7 : 2/ Neural Aspects of Vision 



125 



neither histological nor biochemical evidence is the greatest weakness 

 of this model. Nonetheless, a minimum of three photosensitive pig- 

 ments is needed for any type of theory of color vision. 



Axons from the cell bodies a and b synapse with processes from neuron 

 cell bodies in the next layer of the retina. The latter neurons are called 

 bipolar cells. Several different types can be distinguished called d, e, f, 

 h, i, k, and /. The d cells are large ; they are connected to several rods 



-c 





Daylight 



Cones 



6 



lodopsin 

 Cones 



2 Rods and Cones 



3 Membrane 

 A Cell Bodies 



5 Synapses 



6 Bipolar Cells 



7 Synapses 



8 Ganglion Cells 



Photopic 

 White Centers 

 G,R Centers 



^B,Y Centers 

 Scotopic White Centers 



9 

 Optic 

 !> Nerve 

 Fibers 



Figure 2. Simplified form of Talbot's scheme for assigning 

 function to the known histological elements of the retina. 

 Letters refer to known cell types. Numbers on right refer to 

 retinal layers described in Chapter 2. Arrows with numbers 

 show locations of deficiencies hypothesized to explain four 

 types of color blindness. After S. A. Talbot, "Retinal Color 

 Mechanism," J. Optical Soc. Am. 41 : 936 (1951). 



and at least one cone. The e and /cells are smaller, each connected to 

 several cones. The h cells are midget bipolars which synapse with 

 only one neuron on the side toward the brain. The i cells are called 

 centrifugal amacrine bipolars for they synapse only with the ganglion cells 



