The World According to Cat - Part IV

We can plainly see the cat’s origins as a predator of small rodents in its remarkable hearing abilities remarkable both in the range of sounds it can hear and in pinpointing the source of the sound. The cat is hearing range extends two octaves higher than ours, into the region that because we cannot hear it we refer to as ultrasound.

This extended range enables cats to hear the ultrasonic pulses bats use to orient themselves while flying in the dark, and the high-pitched squeaks of mice and other small rodents.

Cats can also tell different types of rodents apart by their squeaks. In addition to this sensitivity to ultrasound, cats can hear the same full range of frequencies we can, from the lowest bass notes to the highest treble.

Almost no other mammal exhibits such a wide range, about eleven octaves in total. Because cats’ heads are smaller than ours are, their hearing range should be shifted to higher frequencies, so their ability to hear ultrasound is perhaps not all that remarkable; rather, it’s their ability to hear low notes that is unexpected.

The cat’s ability to hear sounds lower than it should, based on the size of its head, is possible because they have an exceptionally large resonating chamber behind the eardrum.

The capacity to hear ultrasound despite this arises from a feature of this chamber not seen in other mammals: it divides into two interconnecting compartments, thereby increasing the range of frequencies over which the eardrum will vibrate.

Mobile, erect ears are the cat’s direction finders, essential when tracking a mouse rustling through the undergrowth. Cats’ brains analyze the differences between the sounds reaching the right and left ear, enabling the cat to pinpoint the source.

For lower-pitched sounds that fall into our hearing range for example, when we talk to our cats—the sound arrives at one ear slightly out of sync with the other. In addition, higher frequencies are muffled by the time they reach the ear farthest from the source, providing a further clue to where the source is.

 This is essentially the way that we too determine where a sound is coming from, but cats have an extra trick: the external parts of the ears are independently mobile, and can be pointed at or away from the sound to confirm its direction.

When it comes to ultra sounds, that are above our hearing range, such as a mouse’s squeak, the phase differences become too small to be useful, but the muffling effect gets larger and therefore becomes more informative.

Therefore, a cat has little difficulty determining whether a sound is coming from the right or the left. In addition, the structure of their external ears the visible part of the ears, technically referred to as pinnae also enables cats to tell with some accuracy how high up the source of a sound is.

First, the corrugations inside the pinnae add stiffness and keep the ears upright, but they also cause complex changes to any sound as it passes into the ear canal; these changes vary depending on how far above or below the cat the sound is coming from.

Somehow, the cat’s brain decodes these changes, which must be difficult, given that the pinnae may be moving. The pinnae are also directional amplifiers, but rather than being tuned to pick up mouse squeaks.

They are especially sensitive to the frequencies found in other cats’ vocalizations, enabling male cats to pick up the calls made by females as they come into season, and vice versa. This is perhaps the only feature of the cat’s ears not refined specifically for detecting prey.

Cats’ hearing is therefore superior to ours in many ways, but inferior in one respect: the ability to distinguish minor differences between sounds, both in pitch and in intensity. If it was possible to train a cat to sing, it could not sing in tune (bad news for Andrew Lloyd Webber).

Human ears are outstanding at telling similar sounds apart, probably an adaptation to our use of speech to communicate, and, within that, our ability to recognize subtle intricacies of intonation that indicate the emotional content of what we are hearing even when the speaker is trying to disguise his or her voice.

Such subtleties are probably lost on cats, although they do seem to prefer us to talk to them in a high-pitched voice. Perhaps gruff male voices remind them of the rumbling growl of an angry tomcat. As with hearing, the cat’s sense of touch features refinements that help with hunting.

Cats’ paws are exceptionally sensitive, which explains why many cats do not like having their feet handled. Not only are a cat’s pads packed with receptors that tell it what is beneath or between its paws, but the claws are also packed with nerve endings that enable the cat to know both how far each claw has been extended and how much resistance it is experiencing.

Since wild cats generally first catch their prey with their fore-paws before biting, their pads and claws must provide essential clues on the efforts the prey is making to escape.

Cats’ long canine teeth are also especially sensitive to touch, enabling the hunting cat to direct its killing bite accurately, sliding one of these teeth between the vertebrae on its victim’s neck and killing it instantly and almost painlessly.

The bite itself is triggered by special receptors on the snout and the lips, which tell the cat precisely when to open and then close its mouth.

The cat’s whiskers are modified hairs, but where the whiskers attach to the skin around the muzzle they are equipped with receptors that tell the cat how far each whisker is being bent back, and how quickly.

Although cat’s whiskers are not as mobile as a rat’s, a cat can sweep its whiskers both forward, compensating  farsightedness when pouncing, and backward, to prevent the whiskers from being damaged in a fight.

Cats also have tufts of stiffened hairs just above the eyes, triggering the blink reflex if the eyes are threatened, and on the sides of the head and near the ankles. All of these, in tandem with the whiskers, enable cats to judge the width of openings they can squeeze through.

 Information gathered from these hairs help keep the cat upright, but the vestibule system, in the inner ear, contributes most to the cat’s exquisite sense of balance.

Unlike our other senses, balance operates almost entirely at the subconscious level, and we barely notice it until something causes it to malfunction for example, motion sickness. Although the information that the cat’s vestibular system produces is used more effectively, it is actually similar to ours.

This system consists of five fluid-filled tubes. In each, sensory hairs on the inside detect any movement of the fluid, which occurs only when the cat’s head twists suddenly because of inertia. The fluid does not move as quickly as the sides of the tube do. dragging the hairs to one side (if you’re reading this with a cup of coffee in front of you, try gently rotating the cup: the liquid in the middle of the cup remains where it is).

Three of the tubes are curved into half-circles, aligned at right angles to one another to detect movement in all three dimensions. In the other two, the hairs are attached to tiny crystals, which make the hairs hang downward under gravity, enabling the cat to know which way is up, and how fast it is moving forward.