The finding: People recall what they’ve read better when it’s printed in smaller, less legible type.

The research: Daniel Oppenheimer and two colleagues, Connor Diemand-Yauman and Erikka Vaughan, asked 28 college students to memorize biological profiles of two fictional species, the pangerish and the norgletti. The pangerish profile was printed in a gray 12-point Comic Sans or Bodoni font; the norgletti profile in an easier-to-read, 16-point Arial pure-black font. After 15 minutes of distraction, the students recalled 87% of the pangerish facts versus 73% of the norgletti facts. And in a semester-long study at an Ohio high school, students who were exposed to slides and handouts using less legible typefaces performed better on tests than students exposed to materials presented in more-readable type.

The challenge: Can funky fonts really improve comprehension and recall? Professor Oppenheimer, defend your research.

Key Number When students were shown two paragraphs in different fonts, they remembered 14% more of the facts printed in the hard-to-read font.

Oppenheimer: When people first hear about this work, they’re surprised. The findings are counterintuitive. Why should making something harder to read make it easier to remember? But the findings are more intuitive if you reframe them. For instance, we’ve all skimmed through text, got to the end, and realized we didn’t process the information very well. Making text harder to skim prevents that from happening. So it’s not terribly surprising that causing people to slow down and read more carefully improves their recall. Of course, we don’t want to make material so hard to read that people can’t understand it. There’s a happy medium here.

HBR: So the difficult fonts act like speed bumps?

It’s more complex than that. There’s a lot of evidence that difficulty in processing is strongly related to confidence. If readers encounter a disfluency—something hard to decipher—they become less confident in their ability to understand, and that nervousness makes them concentrate harder and process the material more deeply.

If we want people to really remember this interview, what font should we use?

I’d suggest Monotype Corsiva. I’m not an expert in typography, and we’ve never looked at what the optimal fonts are to create disfluency. But when people look at Monotype Corsiva versus a “normal” font like Arial Black, there’s 100% agreement that Monotype Corsiva is harder to read, and we see really high recall with it.

Wouldn’t people adapt to a new font over time, weakening the effect?

Good point. You can manipulate disfluency in a number of ways. One of them is by using a font that people haven’t seen before, and indeed, with enough practice people will adapt to it and become fluent. In a textbook you could get around that by using a different font in every chapter. Another way to create disfluency is to manipulate contrast. A gray font on a white background is harder to read than black on white. That isn’t something people can adjust to; the weaker contrast is simply harder to see. The same could be said of small font sizes.

Your research focuses on assigned reading material, often in a classroom setting. Wouldn’t this technique backfire with optional reading—say, in a magazine?

That’s a legitimate concern. Mostly I’ve focused on the effects on learning. The applications are obvious in the educational domain. With a magazine, there is a real danger that people will pick it up, say “This is too hard to read,” and put it down. So if you used Monotype Corsiva to print this article, the people who read it would remember it more clearly, but fewer people might actually read it.

Would this apply in other media, such as video? Would you learn more watching a lecture in low-definition than in high-definition?

As far as I know, there’s no research on that question, but the theory suggests you would. A slightly blurry TV screen would act as a disfluent cue. You’d be less confident in your knowledge, so you’d process the information more deeply.

Could it also be used to increase people’s recall of advertising?

It can be used as a marketing tool, but it’s tricky. Disfluency acts as an alarm signal in your brain, and that alarm makes you feel like something is risky. If you’re about to buy a product and it’s disfluent in some way, you may think there’s something wrong with it. When we varied the fonts on product labels and tested how much people were willing to pay for the products, we found that people thought the ones with hard-to-read labels were less valuable. But other research complicates the picture. For instance, some studies by other researchers show that disfluency can be a sign of scarcity to people. That may have applications in luxury goods, where scarcity is a positive quality and can increase value.

Have you found any evidence that good teachers instinctively make handouts hard to read?

No, but I regularly meet older professors who say they’ve tried using PowerPoint but found students learned better when they had to read handwriting on a chalkboard, perhaps because of disfluency. With PowerPoint, I often find teachers following the conventional wisdom that slides should be very simple and clear. Our research doesn’t support that approach.

What long-term implications do you see from this work?

I think it has huge potential, but let me offer a caveat. Much of our research was done at a high-performing high school, where 90% of the students go on to college, and at Princeton. Both settings have very intelligent, motivated students. It’s not clear how generalizable our findings are to low-performing schools or unmotivated students. Still, this research shows that behavioral interventions can be an important element in school reform. Changing the fonts in textbooks costs almost nothing, and it could have a large effect. Education reform tends to look at the big picture—changing the curriculum or retraining teachers. But lots of labs in addition to ours are doing cool research on how to improve learning at minimal expense. These issues are worth thinking about as we try to strengthen education during a budget crunch.