A frequent call-in question on my radio programme is, "Why does my dog howl when the ambulance is passing?" I have heard many Trinbagonians claim that their dogs are "harden" and do not listen, while many others boast that their dogs can distinguish their owners' car engines from all other cars on the road and their dogs are waiting at the gate when the owners drive up. Today we'll discuss how well our dogs really hear us.
If dogs could talk, they would almost certainly proclaim hearing as their second most important sense; smell, of course, being their first. People are so verbally oriented that we expect our canine companions to listen a lot, and it is not surprising that pets have exceedingly high therapeutic values.
Humans and canines share many of the same anatomical characteristics of the ear. The difference is the pinna, or the outermost section. Our ears are very much plastered to our heads, and the ability to wiggle them even a tiny bit is considered amazing. When a dog hears a sound, he has the ability to move his ears independently from each other, making it easier for him to discriminate and pick up sounds all around.
In order to achieve this, a dog's ears are controlled by at least 18 muscles so consider the amount of damage you do when you choose to crop your dogs' ears.
The external auditory canal leads down from the base of the pinna. It then makes a nearly right angle turn inward to the eardrum. Vibrations reaching the eardrum pass through the tympanic cavity via three tiny bones known collectively as the auditory ossicles. This section comprises the middle ear. The inner ear is responsible for turning vibrations into nerve impulses. Vibrations pass through a snail-shaped tubular structure called the cochlea. This converts the vibrations into nerve impulses and then sends them along the auditory nerve to the brain for processing.
Now that we know how our dogs hear, let's talk about what they hear. Hearing range usually describes the range of frequencies that can be heard by an animal or human. The number of sound pressure level vibrations (sonic waves) per second denotes the frequency. Infrasonic (below hearing), sonic (aural), and ultrasonic (above hearing) frequencies are measured in Hertz (Hz); one Hertz is one cycle wave (or singular pressure wave in audionics) per second.
Reporting the frequency range for hearing in dogs and other species is not a straightforward task-the "how" of determining hearing frequency ranges must first be explained. When determining the frequency range in animals, an investigator must first train the animal to respond to a presented sound stimulus by selecting between two actions using rewards.
Often this response is to try to drink or eat from one of two dispensers when a sound is heard. The sounds are randomly presented from one side or the other, and the subject must select the right dispenser (on the same side as the stimulus) to get the reward; otherwise no food or drink is dispensed. This is done with the animal hungry or thirsty to motivate responding.
The hearing ability of a dog is dependent on its breed and age. However, the range of hearing is approximately 40 Hz to 60,000 Hz, which is much greater than that of humans. As with humans, some dog breeds become deafer with age such as the German shepherd and miniature poodle. As dogs hear much higher frequency sounds than humans, they have a different perception of the world. Sounds that seem loud to humans often emit high frequency tones that can scare away dogs. Ultrasonic signals are used in training whistles, as a dog will respond much better to such levels.
One impressive talent dogs have is the ability to screen incoming sounds. If you have ever watched your dog sleeping soundly through loud music or a blasting television but then suddenly spring into alert at the sound of the fridge opening or the crinkling sound of a food bag, you have witnessed sound screening at work. Their sensitivity to sound is so great that dogs can also differentiate between very similar sounds, hence the reason your dog "knows" your car engine from all others.
Puppies are born deaf and their ears do not open until they are ten to 14 days. If your puppy is not responding to sound after that time, he may be congenitally deaf. This genetic problem is often associated with white coat colouring, and occurs more in Dalmatians, bull terriers, Jack Russells, and Australian Shepherds/ Cattle dogs. Any dog that does not seem responsive to sound, no matter his breed or age, should be checked for effective hearing.
So, why do dogs howl at sirens? The howl is a long-distance form of communication and sirens are within the same frequency range as a howl. The dog therefore hears the siren as a howl from another dog and is simply responding in kind.
