The result of this disadvantage is that in full daylight, cats cannot see as well as we can. The rods become overloaded, as ours do under the same conditions, and have to be switched off. The small number of cones that cats do have are spread all over their retinas, rather than concentrated in the center of the retina, in the fovea, as ours are, so they get a general and not very detailed picture of their surroundings during the day. Because their pupils are so large when wide open, they cannot be shrunk to a pinp.r.i.c.k in bright sunlight, as ours can. Instead, cats have evolved the ability to contract their pupils to narrow vertical slits, less than of an inch wide, which protects their sensitive retinas from being overwhelmed with light. They can further reduce the amount of light entering by half-shutting their eyes, thereby covering the top and bottom of the slit and leaving only the center exposed.
Cats also show little interest in color; among mammals, color seems a uniquely primate, especially human, obsession.1 Like dogs, cats have only two types of cones and see only two colors, blue and yellow; in humans, we call this red-green color blindness. To cats, both red and green probably look grayish.2 Moreover, even colors they can distinguish seem to be of little relevance to them. Their brains contain only a few nerves dedicated to color comparisons, and it is difficult to train cats to distinguish between blue and yellow objects. Any other difference between objects-brightness, pattern, shape, or size-seems to matter more to cats than does color.
Another drawback of having such large eyes is that they are not easy to focus. We have muscles in our eyes that distort the shape of the lens to allow close vision; cats seem to have to move their whole lens back and forth, as happens in a camera, a much more c.u.mbersome process. Perhaps because it is just too much effort, they often don"t bother to focus at all, unless something exciting, such as a bird flying past, catches their attention. Close focus, anything nearer than about a foot away, is also out of the question with such large eyes. Furthermore, the muscles that focus the lens seem to set themselves according to the environment the cat grows up in: outdoor cats are slightly longsighted, whereas all-indoor cats tend to be shortsighted. Despite the largeness of their eyes, cats can swivel them quickly to keep track of rapidly moving prey. To avoid image blurring, the eyes do not move smoothly but in a series of jerks, known as saccades, about a quarter of a second apart, so that the cat"s brain can process each separate image clearly.
Like humans, cats have binocular vision. The signals from each of their forward-facing eyes are matched up in their brains and are converted there into three-dimensional pictures. Most mammalian carnivores have eyes that point forward to provide them with binocular vision, so that they can judge precisely how far away potential prey is, and judge their pounce accordingly. Presumably because their eyes don"t focus any closer than about a foot away from their noses, cats don"t bother to converge their eyes on objects any closer than this.3 To compensate, cats can swing their whiskers forward to provide a 3-D tactile "picture" of objects that are right in front of their noses.
Binocular vision is the best way of judging how far away something is, but it"s not the only method available. Cats that lose an eye because of disease or injury can compensate by making exaggerated bobbing movements of their heads, monitoring how the images of the various objects they can see move relative to one another. Prey animals such as rabbits commonly do this: because their eyes are on the sides of their heads to maximize surveillance, they have little or no binocular vision, and have to rely on other, slightly cruder ways of judging distance.
The cat"s ability to detect tiny movements is another legacy of its predatory past. The visual cortex, the part of the brain that receives signals from the eyes, does not simply construct pictures as if the eyes were two still cameras; it also a.n.a.lyzes what has changed between one picture and the next. The cat"s visual cortex compares these "pictures" sixty times each second-slightly more frequently than our visual cortex does, meaning that cats see fluorescent lights and older TV screens as flickery. Dedicated brain cells a.n.a.lyze movements in various directions-up and down, left to right, and along both diagonals-and even local brightening or dimming of specific parts of the image. Thus, the most important features of the image-the parts that are changing rapidly-are instantly singled out for attention.
Cats learn how to integrate all this information when they are kittens-unlike amphibians, for example, which already have specialized prey-detector circuits formed in their brains when they metamorphose from tadpole to adult. Cats use their movement detectors to behave flexibly when they"re hunting, paying equal attention to a mouse it spots attempting to make an escape, or to a movement of the gra.s.s that betrays the mouse"s position. Both help the hunting cat to find a meal.
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"s hearing range extends two octaves higher than ours, into the region that-because we can"t 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 ba.s.s 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, 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 a.n.a.lyze 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. Also, higher frequencies are m.u.f.fled 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 ultrasounds, that are above our hearing range, such as a mouse"s squeak, the phase differences become too small to be useful, but the m.u.f.fling 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 and foremost, the corrugations inside the pinnae add stiffness and keep the ears upright, but they also cause complex changes to any sound as it pa.s.ses into the ear ca.n.a.l; 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 intensity. If it was possible to train a cat to sing, it couldn"t 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 don"t 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 forepaws 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 basically 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 for longsightedness 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 vestibular 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 doesn"t 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 also how fast it is moving forward.
One reason cats are agile is simply that they walk on four legs rather than two. Four legs need coordinating if they are to work effectively as a team, and the cat has two separate groups of nerves that do this. One group relays information about each leg"s position to the other three, without involving the brain; the other sends information to the brain for comparison with what the inner-ear balance organ relates about the cat"s position. More reflexes in the neck enable the cat to hold its head steady even when it is moving quickly over uneven ground-a necessity for keeping its eyes on its prey.
