BINOCULAR VISION. 121 



case of Caspar Hauser, who is said to have been kept in 

 total darkness and seclusion, from the age of five months 

 until he was nearly seventeen years old, the appreciation of 

 size, form, and distance is acquired by correcting and supple- 

 menting the sense of sight by 'experience, even in binocular 

 vision. This boy at first had no idea of the form of objects, 

 nor of distance, until he had learned by touch, by walking, 

 etc., that certain objects were round, others square, and had 

 actually traversed the distance from one object to another. 

 At first, all objects appeared to be, as it were, painted upon a 

 screen. 1 Such points as these it would be impossible for us 

 to accurately observe in infants ; but we have all seen young 

 children grasp at remote objects, apparently under the im- 

 pression that they were within reach. It must be admitted, 

 however, that the case of Caspar Hauser is rather indefinite ; 

 but it is certain that, even in the adult, education and habit 

 enable us to greatly improve the faculty of estimating dis- 

 tances. 



The important questions for us now to determine relate 

 to the differences between monocular and binocular vision in 

 the adult. We may see an object distinctly with one eye ; 

 but are we able, from an image made upon one retina, to ap- 

 preciate all its dimensions and its exact locality ? 



Accurate observations bearing upon this question leave no 

 doubt of the fact that monocular vision is incomplete and in- 

 accurate, and that it is only when two images are formed, one 



1 Caspar Hauser. An Account of an Individual kept in a Dungeon, sepa- 

 rated from all Communication with the World, from early Childhood to about the 

 Age of Seventeen. Drawn up from Legal Documents. By ANSELM VON FEUR- 

 BACH, President of one of the Bavarian Courts of Appeal, etc. Translated from 

 the German. Second Edition, Boston, 1833. 



As far as we can judge, the history of this remarkable case seems to be au- 

 thentic, though the scientific observations are obscure and indefinite. The ac- 

 count of the gradual development of correct vision is on page 88. 



Helmholtz cites several cases of recovery of sight at a relatively advanced 

 age in persons born blind, which show that the ideas of distance, form, etc., are 

 gradually acquired by experience. (HELMHOLTZ, Optique physiologique, Paris, 

 1867, p. 749.) 



