Eyes are the windows to the soul, they say. Well, they weren’t kidding! New data suggests that measuring the width of the pupil—called “pupillometry,” believe it or not—can reveal how captivated someone is by what they’re seeing. Just as our pupils expand in dim light, they widen when we’re looking at something we want to pay attention to.

Scientists aren’t sure why this happens, but the applications are endless. For example, measuring a baby’s pupils could reveal concepts she recognizes before she can even articulate it. Exciting research awaits!

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