Cats have excellent night vision and can see at only one-sixth the light level required for human vision.:43 This is partly the result of cat eyes having a tapetum lucidum, which reflects any light that passes through the retina back into the eye, thereby increasing the eye’s sensitivity to dim light. Another adaptation to dim light is the large pupils of cats’ eyes. Unlike some big cats, such as tigers, domestic cats have slit pupils. These slit pupils can focus bright light without chromatic aberration, and are needed since the domestic cat’s pupils are much larger, relative to their eyes, than the pupils of the big cats. Indeed, at low light levels a cat’s pupils will expand to cover most of the exposed surface of its eyes. However, domestic cats have rather poor color vision and (like most nonprimate mammals) have only two types of cones, optimized for sensitivity to blue and yellowish green; they have limited ability to distinguish between red and green. A 1993 paper reported a response to middle wavelengths from a system other than the rods which might be due to a third type of cone. However, this appears to be an adaptation to low light levels rather than representing true trichromatic vision.
Cats have excellent hearing and can detect an extremely broad range of frequencies. They can hear higher-pitched sounds than either dogs or humans, detecting frequencies from 55 Hz to 79,000 Hz, a range of 10.5 octaves, while humans can only hear from 31 Hz to 18,000 Hz, and dogs hear from 67 Hz to 44,000 Hz, which are both ranges of about 9 octaves. Cats do not use this ability to hear ultrasound for communication, but it is probably important in hunting, since many species of rodents make ultrasonic calls. Cat hearing is also extremely sensitive and is among the best of any mammal, being most acute in the range of 500 Hz to 32 kHz. This sensitivity is further enhanced by the cat’s large movable outer ears (their pinnae), which both amplify sounds and help a cat sense the direction from which a noise is coming.
Cats have an acute sense of smell, which is due in part to their well-developed olfactory bulb and also to a large surface of olfactory mucosa, about 5.8 cm2 (0.90 sq in) in area, which is about twice that of humans . Cats are very sensitive to pheromones such as 3-mercapto-3-methylbutan-1-ol, which they use to communicate through urine spraying and marking with scent glands. Many cats also respond strongly to plants that contain nepetalactone, especially catnip, as they can detect that substance at less than one part per billion. About 70—80% of cats are affected by nepetalactone. This response is also produced by other plants, such as silver vine (Actinidia polygama) and the herb valerian; it may be caused by the smell of these plants mimicking a pheromone and stimulating cats’ social or sexual behaviors.
Cats have relatively few taste buds compared to humans. Domestic and wild cats share a gene mutation that keeps their sweet taste buds from binding to sugary molecules, leaving them with no ability to taste sweetness. Their taste buds instead respond to amino acids, bitter tastes, and acids.
To aid with navigation and sensation, cats have dozens of movable whiskers over their bodies, especially their faces. These provide information on the width of gaps and on the location of objects in the dark, both by touching objects directly and by sensing air currents; they also trigger protective blink reflexes to protect the eyes from damage.:47