychologists make much of the concept of centers. This concept is on 

 the whole exceedingly vague, but there are two somewhat definite forms 

 which it is important to notice. 



1. The Phrenological Theory of Centers. 



There is a tendency to use the word ' center ' in an occult way, to de- 

 scribe certain parts of the neural mechanism as if certain functions of con- 

 sciousness and of motor control were literally located in particular groups 

 of cells. The ' visual center ' is postulated as the place in which vision 

 takes place. So the other sensory centers — olfactory, auditory, etc. — in 

 the cortex are considered as groups of cells on the action of which depend 

 directly the various states of consciousness (and in fact the various con- 

 tents thereof), described by the various senses. The consciousness of 

 light is supposed, on this hypothesis, to be caused by (or to be concomi- 

 tant with) the action of certain cells in the occipital lobes of the cortex, 

 and of these cells solely. The fact that vision does not occur without 

 stimulation of the retinal endings is explained as due to the impossibility 

 of properly exciting these cortical-visual cells except by a current from 

 the rods or cones of the retina ; but the occurrence of vision is nevertheless 

 supposed to depend in a direct and intimate way on these cortical cells. 



Over against these sensory centers, there are supposed to be a set of 

 motor centers which are in direct control of the various complex activities 

 of the muscles. Not only have centers of various groups of muscles been 

 described, but also centers for the control of various groups in special 



