Frogs, Boxes, Brains, and Babies
Young children’s brains develop continuously during their first few years of life. That’s also exactly when they’re learning to speak. So what’s the interaction between kids’ slowly maturing cognitive skills and their language skills?
One area of the brain that takes a long time to mature in kids is the frontal lobe. A subpart of it, Broca’s area, is often described as being responsible for language. Zooming into Broca’s area, left inferior temporal gyrus (LIFG) is thought to be the seat of a general skill known as cognitive control, which helps you deal with conflicting stimuli. Let’s have an example. Got your stopwatch? Try naming the ink colours as fast as you can:
RED BLACK ORANGE BLUE YELLOW GREEN PINK BROWN RED BLUE
Well done! Alright, try again. Remember, your task is to say the colour of the ink!
PINK ORANGE BLACK YELLOW BROWN RED GREEN ORANGE BLACK
That felt harder, didn’t it? It’s because this time, the words you read weren’t the same as the colour of the ink. Anytime there’s conflict in the sensory input your brain is receiving, cognitive control has to help your brain sift through it. And that’s hard work.
Kids do this task poorly, even in a non-reading version, because their cognitive control skills aren’t fully developed yet. That influences their language comprehension, too, especially when there’s more to a sentence than meets the eye (or ear). Here’s an example. Imagine you’re sitting in front of a display containing a few toys: a frog on a napkin, a box, a napkin, and a horse. Then I tell you to “Put the frog on the napkin in the box.” If you’re like most grown-ups, once you’ve heard the end of the sentence, you’ll pick up the frog and put it in the box. What do most five-year-olds do? They pick up the frog and set it on the napkin. Sometimes, they’ll then also hop it into the box. What went wrong there?
We hear sentences one word at a time, so we start interpreting sentence structure even before we’ve reached the end of the sentence. But until we have the full information, we can get tripped up if the words we’ve heard so far are consistent with several structures. “On the napkin” is ambiguous: it could be the goal of the word put, so it could be a modifier of the verb – or, as you know as soon as you hear “in the box,” it could modify the noun frog. These are two conflicting pieces of information, and children’s underdeveloped cognitive control skills mean that they stick with the incorrect interpretation of “on the napkin” as the goal of put even after they hear “in the box.”
How do we know LIFG is involved? Neuroscientists played the frog game with stroke patients who had suffered damage specifically to LIFG. Like the five-year-olds, the stroke patients put the frog on the napkin, indicating that they too got stuck with the original misinterpretation of “on the napkin” as a verb modifier. That suggests their cognitive control abilities took a hit when they experienced damage to LIFG.
So Broca’s 150-year-old generalisation about the left frontal lobe was on the right track. LIFG in particular seems to be involved in cognitive control, which has a huge impact on our ability to correctly deduce sentence structure from the string of words in a sentence. But cognitive control goes beyond language, as it’s used to deal with conflicting information from any kind of sensory input. (Here’s an example of a purely visual task involving conflicting information.) Next time you have a misunderstanding with a five-year-old or a stroke patient, grab the nearest frog to see if LIFG is to blame!