I’ve long wondered how blind dogs can live what appear to be pretty much normal lives, and questions sent to me such as, “How does my blind dog run and find his ball in another room?” by Adrianne about her dog Woof always grab my attention. I’ve also received wonderful stories of blind dogs living “amazingly normal” lives from a large number of people who wondered, as Marty put it, “How in the world does Zazie, my blind dog, run through my house at breakneck speeds without hitting anything and find her favorite toy?”
Given widespread interest in these sorts of questions, I was pleased to learn of a fascinating essay by Caitlin Hayes titled “Study finds new links between dogs’ smell and vision” about research reported in a paper published by Erica Andrews and her colleagues in the Journal of Neuroscience called “Extensive Connections of the Canine Olfactory Pathway Revealed by Tractography and Dissection.”
Hayes’s review of the research is right on the mark. She writes, “Cornell researchers have provided the first documentation that dogs’ sense of smell is integrated with their vision and other unique parts of the brain, shedding new light on how dogs experience and navigate the world.”1 The scientists did this using magnetic resonance imagining and virtual dissection on 23 dogs.
The Neural Basis and Evolution of Composite Signals
What this research means is that dogs’ brains are wired so that they can integrate information from different sensory modalities—in this case, smell and vision. These results explain why Woof and Zazie can run here and there and find their ball and toy when they can’t see anything but are able to use odors as a guide. And they do it better than humans.
What is really interesting about this research is that it not only provides a neurobiological explanation for Adrianne’s, Marty’s, and countless other dog guardians’ wondering how their blind dogs do the things they do, but also offers a neurobiological explanation for the existence of what ethologists call composite signals that combine information from different senses. A study by dog researcher Ludwig Huber showed that captive dogs could integrate information from sight and sound to identify other dog breeds correctly. In this study, dogs matched a projected visual image of dogs of different sizes with the vocalization that is usually made by dogs of each size.
When dogs scratch the ground after peeing or pooping, they may also be assembling a composite signal to tell other dogs what they did. Dogs have scent glands in their paws, and when they scratch, they might be trying to send an olfactory message to other dogs by spreading the scent from their paws or by sharing the odor of the pee or poop they deposited. Scratching also leaves a visual mark on the ground. Taken together, peeing, pooping, and ground scratching are a good example of how dogs may use composite signals to enhance their messages to other dogs by using both olfactory and visual components.
Dogs might also use composite signals composed of visual and auditory cues when they play.
From an evolutionary point of view, it makes sense that there would be integrated backup systems that go to work when things go wrong and there is a loss of one (or more) of the original sensory modalities. How the remaining senses do what they do remains a mystery.
I’ve seen blind dogs at familiar dog parks behave as if they were sighted; on a few occasions, I was astounded to learn they couldn’t see. I also met a woman who rescued a senior blind dog from her local shelter, but she didn’t know the dog was blind until she read the details about this wonderful canine elder. It wasn’t obvious as they greeted one another, played some, and snuggled.
Life in the wild can be tough, and individuals often get injured and lose an eye or an ear and do quite well. The loss of a dog’s or another animal’s sniffer might be more serious than the loss of eyes or ears because they are so dependent on olfactory input, and it would be good to know how debilitating losing their sense of smell—suffering from anosmia—really is .
Where to From Here? Neuroscience Meets Evolutionary Biology and Ethology
The combination of neuroscience, evolutionary biology, and ethology offers exciting ideas for future research. Thinking of composite signals from these diverse perspectives opens the door for answering a number of common questions that have been difficult to explain and also sets a standard for future work on how dogs and other animals sense their world using different combinations of sensory input. It’s difficult to imagine that dogs are the only nonhumans in which these sorts of neural links exist, and I look forward to the future of comparative studies.