True or false: the macadamia nut is closely related to the peach. Most of us don't have the sort of background information that will let us answer that with confidence. Still, we have a gut feeling about the answer—"Nuts and fruit? Probably not." These sort of gut reactions to things can be key to helping us navigate through a world where we often don't have complete information.

So it's a bit disappointing to find out how easily our gut feelings can be manipulated. All it takes is a bit of extraneous information—a picture of macadamias or a verbal description of them—and we're far more likely to assume that a statement is true.

The authors, based in New Zealand and Canada, performed an "alive or dead" test, showing the names of minor celebrities and asking undergraduates whether the person was still alive. In half the cases, they also showed a photo of the person. When the photo was present, people were more likely to answer that the statement was true.

The obvious explanation for this is that none of the photos were of a corpse, and seeing a person alive would almost certainly bias the participants toward thinking the person was alive. So, they switched the questions, asking another group whether they thought the person was dead. As it turned out, the photo also caused people to evaluate the statement as true, and answer that the person was no longer alive.

To make sure this didn't only work with people, the authors switched to true/false trivia questions, like the macadamia example mentioned above. Again, photos (in this case, images of the subject of the question) caused people to answer "true" more often than they did in a control quiz. And it wasn't just images. They could get a similar effect by reading a short description of the person in question.

The authors equate this with the "truthiness" popularized by Stephen Colbert, going so far as including the term in their paper's title. But it seems to me that they're not really related. Truthiness seems to be something that feels true despite facts indicating the contrary. Here, people typically didn't have enough information to make a call on the question, and were forced to rely on their instincts.

The authors spend a bit of time discussing why this sort of truth bias might arise. In cases where we have rich information—a photo or detailed description of something—it's easier to pull additional information out of our memory. So, even if a photo doesn't tell us much about whether the person is alive, it does make it easier to retrieve relevant information on them—if they're wearing a suit in the photo, we might reason they're a political or financial figure, etc. When the information flows that readily, we're more likely to conclude that we're familiar with the question that's being posed, and will then tend to conclude it's true.

Oh, and macadamia nuts? They do not appear to be very closely related to peaches.

Psychonomic Bulletin & Review, 2012. DOI: 10.3758/s13423-012-0292-0 (About DOIs).