PROTRUDING FROM THE sides of a dog’s muzzle is a set of stiff hairs that are popularly called whiskers or, more technically, “vibrissae.” These are not at all like the nonfunctional whiskers that men sometimes grow on their faces. Cats have similar hairs that people often refer to as “feelers,” which may be a better name, since vibrissae really are sophisticated devices that help the dog feel its way through the world. Vibrissae are quite different from most other hairs on the dog’s body, in that they are considerably more rigid and embedded more deeply in the skin. At the base of each vibrissa is a high concentration of touch-sensitive neurons.
Vibrissae are found in a variety of animals other than dogs, including cats, rats, bears, and seals, suggesting that they must serve a useful function. One way to determine how important something is to an animal is to see how much of the brain it uses. Of those areas of the brain that register touch information in the dog, nearly 40 percent is dedicated to the face, with a disproportionately large amount of that area dedicated to the regions of the upper jaw, where the vibrissae are located. We can actually map each individual vibrissa to a specific location in the dog’s brain, suggesting that great importance is assigned to information from these structures.
The vibrissae serve as an early warning device that something is near the face; thus, they prevent collisions with walls and objects, and they keep approaching objects from damaging the dog’s face and eyes. You can demonstrate this for yourself by tapping gently on the vibrissae of a dog. With each tap, the eye on the same side of the face will blink protectively, and the dog will tend to turn its head away from the side tapped.
The vibrissae also seem to be involved in the location of objects, and perhaps in the recognition of the objects themselves. Most animals use vibrissae in much the same way that a blind person uses a cane. First, the little muscles that control the vibrissae direct them somewhat forward when the dog is approaching an object. Next they actively “whisk” (vibrate slightly) while the dog swings his head to drag these hairs across surfaces. Whisking gives information about the shape and roughness of surfaces near the dog’s head. Since the dog’s eyes can’t focus very well on close objects, and his muzzle blocks his line of sight when the dog is looking at things near his mouth, the information from the forward- and downward-pointed vibrissae appears to help the dog locate, identify, and pick up small objects with his mouth.
Many dog fanciers are unaware of the importance of vibrissae to dogs, and most groomers seem to consider vibrissae a purely cosmetic feature, as if they were the same as human facial hair. Dogs of many different breeds routinely have their vibrissae cut off in preparation for the show ring. It is argued that this grooming technique gives the dog’s head a “cleaner” look. Unfortunately, amputating vibrissae is both uncomfortable and stressful for dogs, and it reduces their ability to perceive their close surroundings fully.
Specifically, dogs whose vibrissae have been removed seem more uncertain in dim light. Under these conditions dogs move more slowly, because they are not getting the information they depend on to tell them where things are that they might bump into. With intact vibrissae, the dog actually does not have to make physical contact with a surface to know it is there. These special hairs are so sensitive that they also register slight changes in air currents. As a dog approaches an object like a wall, some of the air that he stirs up by moving bounces back from surfaces, bending the vibrissae slightly, which is enough to inform the dog that something is nearby well before he touches that thing.
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