SENSES To understand the dog’s mind, we have to enter a different sensory world, the world of canine sensation, and imagine how the dog perceives and responds to life around him. This is not difficult to do with respect to some senses. For other senses, though, it’s almost impossible. How can we ever appreciate the awesome capacity of the dog to differentiate thousands of different odors, some as dilute as one part per million. We, humans, can only really use our own capacities for terms of reference, and it is this massive restriction that inhibits us from really understanding exactly how sensory input--touching, tasting, hearing, seeing, and smelling--affects the dog’s behavior. THE SENSE OF TOUCH A two-day-old pup, when he is separated from his mother, will cry and swing his head back and forth like a pendulum until he touches his mother’s body. Then he stops crying and crawls to her. Touch is the earliest, and possibly the most important, of all the canine senses. Touch is the primal sense in dogs as it is in us. It is more important than any other sense for the development of the normal adult, and dogs that are deprived of touch will grow to become subordinate, fearful, and withdrawn. The importance of touch continues throughout the dog’s life. Touch remains forever the most potent reward that a dog can receive, more important even than food. THE SENSE OF TASTE The only other sense that is functioning at birth is taste. The sensation of taste is closely associated with smell, and it can be difficult to differentiate between these two chemical senses. Dogs don’t have as refined a taste sense as we do, and this is in part an anatomical difference. We, humans, have around 9,000 taste buds on our tongues, whereas a dog has, according to one researcher, 1,706. Most of these are on the anterior portion of the tongue. It has always been assumed that dogs share the human taste world, and although they have taste buds like us that register sweet, sour, bitter, and salty, they do so in such a unique way that it is probably better to discuss a dog’s taste sensation as pleasant, indifferent, unpleasant. For example, unless dogs are trained to eat sweets, they are rather indifferent to them, unlike rabbits and horses, both of which have a genuine sweet tooth. THE SENSE OF HEARING With sounds of low pitch a dog’s ears have about the same ability as ours. At higher pitch, however, the dog is far superior to us. Our upper range when we are very young is about 30,000 cycles a second. This sinks to 20,000 by the time we reach retiring age. Dogs have an upper limit of 35,000 to 40,000 cycles per second or, according to recent Russian research, as high as 100,000. This gives the dog the ability to hear a number of sounds that to us are ultrasonic. If a dog suddenly pricks up its ears and becomes alert, it may be that it has detected the high-pitched squealing of rodents or bats, which is totally inaudible to us. The evolution of such sensitive hearing is clearly related to the hunting needs of the ancestors of our domestic dogs, enabling them to detect the presence and movements of rats, mice, and other small prey. As a by-product of this hunting refinement, pet dogs can today react to tiny clues that make their behavior seem almost telepathic. The best-known examples concern the way in which a man’s dog can tell that he is about to arrive home from work. Long before any humans in the house can hear anything unusual, the dog is up and alert, anxiously waiting at the door to greet its master. If the man is returning home on foot, the dog is capable of detecting his particular style of walking and distinguishing it from any other footfalls in the street outside. If the man is driving home, the dog can distinguish the sound of the family car from all other cars passing by on the road. If these reactions seem difficult to believe, it should be pointed out that in the wild state, wolves are capable of hearing a howl from a distance of at least four miles. THE SENSE OF SMELL Here are some facts. The average dog has around 220 million scent receptors in his nose; we have around five million. If the membranes lining the inside of the dog’s nose were laid out flat, the total surface area of those membranes would be far greater than the total surface area of the dog’s entire body. The average dog has about seven square meters of nasal membrane; we have about half a meter and we’re usually bigger. The average dog has such acutely sensitive scenting ability that it can detect and identify smells that are so dilute that even the most sensitive of scientific instruments cannot measure them. Smell is undoubtedly the most important of the dog’s practical senses but also the most difficult for us to comprehend. In the world of odors and fragrances the human being is an inferior species. Each dog experiences a whole landscape of scents with subtlety and sensitivity that is as far from our comprehension as higher mathematics is from the dog’s. It is difficult to express their superiority in any simple way. Some authorities have said that dogs are one hundred times better than we are at odor detection; others have put the figure as high as a million times; still others have seriously claimed that it is in the region of one hundred million. The truth is that the comparison can only be made with regard to a particular chemical substance. With some sorts of smells, dogs perform little better than we do, because the odors in question have no significance for them--the fragrances of flowers, for instance. But with other substances, such as the butyric acid found in sweat, tests have proved beyond doubt that dogs have a responsiveness that is, incredibly, at least one million times better than ours. Examples of this sweat-detection ability are amazingly impressive. There is the thrown pebble test, in which six men each pick up and throw a pebble as far as they can. A dog is then allowed to sniff the hand of one of these men after which it successfully finds and retrieves his pebble. Just by holding the pebble long enough to throw it, the man deposited sufficient sweat for the dog’s nose to locate it. Even more startling is the glass slide test. In this, one