TEE PERCEPTION OF SPACE. 211 



vrho named circular, triangular, and quadrangular figures 

 at first sight.* 



VISUAL SPACE. 



It is when we come to analyze minutely the conditions 

 of visual perception that difficulties arise which have made 

 psychologists ajDpeal to new and ^'wasi-mythical mental 

 powers. But I firmly believe that even here exact investi- 

 gation will yield the same verdict as in the cases studied 

 hitherto. This subject will close our survey of the facts ; 

 and if it give the result I foretell, we shall be in the best of 

 positions for a few final pages of critically historical review. 



If a common person is asked how he is enabled to see 

 things as they are, he will simj^ly reply, by opening his 

 eyes and looking. This innocent answer has, however, 

 long since been impossible for science. There are various 

 paradoxes and irregularities about tohat we aj^pear to per- 

 ceive under seemingly identical oj)tical conditions, which 

 immediately raise questions. To say nothing now of the 

 time-honored conundrums of why we see uj) right with an 

 inverted retinal picture, and why we do not see double ; 

 and to leave aside the whole field of color-contrasts and 

 ambiguities, as not directly relevant to the space-problem, — 

 it is certain that the same retinal image makes us see quite 

 differently-sized and differenth'-shaped objects at different 

 times, and it is equally certain that the same ocular move- 

 ment varies in its perceptive import. It ought to be pos- 

 sible, were the act of perception completely and simply 

 intelligible, to assign for every distinct judgment of size, 

 shape, and position a distinct optical modification of some 

 kind as its occasion. And the connection between the two 

 ought to be so constant that, given the same modification, 

 we should always have the same judgment. But if we 



* Philosophical Transactions. 1841. In T. K. Abbot's Sight audToucIi 

 there is a good discussion of these cases. Obviouslj^ positive cases are of 

 more importance than negative. An under-witted peasant, Noe M., whose 

 case is described by Dr. Diifour of Lausanne (Guerison d'un Aveugle nC; 

 1876) is much made of by MM. Naville and Dunan ; but it seems to me 

 only to show how little some people can deal with new experiences in which 

 others find themselves quickly at home. This man could not even tell 

 whether one of his first objects of sight moved or stood still (p. 9). 



