IRA FLATOW: Don’t you love to watch a mime? When you watch a mime– someone seemingly pulling an invisible rope or running into an invisible wall– you’re tricked into visualizing something that isn’t there. But why does it work so magically? Is it all in the mime or all in the mind?

That was the question my next guest set out to study in the science of miming. Dr. Chaz Firestone is an Assistant Professor of Psychological and Brain Sciences and Director of the Perception and Mind Lab at Johns Hopkins University in Baltimore. Welcome to Science Friday.

CHAZ FIRESTONE: Thanks for having me. It’s good to be with you, Ira.

IRA FLATOW: So what did you discover? How is the mind helping you see what’s not really there?

CHAZ FIRESTONE: Well, what we were interested to know in our study is not just whether you infer the presence of objects that mimes create, but how? What kind of process in your mind is responsible for giving rise to those impressions you get when a mime seems to be trapped in a box or pulling a rope?

So for example, right now you’re understanding the words I’m saying. And if I were to ask you, hey, Ira, could you stop understanding English, stop understanding the words I’m saying? That’s not something that you can do. Just like you can’t mentally command your body to stop digesting food, or to stop sweating when it’s hot or something like that. And so what we wanted to know is when your mind decides for you that there must be some invisible rope, or box, or wall, is it more like understanding English, is it more like something that happens automatically, or is it more like something that you can control?

IRA FLATOW: This is Science Friday from WNYC Studios. And so you started doing some experiments. Please describe them for us.

CHAZ FIRESTONE: So what we did is we set up some conditions where we showed people videos of someone– it happened to be me, actually– interacting with some invisible objects. And we asked whether the influence that those videos has on people is automatic, whether people can’t help but make the inferences that the actor who’s interacting with the invisible surfaces seems to be wanting them to make.

And then after people watched these videos, what we had happen was a line would appear on the screen in front of them. And they would just have to tell us what the orientation of the line was. So it could either be a vertical line or a horizontal line. And the idea is that sometimes the subject would see the actor step on an invisible box, which has a horizontal surface, and sometimes they would see the actor bump into an invisible wall, which has a vertical surface.

And sometimes after seeing the actor bump into the invisible wall, a vertical line would appear just like the wall. But sometimes a horizontal line would appear. And your job is just to tell us what the orientation of the line is. Forget about the guy who ran into the wall and the box. Just tell us was the line that showed up horizontal or was the line that showed up vertical.

So it turns out that you’re faster to say that a horizontal line is horizontal if just before it you saw a person interact with a horizontal surface, like a box. And you’re slower to say it’s horizontal if you first saw an actor interact with a vertical surface and vice versa. And so in other words, you can’t even inhibit your own mind’s inclination to create for you the impressions of these surfaces.

IRA FLATOW: What if you happen to have a mime– and I’m not talking about you personally. If your mime was not really good, does the brain still help you to see the object?

CHAZ FIRESTONE: I think it’s the case that a mime does have to be pretty compelling in order to make you experience these objects. And one way that maybe we can see this for ourselves is just maybe you’ve ever tried to do this at a party or something. Hey, look at me, I’m pretending to be a mime. And how impressive are we when we do this?

IRA FLATOW: Not very impressive, Chaz. [LAUGHS]

CHAZ FIRESTONE: Not so good. And so just like we might fail to impress our party guests if we ever would try this as just for fun, there’s a sweet spot or tipping point where the interaction with this invisible surface really does have to be sufficiently realistic in order for your mind to do this automatically.

IRA FLATOW: This reminds me of a famous experiment about colors and words. Do you know what I’m talking about?

CHAZ FIRESTONE: I do know what you’re talking about. This is a beautiful and classic experiment. The effect you’re referring to is called the Stroop effect. The way that the Stroop effect works is you’re going to be shown a word and the word is going to appear written in ink of a certain color. And your job is just to name the color of the ink and forget what the word says.

So for example, maybe you’ll see the word red written in red ink, but maybe you’ll see the word red written in blue ink. And the Stroop effect is the finding that if you ask someone to just report the color of the ink and not pay attention to the meaning of the word, they have a hard time doing that. So it’s hard to say the word blue when the word red is in blue ink. It’s harder to do that than when the word red is written in red ink.

And our study is capitalizing on that similar congruence and incongruence, that match and mismatch, where it’s easy to report the orientation of the line when it matches the invisible surface that you’ve just seen and it’s harder to do it when it doesn’t. And so just like in the Stroop effect, we learn that reading is automatic in a certain way. You can’t help but read the words that are in front of you. We learn something similar about mining in our study. We learned that you can’t help but infer the surfaces that a person is portraying for you with their behavior.

IRA FLATOW: And this is because we have so many life experiences, I would imagine. We know how things should be.

CHAZ FIRESTONE: To be honest, it’s not something that we actually know the answer to. So here’s one possibility. It’s possible that over the course of your life, kind of like you just said, you have experienced seeing how objects interact with one another. And you start to learn regularities about how that’s true. And then you come to form expectations about those regularities, say, as a mature adult.

But it’s also possible that this kind of knowledge is built into you. That even as a young baby, as an infant who can’t even speak yet, you might be sensitive to this kind of thing. And in fact, a really interesting research direction that we could take is to ask whether an infant shows something similar like this.

Does an infant get surprised if someone seems to bump into something that the infant can’t see? And if they do, then that might tell us that actually this knowledge is actually a lot more primitive than you might imagine. Not something you had to acquire over the course of your life, but something that might actually be built into who you are.

IRA FLATOW: Yeah, that would be a very interesting experiment. I’d like you to do that for us. Would you please? [LAUGHS]

CHAZ FIRESTONE: I’d love to. In fact, I’m recently the father of a new baby, so maybe I’ll try it on him.

IRA FLATOW: And you can tell us when you come back next time. How about that?

CHAZ FIRESTONE: Fantastic.

IRA FLATOW: Dr. Chaz Firestone, Assistant Professor of Psychological and Brain Sciences and Director of the Perception and Mind Lab at Johns Hopkins University. Thank you for taking time to be with us today.

CHAZ FIRESTONE: Thanks. It was great to be with you.

IRA FLATOW: That’s about all the time we have for this hour. If you missed any part of the program or you’d like to hear it again, subscribe to our podcast. And on the Science Friday VoxPop app this week, Earth Day is right around the corner. How do you plan to celebrate? Tell us about it. That’s on the SciFri VoxPop app, wherever you get your apps. Have a great weekend. I’m Ira Flatow.

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