of a set of glass slides is touched briefly by a single human fingertip. The slides are then put away carefully for a period of six weeks. When they are taken out again for the experiment, the test dog is able to identify the slide that had been touched. The sweat from human feet seems to be even easier for the dog’s nose to detect. Bloodhounds can follow a trail that is as much as four days old and can track a human subject for up to one hundred miles. The scent from human feet is so strong to a dog that it can identify individual feet even in areas where many other feet have trodden, and where shoes have been worn by all concerned. Because of this ability, made possible by the 220 million smell-sensitive cells that a dog’s nose contains, canine assistance has been sought in many spheres of detection, some obvious and some less so. We all know that bloodhounds have been used to trail and track down escaped criminals, but it is less well-known that dogs have been employed to tell whether pairs of twins are identical or fraternal. Since personal human odor is genetically inherited, identical twins have an identical body scent and dogs cannot tell them apart, whereas fraternal twins have different body scents and can easily be distinguished. Other tasks for the canine nose have included truffle-hunting, drug-detecting, bomb-searching, and the rescuing of avalanche victims buried beneath the snow. The three major drugs, marijuana, cocaine, and heroin, all have highly characteristic odors, and dogs can sniff them out even when they are carefully sealed inside objects by smugglers. Attempts by the drug dealers to mask the telltale smells have frequently been uncovered. Surrounding the drug packets with strong perfumes, spices, tobacco, onions, or mothballs has never fooled the specially trained dogs employed by the drug squad. And dogs trained by bomb disposal squads have no difficulty in detecting the sulfur in gunpowder or the acid in nitroglycerine. When it comes to distinguishing strange smells, the dog’s nose is still far more efficient than any machine built by man. During evolution, the main pressure to develop such astonishing olfactory abilities was, of course, the detection of the prey by scent at a great distance. A wolf has been observed to detect the scent of the deer downwind at a distance of one and a half miles. As soon as the odor of the deer reaches the wolf-pack, the wolves freeze in their tracks and point their bodies directly toward the prey. After standing stiffly for a moment, verifying the scent, they cluster together, nose-to-nose, with their tails wagging excitedly. Then, after about ten to fifteen seconds, they take off toward the deer and the hunt is on. For such animals, especially those living in the frozen north, an acute sense of smell makes the difference between life and death. It is this refined ability that our domestic dogs have inherited. THE SENSE OF SIGHT Dogs have good eyesight, but it differs from ours in several respects. For many years it was believed that they had no color vision and lived in a totally black and white world. It is now known that this is not the case, but color is not particularly important to them. Their ratio of rods to cones on the retina of the eye favors the rods much more than ours. Rods are useful for black and white vision in dim light; cones are employed in color vision. The “rod-rich” eyes of dogs are therefore specially adapted to a daily cycle that favors dawn and dusk as the periods of major activity. This is called a crepuscular rhythm and is the typical mode for the majority of mammals. Humans are unusually diurnal and therefore not typical mammals as far as vision is concerned. The small number of cones in the eyes of dogs reveals that, although they may not revel in technicolor excitements of the human kind, they must be able to see at least some degree of coloration in their canine landscape. As the great eye-expert, Gordon Walls, so eloquently expressed it, “To any such seminocturnal, rod-rich animal [as a dog], the richest of spectral lights could at best appear only as delicate pastel tints of uncertain identity.” Quite so, but pastel tints are better than none, and it is pleasant to think that our canine companions can share with us at least some degree of color appreciation as we walk together through the countryside. In the dim light, dogs have the advantage over us. They have a light-reflecting layer called the tapetum lucidum at the back of their eyes, which acts as an image-intensifying device enabling them to make more use of what little illumination there may be. As with cats, who possess the same device, it also makes their eyes shine in the dark. Another difference between our eyes and theirs is that they are more sensitive to movement and less so to detail. If something stands still when at a good distance from them, it becomes almost invisible. This is why so many prey species “freeze” and stand motionless when they become alarmed, before trying to flee. Tests have proved that if a dog’s owner remains motionless at a distance of three hundred yards, the animal cannot detect him. If, on the other hand, a shepherd is one mile distant but making bold hand signals, these can be clearly seen by his sheepdog. This sensitivity to movement is, of course, of paramount importance during the long chases when wild dogs are on the hunt. Once the prey is fleeing, the dog’s eyes are at their peak of performance. An additional aid for the hunting dog is its much wider field of vision. A narrow-headed breed like a greyhound has a visual range of 270 degrees. A more typical dog has a range of 250 degrees. Flat-faced dogs have slightly less; but they all have more than human beings, whose visual field is only 180 degrees. Although this means that dogs can detect small movements over a much wider slice of the landscape, they have to pay for this with a narrower range of binocular vision, a range that is only half the width of ours. So, we are better at judging distances than they are. This information came from two different books written about dogs. One is Dog Watching by Desmond Morris; the other is The Dog’s Mind by Bruce Fogel. 12/2004 DSR/ncn