Knowing something like the back of your hand supposedly means that you’re very familiar with it. But it could just as well mean that you think it’s wider and shorter than it actually is. As it turns out, our hands aren’t as well known to us as we might imagine. According to Matthew Longo and Patrick Haggard from University College London, we store a mental model of our hands that helps us to know exactly where our limbs are in space. The trouble is that this model is massively distorted.

To keep track of where your various body parts are, your brain maps your posture by processing information from your muscles, joints and skin. Close your eyes and move around a bit, and you’ll still have a good idea of what position you’re in even if you can’t see or touch yourself. But there’s no such direct signal that tells your brain about the size and shape of your body parts. Instead, your brain stores a mental model with those dimensions mapped out.

To visualise this model, Longo and Haggard asked volunteers to hide their hand under a board and use a baton to indicate the position of ten landmarks – the tip and base knuckle of each finger. Their answers were surprisingly inaccurate.

They underestimated the lengths of their fingers by anywhere from around 5% for their thumb and over 35% for their ring and little fingers. In contrast, they overestimated the width of their hand by around 67%, and particularly the distance between their middle and ring knuckles. Our mental hand is a shorter, wider version of our real one. Longo and Haggard found the same thing if they asked the recruits to angle their hands at 90 degrees under the board, and if they tested the right hand as well as the left.

These distortions actually reflect how sensitive each part of the hand is. The skewed mental map is remarkably similar to another map called Penfield’s homunculus, which charts the areas of the brain’s somatosensory cortex (the bit that processes touch information) that is devoted to each body part. Regions that have a more acute sense of touch correspond to larger parts of the homunculus, but they also loom bigger in our mental map. Regions that are less sensitive are smaller on both charts.

As we move from the thumb to the little finger, our digits become less sensitive and the mental map increasingly underestimates their true size. The back of the hand is more sensitive to movement across it than movement along it; accordingly, our mental map depicts a wider, shorter hand.

And we have no idea about this. Consciously, the volunteers had a pretty good appreciation of the size and shape of their hands. When Longo and Haggard showed them a selection of hand images and asked them to select the one that best matched their own, they did so very accurately. But even though they passed this test, they still failed to place the baton in the right place when their hands were hidden.

If we hold such a distorted depiction of our own hands, how is it that we ever grasp things successfully? It’s possible that our motor system uses a different model but Longo and Haggard put forward two more plausible ideas: that cues from vision are strong enough to override the warped map; and that we learn to correct for the misshapen model. Only by removing both of these factors did they finally reveal how skewed our perceptions actually are.

Reference: PNAS http://dx.doi.org/10.1073/pnas.1003483107

Image: Hands by Toni Blay

More on perception:

• How our skin helps us to listen
• How wearing a cast affects sense of touch and brain activity
• Blind man navigates obstacle course perfectly with no visual awareness
• Pain in the eye of the beholder
• Brain treats tools as temporary body parts

Two scientists went looking for water on Mars. After closely studying the Martian terrain, they think they might have found it–covering about a third of the planet, 3.5 billion years ago.

In a study published yesterday in Nature Geoscience, Gaetano Di Achille and Brian M. Hynek detail their hunt, which included looking at data from NASA’s Mars Orbiter Laser Altimeter (MOLA), a probe that studied the topography of the planet’s surface for four and a half years, starting in the late 1990s.

Scientists have debated whether Mars once supported oceans for over two decades, and, as the authors claim in their study’s abstract, these oceans remain one of the “largest uncertainties in Mars research.”

The authors of this study, who started out speculating on how water might have formed the apparent deltas and valleys on the planet, eventually looked at the altitudes of these features to determine if they could have been linked to a large body of water.

Gaetano Di Achille and Brian Hynek … had been building a database of Martian river deltas and valleys to examine how they might have been eroded by water, but ultimately realized that they had enough data to tackle the bigger picture. “Our research started as kind of a joke,” says Di Achille. “We were working on this database of deltas and valleys, and we said: why don’t we try to check this ocean hypothesis?” [Nature News]

They found that 17 of 52 deltas were at the same height, which might imply that they fed the same body of water which could have once filled a basin on the Northern hemisphere of the planet. Given that basin covers about a third of planet’s surface, the paper’s author question if these deltas might have channeled water into an ancient Martian ocean.

“If Mars had an extensive hydrological cycle in the past, with rain, groundwater reservoirs, ice sheets and surface run-off towards lakes and possibly a northern hemisphere ocean, then there should be evidence of deltas ringing the margins of these lowlands at a common elevation,” said Mr Di Achille. “Likewise, river valleys draining into such an ocean should also flow down to the same elevation, and shouldn’t be found below this level.” [Australian Broadcasting Corporation]

The research compliments another study from Hynek, which also looks at these river deltas.

