Mind Hacks™: Tips & Tools for Using Your Brain (38 page)

Lights on the joints of a walking person are enough to give a vivid impression
of the person, carrying information on mood, gender, and other details — but only while the
person keeps moving.

Open up your browser and point it at
http://www.lifesci.sussex.ac.uk/home/George_Mather/Motion/BM.HTML
¹
or
http://www.at-bristol.org.uk/Optical/DancingLights_main.htm
(both are QuickTime movies). What do you see?

Both are just points of light moving in two dimensions. Yet the first is clearly a
person walking, and the second obviously two people dancing, fighting, and otherwise
performing.

As with the common fate demos
[
To Be Noticed, Synchronize in Time
]
of how we group objects
by their behavior over time, you can remove the effect by pausing the movies. This
information only makes sense when it is moving (shame we can’t have animations in the
book, really), which is why
Figure 8-4
(a
frame of the first movie) looks more like a random star constellation than a human
figure.

The vivid impression of a walking human shows that we are able to integrate the
correlations of the light points and match them to some kind of template we have developed
for moving humans. It is orientation-specific, by the way. Watch the video upside down
(it’s easier if you have a laptop), and you won’t see anything resembling human motion at
all.

And we don’t perceive just abstract form from the moving lights. The demo at
http://www.bml.psy.ruhr-uni-bochum.de/Demos/BMLwalker.html
, shown in
Figure 8-5
, allows
you to vary the gender, direction, weight, mood, and energy levels of the walker using the
sliders on the left.

Figure 8-4. If this were moving, it’d look like a person walking

You can tell if the moving lights are from a heavyset man who’s happy or if
they are from a medium-build woman who is slightly afraid. All just from way the lights
move.

The effect is obvious. That we can perceive the human form — even mood and gender — just
from moving lights demonstrates that we automatically extract underlying patterns from the
normal human forms we see every day.

Through a combination of experience and specialized neural modules, we have learned
the underlying commonalities of moving human forms — the relationships in time and space
between the important features (the joints) of the human body. Our brain can then use this
template to facilitate recognition of new examples of moving bodies. Being able to do this
provides (for free) the ability to perceive a whole just from abstracted parts that move
in the right way. A similar process underlies the perception of expressions in emoticons
[
Understand What Makes Faces Special
]
. It’s the reason cartoonists and caricaturists can make a
living — showing just the essentials is as expressive, maybe even more
expressive, than the full image with all its irrelevant details.

Figure 8-5. A happy heavyset man, as represented by points of light

Perceiving biological motion from moving lights isn’t something that falls out of
other, normal, visual processes.
²
Brain imaging studies show that the process involves various brain regions,
not only those normally involved with vision are brought to bear, but also those involved
in object memory, spatial processing, and even motor processes.
^3
,
4

Even better, when the lights give the impression of a fearful person, the part
of the brain (the amygdala) that normally responds to fearful expressions on faces is evoked.
⁵
Our specialized mechanisms for recognizing biological motion link direct to
our emotions.

The algorithm for perceiving biological motion doesn’t always get it right. A
light-point walker can actually appear to move in two directions at once. True light-point
walkers are based on real people, and you can tell which direction they’re walking in. The
“chimeric walker” QuickTime movies (
http://www.kyb.tuebingen.mpg.de/bu/demo/chimericwalker
) have been edited to superimpose two walkers moving in opposite directions,
one to the left and one to the right. Your biological motion detection kicks in, and you
see a person moving, as normal, but you’re really looking at only one set of the
superimposed dots — with a little effort you can see the person going the other way instead.
With a little more effort you can flip between seeing the two walkers, voluntarily. The
detection algorithm’s been fooled; you would never see this particular moving dot
configuration in the wild.
⁶

If you are a cyclist, you can use our specialized adaptation to the perception of
biological motion to your advantage. Fluorescent safety markings that are positioned to
tap into this biological motion detection system, by being placed on the joints, have been
shown to make you more conspicuous to motorists.
⁷

Add a few tweaks to the way a thing moves, and you can make objects seem as if they
have a life of their own.

One way of showing that something is pretty psychologically fundamental is to show
that children do it. As soon as children can see, they expect to find animate objects in
their environment and prefer to watch them than simple moving objects.
²
So we’ll show how fundamental it is to perceive animate objects by showing
some movement to a young kid and seeing how he interprets it.

Of course, you’ll need a young kid to try this on, the younger the better, as long as
he can understand and answer your questions.

Get two objects: it doesn’t really matter what they are as long as they definitely
aren’t alive and don’t look remotely like anything alive — it will help if they are
different sizes; two rocks or wooden building blocks will work rather nicely. Put the two
objects on a table and ask the child to pay attention to what you’re about to do. Move the
bigger object slowly toward the smaller. When they’re within 2 inches of each other, move
the small object very quickly to another part of the table. Immediately, have the large
object change direction and head toward the new location of the small object. The large
object always moves slowly toward wherever the small object is; the small object always
stays at least 2 inches away.

Now, ask the child “What’s happening here?”

It should be obvious to you from reading this description, and it will be obvious to
the child, that the large object is trying to catch the small object. Just from physical
movements the child will infer a guiding purpose and attach it to some kind of inner
belief that is a property of the objects (“the large rock wants to catch the small rock”).
He could just as easily say “You are moving the rocks around in a funny way,” but he
probably won’t. He prefers the explanation that involves the rocks having
intentions.

The first experiments with animation involved movies of three simple shapes, two
triangles and a circle, moving around a large rectangle. You can see something similar in
the moving squares and circles by Heider and Simmel (
http://research.yale.edu/perception/animacy/HS-Blocks-Flash.mov
; QuickTime), a frame of which is shown in
Figure 8-6
.
³

Regardless of what they were told to pay attention to, people who watched the movie
attributed personality traits and emotions to the geometric figures. The shapes act alive,
and you can’t avoid thinking about them in those terms.

Figure 8-6. Notice how the static display offers no clues at all that the shapes are in any way
animate

So what do simple objects have to do to look alive? The first, and most
obvious, thing is to move on their own and to move in ways that seem self-caused. Changes
in direction and velocity help.
⁴

If the shapes have an obvious “front” end to them and move along their main axis, that
helps too. You can see this effect in a replication of the first movie, but with
arrowheaded shapes at
http://research.yale.edu/perception/animacy/HS-Darts-Flash.mov
.

Shapes that follow goals and interact with their environment (pushing against things
or swerving to avoid objects, for instance) also seem more alive. It isn’t so important
that the viewer can see the thing that is the goal of the object — merely acting to follow
something is sufficient to create the impression of animacy. This last fact does make a
kind of sense; one of the reasons our visual system has evolved to detect intention is not
just to
recognize it, but to predict what the purpose of someone or something’s
movement is. You may not know what a person is throwing rocks at, but the fact that you
interpret their movements as “throwing rocks at something” means you will look for a
target and that will increase your chance of finding out what it is.