navigating - photo by Somewhat Frank on FlickrA new book asks the question, Why do we get lost? I think the more interesting question is, how do we know where we are?

When I was growing up in Munhall I remember being so confused about the layout of the neighborhood that I gave up trying to make sense of it. If I turned left out of my driveway, I could take a certain route through a certain part of town and end up at school. But if I went down my street the complete opposite direction, and passed through a different part of town, I’d end up at the same place.

(Years later, I found out why: my street was shaped like a squiggly horseshoe. When I walked my dog around the block, the block was not square or triangular but rather shaped like an “S”. No wonder I was confused.)

my neighborhood

But even without a mental map, I got around just fine by recognizing landmarks and street names. Now, several groups of scientists are suggesting that humans navigate by landmarks, while other animals use geometry.

Hamsters, toads, and spiders can all navigate like homing pigeons: take the critter away from home by any route you please, and she’ll fly, or crawl, straight back. According to Jack Loomis at UC Santa Barbara, people do badly on a simplified version of this test; and William Warren at Brown found that people could navigate by landmarks through a maze that, geometrically, couldn’t possibly exist. (The maze was a virtual world with invisible “wormholes”).

But are we really so bad at geometric navigation? A recent study looked at the question of whether people who are lost end up walking in circles. The answer: only if they are blindfolded or have no other cues. Test subjects walking around the Sahara, with only shadows from the sun for guidance, did a decent job of walking in a straight line – even though the sun moved during their long hike.

direction - photo by Kulbowski on FlickrMeanwhile, blindfolded people, asked to walk through a field, wandered wildly but didn’t always prefer circular directions. (You wouldn’t know it, though, from all the headlines of “We really do walk in circles.” Only sometimes! Not even most of us!) The authors figured that “sensory noise” – basically, errors in where we think our body is – accounts for the wiggly path.

But some people are bad at navigating even by landmarks. Giuseppe Iaria and Jason Barton, are studying what happens in the brains of people who have a broken sense of direction. You can take their tests at the catchily named (which, um, I had trouble finding again after my first visit).

The series of tests takes about an hour, but it’s interesting to see what they think a sense of direction is made of. (They especially encourage people who have trouble navigating to take the tests.) The tasks include recognizing objects from different angles, recognizing faces (people with face blindness, called prosopagnosia, often have trouble navigating), recognizing landmarks after you’ve seen them in situ, and a variety of sleep-inducing walks through an almost featureless landscape, reminiscent of an empty Doom set, or a prison yard, where you’re asked whether you were led along two identical or different routes. In the most tedious test, the prison yard gets a couple of storefronts, and you’re asked to repeatedly locate them on a map. Despite my childhood difficulties, I did pretty well on the tests. It seems that landmark-based navigation works pretty well after all.


Whose limb is it anyway?

September 3, 2008

photo by dolbystereobenIt’s a little weird to think of limb ownership as a field of study. Of course my right arm belongs to me; who else would it belong to?

Our brains process a lot of information coming from our extremities. Beyond the usual sensations of touch – heat, cold, pain, tickling, and so on – we have proprioception, the information telling us where our body is in space. It’s how you can touch your nose even when your eyes are closed.

But when your eyes are open, your brain uses that information too.

Hence the strange effect of the rubber hand illusion , where scientists put a rubber hand on a table in front of someone, and stroke both the rubber hand and the subject’s real hand with a paintbrush. The subject ends up thinking she “owns” the rubber hand. To quote a typically intelligent YouTube commenter:

well duh because theyre seeing it, and they already felt the brush on them so your sense mix up ahahah idk.

photo by stagewhisper

photo by stagewhisper

In fact (and this is something the YouTube commenters were eager to see, although it’s not in the video), if you make stabbing motions toward the rubber hand, the subject will freak out. Scientists can detect activity in the “I’m freaked out” section of the brain. (They have that mapped out, I guess). The subject really thinks the rubber hand is hers.

A new study shows an interesting side effect of “owning” a rubber hand: the subject disowns her existing hand. The researchers found that the real hand’s temperature drops during the experiment, and tactile information from that hand is processed more slowly.

photo by raysto

photo by raysto

Rubber hands sit still and look funny, but it turns out there’s a more convincing way of portraying a fake hand: using a mirror.

If you rig up a mirror so that the subject is looking at, say, their real left hand and a reflection of their left hand, they start to believe they are looking at their left and right hands. The standard setup has the person move, clench, and stretch their hands simultaneously. Watch the video and you’ll see how disconcerting it is when, around 1:55, the demonstrator moves his real hand differently from the reflection. I’m not attached to those hands and I still got weirded out!

A surprising result of all this brain confusion is that it even works for people who are missing a limb. If an amputee thinks that their missing limb is clenched, cramped, or painful, a few minutes with a mirror box can convince their brain that the limb looks and acts normally. In a recent study, after 4 weeks of mirror therapy all of the amputees felt a decrease in their everyday phantom pain.

Why do amputees feel phantom pain at all? Some say it’s a problem with the cut ends of nerves; some say it’s all in their head. One theory, supported by the mirror therapy results, says that the brain is just guessing, in the absence of better information, at what sensation the limb should be feeling. The mirror therapy provides more information, untrue though it may be, leading to relief.

In this fascinating story about itch, mirror therapy helps. Here is the patient’s experience:

The first thing he expressed was disappointment. “It isn’t quite like looking at my left hand,” he said. But then suddenly it was.

“Wow!” he said. “Now, this is odd.”

After a moment or two, I noticed that he had stopped moving his left arm. Yet he reported that he still felt as if it were moving. What’s more, the sensations in it had changed dramatically. For the first time in eleven years, he felt his left hand “snap” back to normal size. He felt the burning pain in his arm diminish. And the itch, too, was dulled.

“This is positively bizarre,” he said.