Why that has cells that are sensitive to

Why Cats Cannot Distinguish Rich
Colors like Humans

Erica Ellis

January 14, 2018













 Humans as a species, have the privilege of
having a rich visual system that allows them to distinguish the world in
various colors. The human species, also have the capability of recognizing two
closely arranged stimuli’s. Humans have more retinas than cats which is why the
two differentiate when it comes to vision. 
Retinal depiction movement is a key stimulus parameter for cells in the
visual system. The retina is a layer at the back of the eyeball that has cells
that are sensitive to light and that sets off nerve instincts that travel via
the optic nerve to the brain, where a visual image is formed. Those
photoreceptors are in charge of the transformation of light rays into
electrical cues that are then processed by nerve cells to the brain then eventually
translated into images. Cats have an extremely high application of rod
receptors but low cone receptors. Rods are accountable for vision at low light
levels and cones are accountable for vision at high light levels.What’s
important is why cats can only see certain colors vividly but not the others
and were they always unable to distinguish major colors.

Human Visual System

Human vision contains for the most part of the eye an (image
sensor), optic nerve (conveyance path), and brain (image information processing
unit or computer).  In the cross section
of the human eye; Cornea (outer sturdy translucent membrane that protects
anterior surface), Sclera (outer strong opaque membrane that protects the rest
of the optic globe), Choroid (carries blood vessels and supplies nutrition),
Iris ( anterior section of choroid, pigmented, provides color to
the eye, Pupil (Center gap of the Iris, in charge of the amount of
light accessing the eye (diameter differs from 2-8 mm), Lens (Form of
concentric layers of fibrous cells, that holds 60-70% water), and the Retina
(Deepest layer, “screen” on which image is established by the lens when
thoroughly focused/has photoreceptor (cells sensitive to light).
Retinal Photoreceptors

There are two different types of photoreceptors which are
rods and cones. There are six-seven million cones in the human eye. Cones are
located in the center area of the retina
(fovea) and is in charge of photonic vision (bright-light vision)/ (The
reasoning why humans are able to see things in higher resolution), color
perception, can sort out fine details. There are seventy-five to one hundred
fifty rods in the human eye. Rods are allocated over the whole retina,
responsible for scotopic vision (dim-light vision), is not color sensitive, and
overall offers widespread picture (not details). Fovea is the round hollow part
in the middle of retina and is around 1.5mm diameter, dense with cones.
Photoreceptors throughout fovea are the reasoning for spatial vision
.Photoreceptors throughout the outer-edge are responsible for identifying
motion. The blind spot is the tip on the retina where optic nerve surfaces, and
is free of photoreceptors.


Cats have six to eight times more
rod cells than humans. The issuing of rods and cones in the cat retina was
studied by light microscopy. Cone density in the region of centralism reached a
high point at 26,000-27,000/mm2, and dropped to a plateau of 4000/mm2 in the
periphery and to less than 3000/mm2 near the ora serrata. The density of rods was
more than the density of cones in all areas. 
The  rods reached  a maximum density  of 
460,000/mm2 at an eccentricity of 10-15″,  in a region 
which  totally surrounded the  central 
cone  elevation.  Centrally, the rod allocation was
distinguished by a keen drop in density, reaching a low of 275,000/mm2 at the
point of peak cone density. Peripherally, there was a plateau of high rod density
at above 400,000/mm2, out to about 30 temporal eccentricity (Steinberg, R. H.,
et.al 1973).

