2 LORD ADRIAN 



In the skin, where the receptors are not collected into specialized groups, 

 the character of the stimulus might be indicated by the particular type of 

 nerve fibres which transmit the discharge. But we are still uncertain about 

 the significance of signals in the larger and smaller nerve fibres from the 

 skin in relation to pain and touch and so it is particularly important to 

 learn about the arrangement of the taste receptors. These have a distribu- 

 tion which is half way between that of the scattered receptors in the skin 

 and of the concentrated sheets in the eye, ear and nose. Detailed knowledge 

 of how taste buds signal sweet or bitter will be a great help in deciding 

 how the skin receptors signal pain or touch or temperature. And in fact 

 it is already helping to clear up this difficult problem, thanks, of course, to 

 the leadership and inspiration of our host, Professor Zotterman. 



The eye, the ear and the nose are much more elaborate structures. 

 They have to detect the physical and chemical changes caused by events 

 at a distance from the body and all three give us a wide range of sensory 

 experience. We can distinguish a vast range of sounds, a great variety of 

 smells and innumerable visual patterns and we can do it clearly enough 

 to give them a name and recognize their origin. 



In all three sense organs the stimulus is focused on an extended sheet 

 of receptors joined to the brain by thousands or millions of nerve fibres. 

 With this sort of arrangement there are two possible ways in which the 

 stimulus might give the necessary information about itself. It might 

 produce a particular spatial pattern of excitation over the receptor surface 

 with or without a particular temporal pattern showing the sequence and 

 timing of the excitation in diff'erent regions : or it might excite a particular 

 class of receptor which is specially sensitive to a particular quality. 



In the ear the spatial and temporal analysis seems to be enough. The 

 vibration frequencies in the sequence of sounds cause distinctive patterns 

 of deformation in the basilar membrane and that pattern and its temporal 

 fluctuation contains all the information needed to specify the sound, 

 whether it is a pure tone, a noise or a voice or a tune that we know. 



In the eye the changing pattern of light and shade on the retina gives 

 the same sort of information and most of our visual experience is based 

 on it : but visual stimuh vary in wave length as well as in intensity and 

 distribution and the signaUing of colour seems to involve the other kind of 

 analysis — by receptors specially sensitive to particular wave lengths and 

 distributed over all the colour sensitive parts of the retina. 



The camera structure of the eye gives an immediate clue to the analysis 

 by spatial and temporal patterns ; the convoluted structure of the nose is a 

 less certain guide. The receptor surface may be several times as large as 

 that of the retina and it fines the walls of narrow and elaborately folded 

 passages. With a structure of this kind we should not expect to find that 

 the diff'erent odorous molecules which are drawn through the nose at each 



