On optical resolving ability of the facet eye of Limulus

Abstract

The resolving power of the human eye and the apposition eye in insects is discussed on the basis of Fraunhofer's diffraction theory. It is then shown that diffraction does not play an important role in the Limulus facet eye. In spite of this the visual fields of neighboured ommatidia overlap strongly as Waterman has shown. A mathematical relation which describes the process of imaging the optical surroundings onto the generator potentials of the excentric cells of the receptors is presented. This relation takes into account the overlap of the visual fields and the logarithmic relation between light intensity and generator potential (MacNichol, Fuortes). On the basis of Hartline and Ratliff's reports on lateral inhibition in the Limulus eye it is shown that this process corrects the overlap and therefore increases the resolving power of the eye. The functional mechanism of lateral inhibition is in principle able to create an image of the optical surroundings in the optic nerve. It therefore can compensate for the dioptric apparatus in front of the receptor mosaic. The correction process in the Limulus eye is studied quantitatively and other cases of principle interest are investigated by means of an analog computer. The results are discussed and other inhibitory processes in the visual and auditory system etc. are mentioned.