Eye Tracking

Eye Tracking Photo Credit: Clipart.com.

When we read, our eyes don’t scan the lines at a constant speed. Rather, they move in fits and starts across the page, lingering on unfamiliar words and re-reading confusing phrases or sentences. In this Science Update, you’ll hear how scientists can measure the way we process language by observing people’s eye movements.


Listening with your eyes. I'm Bob Hirshon and this is Science Update.

Spoken language is a complex system of sounds, symbols, and meanings. Yet the brain manages to process speech quickly and easily.

John Trueswell, a psychologist at the University of Pennsylvania, is part of a team trying to learn how this happens. The tool they use is an eye-tracking device -- basically a visor mounted with tiny cameras.


“It’s like a baseball cap -- that records children’s eye movements, as young as 4 or 5, as they hear simple instructions, like for instance ‘pick up the book that’s next to the pencil.’ We can actually see through their eye movements how quickly they took the sequences of sounds ‘the book,’ for instance, and recognize them as a familiar pattern.”

He says it’s especially interesting to watch how kids react to ambiguous sentences, like ‘tickle the horse with the feather.’ will they look for a little stuffed horse that’s holding a feather? Or will they look for a feather to pick up to tickle the horse?

By tracking our eye movements in many different situations, Trueswell is gaining clues into how we process language -- knowledge that will help us better understand the human brain, and help engineers teach computers to understand language as well. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Studying the human brain is difficult, because you can’t just open people’s heads and stick electrodes in their brains. If you’re a scientist, you have to figure out other ways to study the way we think. As you might imagine, it’s hard to do that in a concrete way that’s easy to measure. The best bet is to find something measurable that’s directly or indirectly related to the way the brain works.

Eye movements are one example. As the story explains, the way we move our eyes – either across the page when we’re reading, or around the room when we’re listening – shows how quickly and easily we’re processing the information that’s coming in. If the information is simple or familiar, our eyes usually move smoothly. If it’s tricky or new, our eyes might pause, double back, or even flit back and forth between two words or images, trying to make sense of the contradictions. It all happens super-quickly, but it can be measured, with sensitive devices like the visor-mounted camera that Trueswell describes.

To study these little pauses in our eye movements, Trueswell’s team often uses ambiguous statements: sentences that can have more than one interpretation. For example: “Sam hit the thief with the wart.” Most of us would assume this means that Sam hit a thief, who had a wart on his face. But strictly speaking, you could also imagine Sam using a giant wart to clobber the thief over the head. That might seem ridiculous, but according to Trueswell, most people’s eyes will pause when they read this sentence, and dart back and forth between the words in it, before comfortably moving forward –- which suggests that we need to spend at least a split second figuring out which interpretation makes sense.

Another interesting finding that Trueswell and similar researchers have noticed is that our brains start processing words before we’re even finished hearing them. For example if a child is told: “Look at the frog,” her eyes will shoot over toward a stuffed frog in the room before the “g” sound at the end of “frog” even comes out. So it appears that we process words not just as whole words, but as groups of phonemes. (That’s a term for the shortest unit of language that we can hear, like a “ch” or a “k” sound.)

The goal of the research is to get a better understanding of how humans process written and spoken language. That could lead to better treatments and therapies for people who have trouble with language. It could also help scientists understand the difference between problems with reading and problems in understanding any form of language. Now try and answer these questions:


  1. What do eye movements have to do with the way we understand language?
  2. Why do scientists measure things like eye movements, instead of looking at the brain directly?
  3. What do you think would happen to somebody’s eye movements while reading these sentences?
    A) Bob went to the store.
    B) Jane picked up the cat with the ribbon.
    C) This letter was written by the woman in blue lipstick.
  4. How do you think eye movements might be used to study learning disabilities? What exactly do you think you could find out?
  5. Which of these instructions do you think would be most confusing to children? Why?
    A) Hang up your coat in the closet.
    B) Hang up your coat in the trash can.
    C) Hang up your coat in the clown car.

For Educators

Learn more about Dr. Trueswell’s lab at the Eyetracking Reading Lab Web Page.

See the Max Planck Institute for Psycholinguistics website to read about similar eye-tracking experiments.

BrainConnection.com is a site for all kinds of news about the brain and brain research.

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