When walking from place to place, cats pay close attention to where they are going. Because of their poor close vision, they have little reason to look down at their front feet, so instead they look three or four paces ahead and briefly memorize the terrain in front, allowing them to step over any obstacles in their path. Scientists have recently determined that if a cat is distracted with a dish of tasty food while walking, it forgets what the ground in its path looks like and has to have another look before setting off again. In the experiment, researchers switched off overhead lights while the cat was distracted into looking to one side; it then had to feel its way gingerly forward, indicating that its view of the path had vanished from its short-term memory., However if the cat was distracted after it had stepped over an obstacle with its front paws, and while the obstacle was right under its belly, it remembered that it should lift its hind paws when it started walking again, even after a ten-minute delay-and even if the obstacle, unbeknown to the cat, had been moved out of the way. Somehow the visual memory of the obstacle is converted from ephemeral to long-lasting by the simple act of stepping over it with the front feet.4 A cat"s gravity-detecting system is most impressive when it either jumps voluntarily or accidentally slips and falls. Less than a tenth of a second after all four feet lose contact with a surface, the balance organs sense which way up the head is, and reflexes cause the neck to rotate so that the cat can then look downward toward where it will land. Other reflexes cause first the forelegs and then hind legs to rotate to point downward. All this happens in thin air, with nothing for the cat to push on. While the front legs are being rotated, they are tucked up to reduce their angular momentum, while the back legs remain extended; then the front legs are extended while the back legs are briefly tucked up (see the nearby figure). Ice skaters use the same principle to speed up and slow down spins, simply by retracting and extending their arms and the spare leg. The cat also briefly curves its flexible back as it rotates, which further prevents the twist at the back end cancelling out the twist at the front.5 Finally, all four legs extend in preparation for landing, while the back is simultaneously arched to cushion the impact.
While this intricate midair ballet is happening, the cat could have already fallen as far as ten feet. As such, it"s possible for a short fall to injure the cat as much as, and possibly more than, a longer fall, if there is insufficient time for the cat to prepare itself for landing. If a cat falls out of a high-rise building or a tall tree, it has another trick available: forming a "parachute" by spreading all four legs out sideways, before adopting the landing position at the last minute. Laboratory simulations suggest that this limits the falling speed to a maximum of fifty-three miles per hour. This tactic apparently allows some cats to survive falls from high buildings with only minor injuries.
How a cat rights itself after a sudden fall Like dogs, cats rely greatly on their sense of smell. Cats" balance, hearing, and night vision are all superior to our own, but it"s in their sense of smell that they really outperform humans. Everybody knows that dogs have excellent noses, something humankind has made use of for millennia, and this prowess is located, in part, in their large olfactory bulbs, the part of the brain where smells are first a.n.a.lyzed. Relative to their size, cats have smaller olfactory bulbs than dogs, but theirs are still considerably larger than ours. Although scientists have not studied the cat"s olfactory ability in as much detail as the dog"s, we have no reason to suppose that a cat"s sense of smell is much less acute. Without a doubt, it is certainly much better than our own.
Like those of dogs, the insides of cats" noses have far more surface area devoted to trapping smells than ours do-about five times as much. Indeed, it"s h.o.m.o sapiens who appears particularly deficient in this respect. During the evolution of our primate ancestors, we seem to have traded most of our olfactory ability for the benefits of three-color vision, which evolutionists theorize enabled us to discriminate red ripe fruits and tender pink leaves from their generally less-nutritious green counterparts. Cats" sense of smell is more or less typical of mammals, and dogs" is more acute than the average. As in most mammals, air pa.s.sing into the nose is first cleaned, moistened, and warmed if necessary as it pa.s.ses over skin supported on a delicate honeycomb of bones, the maxilloturbinals. The air then reaches the surface that extracts and decodes the odor, the olfactory membrane, which is supported on another bony maze, the ethmoturbinals. Because, unlike dogs, cats do not pursue their prey over long distances, their maxilloturbinals are not especially large; dogs must sniff and run at the same time, and while they"re doing this their olfactory membranes are constantly at risk from damage by dust, or dry or cold air. Cats" habit of sitting and waiting for their prey places much less strain on the air-conditioning system in their noses.
Nerve endings in the olfactory membrane trap the molecules that make up the smell. The tips of the nerves are far too delicate to come into contact with air themselves, so they are covered in a protective film of mucus, through which the molecules pa.s.s. This film has to be very thin; otherwise, the molecules would take several seconds to move from the airflow to the nerve endings. If this was the case, then the information conveyed by the odor would be out of date before the cat knew it was there. To facilitate a speedy response, the mucus has to be spread so thinly that the nerve endings become damaged from time to time-for example, they may dry out when they become temporarily exposed to the air-and they therefore regenerate about once a month.
The other ends of the olfactory nerves are connected together in bundles of between 10 and 100 before transmitting their information to the brain. Cats have several hundred kinds of olfactory receptors, and the information arises from whichever of these has been triggered by the odor pa.s.sing through the nose. Each bundle contains only nerves with the same kind of receptor, to amplify the signal without muddling up the data it contains. In the brain, the input from the different receptors is compared to build up a picture of the odor in question.
This system is unlike that of the eye, where images are built up by each section of the retina transmitting its information directly to the brain. The nose does not build up a "two-dimensional" image, as each eye does; as the cat breathes in, the air is swirled around so much in the nostrils that whatever receptor each odor molecule strikes is a matter of pure chance. It"s even unclear whether, unlike their vision and hearing, cats can make any sense of the slightly different amounts of odor entering their left and right nostrils.
Cats are probably capable of distinguishing among many thousands of different smells, so they cannot have one receptor dedicated to each one. Rather, cats deduce the character of each odor they encounter from which type of receptor is being stimulated, and by how much, in comparison with other types. Although scientists do not yet know precisely how the resulting information is combined together in any species of mammal, the potential resolution of such a system is staggering. Consider that our brains can generate a million or so distinct colors from just three types of cones. Several hundred olfactory receptors must therefore have the capacity to discriminate among billions of different odors. Whether cats achieve this is difficult to say; we do not even know precisely how many different odors can be discriminated by our own noses, and we have only about one-third to a half the number of receptor types cats have. Based on these extrapolations, the mammalian olfactory receptor system seems rather over-engineered, and science has not yet resolved why this might be. Suffice it to say, that cats should theoretically be able to distinguish between more smells than it is likely to encounter in a lifetime.