In a parallel study published in the Journal of Geophysical Research (Planets), Hynek and colleagues catalogued some 40,000 river valleys on Mars, four times the number previously suspected. “The abundance of these river valleys required a significant amount of precipitation,” Hynek said. “This effectively puts the nail in the coffin regarding the presence of past rainfall on Mars.” [AFP]

Still, many hope for more direct evidence before claiming that this solves the ocean debate.

Taylor Perron, a geologist at the Massachusetts Institute of Technology in Cambridge, says that the result “strengthens the argument in favour of oceans” but leaves some issues unresolved. He says that there is enough variability in the delta elevations to suggest that there is not just one level coastline, and that it is “hard to explain” why some valleys end at much higher elevations than the proposed ocean. “One possible explanation is a large-scale deformation of the planet, which warped the landscape, transforming what was once a level shoreline into one with more variable elevations,” he says. [Nature News]

Of course an ancient Martian ocean leads to other questions: For one, where did all that water go?

Related content:
80beats: Scientist Smackdown: Did Mars Phoenix Find Liquid Water?
Bad Astronomy: New evidence of (transient) liquid water on Mars!
Bad Astronomy: Unpeeling the history of water on Mars
Bad Astronomy: Are Martian gullies formed by water or not?

Image: NASA, Goddard Space Flight Center, Scientific Visualization Studio/ Greg Shirah

Leon Jenkins is the President of the LA chapter of the NAACP, the organization that advocates for equal rights for black people. The work they do is fine by me, and I support their efforts. But organizations are made up of individuals, and individuals can make mistakes.

This is really one of those times. Here’s the story: Hallmark came out with a card for recent graduates, and it’s one of those deals that has a speaker in it that activates when you open it. Like all such cards it’s twee and sugary and over the top. It involves two cartoon characters with squeaky and high-pitched voices talking about how the graduate can now take over the world. It has an outer space theme to it, and what they say, well… watch/listen for yourself:

Um, yeah. It’s pretty clear to just about anyone who hears it — and doesn’t have any particular stake in the claim — that the card is saying “black holes”. The space theme is obvious enough, and black holes are a common topic. So why on Earth would someone think the card is saying “black whores”, as Mr. Jenkins and other LA NAACP members do?

In fact, there’s a good reason. What we have here is a very well-understood topic to skeptics: audio pareidolia. That is, mishearing recorded phrases or words, and thinking they are saying something else. This phenomenon is really strong, and once you think a recording is saying a certain phrase, it’s difficult to not hear it. So once someone thought the Hallmark card was saying “black hos”, they told other people, and that biased them into hearing it as well. I’ve written about this before; go here and here for great (and very funny) examples of this.

So it’s understandable that Mr. Jenkins might hear that… but then his own biases kick in. He looks at the card and finds pretty dubious evidence to support his claims; like saying that the word “ominous” means “evil” and therefore cannot be used for inanimate objects. In reality, ominous means foreboding or menacing like an omen, so of course it can be used for events or objects. Like many people do when making a claim, Jenkins is finding evidence after the fact that simply isn’t there.

Because honestly, when you think about it: Hallmark? Putting out a card that uses a racial slur? Hallmark’s products are the least offensive, blandest I can think of. They’re the lettuce-and-lite-no-transfat-mayo-on-white-bread sandwich of greeting cards.

But that doesn’t really make much of a difference to someone once their mind is made up. Note that Jenkins also says, “If reasonable people can listen to this and interpret it the way I did, you can pull [the card off the shelves].” That’s wrong, and in fact somewhat dangerous thinking; just because a lot of people think something is true doesn’t make it true.

Still, caving to this pressure, Hallmark pulled the card.

That’s too bad. The company took a financial and PR hit because of the customers’ misunderstanding, and that’s a bad precedent.This just reinforces the overall problem of people making decisions in their lives based on bad evidence or the misinterpretation of good evidence. How many ills of this world would disappear if we could make that go away?

Also, and more importantly, when anyone accuses someone else of racism when it’s not there, it hurts the overall cause. Given the press this has received, it’s the LA NAACP’s credibility that has taken a hit, not Hallmark’s. Crying wolf diminishes the NAACP’s work, and will make it harder for them to fight real racism the next time it pops up.

And that, to me, is uncritical thinking’s biggest danger. Not that people actively believe in things that are wrong — that’s here to stay — but that it masks the truth and prevents people from seeing it.

