THE PSYCHOLOGICAL BASIS 21 



discrimination values. The question therefore arises whether sensations 

 can be divided up into elementary qualitative parts. The simplest 

 theory of such psychological analysis is that elaborated by Mach and 

 others that each psychological element has a physiological counterpart, 

 which is itself the expression of a physical counterpart. Each is indeed 

 an accurate image of the other, or, to use Fechner's simile, the psychical 

 and the physical are the concave and convex sides of the same curve, 

 v. Kries, McDougall, and many others are of the opinion that this 

 view is untenable. If two perceptions differ, yet possess a certain similar 

 quality, that quality may be regarded either as made up of the sum of 

 similar preformed parts in the various constituents of the two percep- 

 tions, or as a totally new psychological rearrangement of the under- 

 lying factors. Of these alternatives the latter is the more likely, and 

 we must at present remain content to regard certain psychological 

 similarities as not capable of analysis. 



The psychological analysis of our sensations brings out other funda- 

 mental facts of importance. We not only see a light or a colour, but 

 we see it at a definite time and in a definite place. Leaving aside the 

 temporal element for the moment, we find that our orientation in space 

 is largely dependent on vision. Hence it arises that our visual impres- 

 sions are projected outwards to definite positions in the outer world. 

 In this respect visual " sensations " differ from such sensations as pain, 

 heat, cold, etc. 1 This unconscious projection of impressions is responsible 

 for the fact that we associate our sensations with certain properties of 

 external objects. We speak of objects as being round, bright, red, and 

 so on, an inaccuracy which is responsible for much confusion. A 

 luminous object sets the ether in vibration ; when these vibrations 

 stimulate the retina they give rise to sensations, which we describe as 

 bright, red, and so on. These qualities are therefore subjective and must 

 be strictly dissociated from the physical stimuli which give rise to them. 



This aspect of the subject has been lucidly treated by Hering 2 . As 

 he says, " our visual world (Sehwelt) consists essentially of differently 

 presented colours, and objects, as seen, that is visual objects (Sehdinge), 

 are nothing but colours of different nature and form 3 ." The whole of 



1 Cf. Hering, Grundzuge der Lehre vom Lichtsinn, in Graefe-Saemisch Handb. Tli. I 

 Bd. in. Kap. xii. 1905. 



2 Loc. cit. 



3 " The eye sees no form, inasmuch as light, shade, and colour together constitute that 

 which to our vision distinguishes object from object, and the parts of an object from each 

 other." Goethe (1810). " All vision is colour vision, for it is only by observing differences 

 of colour that we distinguish the forms of objects." Clerk-Maxwell (1871). 