Scientists know little about how cats make use of their sensitive noses. Cats" most dramatic response is to the odor of catnip, but this seems to be an aberration (see box on page 115, "Catnip and Other Stimulants"). We know a great deal about the olfactory capabilities of dogs because we have harnessed dogs" noses for various purposes: finding game, tracking fugitives, and detecting contraband, to name but three. If cats were as easy to train as dogs are, we"d probably discover that their olfactory performance is close to that of dogs. A few minutes cursory observation of any cat will reveal that it sniffs its surroundings all the time, confirming that it places a premium on what things smell like. Remarkably, however, it was only in 2010 that the first scientific account of cats using olfaction in hunting was published.6 This study showed that cats do indeed locate prey using their scent marks. Many of the rodents that cats hunt, especially mice, communicate with one another using scent signals carried in their urine. As mammals, the noses of cats and mice work in much the same way, so it is highly unlikely that mice can disguise their scent marks so that cats cannot detect them. Australian biologists proved this by collecting sand from mouse cages and placing it on the ground on roadside shoulders. Almost all these patches of sand were visited by predators-mostly foxes, but tracks of feral cats were also apparent-while clean sand was not. The collected data did not show how far away the cats had traveled from, but it is possible that significant distances were involved-that is, the cats probably navigated upwind toward the odor sources, rather than only investigating the patches of sand because they looked unusual. We know that many dogs prefer to hunt using their noses, and can detect and then locate sources of odor from hundreds of feet away. While cats prefer to use vision when hunting in daylight, they probably switch to using their sense of smell when hunting at night, when sight, even their sensitive night vision, becomes less reliable.
Catnip and Other Stimulants Scientists do not yet understand why cats respond to catnip, a traditional const.i.tuent of cat toys. Not all cats respond to it. A single gene governs whether or not the cat responds, and in many cats, perhaps as many as one in three, both copies of this gene are defective, with no apparent effect on behavior or general health.
Rolling on catnip The behavior released by catnip is a bizarre mixture of play, feeding, and female s.e.xual behavior, whether the cat itself is male or female. Cats may first play with a catnip toy as if they think it is a small item of prey, but they quickly switch into bouts of a seemingly ecstatic combination of face-rubbing and body-rolling, reminiscent of a female cat in season. Most cats also drool and attempt to lick the catnip. This behavior may continue for several minutes at a time, until the cat eventually recovers and walks away-but if the toy is left where it is, the cat may repeat the whole sequence, albeit with less intensity, twenty or thirty minutes later.
A few other plants elicit the same response, notably the j.a.panese cat shrub or silver vine, and the roots of the kiwifruit vine, which despite its name originated in southern China. In the 1970s, the first growers of kiwi vines in France learned this when they found to their distress that cats had excavated and chewed their seedlings. All three plants contain similar fragrant chemicals, thought to be responsible for the cats" responses.
By some accident of evolution, these chemicals likely stimulate the cat"s nose to trigger circuits in the brain that would never normally be activated at the same time, somehow bypa.s.sing the normal mechanisms that ensure that cats don"t perform two incompatible actions at once. A cat in the throes of catnip-induced oblivion would seem vulnerable to attack, and since cats presumably don"t get any lasting benefit from their experience, evolution should have weeded out the gene responsible. Most species in the cat family, from lions to domestic cats, respond to these plants the same way, so the gene must have evolved several million years ago. Why it did so remains a mystery.
Finding prey from the odors it produces can be difficult. Scent marks rarely indicate the current position of the animal that left them, only where it was when it made the mark, perhaps hours earlier. In the sand experiment, the urine samples continued to attract cats for at least a couple of days. It"s possible that cats, as sit-and-wait hunters, use the scent marks to see whether they will attract other members of the same species that made them. Mice use urine marks to signal to other mice, and the marks contain a great deal of useful information about the mouse that produced them. Thus, the scentmarker doesn"t put itself at risk, so much as other members of the same species that show up to examine the mark.
In addition, odors spread out from their sources in ways that are not predictable. We know intuitively that light travels in straight lines but not around obstacles, and that sound travels in all directions, including around obstacles. However, because we rely so little on odor to give us directional information, it"s not immediately obvious what problems animals face when determining where an odor is emanating from. Of course, odors outdoors are carried by the air-downwind, not upwind-but air movements close to the ground, where cats operate, are usually highly complex. While the wind may be blowing in a consistent direction a few yards above the ground, friction caused by its contact with the ground and especially with vegetation causes it to break up into eddies of various sizes. These carry "pockets" of odor away from the source, so that a cat somewhere downwind of a mouse"s nest will get intermittent bursts of mouse smell.
Tracing these bursts to their source, especially in thick cover, is likely to require diligent searching and possibly some backtracking. Once a cat has located a source of mouse odor, it is potentially able to use the fact that odors don"t travel upwind to position itself downwind of the odor source so its own smell can"t be detected by the mouse, and then wait for mice to turn up. While sit-and-wait is a well-doc.u.mented feline hunting method, we do not know whether cats routinely prefer patrolling the downwind sides of, for example, hedgerows to avoid their own scent betraying their presence. However, it seems likely that a predator as smart as a cat could quickly learn this tactic, even if it is not instinctive.
