Humans and many other mammals see (and hear) in stereo. Working in tandem with the other, each eye helps us find objects near or far by sending different messages to the brain.
But what about creatures that are blind?
If you haven’t already, meet the eastern or common mole, Scalopus aquaticus. In addition to being cute in a kind of creepy way, these mammals are blind and have teeny ears. But they are remarkably good at finding their prey.
Ken Catania, a neurobiologist at Vanderbilt who studies animal sensory systems (he’s one of the researchers responsible for the sensitive alligator study we covered in Science in Action) decided to investigate the mole’s sense of smell.
He didn’t think the moles smelled in stereo—in fact, just the opposite. “I came at this as a skeptic. I thought the moles’ nostrils were too close together to effectively detect odor gradients.” But he’s a scientist—he needed evidence to support his assumption.
To test the theory of stereo smell, he created a radial arena with food wells spaced around the 180-degree circle with the entrance for the mole located at the center. He then ran a number of trials with pieces of earthworm placed randomly in different food wells.
When the mole first entered the arena, it moved its nose back and forth as it sniffed. Then, it seemed to zero in on the food source, moving in a direct path. This was pretty remarkable, and made Catania reconsider the idea of stereo sniffing.
“It was amazing. They found the food in less than five seconds and went directly to the right food well almost every time,” Catania said. “They have a hyper-sensitive sense of smell.”
Catania then blocked one of the moles' nostrils with a small plastic tube. When their left nostrils were blocked, the moles' paths consistently veered off to the right, and when their right nostrils were blocked, they consistently veered to the left. They still found the food but it took them significantly longer to do so.
Voilà! Stereo-smelling! (A video of the trials demonstrates this very clearly.)
Catania proved himself wrong and published his findings this week in Nature Communications.
What about the rest of us mammals? Do we smell in stereo?
“The fact that moles use stereo odor cues to locate food suggests other mammals that rely heavily on their sense of smell, like dogs and pigs might also have this ability,” Catania says. But as for humans, he remains skeptical. I guess stereo- vision and hearing is enough…
Image: Ken Catania