Biology Reference
In-Depth Information
of sensory quality solely to the brain. Here he assumed that there
were no qualitative differences as regards nerve conduction, so that
the nerve fibres were like telegraph wires which passively conduct
electricity.
Of course, Helmholtz knew that the ether waves of light did
not directly activate the nerve fibres. Instead, he assumed that the
nerve activity was generated by processes in light-sensitive elements,
and that these elements had to be cones, since only cones were found
in the central fovea, where vision was best developed, and also
because vision deteriorated with eccentricity, where the number of
rods relative to cones increased. The transformation of light to nerve
impulses (the phototransduction in the receptors) was, however,
completely unknown in the 1860s (Helmholtz,
1867
, pp. 214-215).
