308 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



they represent. Thus we see that physically considered the eccentric 

 retina receives less light than the central part, and yet we do not notice 

 anything of this deficiency. If we look at a uniformly illuminated 

 surface it does not appear to us as it should according to the optical 

 nature of the retinal image, that is, darker at the edges and brighter in 

 the centre, but it appears uniformly bright. On closer examination it 

 has been shown that the light intensity becomes even a trifle greater 

 toward the periphery. Thus the eccentric retina, as compared with the 

 centre, seems to have a greater sensitiveness to light, which not only 

 makes up for the physical decrease in the brightness of the retinal 

 image, but even over-compensates the latter a little. This over- 

 compensation has been experimentally ascertained by myself for 

 ordinary conditions of illumination,* and in the case of adaptation for 

 the dark by Dr. A. E. Fick.f Now this over-compensation is by no 

 means an accidental affair, as its high proportionate value proves, it 

 certainly serves a certain purpose. Our eye is not only a most 

 accurate optical apparatus, but it is also a motory mechanism of the 

 highest precision. Motion is of the very nature of the eye, and the 

 qualitative division of labour of the different parts of the retina, to 

 which corresponds the gradual differentiation of indirect vision from the 

 fixation point outwards, seems to be established chiefly with regard to 

 these motor functions. As a rule we pay attention to that part of the 

 vision field whose image is projected on the fovea centralis and its 

 immediate surroundings. To this fact Wundt has given the name 

 " coincidence of apperception and fixation." This rule, however, is 

 transgressed in every case in which we give our attention to a point in 

 indirect vision, or, in other words, whenever we change the direction 

 of our attention. Whenever a change of light intensity or of space 

 configuration occurs in indirect vision there is a tendency to bring the 

 new impression into the fixation point. This function of the visual 

 organ will be more perfectly carried out the more prompt the peripheral 

 regions of the retina react. Thus the greater sensitiveness of indirect 

 vision will not only foster the efficiency of the motory mechanism of 

 the eye, but it will, so to say, condition it. It is, therefore, the greater 

 sensitiveness of the eccentric regions of the retina for light intensity 

 and movements, which makes the eye respond so readily to even the 

 slightest changes in configuration or brightness occurring in eccentric 

 parts of the vision field. 



We, therefore, recognize on the one hand, the superiority of the 



^Kirschmann — Die Hellijjkeits Empfindiing in Indirccten — Sehen. Philosophische Stuiiien, Vol. V., p. 

 4.7ff. 



t.\. E. Pick — Studien uber Licht und Farben Empfindungen. Pflugers Archiv, Vol. 43, p. 44iff. 



