Steve Chiotakis: Makers of consumer products spend nearly $30 billion a year to figure out what sells, what doesn’t, and why. And these days, some are using technology first developed for British fighter pilots — called “eye-tracking.”

We sent reporter Christopher Werth to have a look.

Christopher Werth: First, I want to find out what eye-tracking is. So I’ve come to this supermarket in West London to meet Iain Janes from a company called eyetracker. It’s one of a growing number of agencies studying what consumers actually look at when they see ads or packaging on store shelves. Janes hands me a pair of glasses straight out of a sci-fi movie.

Ian Janes: If you can pop those on.

Mounted on top are two small cameras.

Janes: One is a — we call it a field of vision camera, which collects everything that’s in front of you.

And the other camera is pointed at my pupil and follows it wherever I look. When that’s laid over the video of what I actually see, you get a set of crosshairs tracking every detail I focus on in the store.

Janes: And if you go off and do your shopping. And come back, and we’ll have a look at the tape.

Werth: Sorry to bother you. Could you point me to the laundry detergent aisle?

The clerk leads me to a long row with at least a dozen brands to choose from.

Werth: Liquid detergent. Powdered detergent.

But my eyes quickly settle on a big blue box with a red logo and an image of a father and son playing in the grass — a detergent called Persil. I pick it up.

Werth: And it costs six pounds, 40 pence.

I bring the glasses back to Janes and we look at the tape of my purchase.

Janes: OK, so you’re now going to the detergent aisle. You’re trying to decide which one to go for.

I like to think of myself as a price-conscious shopper. But when we watch the tape, I realize I hardly look at price tags at all. Janes says most shoppers are surprised to learn this about themselves.

Janes: The amount of time people actually spend looking at price is very, very small.

Janes says my little test shows why eye-tracking is so useful. Instead of relying on what people in focus groups say they look at, marketers can see for themselves what packaging catches a shopper’s eye. And eye-tracking can also help marketers figure out why we connect with certain products.

Nick Widdowson: Generally, we shop in a subconscious mode.

I played my video for Nick Widdowson, who works with eye-tracking at Unilever. It’s the company that makes that box of Persil laundry detergent. Remember that picture of the father and son on the front? Widdowson notices I can’t take my eyes off it.

Widdowson: From the amount of time you were looking at it, suggests that image seems to have struck a chord with you as a shopper.

And when I think about it, he’s probably right. I am getting married soon, and my fiancee and I are thinking about starting a family. Who knew shopping could be so — revealing?

In London, I’m Christopher Werth for Marketplace.