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the same structure and synaptic relationships. Polyak, therefore, like
Schultze, presumed that they were functionally equivalent.
Yet, Polyak found that the cone receptors in different regions of
the primate retina had somewhat different structures and that they,
therefore, probably also differed somewhat with regard to function.
Thus, Polyak held that the cones in the foveal centre were farthest
advanced in their structure and biochemical differentiation and
capable of the most elaborate and diverse responses, and that the
responses gradually became more crude and summary in character as
the ora serrata was approached.
6.1 Trichromacy of colour vision explained
by three types of bipolar cell
Schultze had explained trichromacy, demonstrated by Maxwell
( 1860 ), by suggesting that different spectral lights affected different
outgoing fibres connected to the inner segment of each cone in a
qualitatively different manner. Polyak, however, did not agree with
Schultze that the mechanism of trichromacy was located in each
cone receptor. Using the Golgi technique, he could find no evidence
of three distinct varieties of minute structures or organelles that
could serve as chromatic analyzers in the cone receptors of primates.
He therefore, at variance with Schultze, presumed that the cone
response, over short time intervals, was rather uniform and homoge-
neous, spreading over the entire cone cell, including all its extensions.
To explain the close connection between wavelength of light and hue
sensation, he suggested that at different times the photosensitive
cone substance would generate different kinds of dynamic changes
subserving different kinds of colour sensations when activated by
different wavelengths or different wavelength combinations.
But if each cone may mediate hundreds of different kinds of
uniform colour-related reactions in response to different wavelengths,
then how could the trichromacy of colour vision be explained?
Obviously, the numerous colour-related cone excitations had to be
reduced to three basic processes somewhere in the visual pathway.
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