Mind Hacks™: Tips & Tools for Using Your Brain (21 page)

Our ability to notice things suffers in the half-second after we’ve just spotted
something else.

Another reason we continually pare down perception, using attention as a final
limiting stage before reaching conscious awareness, could be that perception causes
action. Maybe processing capacity doesn’t intrinsically need to be limited, but our
ability to act definitely is: we can do only one major task at a time. Attention might
just be a natural part of conflict resolution over what to do next.

— M.W.

There’s a standard experiment used to induce the attentional blink, using a technique
called rapid serial visual presentation (RSVP). RSVP consists of projecting black letters
onto a gray screen, one at a time, at about 10 letters a second.

You’re instructed to watch the stream of letters and be on the lookout for two
particular targets: a white letter and the letter
X
. Spotting either
on its own is easy enough. One-tenth of a second (the length of time a letter is
on-screen) is enough time for recognition and awareness. Spotting the targets when they’re
close together in time, however, is much harder.

If the letter
X
follows the white letter by five places or fewer,
you’ll probably miss it. Spotting the white letter, the first target, stops the second
target, the
X
, from reaching conscious awareness. That’s the
attentional blink.

Obviously this isn’t an easy test to do at home, but we can approximate it using
speed-reading software. Speed-reading software often has a function to run through a text
file, flashing the words up sequentially — and that’s what we’ll use here.

You can use whichever software you like. I used AceReader Pro (
http://www.stepware.com/acereader.html
; $49.95; trial version available).

Whichever piece of software you choose, you’ll need it to have a mode that lets you
load an arbitrary file and step through it at about 300–400 words a minute. For AceReader
Pro, that means choosing the Online Reader & Expert Mode option.

You’ll need a text file, preferably one you haven’t read. Ask a friend to choose two
relatively unusual words for you from a random place in the text, making sure they’re only
two or three words apart. These are the words you have to look out for — your
targets.

Now load the text into the speed-reader software (in AceReader Pro, choose File → Load
File), set the words per minute (WPM) to 400, and click the Play button (the green
triangle) to begin. What you’re expecting to experience is that you’ll spot the first word
easily and miss the next one completely.
Figure 3-7
shows AceReader Pro in action; you’d
notice the first (left), but the second (right) would go utterly without notice.

Figure 3-7. AceReader Pro presenting target words

With this particular experiment, nobody experiences the attentional blink
every time. For instance, if you’re already good at speed-reading or it’s easy to guess
the sentences in the text document as they come up, it probably won’t work. We’re using
this software to simulate the controlled RSVP experiment, which uses random letters. Doing
it this way isn’t as reliable.

That said, it worked for me about half the time, and I can only describe the
attentional blink itself as a peculiar experience. At about five words a second (300 words
a minute), I wasn’t overwhelmed by having to read every word and decide whether it was one
of my targets — but I was certainly on the cusp of being overwhelmed. I had to sustain a
high level of concentration on the screen.

The first word jumped out at me, as I expected it would. OK, I’d recognized that one;
now I could look out for the next. But the next word I remember reading properly was four
places after. I’d somehow missed my second target. What had occurred in between was my
attentional blink. Thinking back, I could remember the sensation of having seen my second
word on the screen, but somehow, although I’d seen it, I hadn’t twigged that it was
actually my target. My memory was distinctly less visual and sure than for the first word,
and all I could really remember, for the duration of the blink, was the feeling of doing
two things at once: processing the first target and trying to keep up with the fresh words
on-screen. If I hadn’t been able to stop and figure out why I hadn’t noticed my second
target, knowing it had to have flashed up, I would’ve missed it completely.

Clearly the attentional blink does exist. The half-second recovery time after noticing
a target has been shown many times in experiments. Like attention in general, however,
precisely how it arises in the brain is still subject to research.

One strong theory assumes there’s a limited amount of attention to go round, which is
rapidly transferred from one letter to the next in the rapid serial visual presentation
task. Due to the amount of processing each letter needs — to see if it’s white or if it’s
the
X —
and the speed of change of letters, attention is forced to
operate at maximum capacity. When the white letter, the first target, is spotted,
additional attentional resources are suddenly needed to lift it to a level of conscious
awareness. These extra resources have to come from somewhere, and the process of raising
one’s awareness takes time; for that period of time, new incoming letters aren’t given as
much attention as they really need.

