Our sense organs 45

freezing. But this is impractical, and is technically
impossible for signals having the same strength
as the (statistical) noise. A certain trick helps –
transmit the signal on two separate channels and
subsequently combine them. In this way the random
noise fluctuations in each partially cancel
each other out, resulting in an appreciable reduction
in noise.
This method is also employed in the eye. In sensory
organs and nerve cells, “noise” is not so
much a result of fluctuations in electron density,
but is caused by fluctuations in the voltage on
the interfaces between sensory and nerve cells.
The Creator made our optic cells as sensitive as
physically possible. As mentioned, one single
light quantum (photon), the smallest physical
unit of light, is sufficient to cause an electric
impulse in an optic cell. Any possible illusion
which might be caused by “noise”, is eliminated
as follows:
Several hundred rods, the most highly sensitive
cells, are connected to only one nerve cell. These
special nerve cells only transmit an impulse if a
sufficiently strong signal has been received from
at least four or five optic cells within a certain
time period, about 0.02 seconds. This means that
the individual optic cells are as sensitive as at all
physically possible, but the nervous system only
transmits signals when several impulses arrive
more or less at the same moment, after a certain
summation period. Thus the maximum possible
sensitivity only comes into play when the light
stimulus arises virtually simultaneously from
receptor cells spread over a sizeable area, and not
from just a single point. Random “noise“ fluctuations
would arise at different times in each cell,
so are never transmitted.
Visual acuity: Visual acuity (sharpness), the ability
to resolve objects, is very important in the
assessment of vision. Under good illumination a
normal eye can distinguish between two points if
the incident light rays make an angle of 1 minute
(1’ = 1/60 degree).
Adaptation (Latin: adaptio = adjustment, especially
that of sensory organs to the prevailing
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conditions): Our eyes are able to process bright
and dim light over a wide range. At night we can
observe dim stars, and we can also adapt to the
glaring intensity of bright sunlight reflected from
snow and ice. This amazing adaptability of the
eye spans an immense range – a factor of 1 to
1 million million!
Colour perception: We would have missed
something wonderful if we could not see colours!
Colours may bring joy, and can even affect our
moods. They contribute to happiness and affect
our state of mind. Colours fascinate all of us, not
just artists and fashion designers.
Colours can be characterised by three aspects,
namely hue, brightness, and saturation (= the
degree of admixture with white). Our eyes can
distinguish 300 different hues or shades of
colour, and if, in addition, the brightness and saturation
are varied as well, several million possible
colour values can be distinguished. The brightness
of a colour is determined by the strength of
illumination, and the saturation.
In our eyes it is only the cones which can detect
colours. The chemical involved is called rhodopsin
(Greek rhodon = a rose), or visual purple. It consists
of protein molecules (comprising approximately
350 amino acids), including the so-called
retinal which colours the rhodopsin. Retinal also
makes the rhodopsin sensitive to light, similar to
the way a detonator makes a cartridge sensitive
to being struck by a firing pin. The rhodopsin of a
cone cannot absorb all the light quanta (photons)
which strike it; it “selects” quanta of a certain
size (wavelength). It will capture most or all of
such quanta, but will also capture one out of ten
to one out of fifty of those which are exactly
double or half the preferred size. However, each
photon captured has the same effect, regardless
of the wavelength.
There are three types of cones, each preferring
a specific, optimal quantum size. They are known
respectively as red-, green-, or blue-sensitive
cones, according to the optical pigments and the
preferred quantum size (wavelength of the incoming
photons of light). But all this still does