Cats possess a second olfactory apparatus, which humans lack: the vomeronasal organ (VNO; also called the Jacobson"s organ).7 A pair of tubes, the nasopalatine ca.n.a.ls, run from the roof of the cat"s mouth, just behind the upper incisors, up to the nostrils; connected roughly halfway up each one of these tubes is a sac, the VNO itself, filled with chemical receptors. Unlike the nose, the entire VNO is full of fluid, so odors must be dissolved in saliva before they can be detected. Moreover, the ducts connecting the VNOs to the ca.n.a.ls are only about one-hundredth of an inch wide, so thin that the odors must be pumped in and out of the sacs by a dedicated set of tiny muscles.8 This gives the cat precise control over when it uses the VNO-unlike the nose, which automatically receives odor every time the cat breathes. Thus, the VNO"s function lies somewhere between our senses of smell and taste. Appreciating how cats make use of this faculty requires a great leap of imagination.
Cats, unlike dogs, perform an obvious facial contortion when bringing the VNO into play. They pull their top lip upward slightly, uncovering the top teeth, while the mouth is held partially open. This pose is usually held for several seconds: it"s sometimes known as the "gape" response, although it"s usually referred to by its German name, "Flehmen." Researchers theorize that during this pose, the tongue is squeezing saliva up into the ca.n.a.ls, from where the pumping mechanism delivers it to the VNO.
Cats perform Flehmen exclusively in social situations, so by implication they must use their VNO to detect the smells of other cats.9 Male cats perform it after sniffing urine marks left by females, including during courtship, and female cats will do the same toward urine marks left by tomcats, although usually only if the tom is not present.
The cat"s VNO can probably detect and a.n.a.lyze a wide range of "smells," since it contains at least thirty different kinds of receptors; more than the dog"s, which has only nine. These receptors are distinct from those found in the nose, and are connected to their own dedicated area of the brain, known as the accessory olfactory bulb.
Cat displaying "Flehmen"-using its vomeronasal organ to detect the odor left by a cat that has cheek-rubbed the twig Why do cats-and, indeed, most mammals, apart from primates-need two olfactory systems? The answer seems to change from species to species. Mice have highly sophisticated VNOs, with several hundred receptor types and two distinct connections to the accessory olfactory bulb, rather than the cat"s one; the odorants mice pick up regulate reproduction, as well as enabling recognition of every other mouse in the neighborhood from its unique odor "fingerprint." In many species, some odor communication takes place through the VNO and some through the nose. For example, in rabbits, chemical communication between adults involves the VNO, but the scent emanating from the mother that stimulates her kits to suckle is picked up by their noses. Sometimes the balance between the two changes as the animal matures: the VNO and the nose are used in tandem during a guinea pig"s first breeding season, but the following year its nose alone will suffice. Although cats have not been studied in this amount of detail, it"s feasible that they also interpret olfactory information in a flexible way.
If we accept that the VNO is primarily designed to a.n.a.lyze odors coming from other members of the same species, then the fact that dogs are generally more sociable than cats doesn"t really fit the fact that their VNOs are less discriminating. Dogs, descended from social ancestors, conduct much of their relationships with other dogs face to face, and thus use visual cues to confirm who another dog is and what it is likely to do next, so their VNOs may not be required very often.
The domestic cat"s solitary ancestors only rarely had the opportunity to meet one another; the exceptions are males when they are courting females, and females interacting with their litters for a few months. In the wild, much of the social life of cats must be conducted through scent marks, which can be deposited for another cat to sniff days, sometimes weeks later. Since wild cats rarely get to meet other members of their own species, any information they can pick up from scent marks is crucial for making decisions on how to act when they do encounter each other. Most critically for the survival of her offspring, a female cat must a.s.sess her various male suitors, who themselves have been attracted by the change in her own scent as she comes into season. She may already have gained useful information about each of them by sniffing the scent marks they have left as they roamed through her territory, information she can use to supplement what she can see of their condition and behavior when she finally meets them. She may also be able to distinguish those that are unrelated to her from those that are-perhaps a son who has roamed away and then happened to return to the area a few years later-thereby avoiding inbreeding. Scientists have not yet studied any of these possibilities in cats, but we know them to occur in other species.
Cats" sense of smell has evolved not purely for hunting, but also for social purposes. Successful hunting was, until domestication, crucial to the survival of every individual cat. However, it cannot in itself ensure the survival of an individual cat"s genes; that also requires an effective mating strategy. Each female cat tries to select the best male for her purposes every time she mates to ensure that her genes pa.s.s down to successive generations. Ideally, she should take a long-term view, trying to gauge not only how likely her own offspring are to survive, but also how successful they are likely to be when they in turn become old enough to breed. If she picks the strongest and healthiest male(s) to mate with, then her male kittens are likely to be strong and healthy also when they are old enough to mate. She will of course be able to make a judgment based on her suitors" appearance, but she may be able to obtain a better idea of how healthy they are based on their odor. Her sense of smell may thus provide her with extra information to make these crucial mating decisions.
Cats probably perceive most of the scents that have social meaning using the nose and the VNO in tandem. While both may be needed the first time a particular smell is encountered-for example, the first time a young male detects a female in estrus-on subsequent occasions either one will do the job, the brain presumably using memories of previous encounters to "fill in" the missing input.
