Everyone wonders what it’s like to see the world through the eyes of another creature. Now it appears the textbook accounts of how dogs see the world has been wrong. It was thought, that like humans, all dogs have the same eye structure and see the world the same way. But to Veterinary Scientist Paul Mc Greevey that just didn’t make sense. He measured different kinds of dog’s skull, nose, and shape of their head, and he collected eyes from dogs that had died, and measured their eyeballs. Remarkably he found eye shape did change with the breed of the dog. It was a finding that overturned the standard texts on dog eyes. But then his collaborator Perth neuroscientist, Alison Harman examined the cells from the retina at the back of the eye. She found different dogs had a completely different retina. Amazingly, it means different dogs see the world completely differently. As this very amusing story explains this work goes a long way to explaining why some dogs chase cars and other just sit in your lap staring into their owners face.

TRANSCRIPT

Narration: Everyone wonders what the world looks like through the eyes of their pets. But for Paul McGreevey, one day, idle curiosity became a quest. It began when he heard about some research, featured on Catalyst last year. A Perth neuroscientist, Alison Harman had discovered amazing things about how horses see.

NARR (ex Riding Blind) To us, this view of Kings Park is from the front only. But a horse sees a clear, narrow strip going right around 320 degrees. Above and below that strip is blurred. What’s more, it can’t see the colour red.

And that got Paul wondering. What other secrets might be hiding in the eyes of the dog. Paul lectures in animal behaviour at Sydney University’s Veterinary School, usually accompanied by his dog Wally. And he had a hunch the textbooks had got something very wrong about dog vision.

Dr Paul McGreevey, Animal Behaviourist: Like many of the text books this is telling me that dogs have the same sized eyes regardless of their body size or their breed. Now that seemed very strange to me that the optics of the wolf were in a chihuana or a great dane.

Narration: So - did every breed of dog have exactly the same eyes, like the textbooks said? Paul contacted Alison, the woman who’d done the great work on horse vision. She didn’t know the answer, but she’d often wondered why her Pug dogs watch telly, when most dogs seem to ignore it.

Dr Alison Harman, Neurologist: Bertie watches television quite often. He likes horse programs and animal programs. I had another pug who would also watch television. If, for instance, another animal crossed the screen when he was watching it he would jump down and rush to look at the back of the television to see if it was coming out at the back.

Narration: They decided to team up and investigate. The first thing to look at was whether the size of the dog’s eye changed with different breeds. Paul started taking measurements of different kinds of dogs. He measured the skull, nose, shape of head. And, by collecting eyes from dogs who had died, he measured their eyeballs. To his delight the difference was really obvious.

Dr Paul McGreevey: This is the eye from a Rottweiler, and this is an eye from a Maltese, so you can see that there’s a clear difference in their dimensions.

Narration: So the textbooks were wrong. But they’re next discovery would blow the textbooks out of the water. Alison began looking inside the eye. She was examining the cells we actually use to see, which form the retina.

Dr Alison Harman: OK Jonica, now here’s a retina I’ve put under the microscope for you from a dog and you can see that this one has what we call a visual streak.

Narration: The visual streak is a high density line of vision cells which runs across the retina. You can see it clearly on this computer image. Scientists already knew dogs had a visual streak. But then Alison found something completely unexpected. Some dogs – didn’t.

Dr Alison Harman: This one doesn’t have a visual streak. …It has something called an area centralis.

Narration: Unlike the visual streak, the area centralis has the high density vision cells arranged in a spot. It could mean only one thing. Alison suddenly realised that different breeds of dog don’t just have different eyes, they see the world completely differently. And this is how.

Jonica Newby, Reporter: Howdy, hello Wally, no you can’t have the ball. Ok, what we’re going to do is Paul and I, we’re going to spread out, and then we’re going to show you this scene from each dog’s point of view.

Dr Alison Harman: You go over there and I’ll take the dogs, come on ... sit ...

Narration: Bertie and Wally both see in colour. Contrary to popular belief, dogs don’t see in black and white. They just can’t see the colour red very well. But that’s where the similarity in their worldview ends. Wally has the type of retina with a visual streak.

Dr Alison Harman: So what Wally can see is from all the way over there, all the way round here and over to there in a really good vision, not like us. We can only see the middle bit. But he can see really well all the way round.

Narration: But Bertie sees much more like a human. He has the type of retina with a dense, area centralis. Unlike Wally, he really isn’t getting the full picture.

Dr Alison Harman: He can see the middle quite clearly. But he can’t see the sides well at all, it’s more blurred for him. We were really amazed to discover that there was such variation in one species. It’s absolutely amazing.

Narration: But what’s most exciting Paul about this discovery is that at last it helps solve some of the great mysteries of dog behaviour. Like why some dogs chase things – and others don’t.

Dr Paul McGreevey: Well they chase things because they see them…

Narration: With his visual streak, Wally sees the bike clearly all the way across his field of view.

Dr Paul McGreevey: Wally is seeing the moving stimulus in his peripheral field, and following it… locking in on it and chasing after it.

Narration: Whereas Bertie only sees when it flashes through his central vision and it’s gone. There’s a bit of a blur happening but Bertie, really doesn’t see it at all.

Paul now realises the dogs most likely to hunt and chase are the ones with a visual streak. So how do you tell what kind of retina your dog has? Well, it’s directly related to the length of nose. Short nosed dogs have an area centralis. Long nosed dogs have a visual streak. And the dogs with the longest nose of all are these. The afghans are part of a group of dogs known as sight hounds. They’re born to chase. And we made them that way. Afghans were bred for hunting.

Dr Paul McGreevey: So now we know why the sight hounds have long noses. They need long noses to be able to hunt and see things in their periphery. When this dog sees something in her peripheral vision, she goes.

Jonica Newby: Can you ever let these things off the lead?

Dr Paul McGreevey: Very, very few owners risk that.

Narration: Not easy on the owner – which may explain why we also bred dogs without a visual streak.

Dr Paul McGreevey: It may be that we have developed the lap dogs and house dogs because they are less reactive to things that are going on around them because they’re not seeing them.

Narration: But was there anything the area centralis kind of eye was particularly good at? Alison took a closer look at the retinas. And that’s when the team got their biggest surprise of all. It turned out Bertie’s area centralis had three times the density of nerve endings as a visual streak. It means that short nosed dogs with their area centralis see in much higher definition than other dogs. And there’s one thing that’s really good for …

Dr Paul McGreevey: So when they’re looking at the owners face and different nuances of the owners expressions maybe they’re getting a bit more information than a long nose dog. This is perhaps a way of explaining how attentive and charming short nosed dogs are.

Narration: And it might just help explain something else.

Jonica Newby: Would this explain his tendency to watch Tv?

Dr Alison Harman: Yes it does, and he does watch television quite often

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