Not so long ago I wrote a three-part series on on how infants experience the world in completely different ways than adults do. Although infants in the first year of life might be the only kids whose minds qualify as “alien”, even older children think in fundamentally different ways than adults, rather than just like weaker or imperfect versions of adults. My very first introduction to this idea came from a study run by a fellow graduate student, Chris Chatham. And one of the most fascinating things about this study is how the researchers showed that preschoolers think differently than older children: By measuring the size of their pupils. You’re probably aware that pupil dilation is a sign of sexual arousal, and also of a concussion (or, in the most boring scenario, of being in a low-light environment), but dilated pupils can signal even more – including how hard you’re thinking.
The task children completed is called the AX-CPT. The name is an opaque mouthful, but the task setup is easy enough: A picture of a cartoon character, either Blue (from Blue’s Clues) or Spongebob (from the pineapple under the sea), shows up on the computer screen for a moment; then it goes away and is replaced by a picture of a watermelon or a slinky. Each time the object appeared, children had to press either a happy face or a sad face. The rules are simple enough for even a 3-year-old to understand: Blue likes slinkies, so if you see Blue then a slinky press the happy face (because Blue would be happy). But Spongebob doesn’t like slinkies, so if you see Spongebob and then the slinky press the sad face. And neither of them like watermelon, so if you see either of them followed by the watermelon press the sad face.
(Parents, fret not too much; only half the children were told no-one liked the watermelon, while the other half were told at least one character did like the watermelon.)
In an adult pattern of thought, the moment you see Blue you would probably start preparing, getting ready to press one thing if the next picture is a watermelon and another if it’s a slinky. Actually, since the experiment is biased so Blue is followed by a slinky 80% of the time, you’re probably getting ready to press the happy face. And this is exactly what 8-year-olds seem to do: The moment Blue appears, their pupils dilate, show they’re making an effort to plan ahead. If this is one of those relatively rare trials where Blue is followed by watermelon instead of a slinky, they are more likely to press the happy face anyway, or to take a long time to press the sad face. These children are like little adults with imperfect systems, trying to think ahead and sometimes suffering from having prepared for the wrong thing.
The preschoolers were completely different. Their pupils didn’t start dilating when they saw Blue – but as soon as that slinky appeared, pupils got wide with the effort of remembering whether the character had been Blue (and they should press the happy face) or Spongebob (press the sad face). They still made mistakes, but they didn’t follow a pattern like they were preparing to do one thing an then having to change it. In other words, preschoolers don’t try to plan ahead by anticipating what they might need to do; they simply wait until they find themselves in a situation, and think back to what they need.
For parents and preschool teachers, there are some important practical implications: three-year-olds live in the present, and don’t think ahead to what they might have to do in just a few seconds. They aren’t likely to think ahead to what they have to do that afternoon, no matter how many times you remind them. For those of us who don’t have the mixed blessing of supervising preschoolers on a regular basis, it’s a fascinating glimpse into how we come to be, and a reminder that the way we think now didn’t always come so naturally.
Or if you like your science with more immediate implications: Now you know better to rely on someone’s pupil dilation as evidence that they’re attracted to you. Their pupils would also dilate if they were thinking very hard about an excuse to give to escape your presence. Our eyes are windows to a half-dozen or more different mental processes, and it’s not always going to be obvious which one is making our eyes wide right now.
Chatham, C., Frank, M., & Munakata, Y. (2009). Pupillometric and behavioral markers of a developmental shift in the temporal dynamics of cognitive control. Proceedings of the National Academy of Sciences, 106, 5529-5533 DOI: 10.1073/pnas.0810002106