[music playing]
Narrator: The difference between these two men seems obvious. Their faces are different. Their hair is different. Even their shirts are a different color. And yet an experiment by psychologists Dan Simons and Chris Chabris at Harvard reveals that our brains actually process very little of what comes in through the eyes.
Professor: In this experiment the subject comes up to a counter. And a first experimenter hands them a consent form. As soon as they finish signing the consent form they hand it back to the first experimenter, who then takes the consent form, ducks down behind the counter to put it away. And a different experimenter then stands up, and hands the subject a packet of information, and sends them into a hallway where we ask them questions about it.
Narrator: This wonderful experiment uncovers an aspect of the brain's attention system, known as change blindness.
Professor: Change blindness is the idea that we often miss large changes to our visual world from one view to the next. We're often not able to see large changes that would appear to be perfectly obvious to somebody who knows they're going to happen.
Narrator: And incredibly, in 75% of cases, the subjects don't notice a thing.
Male Subject 1: The lady who took me up here, she opened the door for me and told me to walk over to the desk. I think there was a sign that said experiment. And a man there gave me a form to sign.
Female Subject: There was the guy standing under a big sign that said experiment. And to my left there was like a pot with some dirt in it and some plastic containers.
Male Subject 2: Oh, I filled out a form. How long would it be about before—
And then I asked him how long it would take. And he said about 10, 15 minutes or so.
I guess I have the time to do that.
Experimenter: Did you notice anything unusual at all, after you had signed the consent form?
Male Subject 2: I just signed it. And I didn't even pay attention to anything that was written on it.
Experimenter: OK, after you handed it back to him, did you notice anything unusual happen at all?
Man In Experiment 2: If you could just take this into the next room—
Male Subject 2: No, no I probably wasn't even looking in that direction. I probably turned and looked towards the clear door. I saw some people there. And then I turned back. And looked at him for a second.
Experimenter: Did you notice anything unusual at all after you signed the consent form?
Male Subject 2: No.
Male Subject 3: This is only going to take five or ten minutes?
Man In Experiment 1: Yeah, it will be real short.
Male Subject 3: OK.
Experimenter: The person who stood up was actually a different person.
Female Subject: OK.
Experimenter: I gather you didn't notice that was different?
A different person actually stood up and handed you this form, and sent you out towards me. I gather from your reaction you didn't notice that?
Male Subject 3: No.
Experimenter: Don't feel bad about that. Actually most of the time, we find about 75% of people don't notice.
Male Subject 3: You serious?
Experimenter: Yeah.
The person who stood up with the packet was actually a different person—
Male Subject 1: Wow.
Experimenter: —than the first person.
Male Subject 1: That is incredible.
Experimenter: I gather you didn't see it then.
Male Subject 1: I didn't catch that, no.
Experimenter: OK.
Professor: What's really interesting is that some people notice these changes and other people don't notice these changes.
Man In Experiment 1: OK, if you could just take this—
Professor: And we really don't yet have a good idea what separates those people who don't from the people who do. It might be that there are individual differences. And some people are better able to detect these sorts of changes. But it's also possible that it's just coincidence. That the people who noticed it just happened to be focusing on a feature that changed. They just happen to be paying attention to the color of a person's shirt. And the people who failed to notice it just happened to be paying attention to something else.