Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Tuesday, May 21, 2019

The stone hand illusion

One of the reasons I trust science is that I have so little trust in my own brain's ability to assess correctly the nature of reality.

Those may sound like contradictions, but they really aren't.  Science is a method that allows us to evaluate hard data -- measurements by devices that are designed to have no particular biases.  By relying on measurements from machines, we are bypassing our faulty sensory equipment, which can lead us astray in all sorts of ways.  In Neil deGrasse Tyson's words, "[Our brains] are poor data-taking devices... that's why we have machines that don't care what side of the bed they woke up on that morning, that don't care what they said to their spouse that day, that don't care whether they had their morning caffeine.  They'll get the data right regardless."

But we still believe that we're seeing what's real, don't we?  "I saw it with my own eyes" is still considered the sine qua non for establishing what reality is.  Eyewitness testimony is still the strongest evidence in courts of law.  Because how could it be otherwise?  Maybe we miss minor things, but how could we get it so far wrong?

A scientist in Italy has knocked another gaping hole in our confidence that our brain can correctly interpret the sensory information it's given -- this time with an actual hammer.

Some of you may have heard of the "rubber hand illusion" that was created in a study back in 1998 by Matthew Botvinick and Jonathan Cohen.  In this experiment, the two scientists placed a rubber hand in view of a person whose actual hand is shielded from view by a curtain.  The rubber hand is stroked with a feather at the same time as the person's real (but out-of-sight) hand receives a similar stroke -- and within minutes, the person becomes strangely convinced that the rubber hand is his hand.

The Italian experiment, which I found out about from an article in Discover Online, substitutes an auditory stimulus for the visual one -- with an even more startling result.

Irene Senna, professor of psychology at Milono-Bicocca University in Milan, rigged up a similar scenario to Botvinick and Cohen's.  A subject sits with one hand through a screen.  On the back of the subject's hand is a small piece of foil which connects an electrical lead to a computer.  The subject sees a hammer swinging toward her hand -- but the hammer stops just short of smashing her hand, and only touches the foil gently (but, of course, she can't see this).  The touch of the hammer sends a signal to the computer -- which then produces a hammer-on-marble chink sound.

And within minutes, the subject feels like her hand has turned to stone.

[Image licensed under the Creative Commons Tony Hisgett from Birmingham, UK, Hand Sculpture 1 (22797821268), CC BY 2.0]

What is impressive about this illusion is that the feeling persists even after the experiment ends, and the screen is removed -- and even though the test subjects knew what was going on.  Subjects felt afterwards as if their hands were cold, stiff, heavier, less sensitive.  They reported difficulty bending their wrists.

To me, the coolest thing about this is that our knowledge centers, the logical and rational prefrontal cortex and associated areas, are completely overcome by the sensory-processing centers when presented with this scenario.  We can know something isn't real, and simultaneously cannot shake the brain's decision that it is real.  None of the test subjects was crazy; they all knew that their hands weren't made of stone.  But presented with sensory information that contradicted that knowledge, they couldn't help but come to the wrong conclusion.

And this once again illustrates why I trust science, and am suspicious of eyewitness reports of UFOs, Bigfoot, ghosts, and the like.  Our brains are simply too easy to fool, especially when emotions (particularly fear) run high.  We can be convinced that what we're seeing or hearing is the real deal, to the point that we are unwilling to admit the possibility of a different explanation.

But as Senna's elegant little experiment shows, we just can't rely on what our senses tell us.  Data from scientific measuring devices will always be better than pure sensory information.  To quote Tyson again: "We think that the eyewitness testimony of an authority -- someone wearing a badge, or a pilot, or whatever -- is somehow better than the testimony of an average person.  But no.  I'm sorry... it's all bad."


Back in 1989, the United States dodged a serious bullet.

One hundred wild monkeys were imported for experimental purposes, and housed in a laboratory facility in Reston, Virginia, outside of Washington DC.  Soon afterwards, the monkeys started showing some odd and frightening symptoms.  They'd spike a fever, become listless and glassy-eyed, and at the end would "bleed out" -- capillaries would start rupturing all over their body, and they'd bleed from every orifice including the pores of the skin.

Precautions were taken, but at first the researchers weren't overly concerned.  Most viruses have a feature called host specificity, which means that they tend to be infectious only in one species of host.  (This is why you don't need to worry about catching canine distemper, and your dog doesn't need to worry about catching your cold.)

It wasn't until someone realized the parallels with a (then) obscure viral outbreak in 1976 in Zaire (now the Republic of Congo) that the researchers realized things might be much more serious.  To see why, let me just say that the 1976 epidemic, which completely wiped out three villages, occurred on...

... the Ebola River.

Of course, you know that the feared introduction of this deadly virus into the United States didn't happen.  But to find out why -- and to find out just how lucky we were -- you should read Richard Preston's book The Hot Zone.  It's a brilliantly-written book detailing the closest we've come in recent years to a pandemic, and that from a virus that carries with it a 95% mortality rate.  (One comment: the first two chapters of this book require a bit of a strong stomach.  While Preston doesn't go out of his way to be graphic, the horrifying nature of this disease makes some nauseating descriptions inevitable.)

[Note:  If you purchase this book through the image/link below, part of the proceeds will go to supporting Skeptophilia!]

1 comment:

  1. "To quote Tyson again: 'We think that the eyewitness testimony of an authority -- someone wearing a badge, or a pilot, or whatever -- is somehow better than the testimony of an average person. But no. I'm sorry... it's all bad.'"

    Tyson himself is a fantastic example of this. For eight years he gave his (wrong) eyewitness testimony of President Bush's 9-11 speech. Where supposedly Bush was "attempting to distinguish we from they."

    When confronted with Bush's actual 9-11 speech he responded that's the speech he heard. Turns out Tyson had conflated Bush's 9-11 speech with his eulogy for the Space Shuttle Columbia astronauts. However Bush didn't attempt to elevate Christians above Muslims in either speech. See this Washington Post column.

    A strong confirmation bias can have a strong effect on what you think you see or hear.