That’s not to say new letters aren’t given any attention at all, and that’s
where the analogy with eye blinking breaks down. Eye blinks shut off vision almost
completely, but attentional blinks just reduce the
probability
of
spotting a target during the blink. The success rate for spotting the second target, the
X
, dips to its minimum of 50% if the second target occurs a quarter
of a second (250 ms) after the first target and then gradually recovers as the half-second
plays out.

In this view, it’s not so much that the second target doesn’t get seen at all, it’s
that it gets processed but there just isn’t enough attentional resource to go around and
so it isn’t brought up to conscious awareness. Additional, random letters keep coming in
and claim the processing resource for themselves, and so you never notice that second
target.

Two pieces of evidence back this up. First, the processing demand contributed by the
random letters is essential for the attentional blink to show up. If the letters aren’t
there, or instead something that is easily ignored is used (like blocks of random colors,
perhaps), they don’t act as a processing drain. The second target is seen as easily as the
first target in that case.

Second, although the second target may never reach conscious awareness, it can still
influence the subconscious mind. There’s an effect called
priming
, in
which seeing a word once will make it, or a related word, easier to notice the second time
[
Bring Stuff to the Front of Your Mind
]
. So, for example, in the RSVP task, if shown the word “doctor,” the
subsequent word is faster and easier to spot if it’s the word “doctor” or “nurse.”
¹
It turns out that the second target, even if it isn’t consciously noticed,
can prime the next item. This means that the items shown during the attentional blink
reach the level of processing required for meaning, at least, and aren’t just discarded.
The limited-resources-for-attention theory appears to be a good one: there’s just not
enough attention to lift two items to awareness in quick succession.

Think of the attentional blink next time you’re looking along a bookshelf for
particular titles or down a list of names for people you know. I’ve had experiences
looking down lists when I miss one of the names I’m after time after time, only to look
again — slower the second time — and see it was shortly after another name that had jumped out
at me each time for some other reason.

We don’t memorize every detail of a visual scene. Instead, we use the world as its own
best representation — continually revisiting any bits we want to think about. This saves the
brain time and resources, but can make us blind to changes.

You can try an animated GIF demo, which we made, at
http://www.mindhacks.com/book/40/changeblindness.gif
, both frames of which are shown in
Figure 3-8
. Shown side by side, the difference
between the two versions of this picture is obvious.

Figure 3-8. The difference is easy to spot when you’re allowed to look at both versions of the
“same” picture at once
¹

But if you don’t know what you’re looking for, it can be impossible to spot. Load the
images in the following URLs and have a look. If you’re finding the first one hard, have a
look at the man’s nose — you can be looking right at the change in the image and still not
spot it for a frustratingly long time.

You need the momentary blink between the pictures so you are actually forced to
compare the two pictures in memory rather than noticing the change as it happens.
Interestingly enough, the blink doesn’t actually even need to cover the feature that’s
changing, as another demonstration at
http://nivea.psycho.univ-paris5.fr/ASSChtml/dottedline.gif
shows. Rather than blanking out the entire image, distracting patterns
momentarily appear overlaid on it to divert your attention from the change.

You’re just as blind to the altering feature when patterns flash up, even
though the picture as a whole remains present the entire time. It’s enough that your
attention is momentarily distracted from picking up on the change, forcing you to rely on
your memory for what the scene looked like half a second ago — we’re not talking long-term
memory here.

This isn’t just lab theory. Change blindness can help you pull some great tricks
outside of the lab and without the aid of a computer. A classic experiment by Daniel
Simons and Daniel Levin
²
is a perfect example. One of the pair would stop a passerby to ask for
directions. In the midst of the kindly passerby’s attempt at giving directions, two men
would carry a door between the experimenter and passerby. During this distraction, the
experimenter switched places with his colleague, who was a different height and build,
sounded different, and was wearing different clothes. Despite these blatant differences, a
full half of the people they tried this on didn’t notice any difference between the man
who started asking for directions and the man who finished listening to them.