Here's a quote from Kahneman's Thinking, Fast and Slow:
The experimenters recruited 40 Princeton students to take the CRT (Cognitive Reflection Test). Half of them saw the puzzles in a small font in washed-out gray print. The puzzles were legible, but the font induced cognitive strain. The results tell a clear story: 90% of the students who saw the CRT in normal font made at least one mistake in the test, but the proportion dropped to 35% when the font was barely legible. You read this correctly: performance was better with the bad font. Cognitive strain, whatever its source, mobilizes System 2, which is more likely to reject the intuitive answer suggested by System 1.
Interesting new paper (anyone have a link to an ungated version). Abstract (emphasis added):