Smell and vision in dogs appear to be integrated in some way, although it’s not known how dogs experience the two senses functioning together.
Dogs are excellent trackers and are known to rely on their ability to identify scents and trace them. A recent study shows that there may be more to it than just a keen sense of smell. The study published in this month's Journal of Neuroscience highlighted the discovery that smell and vision are connected in the brains of dogs, something that hasn't been found in any other species. For other species, including humans, smell and vision are two separate senses but the new findings published in the study state that they are somehow linked in dogs. “The most interesting thing about this research is the connections from the nose up to the occipital lobe, which houses the visual cortex,” said Veterinary Neurologist Philippa Johnson, an associate professor at Cornell University’s College of Veterinary Medicine and senior author of the study, reported NBC News. It further highlights how important smell is to dogs.
Philippa Johnson and her colleagues cited the MRI scans of the brains of 23 dogs to highlight the connection between their smell and sight. The scans showed neurological connections between the olfactory bulb, where scents are recognized, and their occipital lobe, where vision is processed. This has not been noted in any other species. Johnson hinted that this could also be the case in some other animals as well. While it may seem unfathomable to humans, the two senses — smell and vision — work in tandem to give dogs a fuller picture of what is before them. “Scent contributes to the visual cortex in dogs, but a dog’s experience is hard for us to know,” said Johnson. “But I think they can use scent to work out where things are.”
Johnson listed an example to highlight the difference between how a dog and a human would approach and assess a new room. She said humans would primarily rely on vision to establish the room and its occupants whereas dogs integrate scents as well to understand the environment and those present. This is also a pattern noted in blind dogs who are more equipped than blind people to navigate their surroundings despite having no vision. The author suggested that there have been indications that a dog's vision isn't as "acute and complex" as human vision but this study further confirms that their smelling powers fill in a lot of information through integration with visual senses. "Dogs might have a completely different experience of the world compared to us,” she said.
“One of the ophthalmologists at the hospital here said he regularly has owners that bring their dogs in, and when he tests their eyesight, they are completely blind — but the owners literally won’t believe him,” she said. “The blind dogs act completely normally. They can play fetch. They can orientate around their environment, and they don’t bump into things.” This is also largely aided by the fact that the olfactory bulb in a dog’s brain is about 30 times larger than that found in a human brain. Johnson noted that dogs can have up to a billion smell receptors in their noses, as opposed to just 5 million smell receptors in people.
Johnson and her colleagues plan to extend their study to other animals to find out if they have a connection between their sense of smell and vision. Johnson believes it's more likely to be noted in animals who rely heavily on smell. ”A horse’s head is predominantly a nasal organ, but they use scent in a different way to dogs because they are prey animals and they use it for alerting themselves,” she said. Johnson believes different application of the same organ can throw up a completely different picture as to how the two senses are integrated.
Palaeoanthropologist Pat Shipman, the author of “Our Oldest Companions: The Story of the First Dogs” believes the superior sense of smell in dogs was one of the main reasons for their domestication from wolves up to 40,000 years ago. Their ability to see in the dark and run faster than humans also helped humans hunt in tandem with them. “The whole advantage of domesticating another predator has to have been that the human gets something out of it that they didn’t have otherwise,” she said.