Like dogs, cats pay a great deal of attention to scent marks left by other cats, both those carried in urine and those that they rub onto prominent objects, using the glands around the mouth. To distinguish it from the rubbing that cats perform on people and on one another, which is mainly a tactile display, this is sometimes referred to as "bunting," a term whose origins are obscure. Cats" faces have numerous scent-producing glands, one under the chin, one at each corner of the mouth, and one beneath the areas of spa.r.s.e fur between eye and ear, while the pinna itself produces a characteristic odor. We know little about how cats use these scent marks, but they certainly display an interest in the scents other cats produce. For example, male cats can distinguish between females at different stages in their estrus cycle based on their facial gland secretions alone. Each gland produces a unique blend of chemicals, some of which have even been used in commercial products that can have a positive effect on reducing stress in anxious cats.10 Apart from the social role of the VNO, and to a lesser extent the nose, all the cat"s other senses are exquisitely tuned to the hunting lifestyle of their ancestors. They have quite an a.r.s.enal at their disposal: they can locate prey visually, their eyes effective in the half-light of early dawn and late dusk; aurally, detecting high-pitched squeaks and rustles; or olfactorily, through detecting the odors that rodents leave in scent marks. As they approach their prey, cats" exquisite sense of balance and the sensory hairs on their cheeks and elbows allow them to do so silently and stealthily. As they pounce, the whiskers on their faces sweep forward to act as a short-range radar, guiding the mouth and teeth to precisely the right place to deliver the killing bite. Cats evolved as hunters, something domestication has done little to change.
What the cat senses is only half the story. Their brains have to make sense of the vast amounts of information that their eyes, ears, balance organs, noses, and whiskers produce, and then turn that information into action, whether correcting the cat"s balance as it tiptoes along the top of a fence, deciding on the precise moment to pounce on a mouse, or checking the yard for the scent of cats that have visited during the night. The sheer volume of data that each sense organ generates has to be filtered every waking second. An a.n.a.logy might be the vast banks of TV screens and monitors at NASA headquarters during the launch of a s.p.a.cecraft: at any one moment, only a minute fraction of what they display is important, and it takes a highly trained observer to know which ones to watch and which can safely be ignored. Unfortunately at present we know much less about how sensory information is processed than how it is generated.
The size and organization of the cat"s brain can give us some clues as to their priorities in life. The basic form of the felid brain, as shown by the shape of the skull, evolved at least 5 million years ago. Some parts of the brain, especially the cerebellum, are disproportionally geared to processing information relating to balance and movement, reflecting cats" prowess as athletes. While this is apparently contradicted by the occasions that cats get stuck up trees, the problem here is not their intelligence or their sense of balance, but rather that their claws all face forward, so they cannot be used as brakes when descending. The part of the cortex that deals with hearing is well-developed; so too, as we have seen, are the olfactory bulbs.
In cats, the parts of the brain that seem to be important in regulating social interactions are also less well-developed than they are in the most social members of the Carnivora, such as the wolf and the African hunting dog. This is unsurprising, given the solitary lifestyle of the domestic cat"s immediate ancestors. Nevertheless, domestic cats are remarkably adaptable in their social arrangements; some form deep attachments with people, and others remain in a colony with other cats for their entire lives, their only interactions with humans consisting of running away and hiding. Once made, these choices cannot be reversed, since they are set during socialization: the cat as a species can adapt to a number of social environments, but individual cats generally cannot. This lack of flexibility must ultimately lie in the way that their brains are constructed, and in particular, the parts of their brains that process social information. Science has yet to unravel the factors that lie behind these constraints, so that today"s cats have limited options when faced with changes in their social milieu.
CHAPTER 6.
Thoughts and Feelings Historically, scientists have avoided words such as "thinking" and "feeling" when talking about animals. "Thinking" runs the risk of being too imprecise: it can mean anything from simply paying attention to something ("I"m thinking about cats"), to complex comparisons between memories and projections into the future ("I"m thinking about the best way to get my cat to come in at night"), to expressions of opinion ("I think that cats are such fussy eaters because they have such unusual nutritional needs"). To avoid the implication that animals such as cats possess human-type consciousness, biologists tend to use the term "cognition" to refer to their mental processing of information.
With "feelings," our intuitive grasp of our own emotions is bound up in our consciousness: we are aware of our emotions to an extent that cats almost certainly are not.1 However, new scientific techniques such as brain imaging have revealed that all mammals, and therefore cats, have the mental machinery necessary to produce many of the same emotions we feel, even though they probably experience them in a much more in-the-moment way than we do. We do not have to presume that cats are conscious animals to allow that they are capable of making decisions-decisions based not just on information they are receiving and their memories of similar events, but also their emotional reactions to that information. In other words, it"s now scientifically acceptable to explain their behavior in terms of what they "think" and "feel" as long as we bear in mind that cats" thought processes and their emotional lives are both significantly different from our own.
Bearing this in mind is a challenge: we are accustomed to thinking about cat behavior on our own terms. Part of the pleasure of owning a pet comes from projecting our thoughts and feelings onto the animal, treating it as if it were almost human. We talk to our cats as if they could understand our every word, while knowing full well that they certainly can"t. We use adjectives like "aloof" and "mischievous" and "sly" to describe cats-well, other people"s cats, anyway-without really knowing whether these are just how we imagine the cat to be, or whether the cat knows it possesses these qualities (and is secretly proud of them).
Nearly a century ago, pioneering psychologist Leonard Trelawny Hobhouse wrote, "I once had a cat which learned to "knock at the door" by lifting the mat outside and letting it fall. The common account of this proceeding would be that the cat did it to get in. It a.s.sumes the cat"s action to be determined by its end. Is the common account wrong?"2 As this ill.u.s.trates, scientists have long struggled to find a coherent way to interpret cats" behavior rationally and objectively. Scientists still argue the extent to which cats and other mammals can solve problems by thinking them through in advance, as we do. We can easily interpret cat behavior as if it had purpose behind it, but is this mere anthropomorphism? Are we a.s.suming that because we would solve a problem in a particular way, cats must be using similar mental processes? Often, we find that cats can solve what appear to be difficult problems by applying much simpler learning processes.
