Mind Hacks™: Tips & Tools for Using Your Brain (22 page)

What you pay attention to determines what you see, so much so that you can
miss things that are immensely obvious to others — like dancing gorillas, for
instance.

You can watch the basketball video used in the gorilla experiment by Daniel Simons and
Christopher Chabris.
¹
Find it from the University of Illinois Visual Cognition Lab’s page at
http://viscog.beckman.uiuc.edu/media/mindhacks.html
.
²

OK, because you know what’s going to happen, this isn’t going to work for you, but
here’s the procedure anyway. Watch the basketball game, and count the number of passes
made by the team in white shirts only. Find a friend and set her on the task.

If you were a subject in this experiment for real, counting those passes, what happens
next would be completely unexpected: a woman in a gorilla suit walks through the group
playing the game and stands in the middle of the screen before walking off again. About
half the observers tested in Simons and Chabris’s experiment missed the gorilla.

Following the passes in the game and counting only some of them is a difficult task.
There are two balls and six players, everyone’s moving around, and the balls are often
obscured. It’s all your brain can do to keep up.

Actually, there’s a little too much to keep up with. The bottleneck is in visual
short-term memory, where the results of visual processing have to be stashed while the
actual analysis — looking for passes by players in white shirts — happens.

Visual short-term memory
, or VSTM, can hold only a small
amount of information. Its capacity is limited to the equivalent of about four objects.
Now, there are tricks we can use to temporarily increase the size of short-term memory.
Repeating a word over and over can lengthen the time it’s remembered, for example. When
two researchers at Vanderbilt University, J. Jay Todd and René Marois, performed
experiments to measure the size of short-term memory,
³
they devised their task in such a way that tricks weren’t possible. Not
only did subjects taking part have to do the memory experiment — looking at a pattern of
colored dots and answering a question on it a second later — they also had to speak numbers
out loud for the duration, preventing the word repeating trick from being used. While the
full load of the experiment was on VSTM, Todd and Marois looked at their subjects’ brain
activity using functional magnetic resonance imaging
[
Functional Magnetic Resonance Imaging: The State of the Art
]
, a technique that
produces images in which busy parts of the brain show up brighter.

What they found was a small area on the back surface, in a region called the
posterior parietal cortex
where the activity increased as the
pattern presented in the experiment became more complex. They could see that, as the
pattern contained more colored dots, the brain activity grew proportionately — but only up
to four dots. At that point, not only did activity reach its peak, but performance in the
short-term memory task did too. This points to a real capacity limit in VSTM.

The capacity is a major factor in counting passes in the basketball game too. There’s
simply too much going on. That’s where attention comes in. Attention is our everyday word
for the mechanisms that prioritize processing of some objects, making sure they get into
VSTM, and suppress irrelevant information. In this case, when you’re watching the gorilla
video you have no choice but to pay attention only to fast-moving people dressed in white
and concentrate on the ball and whatever it goes behind. That automatically means you’re
discarding information about slow-moving objects, especially those colored black — like the
gorilla.

So when the dark gorilla suit slowly walks into the game, not only is your attention
elsewhere, but also your visual processing system actively throws away information about
it, to ensure the short-term memory doesn’t get swamped. You don’t even perceive the
gorilla, despite the ball going behind it so that you’re looking through it at some
points.

To add a little proof to the pudding: when Simons and Chabris asked viewers to count
the passes of the team dressed in black, they became significantly more likely to notice
the gorilla, as this time the observation of it wasn’t being actively discarded by the
brain.

This example shows in a fun way just how powerfully attention affects our
perception. It’s also an example of the moment-by-moment way we allocate attention,
picking some things to focus on and some to ignore, and how this is determined within an
overall scheme of the priorities we’ve set ourselves. Psychologists call this the
attentional set
, which is the keyword phrase to use if you’d like
to find out more.

The act of focusing on just one object goes hand in hand with actively suppressing
everything you have to ignore. This suppression persists across time, in a phenomenon
called negative priming.

Negative priming can be picked up only in experiments with careful timing and many
trials — it’s a small-scale effect, but it’s been demonstrated in many situations.

Look at the flash card in
Figure 3-9
, and
say what the gray picture is as fast as you can. Speak it out loud.

Figure 3-9. An example negative priming flash card

Now look at
Figure 3-10
, and do the same: name
the gray picture, out loud, as quickly as possible.

Figure 3-10. The next flash card in the sequence

You may find the picture in the second flash card slightly harder to make out,
although really you need a controlled situation to pick up the reaction time difference.
Both cards have a gray drawing to pick out and a black drawing to ignore, and you suppress
both the black ink and the black image in order to ignore it. If, as is the case here, the
image you have to identify in the second flash card is the same as the one you had to
ignore in the first,
you’ll take a little longer about it. Your brain is acting like the second
time the villagers hear the boy shouting “Wolf!” — they still get out of bed, but it takes
slightly longer to pull their clothes on.

Negative priming has been found in situations much wider than when two colored
pictures overlap. In that case, it’s one of the pictures that has been negatively primed.
But if you set up the experiment so one feature is selected at the expense of another, you
can get negative priming for color, location, or shape. All it requires is for a feature
to have been in your visual field but actively ignored, then subsequently that feature
will take slightly longer to attend to.

What’s curious is, in the flash cards used earlier, you’re concentrating on the ink
color (gray or black), thus ignoring the black ink...but the negative priming occurs for
the picture itself too. You’ve not even had to consciously ignore the distracter picture,
because you can just look past the black ink, but it gets suppressed anyway.

In a more extreme way, this is what is happening in inattention blindness
[
Blind to Change
]
. You’re concentrating on a
certain set of features (white T-shirts, fast-moving), so you implicitly ignore anything
that’s colored black and is slow-moving — and that’s why an ape walking across the
basketball game gets blanked. You’re ignoring the features, not the objects
themselves.

Looking at the ape in the basketball game
[
Make Things Invisible Simply by Concentrating (on Something Else)
]
is a good way to
figure out what negative priming is happening for. Attention’s resources are scarce, and
we simply don’t have enough to allow them to be consumed by every event that comes along.
We need to be able to avoid being distracted by the ape if we’re concentrating on
basketball. It’s the ability to suppress perceptions that makes actions truly voluntary.
¹

What’s happening is that attention is being allocated to one set of features, then
selectively disabled for potential disrupters. This inhibition function is pretty
indiscriminate too, so any feature that’s being discarded gets added to the ignore pile,
whether it’s relevant to the task at hand or not. It looks like a piano? Ignore. It’s in
black ink? Ignore. Contextual information, whether you focus on it or not, is inhibited,
and you’ll take longer to notice it when you next have to. Features stay on the ignore
pile for much longer than they have to. Traces can be found not just seconds, but days and
even weeks later.
²

(Incidentally, this also provides evidence that we — at least initially — perceive objects
as bundles of features that can be separately perceived and inhibited.)

In a sense, negative priming is performing a similar selection function to
focusing attention. It narrows down the quantity of perceptions that reach conscious
awareness and can be responded to. In everyday life, you can see echoes of information
filtering in action: you soon learn what noises foreshadow your car breaking down and
which aren’t relevant. And then, of course, there’s the boy and the villagers. But these
are long timescale, large effects. What’s surprising is negative priming uses the same
strategy, acting very quickly and almost entirely automatically. The narrowing down of
information starts here, at the moment-to-moment and completely preconscious level.