Monday, December 3, 2012

Infants don’t see fast changes



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.

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