160 COLOUR VISION 



Colour vision is often affected in disease of the eyes or brain^. I do 

 not propose to discuss acquired colour blindness, though some few 

 references to it may be necessary. 



The outstanding characteristic of all known abnormalities of colour 

 sensations is that the abnormal people see fewer hues than the normal. 

 The great difficulty in arriving at a true conception of the relationship 

 of any abnormal colour system to the normal is psychological. No 

 individual can judge with certainty the sensations of any other 

 individual. We in general assume that another person has the same 

 sensations as ourselves until, either by accident or research, we discover 

 differences between their judgments of external stimuli and our own. 

 Investigation of the sensations produced by various stimuli, through 

 the mediation of aft'erent nervous impulses, is similarly extremely 

 difficult in lower animals. We have to judge for the most part by motor 

 responses which may or may not be directly contingent to the afferent 

 impulses, and which are in any case particularly liable to misinter- 

 pretation. The investigation is rendered easier in man owing to the 

 faculty of speech. Amongst the majority of mankind, however, 

 multitudinous nuances of sensation, perception, and conception are 

 often conveyed by the same word. The higher the intellectual status 

 the greater is the discrimination of these shades of feeling and thought 

 and the more elaborate is the terminology employed to express them. 

 Education is, or should be, largely concerned with the equipment of the 

 individual with a sufficiently comprehensive and finely discriminating 

 vocabulary. 



So far as these considerations apply to colour vision the majority 

 of people are equipped with a vocabulary of colour names, such as white, 

 black, red, yellow, green, blue, violet, purple, which are in common use 

 and are used by most people in such a manner that no glaring discrepancy 

 is noticed between the sensations of the various individuals as thus 

 expressed. The more minutely trained observers have added to this 

 vocabulary subsidiary terms which express the finer nuances of colour 

 perceptions, such as orange, indigo, mauve, puce, drab, and so on. 

 Unfortunately increased complexity of nomenclature has not been 

 accompanied pari passu with accurately defined discrimination of 

 meaning. Consequently many such terms are used in a loose and ill- 

 defined manner, and it would be quite unreasonable from the use made 

 of the terms to deduce differences of perception which may or may not 

 exist amongst the various individuals. 



1 Kollner, Die Storungen des Farbensinnes, Berlin, 1912. 



