Mind Hacks™: Tips & Tools for Using Your Brain (31 page)

Your conscious experience of the world and control over your body both feel
instantaneous — but they’re not.

One such sensation can be felt when you walk onto a broken escalator. You know it’s
broken but your brain’s autopilot takes over regardless, inappropriately adjusting your
posture and gait as if the escalator were moving. This has been dubbed the
broken escalator phenomenon
.
¹
Normally, the sensory consequences of these postural adjustments are
canceled out by the escalator’s motion, but when it’s broken, they lead to some
self-induced sensations that your brain simply wasn’t expecting. Your brain normally
cancels out the sensory consequences of its own actions
[
Why Can’t You Tickle Yourself?
]
, so it feels really
weird when that doesn’t happen.

To try it out yourself, the best place to look is somewhere like the London
Underground (where you’re sure to find plenty of broken escalators) or your favorite
run-down mall. You need an escalator that is broken and not moving but that you’re still
allowed to walk up. You could also use the moving walkways they have at airports; again,
you need one that’s stationary but that you’re still permitted to walk onto. Now, try not
to think about it too much and just go ahead and walk on up the escalator. You should find
that you experience an odd sensation as you take your first step or two onto the
escalator. People often report feeling as though they’ve been “sucked” onto the escalator.
You might even lose your balance for a moment. If you keep trying it, the effect usually
diminishes quite quickly.

Unless we’ve lived our lives out in the wilderness, most of us will have encountered
moving escalators or walkways at least a few times. And when we’ve done so, our brain has
learned to adapt to the loss of balance caused by the escalator’s motion. It’s done this
with little conscious effort on our part, automatically saving us from falling over. So
when we step onto an escalator or moving walkway now, we barely notice the transition, and
continue fluidly on our way. The thing is, when the escalator is broken, our
brain adjusts our balance and posture anyway, and it seems we can’t stop it
from doing so.

Until recently, evidence for this phenomenon was based only on urban anecdotes. But
now the phenomenon has actually been investigated in the laboratory using a
computer-controlled moving walkway.
^1
,
2
Special devices attached to the bodies and
legs of 14 volunteers recorded their posture and muscle activity. Each volunteer then
walked 20 times from a fixed platform onto the moving walkway. After that, the walkway was
switched off, the volunteers were told it would no longer move, and they then walked from
the platform onto the stationary walkway 10 times.

The first time the subjects stepped onto the moving walkway, they lost their balance
and grasped the handrail. But over the next few attempts, they learned to anticipate the
unbalancing effect of the walkway by speeding up their stride and leaning their body
forward.

Then crucially, when the volunteers first walked onto the walkway when it was switched
off, they continued to walk at the increased speed and also continued to sway the trunk of
their body forward. They performed these inappropriate adjustments even though they could
see the walkway was no longer moving and even though they had been told it would no longer
move. However, this happened only once. Their brain had apparently realized the mistake
and the next time they walked onto the stationary walkway they didn’t perform these
inappropriate adjustments. Consistent with anecdotal evidence for the broken escalator
phenomenon, most of the volunteers expressed spontaneous surprise at the sensations they
experienced when they first stepped onto the stationary walkway.

There are obviously differences between the lab experiment and the real-life
phenomenon. Our brains have learned to cope with escalators over years of experience,
whereas the experimental volunteers adapted to the lab walkway in just a few minutes. But
what the real-life phenomenon and lab experiment both represent is an example of
dissociation between our conscious knowledge and our brain’s control of our actions. The
volunteers knew the walkway was motionless, but because it had been moving previously, the
brain put anticipatory adjustments in place anyway to prevent loss of balance. Usually
these kinds of dissociations work the other way around. Often our conscious perception can
be tricked by sensory illusions, but the action systems of our brain are not fooled and
act appropriately. For example, visual illusions of size can lead us to perceptually
misjudge the size of an object, yet our fingertip grasp will be appropriate to the
object’s true size.
The motor system gets it right when our conscious perception is fooled by the
illusion size (see
Trick Half Your Mind
to see this in action).

These observations undermine our sense of a unified self: it seems our consciousness
and the movement control parts of our brain can have two different takes on the world at
the same time. This happens because, in our fast-paced world of infinite information and
possibility, our brain must prioritize both what sensory information reaches consciousness
and what aspects of movement our consciousness controls. Imagine how sluggish you would be
if you had to think in detail about every movement you made. Indeed, most of the time
autopilot improves performance — think of how fluent you’ve become at the boring drive home
from work or the benefits of touch-typing. It’s just that, in the case of the broken
escalator, your brain should really have handed the reins back to “you.”

— Christian Jarrett

How do we keep the sensations on our skin up to date as we move our bodies around in
space?

