Biology Reference
In-Depth Information
Part V
Factors that triggered the
paradigm shifts in the development
of the duplicity theory
In retrospect, it can be seen that all the classical theories in vision
research with the exception of Hering's opponent colour theory were
instigated by what may be termed observational facts. The theories
of Newton (
1671
/1672) about light and colour, for instance, were
triggered by his observation that the prismatic solar spectrum was
rectangular in form.
Accepting the laws of refraction, he had expected the form to be
circular. Yet, comparing the length of the spectrum with its breadth,
he found to his surprise that it was about five times greater. He also
found the two sides of the rectangle to be straight lines and the ends
to be semicircular. It is important to note that Newton's observations
did not result from an attempt to confirm or falsify the refraction
laws. Instead, the observations were made quite accidentally.
To explain his observations, Newton initiated a series of experi-
ments, testing various hypotheses and soon reached the famous
conclusion that white sunlight was compounded of an innumerable
number of different rays and that the colours of the prismatic
spectrum were original and connate properties of these rays - all
in sharp contrast to the generally held view that the colours of the
spectrum were qualifications of the white homogeneous sunlight
caused by prismatic refraction.
Schultze's duplicity theory was also based on observational
facts. Thus, he arrived at his theory by combining two different
sets of data. (1) Diurnal and nocturnal animals tended to have
retinas dominated, respectively, by cone and rod receptors. In fact,
some diurnal species had only cones and some nocturnal species
only rods in their retina. (2) Night vision was achromatic.
