[Campos] Emotion is a nonverbal language.

[woman] Is your tummy ticklish?

[Campos] Emotions reveal the cognition,
the understanding of the baby.

And, furthermore,

emotions are the nonverbal communication

of the baby towards the parent,
and the parent towards the baby.

Therefore, I thought that emotions

were a royal road—
one royal road—

to the study 
of the baby's development.

[narrator] In this study, 
babies between 9 and 12 months

are brought into the lab and placed 
on a large, plexiglass top table.

Half of the table 
has a checkerboard pattern,

just underneath the surface.

But halfway across is a visual cliff,

which the baby can tell 
drops off steeply.

The plexiglass top continues,
so it's perfectly fine to proceed.

But the baby isn't so sure,

and this is a big drop 
for a baby just starting to crawl.

She wants to get across
to get the toy,

but she's cautious, and looks 
to the opposite end of the table

where her mother is.

The parent is instructed to smile 
or make a fear face.

If the mother is posing a fear face,
the baby typically does not cross

this stair step downward,

this modified visual cliff
or visual step.

On the other hand, 
if the mother poses a smile,

or somehow poses 
a nonverbal communication

that is not prohibitive,
but encouraging,

the child is much more likely

to cross over to her.

This particular study demonstrates

the role of nonverbal communication

in determining the child's
behavior in uncertain context.

A baby will, when they encounter 
something ambiguous, something uncertain,

will typically look 
to the significant other—

the mother, the father,

a grandparent, the caregiver—

in order to figure out what to do.

So, by 11-12 months of age,
the baby is already doing

what all of us do 
when something unusual happens.

We look around to figure out 
how other people are reacting.