The Science Behind Why We Can't Hear A Dog Whistle
BLUE STUDIOS: STEM CLASSES FOR KIDS
BLUE STUDIOS: STEM CLASSES FOR KIDS
Francis Galton developed the first high-frequency sound device, back in the 1870s. He was a curious man, in all senses of the word. To test the limits of human hearing, he built a pipe whistle with a length that could be precisely adjusted to produce different frequencies. He was a half-cousin to Charles Darwin and maybe that inspired him to also test animals at the London Zoo, as well as cats and dogs in the streets. Humans and other mammals have tiny hairs in their ears that react to different frequencies and send electrical signals to their brains. For humans, the upper limit is around 20 kilohertz or about 20,000 vibrations per second, but this varies between individuals and drops off as adults age. Dogs can hear up to 45kHz, with smaller dogs usually being more sensitive. Many mammals can hear higher frequencies than humans—even cats. I would imagine that good hearing must be important to the survival of mammals, especially those scuttling around at night. Two distinct ears enable them to identify the direction that sounds come from, which could be the difference between getting eaten or not. For smaller mammal heads, higher frequencies and their correspondingly shorter wavelengths are required for comparable resolution.
The science behind why we can’t hear a dog whistle
As they age, dogs lose their ability to hear higher frequencies, as the cells responsible for their hearing die. They compensate by increasing sensitivity to lower frequencies and become less sensitive to higher ones. The same phenomenon occurs in the ears of humans. The shorter wavelengths that are needed for small ears require very short, quick vibrating pulses to stimulate the eardrum or external eardrum. At this stage, even a fast movement by the person or animal can be picked up. Higher frequencies don’t require such rapid movements so can be picked up more easily. There are two ways to reduce the chances of a dog hearing high-frequency noises. The first is to reduce the level of a sound. The second is to limit the sounds that can be heard by the dog.
Galton worked with some labs at London Zoo, but he also tried out pet dogs and cats. As the owner of a purebred English Setter, I always wondered why the dog I had developed a fear of storms was very sensitive to higher frequencies, even when trained to ignore them. Why would a dog be afraid of a dog whistle? Did they believe it was a sign of thunder or something more sinister? In the dog study, the whistles were fed into a speaker and the animals were allowed to choose which to hear. Those that saw the whistles and heard them had a significant reduction in response to low-frequency noise. Dogs that heard the low whistles showed a reduced response to high-frequency noises, suggesting a hearing adaptation.
What frequencies can we hear?
The brain interprets these electrical signals to activate neurons in our ears to receive the sound. When a high-frequency sound is received by our ears, the muscles in the head and neck move more slowly, which also helps to focus the signal onto the specialized hair cells that are embedded in the cochlea—the circular tissue at the base of the inner ear. A high-frequency sound then vibrates these hairs. When the sound passes through the cochlea and the head again, the hair cells in the ear canal read the signals on the hair shafts and send the corresponding signals to the brain. I would imagine that good hearing must be important to the survival of mammals, especially those scuttling around at night.
Why is good hearing important?
Good hearing is crucial for animals in the dark, or in locations where they can't see their surroundings. In the dark, your eyes are the only method for detecting the direction and distance of sounds. If you want to avoid becoming the dinner of a hungry predator, you have to pinpoint where sounds are coming from. This is impossible when you are at sea level. You are also not able to hear the subtle sounds that you would need for survival if you're up high in a tall tree. We can see only a narrow portion of the entire visual field, which is between 3 and 25 degrees in each direction, and this decreases with every step. Our peripheral vision is pretty limited.