How to make yourself disappear

I've always found it intriguing how easily tricked our perceptual systems are.  Not only is this capacity for "brain failure" (as Neil deGrasse Tyson calls it) the cause of most optical illusions, it also highlights how important it is to have science as a protocol, and measuring devices to collect the data.

To once again quote the eminent Dr. Tyson, "Machines don't care what side of the bed they got up on.  They don't care if they just got in an argument with their spouse.  They don't care if they've had their morning coffee.  They'll get it right."

And yet, we still walk around with the feeling that what we're experiencing is the world as it is.  How many times have you heard people say, "I know it happened, I saw it!"?  But if you want to punch another neat hole in your confidence that your brain's view of the world is infallible, consider a piece of research just conducted by Arvid Guterstam of the Karolinska Institutet of Stockholm.

You might have heard about earlier experiments that convinced volunteers that a rubber hand was theirs, and one that extended that perception to the entire body, creating the illusion that a mannequin was actually the participant's body.  Now, Guterstam has tricked his test subjects into thinking that their body was still there -- but invisible.

[image courtesy of the Wikimedia Commons]

In his experiment, subjects were wearing virtual reality goggles that interfaced with a set of cameras, so that what they saw was what the camera was pointed at.  In this case, the camera was pointed at an empty space.  The experimenter and a helper then used a pair of soft brushes, and one of them stroked the volunteer's bare belly at the same time as the other, standing in the camera's field of view, stroked the air over and over in a way suggestive that there was a body there that was invisible.

If the movements of the brushes were synchronized properly, the volunteer got the distinct sensation that the camera was pointed at his/her body -- but it was completely invisible.

"We put a lot of effort into perfecting the actual brushstrokes," Guterstam said.

What is interesting is how simple the protocol was, and how convincing the illusion that resulted.  "I am very susceptible to illusions, so for me it worked," Guterstam said.  "You have a vivid sensation of having a body, but it's not directly visible.  I don't know what it would feel like to have a phantom body, but I imagine that's what it'd feel like."

The research team then performed their experiment on a group of twenty test subjects.  75% reported feeling a powerful illusion of invisibility.  "Most were surprised, and some started giggling.  It's a very unnatural, unexpected experience," Guterstam said.  "It's the first time that anyone has shown that you can embody a full invisible body."

If it's hard to believe that your brain could be so easily tricked into accepting such a bizarre view of its own body, Guterstam agrees. "The invisible body illusion is definitely pushing the boundaries of what the brain can accept as part of the bodily self," he said. "(But) it tells us that body representation in the brain is even more malleable than previously thought."

Guterstam, being a neuropsychologist, immediately thought of clinical applications of this malleability.  I, not being a neuropsychologist, immediately thought of how we could turn this into virtual reality for entertainment purposes.  If a digital camera and a pair of brushes are all that's needed to twist our perceptions of reality in such a fundamental way, how much more would it take to drop a person into a completely invented world, in which we could interact and perform in ways not limited by our actual physical capabilities?

Holodeck, here we come.

I know some of my readers are probably appalled by all this -- the idea that our mental abilities are so unreliable, so easily fooled.  Myself, I think it's kind of cool.  For one thing, I never had that much confidence in my own brain to begin with.  I've always recognized the shifting sands on which my consciousness rests, dependent as it is on my moods, focus, and level of fatigue, and even such factors as whether I've eaten lunch or had my required two cups of coffee or just caught a glimpse of an attractive and scantily-clad woman.  Now, we might be able to harness this plasticity to expand our own perception into realms that were previously inaccessible, using our capacity for "brain failures" to experience things our real perception never could.

How awesome is that?

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 just 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 an experiment 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 was just written up this week 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 courtesy of the Wikimedia Commons]

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... but it's all bad."