Most of what I write about in this blog focuses on
motivation, action, and choice in adults.
Every once in a while, though, I come across a study that I just think
is cool, and I write about that. This is
one of those times.
A paper by Faraz Farzin, Susan Rivera, and David Whitney in
the August, 2011 issue of Psychological
Science addresses a question I would never have thought to ask. How quickly can infants notice changes in the
world?
We live in a world in which we often need to notice the way
things are changing. If you are driving
down the street and a squirrel suddenly runs into the road, you need to see it
in time to apply the brakes. If you are
playing a sport, you need to be able to see where other players have moved,
find the ball, or observe a play develop.
Studies with adults show that most people can detect
differences that occur in about a tenth of a second. One way to study this is to have adults look
at a screen with four squares on it. The
squares are set to flicker between black and white. Three of the squares are in phase. That is, they change from black to white and
back at the same time. The fourth is out
of phase. When the others are black it
is white and when the others are white it is black. Over the course of an experiment, the squares
are set to flicker at different rates, and the question is when can adults
detect which square is not in phase with the others. When the rate of change is less than 10 Hertz
(one change every 10th of a second) adults can do this
reliably. When the squares flicker
faster than that, adults can’t figure out which square is changing differently
from the others.
The authors of this paper used the same technique with
infants ranging in age from 6 months to 15 months. With infants, of course, you can’t ask them
what is changing. However, infants have
a tendency to look at things that are different in a display. So, you can focus on what infants are looking
at to see if they reliably start to look at the square that is changing out of
phase with the others.
Infants are terrible at this task at the speeds where adults
do well. In fact, up to about 2 Hertz
(two changes a second) infants up to 15-month-olds don’t seem to distinguish
between the squares that are in phase and the one that is out of phase. At 1 Hertz (one change per second), though,
the older infants do well. At one change
ever 2 seconds, infants as young as 6-months look longer at the square that is
out of phase compared to the ones that change together.
A control study suggests that kids are able to see flickers
at high speeds just as adults do. So,
the problem isn’t that infants are not able to see that something is flickering
between black and white. So, the infants are able to see that something is changing, but not able to detect what is changing and exactly when that change is occurring.
There isn’t really a valuable life lesson here. Infants live in a world in which the changes
they can pay attention to are the ones that happen more slowly. That is probably useful for infants who are
just learning about how the world works.
Many of the most important things that infants need to learn about are
the ones that are a constant presence in their world. People and objects that are always present
are the ones that infants have to focus on to learn how language works and what
kinds of activities other people perform.
Infants only need to be able to detect really fast changes
in the world at the time that they are moving around on their own well enough
to have to deal with rapidly changing situations. It seems that the infant visual system is set
up to give infants the kinds of information that is likely to be useful for
them to develop.
Neat.