Try closing your eyes and feeling an object on a table in front of you with
the fingers of both hands. Now, cross your hands and return your fingers to the object.
Despite swapping the point of contact between your two hands, you do not feel that the
object has flipped around. The next two illusions attempt to make this remapping
fail.

First, try crossing your index finger and middle finger and run the gap between them
along the ridge and around the tip of your nose (make sure you do this quite slowly). You
will probably feel as if you have two noses. This is because your brain has failed to take
account of the fact that you have crossed your fingers. Notice that you are unable to
overcome this illusion even if you consciously try to do so. This is sometimes called
Aristotle’s Illusion, as he was apparently the first person to record it.

Now, try out the
crossed hands illusion
. You’ll need a friend to
help. Cross your hands over in front of your chest, at arm’s length. Then turn your palms
inward, so your thumbs point downward and clasp your hands together, so your fingers are
interleaved. Next, rotate your hands up toward your chest, until your thumbs are pointing
away from you, as shown in
Figure 6-1
.
Now, if a friend points to one of your fingers and asks you to move it, you will probably
fail to move the correct finger and instead move the same finger but on the opposite hand.
Again, you have failed to take account of your unusual posture; you assume that the finger
you see corresponds to the finger that would be in that position if you had simply clasped
your hands, without crossing them over. You may find that you are able to overcome the
illusion if your friend indicates which finger he wants you to move by touching it. This
can help you to remap and take your posture into account.

Charles Spence and colleagues
¹
have shown that we can update how we bind together vision and touch when we
cross our hands over. They asked people to attend to and make judgments about vibrations
that they felt on their hands, while ignoring lights presented at the same time. When
feeling a vibration on their right hand, the lights on the right side — closest to their
right hand — interfered much more (made people slower to carry out the task), than lights on
their left side. That is, we tend to bind together vision and touch when they come from
the same part of the outside world. So what happened when they crossed their hands over?
The interaction between vision and touch changed over: lights over on the left side of
their body were now closest to their right hand and interfered more with the right hand
than
the lights over on the right side. So, when we change where our hands are in
space, we integrate different sets of visual and tactile signals.

Figure 6-1. Tom tries out the crossed hands illusion

But remapping can sometimes fail, even without intertwining our fingers. Two recent
experiments
^2
,
3
have shown that we are particularly bad at dealing with
information in quick succession. If your hands are in their usual uncrossed position and
you are asked to judge which hand is touched first, it is relatively easy. On the other
hand, if your hands are crossed, the same task becomes much more difficult. This
difficulty in coping with stimuli presented in quick succession, suggests that remapping
can be a time-consuming process. Shigeru Kitazawa
⁴
has suggested we do not become conscious of a sensation on a particular
part of our skin and then attribute it to a particular location in space. Rather, our
conscious sensation of touch seems to be delayed until we can identify where it’s coming
from.

So where in the brain do we remap and update our connections? Some clues have come
from investigating the monkey brain. Cells that respond to both vision and touch have been
found in the parietal and premotor cortex — higher areas, upstream of the somatosensory
[
Build Your Own Sensory Homunculus
]
and visual areas, which deal mainly with touch and vision alone.

These cells usually respond to stimuli coming from the same region of space: a cell
might respond to a finger being touched and to a light close to that finger. The most
fascinating thing about some of these cells is that when the monkey moves its arm around,
the region of visual space to which the cell responds also moves. Such cells are thought
to represent the space that is close to our bodies. It is particularly important for us to
merge together information from our different senses about this, our peripersonal space,
which is within our immediate reach.

Spence and colleagues
⁵
gave a patient with a split brain (whose left and right hemispheres were
disconnected
[
Use Your Right Brain — and Your Left, Too
]
) the same touch and
vision distraction task as described earlier. The patient behaved as normal with his right
hand in the right side of space. That is, the lights on the right side produced the
greatest interference. In this case, both touch and vision arrived first at the left
hemisphere of his brain. When he moved his right hand over to the left side of space, we
would now expect his right hand to be disrupted most by the nearby lights on the left
side. However, the lights on the right side still interfered most with touches to the
right hand (despite being on the opposite side of space to his hand). In this case, the
lights on the left arrived first at the right hemisphere and touches to the right hand at
the left hemisphere, and without connections between the two halves of his brain, he was
unable to update. This shows how important the long-range connections between distant
cortical areas of the brain are for remapping.

The fact that the updating of our posture and remapping of our visual-tactile links
appears to occur before conscious awareness could explain why we take them for granted in
our everyday lives. Some people seem to find such processing easier than others. Could
experience affect these abilities? Might drummers who spend many hours playing with their
arms crossed find remapping easier?

— Ellen Poliakoff