One of the reasons that cats are so appealing to people is their large, prominent eyes. Large eyes are necessary for seeing (and hunting) in dim light. Cats’ eyes have many characteristics to maximize the visual field and collect light entering the eye to stimulate the retinal cells.2 The cornea is large and bulges outward, which allows about five times more light to enter the eye than does the human cornea.¹ The retina has approximately 25 light-sensitive rod cells for every color-sensitive cone cell. When rod cells in a cluster are stimulated by light, they all stimulate one nerve fiber. This results in cats being able to see in very dim light, albeit a fuzzy image.¹ The tapetum lucidum under the retina reflects light back to maximize the chance of rods being stimulated. This layer is what makes cat eyes glow yellowish green when light shines into them. Cats have little need for color vision because they hunt mainly at night, and, like most prey species, non-purebred cats do not have a wide range of coat colors. It appears that cats can see yellow and blue wavelengths of light and can be taught to distinguish among red and other colors. However, this is difficult for them to learn, which suggests that cats are just not interested in colors.¹

The lens of the eye has a limited capacity for accommodation. This means that a cat’s vision is best at approximately 2 to 6 meters (6.5 to 19.7 feet) from the viewed object.¹ This is why cats may have trouble taking treats from an owner’s hand. To maximize visual acuity, they have multifocal lenses that focus light at particular wavelengths. The slit pupil prevents the loss of visual fields that can focus at set wavelengths and maximizes the cat’s vision.³

Binocular vision aids the cat in judging distances for catching prey, climbing, and jumping. The binocular overlap is about 98 degrees, which allows cats to judge distances very accurately.^1,2 Their accuracy is even more amazing considering how short-sighted they are. Cats are very attuned to even small movements in their visual field.

The eyes of cats are not functional at birth. The eyelids open between days 14 and 21. Vision develops with experience. If kittens are deprived of vision through blindfolding before their eyes open⁴ or are housed in environments that are altered to show no horizontal lines, the kittens do not develop normal vision, even though the eyes are structurally and functionally normal.^5,6

When tracking a sound, such as that of a prey animal, cats use a combination of the interaural time differences for sounds to reach both pinnae, level differences between the pinnae, and directional amplification effects of the pinnae to localize the sound and orientate their head.7

Cats have a well-developed sense of smell at birth. These nerves are myelinated at birth, in contrast to most other neurons in the nervous system. This allows signals to pass rapidly to the brain. The kittens use their sense of smell and touch to find the queen’s teats. If they are unable to smell (e.g., because of an upper respiratory tract infection), kittens cannot find the queen’s teats and feed.8

Cats use their sense of smell for locating prey and evaluating communication signals left by other cats. Odors play an important role in the social organization of cats and in reproduction. The feline nasal mucosa is between 20 and 40 square centimeters in area, small when compared with dogs, although it still eclipses the human nasal epithelium. To further aid in scent detection, the cat has two structures: the subethmoid shelf¹ and the vomeronasal organ (VMO).⁹

The subethmoid shelf traps air and scent particles taken into the nasal cavity allowing more time for them to stimulate receptors in the olfactory mucosa.^10,11 The VMO sits between the oral cavity and the nasal cavity. It has connections with the nasal cavity and the oral cavity. The receptors of the VMO are different from those of the nasal epithelium. The gape or flehmen response may be performed after the cat has sniffed or even licked at a scent source. By wrinkling the upper lip and opening the mouth, the cat opens the ducts of the VMO and pumps saliva and the scent into the VMO.⁹ Cats cannot fully evert their upper lip as horses and cattle can because of the frenulum between the upper lip and upper jaw. The gape or flehmen response is seen when tomcats encounter urine from another cat. However, queens and neutered cats also exhibit this behavior when investigating odors.

Cats have specialized tactile vibrissae on their faces and forelegs. The vibrissae are long, thick hairs that are obvious against the coat of the cat. They sit in a large follicle with a sebaceous gland attached. Striated muscle attached to the follicle allows the vibrissae to be voluntarily moved. The follicle has several nerve receptors associated with it. These are sensitive to pressures on the vibrissae as light as 2 mg or displacement of the whisker by as much as 5 Angstrom (or 0.0005 micrometers),12 and they are sensitive to movement of the vibrissae from the normal position.

The facial vibrissae, better known as the whiskers, are synonymous with cats. These are arranged in rows on the upper lips. The upper rows move independently of the lower rows. Cats fold the whiskers back when relaxed and spread them when walking or showing interest in something. Because cats cannot see things that are close, their whiskers are important for the location of prey, food, water, and other objects close to the face. Whiskers also aid in spatial awareness. They are also used to locate prey at the final pounce, especially in dim light. Cats have a superciliary tuft above each eye and two tufts between the ear and point of mandible known as genal tufts 1 and 2. Genal tuft 1 is dorsal to genal tuft 2. These vibrissae also help in spatial awareness. There are also vibrissae on the back of both carpi just dorsal to the accessory pad. It is thought that these tufts aid the cat in using its forelimbs for activities such as hunting.

The sense of taste is important to cats. They have two types of taste buds on their tongues: mushroom-shaped papillae at the front and sides of the tongue and cup-shaped papillae at the back of the tongue. Cats can taste salty, bitter, and acid. They have little reaction to sucrose and tend to drink sweet water only if the sugar is masked by salt. In fact, cats lack the ability to taste sweetness, unlike other mammals. The taste receptor for sweetness is made up of two proteins generated by the genes Tas1r2 and Tas1r3. In cats the Tas1r2 gene does not code for the normal mammalian protein, thereby impairing the function of taste receptors for sweetness.13