Inside of a Dog_ What Dogs See, Smell, and Know - Alexandra Horowitz [38]
The kind we notice first is the one that most closely matches our own language: communication out loud.
DOG-EARED
Thunder outside. Pump's ears, velvet equilateral triangles that fold perfectly along the side of her head, prick into long isosceles. Head up, eyes to the window, she identifies the sound: a storm, a frightful thing. Her ears pivot back, flattened along her skull as if to hold them shut by their own force. I coo to her consolingly and watch her ears for feedback. The tips soften but she relaxes only slightly, still holding them tight against the roar.
Without prominent ears ourselves, we can envy dogs' proud ears. They come in a dazzling array of equally adorable variants: extremely long and lobular; small, soft, and perked; folding gracefully alongside the face. Dogs' ears may be mobile or rigid, triangular or rounded, floppy or upright. In most dogs, the pinna—the outer, visible part of the ear—rotates to better open a channel from the sound source to the inner ear. The practice of cropping ears, severing the pinnae to make floppy ears stand upright, long mandated in many breed standards, is becoming less popular. This designing of dogs, sometimes defended as reducing infections, has unknown consequences in auditory sensitivity.
By natural design, dogs' ears have evolved to hear certain kinds of sounds. Happily, that set of sounds overlaps with those we can hear and produce: if we utter it, it will at least hit the eardrum of a nearby dog. Our auditory range is from 20 hertz to 20 kilohertz: from the lowest pitch on the longest organ pipe to an impossibly squeaky squeak.* We spend most of our time straining to understand sounds between 100 hertz and 1 kilohertz, the range of any interesting speech going on in the vicinity. Dogs hear most of what we hear and then some. They can detect sounds up to 45 kilohertz, much higher than the hair cells of our ears bother to bend to. Hence the power of the dog whistle, a seemingly magical device that makes no apparent sound and yet perks the ears of dogs for blocks around. We call this sound "ultrasonic," since it's beyond our ken, but it is within the sonic range for many animals in our local environment. Don't think for a moment that apart from the occasional dog whistle, the world is quiet for dogs up at those high registers. Even a typical room is pulsing with high frequencies, detectable by dogs constantly. Think your bedroom is quiet when you rise in the morning? The crystal resonator used in digital alarm clocks emits a never-ending alarm of high-frequency pulses audible to canine ears. Dogs can hear the navigational chirping of rats behind your walls and the bodily vibrations of termites within your walls. That compact fluorescent light you installed to save energy? You may not hear the hum, but your dog probably can.
The range of pitches we are most intent on are those used in speech. Dogs hear all sounds of speech, and are nearly as good as we are at detecting a change of pitch—relevant, say, for understanding statements, which end in a low pitch, versus questions, which in English end in a raised pitch: "Do you want to go for a walk(?)" With the question mark, this sentence is exciting to a dog with experience going on walks with humans. Without it, it is simply noise. Imagine the confusion generated by the recent growth of "up-talking," speech that ends every sentence with the sound of a question?
If dogs understand the stress and tones—the prosody—of speech, does this hint that they understand language? This is a natural but vexed question. Since language use