(Originally written for DogWatch, a newsletter for the general public from the Cornell University College of Veterinary Medicine)

My dog, Alfie, loves to ride in the car with his head hanging out the window. He has such an entranced look on his face, I can’t help wondering what’s going through his mind.

Until we humans master dog-think, we can only guess Alfie’s thoughts as he rides down the road. However, we can make a few assumptions based on what we know about canine perception. Recall that the dog’s evolution as a social predator who often hunted in limited light led to the development of senses that complimented this lifestyle. These senses included vision that’s more sensitive to motion than detail or color, better hearing, and a much more developed sense of smell than ours.

What happens when we take that kind of perception and give it to a fur-covered passenger inside a moving vehicle? First, it seems safe to say that Alfie probably sees little more than a blur whipping by him at 35-65 miles per hour. However, while that would bother most vision-oriented humans, it doesn’t bother him because he doesn’t depend on his vision nearly as much as we do. Instead, he relies far more on his hearing and sense of smell to inform him about his surroundings.

To understand how this works, imagine driving to a friend’s home. Chances are that you find your way there using key visual landmarks, such a service station with a distinct sign just before you make the left hand turn onto your friend’s street. Now imagine making that same trip blindfolded (with someone else driving, of course!). Under those circumstances, most of us automatically will focus on sounds and scents to orient ourselves. Where we previously looked for the service station’s bright red sign, now we strain to hear the sound of the bell at the gas pumps or to catch a whiff of gasoline to tell us when we approach it.

For dogs like Alfie, that air streaming by an open car window presents an incredibly rich array of scents and sounds, many beyond human comprehension, to help him orient as well as entertain himself. However, not all dogs respond to this flood of input the same way. Those with confidence like Alfie will collect all the sensory data that they comfortably can until the speed of the car exceeds their ability or desire to process all this input. Then they curl up and go to sleep until the car slows down again.

However, a completely different scenario unfolds for the dog with less confidence and/or for those who feel obligated to protect their owners as they ride in the car. Under these conditions, that flow of sensory data streaming by the open (or even closed) window may cause such animals to succumb to stimulus overload. Instead of mining that air current for nuggets of interesting data like Alfie, these pets perceive it as a torrent of potential dangers. The faster the car moves, the more scents and sounds assault them and the less time they have to process it all. They become ever more frightened and confused, to the point that they may drool, vomit, or develop diarrhea.

Apart from any negative physical effects related to the dog’s fear, owners whose pets love to hang their heads out car windows often ask if this behavior sets the animals up for ear or eye infections. Although a clear link between this behavior and most ear and eye infections doesn’t exist, that doesn’t mean it can’t happen. Moreover, exposing an infected eye or ear to a high speed current of air bearing pollutants of one sort or another certainly could aggravate an existing problem. Because of this, the safest approach means opening the window wide enough for an inquisitive pet to collect enticing data, but not wide enough to allow the dog’s whole head to stick out.

For many dog owners the canine response to the invitation, “Wanna go for a ride?” ranks as one of the most enjoyable aspects of pet ownership. By appreciating the unique ways our dogs respond to the world zipping by as we drive down the road, we can ensure that their trips with us will be safe as well as fun for them.