Cognitive processes-"thoughts"-begin in the sense organs and end in memory. At every stage, information is filtered out: there is simply not enough room in the cat"s brain (or for that matter the human brain) to store a representation of every sc.r.a.p of data picked up by its sense organs. Some of the filtering takes place as the sense organs relay their information to the brain; for example, the motion detectors in the cat"s visual cortex draw attention to what is changing in the cat"s field of vision, enabling it for an instant to ignore everything else. Within the brain, representations of what is happening are generated and held for a few seconds in working memory before most are discarded. A small fraction of these representations, particularly those that have triggered changes in emotion, transfer into long-term memory, enabling them to be recalled later on. Short-term memory, long-term memory, and emotion are all used when a cat needs to make a decision as to what action to take.
Much of the everyday behavior we observe in our pet cats can be explained by simple mental processes. First, the information gathered by the sense organs has to be categorized: is the animal over there a rat, or could it be a mouse? Then, it must be compared with the situation as it was a few moments before: Has the rat moved, or is it still in the same place? More or less at the same time, the cat"s long-term memory is being trawled for similar situations: What happened last time it saw a rat?
As far as we can tell, recollection of such memories affects the cat"s decisions through two mechanisms. The first is an emotional reaction: a cat that has been bitten by rats in the past will immediately feel fear and/or anxiety, and a cat skilled at killing and eating rats will feel something like excitement. The second mechanism guides the cat in selecting the most appropriate action for the situation-depending on the emotional reaction, either the best way of getting out of the rat"s way or the hunting tactic that has worked best on previous rats.
Our minds continually categorize objects without being aware of what we are doing, a process that requires sophisticated mental processes. Scientists are now studying whether cats" minds use the same processes, and if their brains can fill in gaps, as ours can. Let"s say a cat sees a mouse"s nose and tail, but the mouse"s body is obscured behind a plant. Can the cat imagine the mouse"s body in between, or does it perceive the nose and tail as somehow belonging to two separate animals? Cats can be trained to distinguish drawings that-to our eyes-create visual illusions, such as the one shown, from those that do not, so it is likely they can indeed "join the dots," and visualize the body of the mouse between its head and tail. Cats can also use changes in texture to piece together shapes of particular interest to them-to a cat, a negative image of a bird, with the contrasts shifted the wrong way around, is still recognizably a bird.3 However, they do not seem to have an inbuilt rat/mouse detector as such-unlike toads, for example, which reflexively pounce on anything wormlike.
Cats presumably do not know in advance what type of prey is likely to be available when they first leave their mothers and start hunting for themselves, so they rely on what they"ve learned as kittens, rather than robotically pouncing on mice or other prey.
Cats can recognize outlines even when they are broken up or unusual. They know the difference between pictures that produce an illusion, like the "falling square" in the three pictures at top left, and those that don"t, like the three at bottom left. They also recognize the negative image as a bird.
Cats can also make sophisticated judgments on how large or small something is. If they are trained to pick out the smallest or largest of three objects, they continue to pick out the smallest when all three objects are made smaller, so that what was originally the small object is no longer the smallest of the three. Prey will appear larger or smaller depending on how far away it is, so making a judgment about relative size is important in deciding whether to run away (from a large rat, still some distance away) or attack (a small rat, close by). Mysteriously, cats also seem to cla.s.sify shapes according to whether they are closed-for example, a filled circle or square-or open-for example, an uppercase I or U. We do not know why this skill evolved as it did, since its contribution to cats" survival is obscure.
That all these examples relate to vision is a consequence of our own biases: because we are a visual species, scientists tend to focus on an animal"s visual abilities to get an idea of how their brains work. Cats must also be able to cla.s.sify what they hear, and although we don"t know how they categorize sounds, we can guess from their hunting behavior that they probably have categories for each of the sounds made by the various species they prey upon. Presumably they also have categories for the odors that they pick up with their noses and their vomeronasal organs, but with our comparatively poor sense of smell, we have trouble imagining how such a system might work.
Humans also categorize events by when they happened, but cats probably do not. We know little about cats" conception of time, but they are definitely much better at judging short durations than long ones. Cats have been successfully trained to discriminate sounds that last four seconds from those that last five, and also to delay their response to a cue for a few seconds (because they only get the reward if they wait for the correct time).4 However, cats are poor at discriminating longer periods of time, and their perception is likely limited to the few seconds provided by their working memory. We have no evidence to suggest that cats can spontaneously recall memories and place those events as having happened a few days ago, as opposed to a few hours or weeks previous-something we find easy to do.
Cats have a general sense of the rhythm of the day. They have a free-running daily rhythm that is reset every day by the onset of daylight, and they also take other cues from their environment about what time of day it is. Some are natural, such as the sun rising and setting, and some are learned, such as their owner feeding them at roughly the same time every day. Still, they don"t seem to think about time pa.s.sing, in the way that we do.
Once a cat has worked out what it is observing through sight, smell, or hearing, it must work out what to do next. If its survival might be threatened, the cat may need to act first and think later. When a cat is startled, say by a sudden loud noise, it instantly prepares itself for action through a set of preprogrammed and coordinated reflexes. It crouches, ready to run if necessary. Its pupils dilate while its eyes quickly focus as closely as possible, regardless of whether there is anything there to focus on; this presumably maximizes the chances of pinpointing the threat if it is close by. If the threat is still far away, then the cat has less urgency to identify what it is.
Almost every other reaction a cat makes changes with experience: over time, its reactions change. Even the startle reflex gradually wanes and may eventually disappear, say if the same loud noise is repeated over and over again. In this process, habituation, something initially excites the cat, but then becomes progressively less interesting until it eventually evokes no reaction at all.
