Reporter: Hi, I'm nick watt from abc news, and I'm here with my friends shaseer and shot. We're going to unlock the secrets of human behavior. Psychological experiment. People that pass us by.... See More
Reporter: Hi, I'm nick watt from abc news, and I'm here with my friends shaseer and shot. We're going to unlock the secrets of human behavior. Psychological experiment. People that pass us by. Reporter: Exactly. Hey man, do you mind taking a picture of me? Reporter: We all like to think we have perfect recall. Look at this. Do you think that's a good pose? Reporter: But watch as this helpful chap agrees to take a photo. Notice anything? That guy agreed to take a picture of scott. Then, without batting an eyelid, totally oblivious to the switch, took a picture of me. Reporter: You got it? Scott, sashee re and I are outside the federal courthouse in new york city for a real world test of a psychological phenomenon known as change blindness. All right, I've got a question. Let's say you are standing on the street, scott walks up, starts a conversation and halfway through, he and I switch places. Would you notice? Of course. Even if we were strangers? Reporter: Never seen us before? I think I could tell the difference. Reporter: I'm not sure you could. Because it turns out, the way or brains are wired, you will often fail to notice a massive change, even when it's right in front of our face. And with the help of this camera and a couple of great cities, we'll show you how. Okay, scott. Reporter: Nick. Oh. I'm scott. Oh. Reporter: Now, we are posing as dumb tourists. Can we try in there? We have cameras hidden in the bushes and on benches, we have a couple of guys holding a gigantic board, scott and I walk behind it and switch. And we have a legion of worried producers convinced this can't possibly work. People will definitely notice when a bearded 20-something transforms magically into a clean shaven, let's say, more mature gentleman. All right, all right, that's enough. Miss, can you take a picture for me? Is that possible? Sure. Can you actually get like a vertical? Okay, yeah, sure. Reporter: And the sign comes through. We make the switch. Surely she noticed. Surely? Here you go. Perfect. Thanks very much. Bye-bye. Not even a flicker. Let's hope she isn't headed into the courthouse to give eyewitness testimony. Do you mind taking a picture of me? Oh, of you, is that okay? That's okay. Reporter: Here's a lovely lady. Seems totally aware of her surroundings. You press that down like that. I'm trying to get this building in the background. That's my great uncle. Oh, okay. So, yeah. Stand over here and -- Reporter: They've had a long conversation. They connected. She'll definitely notice the switch. She even reads the question "would you fall for that?" On the sign as it passes. But, wow, she is totally blind to the change from scott to me. You know that, right? Reporter: You can't see his name? Like that? Can you see his name? There's the beard, the height. And we have entirely different accents. Okay, okay. And here is the sign. She is so wrapped up in talking about the building, trying to work out the camera that she clean didn't notice our switch. My aunt and uncle know the building, so, it's okay. Just wanted to make sure. Reporter: Then scott wanted to try the double switch, to put things back the way they were. Want me to take another one? Yeah. Reporter: Yup, she fell for the double switch. Time after time people fail to catch the switch even though they are looking right at it. What do you think? Like that? Does it look like I'm pushing up against it? Yes. All right. Reporter: You do it? See if that's good enough for you. Reporter: Did you notice anything weird just happened? Like what? Reporter: Like I'm not the guy who gave you the camera in the first place? You didn't know. Ma'am, ma'am, ma'am, look. A camera right there. Wave at ken. Change blindness doesn't affect everyone. Good switch. Reporter: Huh? Nice switch. Reporter: You noticed? Of course I noticed, yes. I'm from connecticut. Reporter: And we discovered the heart can help focus the eyes. This lady noticed right away i wasn't scott. What's so funny? What gave it away? How did I know? Reporter: How did you know that I wasn't the same guy? Actually, I like him more. Reporter: You think he's more attractive? That's what you're saying? Kind of? I mean, for me. I'm sorry. Reporter: That's okay. All right, can we kick this up a natch? Try and get the building in there. Yeah. Just the building back there. Okay, that was good. Reporter: Okay, that change was black and white. Too obvious. Sasheer doesn't have a beard. Nice try. But before we called it a day, we wanted to take change blindness where no one had dared take it before. Can you take a picture of us really quick? Reporter: The three person, now you see me, now you don't, now you do again triple switch. Don't try this at home. We're trained "would you fall for that" professionals. I think if you stand right here that would be the best. Reporter: Okay. So scott and sasheer are posing as a couple. Yeah. Uh oh. Yeah. Reporter: Bam. Now sasheer and I are the couple. Did it look good? Reporter: Totally oblivious. Yeah, that's great. Reporter: Can we do one portrait? You're so good at it. Reporter: Let's go again. Scott is back. And she's still oblivious. Yeah? Yeah. Reporter: So, scott ushers me in, audacious. The first time. Can we take another one, the three of us? Reporter: Now there's sasheer and two dudes wearing hoodies. Come on. Um -- she didn't notice. Great. Thank you so much. Did you notice anything different? What? In the pictures? Yeah. No. How many people -- oh! Reporter: Ma'am -- we've got a camera right here. For abc. That was amazing. Reporter: Nobody noticed the difference. You know why? They are all looking at sasheer. No one cares about me and scott! Would you have fallen for that or do you think you're too clever? We're on twitter right now with #wwfft. My mom joined twitter just so she can tweet at the show. My mom only talks to me
This transcript has been automatically generated and may not be 100% accurate.