SECTION I.—PHYSIOLOGY. 
NORMAL AND ABNORMAL COLOUR 
VISION 
ADDRESS BY 
PROF... H..E..ROAF, M.D., D.Sc., 
PRESIDENT OF THE SECTION. 
Tue choice of a subject for a Presidential Address is a difficult matter. 
In this case, however, the following consideration seemed of importance 
in making the crucial choice. 
Recently attention has been drawn to the number of accidents caused 
by mechanically propelled vehicles. The use of coloured signals may 
lead to difficulties for drivers with defective colour vision. History 
seems to be repeating itself with reference to the use of coloured lights. 
At one time it was claimed that no railway or marine disaster had been 
shown to be due to defective colour vision—which is not surprising, as 
the individuals concerned were never examined after the accident to see 
if they had normal colour vision. 
One person with defective colour vision (hypochromat) has advised 
me not to say that coloured traffic lights cause any difficulty, as he can 
recognise them quite easily. On the other hand, I have heard that some 
drivers with defective colour vision do experience difficulty. Until the 
colour vision of persons who seem to disregard the coloured lights is 
tested, we do not know to what extent coloured lights constitute a difficulty 
to motor drivers with defective colour vision. In any case the remedy 
is simple, as a difference in shape of the coloured lights would be sufficient 
to prevent mistakes. It is true that the relative positions of the lights and 
other data may help in the recognition of the colour, so that the problem 
is not so serious as in the case of railway and marine services. 
It is not my intention to give a detailed documentary description of 
recent work, as those interested will find references to many papers in 
some of the reviews of the subject.t 
The aim of this address is to discuss three aspects of the Physiology of 
Colour Vision. The first aspect is the validity of the trichromatic 
hypothesis. There may not be many new things to be said, but a 
restatement of the arguments is useful as showing to what extent the 
1 H. Piéron, Bull. Soc. d’Ophthal. de Paris, p. 1 (1930). H.E. Roaf, Physiol. 
Rev., 18, p. 43 (1933). 
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