For example, cats are renowned for quickly getting "bored" with toys. Intrigued as to why this should be, in 1992 I set up a research project at the University of Southampton to look into cats" motivation for playing with objects. Do they literally "play" for the sheer fun of it, as a child might, or are their intentions more "serious"? The manner in which cats play with toys is highly reminiscent of the way that they attack prey, so we designed our experiments with the presumption that whatever was going on in their heads, it was probably related to their hunting instincts. My graduate student Sarah Hall and I found that habituation is the main underlying reason for this apparent boredom. We presented cats with toys-mouse-sized, fake-fur-covered "pillows" tied to a piece of cord-and at first they usually played intensely, appearing to treat the toy as if it was indeed a mouse. However, many cats stopped playing within a matter of a couple minutes. When we took the toys away for a while and then presented them again, most of the cats started playing again, but neither as intensely nor for as long as the first time. By the third presentation, many of the cats would scarcely even begin to play. They clearly became "bored" with the toy.
If we switched the toy for a slightly different one-a different color (say, black to white, since cats" perception of colors is different from ours), texture, or odor-almost all of the cats would start playing again. Thus, they were "bored" not by the game, but by the toy itself. In fact, the frustration of being offered the same toy repeatedly actually increased their desire to play. If the interval between the last game with the original toy and the first game with the new toy was about five minutes, they attacked the second toy with even more vigor than they did the first one.5 To understand why playing with a toy would make a cat frustrated, we considered what might motivate cats to play in the first place. Kittens sometimes play with toys as if they were fellow kittens, but adult cats invariably treat toys as if they were prey: they chase, bite, claw, and pounce on toys just as if the toys were mice or rats. To test the idea that cats think of toys in the same way they think of prey, we tried different kinds of toys to see which ones cats prefer. Our findings showed that, unsurprisingly, they like mouse-sized toys that are furry, feathered, or multi-legged-toy spiders, for example. Even indoor cats that had never hunted showed these preferences, so they must be hardwired in the cat"s brain. The cats played with rat-sized toys covered in fake fur in a subtly different way from the mouse-sized toys. Instead of holding them in their front paws and biting them, most cats would hold the rat-sized toys at arm"s length and rake them with their hind claws-just as hunting cats do with real rats. The cats were apparently thinking of their toys as if they were real animals, and as if their size, texture, and any simulated movement (such as our pulling on the toy"s string) had triggered hunting instincts.
We then examined whether a cat"s appet.i.te has similar effects on the way it hunts and the way it plays with toys. If cats play with toys just for their own amus.e.m.e.nt, as many people a.s.sume they do, then they should be less inclined to play when they are hungry, since their minds should be focused instead on how to get something to eat. Conversely, as a hunting cat gets hungrier, it will hunt more intensely and become more inclined to take on larger prey than usual. We found exactly the latter when we offered toys to our cats. If their first meal of the day had been delayed, they played more intensely than usual with a mouse-sized toy-for example, biting it more frequently. Moreover, many of the cats that normally refused to play with a rat-sized toy at all were now prepared to attack it.6 This convinced us that adult cats do think that they are hunting when they"re playing with toys.
Cats don"t easily get "bored" with hunting, so we were still puzzled as to why our cats stopped playing with most toys so quickly. Indeed, they appeared to get "bored" with most commercially available toys and with the kinds of toys we made for our first experiments. The few toys that sustained our cats" interest all shared one quality: they fell apart as the cat was playing with them.7 Although we had to abandon experiments that involved these toys, which came apart at the seams as our cats batted them about, we noticed that several of the cats were extremely reluctant to give them up. We then realized that our original swapping experiments mimicked one aspect of what happens when a cat rips a toy apart: when we exchanged the toy for a slightly different one, the cat"s senses told it that the toy had changed. It didn"t seem to matter to the cat that it had not caused the change itself; what was important was that a change seemed to have occurred.
We deduced that not only do cats think they are hunting when they"re playing with toys, but their behavior is being controlled by the same four mechanisms whether they"re hunting or playing. One of these mechanisms is affected by hunger, and the same one that makes a cat more likely to play with a toy makes it likely to make a kill when it"s hungry.8 The second is triggered by the appearance-and presumably the smell and sound-of prey, and certain specific features, such as fur, feathers, and legs, that the cat recognizes instinctively are likely to belong to prey animals. The third mechanism is affected by the size of the toy or prey. Attacking a mouse puts the cat in much less danger than attacking a rat, so the cat attacks the rat much more carefully; likewise, cats treat large toys much more circ.u.mspectly than small toys, as if they were capable of fighting back. Even though cats should quickly learn that the toys are unlikely to retaliate, most cats don"t seem to do so. The fourth mechanism is the source of the cat"s apparent frustration: if all that biting and clawing doesn"t seem to have any effect on its target, then either the target wasn"t a meal, or if it is prey, then it"s proving difficult to subdue. A toy that starts to disintegrate, or is taken away but looks different when it comes back (as in our original experiment), mimics the early stages of a kill, thus encouraging the cat to persist.
Overall, many of the cat"s hunting tactics can be explained in terms of simple reflexes, modified by emotion-specifically, the fear of getting hurt by large prey animals-and habituation, which ensures that the cat continues to grapple with its prey only if it is likely to end up with a meal. However, these are only the basic building blocks of hunting behavior; cats undoubtedly perfect their hunting skills through practice, by learning how to a.s.semble the various elements in the most productive ways.
Habituation can explain many short-term changes in a cat"s behavior, but its effects wear off after a few minutes; longer-term, more permanent changes in the way a cat reacts require a different explanation. These must be based on learning and memory.