Tip o’ the mortar board to Fark.

The Food and Drug Administration has a message for the personal genomics revolution: slow down.

Personal DNA tests have been available for years now from companies like 23andMe and Pathway Genomics, and the direct-to-consumer tests have sold briskly even while the companies tried to sort out whether or how their systems would be regulated by the FDA. Then last month, Pathway took the next big step, offering to sell their tests over the counter in the nation’s largest drugstore chain, Walgreens.

For the FDA, that was one step too far, and it began to make noise about regulation. Now the agency’s leader in this field, Alberto Gutierrez, has sent official letters to all the major personal DNA-testing companies saying it intends to regulate the tests as medical devices, and that the companies must provide evidence of their scientific validity.

The letters, posted on the F.D.A. Web site on Friday, say the companies must apply for approval or discuss with the agency why certain test claims do not require such approval. But the letters stop short of saying the tests must be taken off the market until they are approved. Dr. Gutierrez said in an interview that it would be unfair to remove the tests from the market because the agency had not clearly told the companies that the devices needed approval [The New York Times].

Should your access to your own genome really be controlled by the FDA? As we noted when we covered the reasons why it might be a bad idea for Walgreens to carry the tests, it’s the consequences of that information that have the regulators concerned. The personal genomics companies don’t just send you a report with a bunch of A’s, C’s, G’s and T’s: They interpret the data, and sometimes give risk assessments for disease. Gutierrez says the companies must account for that.

Gutierrez said in an interview that if a person can do nothing about a genetic risk discovered through a test, “that at least should be stated somewhere.” He added that companies are also responsible for anticipating possible harm from a test — such as a person adjusting their drug doses on the basis of a result — and should take steps to “mitigate that risk” [Washington Post].

Just how those companies will “mitigate that risk” enough to satisfy the FDA remains unclear. But the risk of people using information that hasn’t been seen by doctors to self-medicate was enough for the FDA to reverse its previous position. Genome.gov, the site of the National Institutes of Health’s National Human Genome Research Institute, states:

The Food and Drug Administration (FDA) regulates tests sold as “diagnostic devices,” that is, tests manufactured by one company and then sold as a kit to a laboratory for genetic testing. However, the FDA does not regulate “home brew” tests, that is, tests that are both manufactured and performed by the same laboratory. Many common genetic tests (including the BRCA breast cancer gene tests) fall into this category. Because of this regulatory exception, genetic testing services using home brew tests can be marketed directly to the medical community — and the public — without FDA regulation or oversight.

Not anymore. These tests qualify for that “home brew” definition, The New York Times says, but the FDA has clearly chosen to jump into the regulation ring.

The companies’ statements sound like they intend to comply. But this new regulatory process could slow the race to get more and more genetic testing into the hands of consumers. Walgreens first said that Pathway Genomics had reassured them the tests it was going to sell didn’t require FDA approval, but then decided to put its plans on hold after the FDA complained and Congress said it might investigate. And 23andMe, one of the highest-profile companies in the group, didn’t do itself any favors this month when it goofed and gave up to 96 customers the wrong genetics reports.

Related Content:
80beats: 5 Reasons Walgreens Selling Personal DNA Tests Might Be a Bad Idea
80beats: Walgreens’ Genetic Tests on Hold, Under Congressional Investigation
DISCOVER: How Much Can You Learn from a Home DNA Test?
Discoblog: Welcome, UC Berkeley Freshmen! Now Hand Over Your DNA Samples
Discoblog: 23andMe To Customers: Oh Wait, Those Are Somebody Else’s Genes

Image: flickr / nosha

We were initially surprised that our co-authored book, Unscientific America, was so strongly attacked for observing that scientists should strive to improve their skills at public communication--and that this probably includes not alienating potential religious allies or mainstream America. But in a sense, the attacks made a kind of sense. Mostly, they came from those for whom this advice ran contrary to their particular project of denouncing much of America and the world for alleged ignorance and superstition--the New Atheists. However, with a recent review in The New Atlantis, it appears that we also touched a nerve on the political right. As this is a more interesting phenomenon, I want to explore it in this post. First, The New Atlantis introduces me as the author of The Republican War on Science, a book whose argument runs directly contrary to the publication's own project of articulating and defending conservative approaches to science, and pinning anti-science sentiment on liberals. So, there's that. It is more surprising, though, to find that the critique (from Ari N. Schuman) echoes the perspective of those traditionalists--apparently over-represented in the science blogosphere--who instinctively distrust calls for improved scientific communication. These critics tend to argue that any hint of message framing ...