How Humans/Cats use vision to

Cats’ lenses are bigger than human
lenses, which allows the cat to obtain more light. There’s a trade-off:
although the very small human lens can alter its shape to focus light from a
far range of distances, the cat lens can barely alter its shape at all. As a
result, cats have trouble focusing on objects that are near them, sort of like
an elderly person who needs to use reading glasses. Just like many other
organisms, humans benefit from having vision even though not every human has
vision. Having the ability to see is crucial in executing everyday activities
whether it be running, eating, going to work, and etc. Although there are other
sensory systems that could help us perform our daily activities, vision seems
to give organisms an advantage.
A Birds Eye View

Researchers say that birds have the
most experienced visual system of any vertebrate. Birds have five categories of
cones and some breeds of birds see ultraviolet (Gerl & Morris 2008).Also, a
bird’s visual system incorporates oil droplets with a notion to act as filters
of light entering individual cones (Bennett et.al 1994). Binocular vision in
birds appears to be solely for the control of bill or feet position in foraging
(pecking, lunging, taking prey) and/or in the feeding of young. In some
species, binocularity ((a portion of the
world around an animal’s head viewed simultaneously by its two eyes) may be
useful for the inspection of items held by the bill or lying between the opened
jaw/jawbone. Binocular vision used for the control of locomotion (flight,
obstacle avoidance, and landing). Those functions are positioned in order since
certain species who do not use vision for the control of bill or feet position
during foraging, or for provisioning their young, frontal binocularity is  lessened and periscopy is attained by having
binocular vision from in front to directly behind the head. If there is a
strong impulse or vital importance in visual field topography among birds, it
is for periscopy (more comprehensive visual coverage of the space around the
head), not for binocularity (Martin, 2009).

Color vision in fallow deer

Researchers explored whether fallow deer’s
have the ability to see color, by training hand-reared individuals on a two
option discrimination task. To prohibit the chance that the hinds used small
distinctions in reflectance, or perceived brightness, to differentiation
between the medium grey and the medium green plate, researchers examined deer’s
ability to see color by utilizing six light grey, six dark grey, six light
green and six dark green plates. Those were put together so that a light
greyplate was matched with a dark green, and a dark grey with a light green.
(Birgersson,  Alm, & Forkman, 2001).
Researchers concluded that fallow deer’s can use color to differentiate between
two visual stimuli’s. Fallow deer’s may use color vision to detect predators.

Similarities/Differences in regards
to organisms and vision

            All organisms generally use vision
for the same fitness and reproductive goals. Whether it be to spot a prey or
food/to mate/to survive/to adapt. 
Although few similarities, there are many differences. Fallow deer’s
have “dichromatic” vision due to the result of having two types of cones,
lacking the cone that’s vulnerable to lengthy wavelengths like red and orange
unlike humans who have three types of cones . 
Both the bird and human species have trichromatic vision but the eagle’s
vision is one of the more powerful. They have an eyesight roughly at four to
eight times stronger than humans although their eyes are around the same size
as humans. Eagles are capable of seeing colors more vividly than humans can
because they have the ability to see ultraviolet light. Having the power to see
UV light helps them to see the internal fluids left behind by their prey. It
makes their prey an easier target even when the eagle is hundreds of feet’s
above ground.

Cats have scent glands on their
paws, head cheeks, and other areas as well. They use their scent glands to
communicate. Domestic cats usually rub against objects in their area in a
movement which purpose is to free pheromones from all these glandular areas, starting
with the perioral, to the temporal, then ending at the caudal area (Fox 1975;
Feldman 1994). The substance secreted is fatty and strongly scented. In female
cats, the chemical balance changes according to current reproductive status
(Soennichsen & Chamove, 2002). Another reason cats use scent marking
according to some researchers, is to be used as a territorial signal to alert
other members of the same species of their existence (Peters and Mech 1975;
Bel, Porteret and Coulon 1995; Blumstein and Henderson 1996). There is little
to no evidence proving that the alleged hypothesis is factual.

             A cat’s eye view is broader (two hundred
degrees) in comparison to humans (one hundred eighty degrees) view. Cat’s
additional rod cells enables them to perceive motion when it is dark much more
effective than humans. Their eyes have a cryptic shape, and bigger corneas and tappet
(coating of tissue (reflective cells) that reflects light back to the retina
helping gather more light. The tapetum can also move wavelengths of light that
only cats can see, making prey or other objects more defined in the dark more
important. The tapetum is in charge of the glowing look of the eyes when light
hit them.Humans are capable of seeing vibrant colors in the daytime versus cats
who have better vision at night.