36 Foster, Physical Basis of Psychical Events. 



units, the simple sensation gives rise to "higher" psychical 

 life. What is wanted is a careful analysis (as yet only 

 just begun) of the complex tangle of neural units which 

 make up the brain, an analysis at once physiological and 

 anatomical. And what perhaps is wanted even more is 

 that this objective analysis should be guided and, if need 

 be, corrected by an adequate subjective analysis on the 

 purely psychological side, for hitherto these have not been 

 found too often in company. The instance of word-blind- 

 ness on which I just now dwelt, and I might bring forward 

 others, gives us, I say, great hope for the fruitfulness of 

 future inquiry. 



I must now turn to another aspect of my subject. 

 Leaving the higher psychical development, and returning 

 to the general characters of simple sensation, I will ask 

 your attention to the influence of various circumstances 

 and conditions on the production of psychical effects. 



I have spoken of the visual mechanism as a bundle of 

 chains of units. But it must not be inferred from this 

 that such chain in the optic bundle is wholly separate 

 from its neighbours. It is not the case that one cone 

 unit is linked to one bipolar unit only in the retina, this 

 to one ganglion unit only, this to one unit only in the 

 corpus geniculatum, and this to one unit only in the 

 cortex, so that in the cortex each cone (or rod) is 

 represented by one unit only, apart from and distinct from 

 neighbouring units. On the contrary, there is a mingling 

 at the very outset ; each cone fibre is linked to and can 

 influence more than one bipolar unit. The mingling is 

 repeated at each successive link, and is especially 

 prominent in the corpus geniculatum and its allies. Now, 

 when two parts of the retina are stimulated by light at 

 the same time, the condition that two distinct sensations 

 are produced is that the two points should be separated 



