A close-up of a cat's eye. Many zoologists believe
that the feline is the most sensual of all
mammals. While its smell and hearing may not be as
keen as, say, those of a mouse, its highly
advanced eyesight and superior (by human
standards) aural (sound) and olfactory (smell)
senses combine with highly evolved taste and touch
receptors to make the cat arguably the most
sensitive of any mammal. Measuring the senses of
any animal can be difficult, because there is
usually no explicit communication (e.g., reading
aloud the letters of a Snellen chart) between the
subject and the tester. However, testing indicates
that a cat's vision is superior at night in
comparison to humans, and inferior in daylight.
Cats, like dogs, have a tapetum lucidum that
reflects extra light to the retina. While this
enhances the ability to see in low light, it
appears to reduce net visual acuity, thus
detracting when light is abundant. In very bright
light, the slit-like iris closes very narrowly
over the eye, reducing the amount of light on the
sensitive retina, and improving depth of field.
The tapetum and other mechanisms give the cat a
minimum light detection threshold up to 7 times
lower than that of humans. Variation in color of
cats' eyes in flash photographs is largely due to
the interaction of the flash with the tapetum.
Average cats have a visual field of view estimated
at 200°, versus 180° in humans, with a binocular
field (overlap in the images from each eye)
narrower than that of humans. As with most
predators, their eyes face forward, affording
depth perception at the expense of field of view.
Field of view is largely dependent upon the
placement of the eyes, but may also be related to
the eye's construction. Instead of the fovea which
gives humans sharp central vision, cats have a
central band known as the visual streak. Cats can
apparently differentiate among colors, especially
at close range, but without appreciable subtlety.
Cats have a third eyelid, the nictitating
membrane, which is a thin cover that closes from
the side and appears when the cat's eyelid opens.
This membrane partially closes if the cat is sick;
although in a sleepy, content cat this membrane is
often visible. If a cat chronically shows the
third eyelid, it should be taken to a
Humans and cats have a similar range of hearing on
the low end of the scale, but cats can hear much
higher-pitched sounds, even better than dogs. When
listening for something, a cat's ears will swivel
in that direction; a cat's ear flaps (pinnae) can
independently point backwards as well as forwards
and sideways to pinpoint the source of the sound.
Cats can judge within three inches (7.5 cm) the
location of a sound being made one yard
(approximately one meter) away.
A domestic cat's sense of smell is about 14 times
stronger than a human's. Cats have twice as many
smell-sensitive cells in their noses as people do,
which means they can smell things we are not even
aware of. Cats also have a scent organ in the roof
of their mouths called the vomeronasal, or
Jacobson's, organ. When a cat wrinkles its muzzle,
lowers its chin, and lets its tongue hang a bit,
it is opening the passage to the vomeronasal. This
is called gaping. Gaping is the equivalent of the
Flehmen response in other animals, such as dogs
Cats generally have about a dozen whiskers in four
rows on each upper lip, a few on each cheek, tufts
over the eyes and bristles on the chin. Whiskers
may also be found on the cat's "elbows." The
Sphynx (a nearly hairless breed) may have full
length, short, or no whiskers at all.
Whiskers (technically called vibrissae) can aid
with navigation and sensation. Whiskers may detect
very small shifts in air currents, enabling a cat
to know it is near obstructions without actually
seeing them. The upper two rows of whiskers can
move independently from the lower two rows for
even more precise measuring.
It is thought that a cat may choose to rely on the
whiskers in dim light where fully dilating the
pupils would reduce its ability to focus on close
objects. The whiskers also spread out roughly as
wide as the cat's body making it able to judge if
it can fit through an opening.
Whiskers are also an indication of the cat's
attitude. Whiskers point forward when the cat is
inquisitive and friendly, and lie flat on the face
when the cat is being defensive or aggressive.