Fundamentally, cats learn the same way as dogs, even though dogs are self-evidently much easier to train. Two factors lie behind this difference between cats and dogs. First, most cats do not find human attention rewarding in its own right, whereas dogs do; we therefore train cats using food as a reward, rather than affection. Second, dogs instinctively behave in ways we can easily shape into something useful: for example, the herding behavior of a sheepdog is composed of elements from the hunting behavior of the wolf, the dog"s ancestor. Cat behavior features little that we can usefully refine by training, except for our own amus.e.m.e.nt. Obviously, we have benefited from the cat"s hunting abilities for ages. However, we usually leave cats to their own devices: they will seek out the mice that invade our grain stores regardless of whether we want them to do so. Dogs, on the other hand, are specialized for cooperative hunting of much larger prey. They are a nuisance when unsupervised and useful only when trained. We take on the responsibility of gearing their attention toward particular prey, when that is what we need from them.
Much of what cats learn is based on two fundamental psychological processes: cla.s.sical and operant conditioning. Both of these involve new a.s.sociations forming in the cat"s mind. The first involves two events that regularly occur closely together in time; the second involves something the cat does or does not do, and a predictable consequence of that action, which may be good for the cat (a reward), or bad (a punishment). Because cats seem to have little or no instinctive appreciation either of how humans behave or the best ways to interact with them, virtually all their dealings with us are built up through this sort of learning.
Cla.s.sical conditioning is also known as Pavlovian conditioning, after Ivan Pavlov, the first scientist to map out how such learning works in a series of experiments with dogs in the 1890s. In fact, his principles apply equally well to cats.9 A hungry cat that smells food will instinctively seek it out and then eat it. For a wild cat, food is the result of a successful hunting expedition; for a pet cat, the owner makes this trip unnecessary by buying food at the supermarket and presenting it to the cat. Cats don"t need to learn that food can appear without being preceded by hunting, because this is precisely what happens when, in the wild, their mother brings food back to the nest. What they do learn, via cla.s.sical conditioning, are the cues that indicate that food is on its way-for example, the sound of a can opener. In psychologist"s jargon, this action by the owner is the conditioned stimulus, which becomes a.s.sociated in the cat"s mind with the unconditioned ("instinctive") stimulus, the smell of the food. Nothing in the cat"s evolution has prepared it to respond automatically to the sound of a can opener: the a.s.sociation is something that every cat would have to learn for itself. Of course, this is hardly a difficult lesson, nor is the underlying process complex; scientists have found such behavior even in bees and caterpillars. Nevertheless, cla.s.sical conditioning is the main way that cats find out how the world around them is constructed: which parts occur in predictable sequences, and which do not.
The result-the unconditioned response-doesn"t have to be a "reward," such as food. In fact, learning occurs more quickly when it helps the animal to avoid something unpleasant or painful. A cat that is attacked by another, larger cat will certainly experience fear and possibly pain, and will instinctively try to run away. It will also probably remember what the attacking cat looked like, a.s.sociating its appearance with the unpleasant feelings it experienced at the time.10 The next time it sees that cat, it will feel the fear before any attack takes place-and may immediately run away, as it ultimately did the first time they met. However, relatively sophisticated animals such as cats can respond flexibly: they do not automatically have to perform the original response simply because stimuli are similar. In this way, the cat may not run away immediately, but instead "freeze," hoping to avoid detection, having previously learned that running away can invite a chase.
This simple learning has one major constraint: the events that a cat a.s.sociates together must occur either at precisely the same moment or no more than a second or two apart. Say a cat has done something that its owner doesn"t like-for example, depositing a dead mouse on the floor. The cat"s owner finds the mouse several minutes after the cat has left it there and shouts at the cat. In this case, cla.s.sical conditioning does not link the two events together: rather, it links the unpleasantness of being shouted at with whatever happened immediately before the shout-probably the owner"s arrival in the room.
This rule has one exception: if a cat eats something that makes it feel ill, it will thereafter avoid foods with the same flavor. Moreover, forging this a.s.sociation requires only one such experience. This food-aversion learning differs from cla.s.sical conditioning both in the speed with which the lesson is learned and in the delay between the sensation-the odor of the food-and the consequence-the upset stomach. It is obviously in the cat"s best interest to avoid repeating any action that could kill it, which accounts for the irreversibility of this learning. Likewise, there would be little point in the cat a.s.sociating its first feelings of sickness with something else that occurred at the same time-the problem food would have been eaten many minutes, even hours, before. Nevertheless, this is still cla.s.sical conditioning, except that the "rule" for the time frame has been both extended and made much more specific, to the flavor of the last food that the cat ate before feeling ill; other cues, such as the characteristics of the room where it ate the meal, are ignored as irrelevant. Of course, feeling nauseous can also be a symptom of an infection unconnected with something the cat ate, so this mechanism occasionally has unexpected consequences: a cat that succ.u.mbs to a virus may then go off its regular food even after it has recovered, because it has incorrectly a.s.sociated the illness with the meal that happened to precede it.
Cats can also learn spontaneously, when there is no obvious reward or penalty involved. This becomes especially useful when they are building up a mental map of their surroundings. A cat will learn that a particular shrub it pa.s.ses every day has a particular smell. If the cat sees a similar shrub elsewhere, it will expect that shrub to have the same odor as the first one. If it turns out not to-perhaps because an unfamiliar animal has scent-marked it-the cat will give it an especially thorough inspection. Such "behaviorally silent" learning can be explained by cla.s.sical Pavlovian learning-that is, if the cat spontaneously feels rewarded by the information it has gained. In other words, cats are programmed to enjoy their explorations; otherwise, they wouldn"t learn anything from them.
This kind of learning allows cats to relax in what must be, for them, the highly artificial indoor environments we provide for them. Domesticated cats are happy once they have been able to set up a complete set of a.s.sociations between what each feature of that environment looks, sounds, and smells like. This explains why cats immediately pay attention to anything that changes-move a piece of furniture from one side of the room to the other, and your cat, finding that its predictable set of a.s.sociations have been broke