Babies have boundary extension, too

Boundary extension -- misremembering the boundaries of a scene as wider than they really are -- has been observed in adults as old as 84 and children as young as 6. But for kids much younger than 6, the phenomenon becomes quite difficult to study. How do you ask a 6-month-old whether the picture they're looking at has the same borders as one they saw a few minutes ago? You can't ask them to draw the picture for you -- they can barely sit up, let alone hold a pencil.

Yet the development of boundary extension is an important aspect of the study of vision. Do babies experience the phenomenon from birth, or is it something that is learned or acquired later in life? Helene Intraub and her colleagues believe that boundary extension is a fundamental aspect of processing scenes. When we view a scene, we don't just hold a picture of that scene in memory, we build a representation that extends beyond the boundaries of what we can see.

This makes sense as we try to navigate around the world: if we couldn't picture what was just coming up around the next corner as we walked, then walking would become a hesitant and halting business. And since only a small portion of our visual field (corresponding to the foveal region of the retina) is actually in precise focus at any one time, even building a picture of what is right in front of us can require some active imagination.

If boundary extension is so basic to the visual system, then we might expect babies to experience it too. Paul Quinn and Intraub believe they have found a way to find out if babies might have boundary extension.

They showed two identical pictures of a teddy bear to two groups of infants -- aged 3 to 4 months and 6 to 7 months. They did this four times, for fifteen seconds at a time, until the babies were bored with the pictures:

Next they showed the babies two new pictures, one showing ten percent more area, and one cropped in ten percent closer:

An experimenter who couldn't see the pictures (and didn't know which was which) viewed the babies through a peephole and timed how long they looked at each picture (using a separate stopwatch for each picture). Here are the results:

Both groups of babies looked at the close-up shot significantly longer than they looked at the wide shot. Quinn and Intraub say this suggests that babies experience boundary extension: if they were bored with the original picture, then if they had extended its boundary, the wide shot would have looked just like the boring original. But the close-up would look different, and would be relatively interesting by comparison.

But there's another possibility: maybe babies just prefer close-ups to wide shots. So in a second experiment, the babies never saw the two identical mid-distance shots. They were just shown the close-up side-by-side with the wide shot, and looking time was measured as before. Here are those results:

Now there was no significant difference in looking time between the two pictures, suggesting babies had no preference for either shot. In another experiment, Quinn and Intraub verified that adults experienced boundary extension with these pictures.

So boundary extension, at least in this type of scene, seems to be experienced by babies in very much the same way adults experience it. Babies as young as three months may already be building representations of scenes just like older kids and adults do.

Quinn, P.C., Intraub, H. (2007). Perceiving "Outside the Box" Occurs Early in Development: Evidence for Boundary Extension in Three- to Seven-Month-Old Infants. Child Development, 78(1), 324-334. DOI: 10.1111/j.1467-8624.2007.01000.x