Stereo Seeing and Smelling

Welcome back. Watching the centerfielder make an impossible catch, I flashed back to standing in right field, hearing the crack of the bat, waiting and repeatedly misjudging the whereabouts of fly balls. You guessed that if you read my blog post Sports Talk--Baseball. I described being told after an Air Force physical that I had zero depth perception.

With all due respect to the Air Force, it’s not that bad. I, like most people with two functioning eyes, have stereovision. Each eye sees the same scene from a slightly different perspective, the brain pulls the two views together and…ta-dah…we see the scene in three dimensions.

Seeing 3-D offers advantages besides being a centerfielder or pilot; yet lots of people don’t have stereovision and they get along fine. In case you were wondering, that’s also true of rats. And rats can smell in stereo! I learned that when I learned moles smell in stereo.

Rat’s Non-Stereovision

Although eye coordination in freely moving rats is still unknown, a recently published study from Germany’s Max Planck Institute for Biological Cybernetics found the visual fields of their two eyes are not continuously aligned. As rats run about, their eyes are going in opposite directions.

A cute rat. Note the directions of the
eyes. (photo on multiple websites)

The researchers attached miniature high-speed cameras to rats’ heads and tracked the head position and direction. They determined that the lines of vision of the two eyes didn’t fuse to produce a stereoscopic image but instead varied by as much as 40 degrees horizontally and 60 degrees vertically. (The videos with the paper are great!)

An interesting finding is that, while rats’ eyes are all over the place, they’re always monitoring above. That suggests an adaptation to avoid overhead attack.

Rats Can Smell in Stereo

Although I missed the account in 2006, investigators at India’s National Centre for Biological Sciences showed that rats can use their two nostrils to tell if odors are coming from their left or right.

Confined rats were trained to respond to an odor on their left or right by letting the rats get thirsty, then placing water on the side with the source of the odor. Once trained, the rats needed only a fraction of a second to select the side with the odor regardless of the odor used.

The rats chose the correct side at least 80 percent of the time until one nostril was blocked. Lacking both nostrils for stereo smelling, the rats lost the capability to distinguish the side with the odor.

Moles Smell in Stereo

While the rats were trained and stationary, recent experiments at Vanderbilt University demonstrated that blind moles--common or eastern American (Scalopus aquaticus)--smell in stereo as part of their ordinary search behavior.

In multiple trials, a mole was released into a circular chamber, which had yummy pieces of earthworm placed randomly around the perimeter and whose air pressure could be monitored to determine if the mole sniffed. Within five seconds, the mole would wiggle its nose, sniffing, and go directly to the food.

A cute blind mole. Note the nostrils.
(photo on multiple websites)

To test the importance of stereo smelling, the researcher blocked one nostril. Although the moles still headed toward and eventually found the food, their aim was off toward the side opposite the blocked nostril--left nostril blocked, off to the right; right nostril blocked, off to the left. The same results were obtained in a different chamber where the food was placed directly in front of the entrance.

Next, small tubes were inserted to cross the two nostrils. With right nostril sniffing air from the left and left nostril sniffing air from the right, the poor perplexed little guys just kept searching. If they found the food, it was likely because they relied on the strength of the odor.

Wrap Up

I hope you enjoyed this peek into the world of rats and moles and that your own vision and olfactory capabilities are performing well. Thanks for stopping by.

P.S.

- Links to rat vision study in journal Nature (URL must be pasted in) and Science Daily:
www.nature.com/nature/journal/v498/n7452/full/nature12153.html
www.sciencedaily.com/releases/2013/05/130527100530.htm
- Links to rats’ stereo smelling study in Science magazine and Nature News:
www.sciencemag.org/content/311/5761/666.abstract
www.nature.com/news/2006/060130/full/news060130-10.html
- Links to moles’ stereo smelling study in online journal Nature Communications, Research News at Vanderbilt and National Geographic:
www.nature.com/ncomms/journal/v4/n2/full/ncomms2444.html
news.vanderbilt.edu/2013/02/moles-smell-in-stereo/
news.nationalgeographic.com/news/2013/02/130205-moles-smell-stereo-animals-weird-science/