Jacewicz: How did you begin studying left-handed and right-handed biases?

Casasanto: I was trying to figure out questions about language and cognition. In language, there’s a link between space and these abstract concepts that are not themselves spatial. For example, we talk about positive and negative things as up and down. Your spirits are “soaring” or they’re “sinking.” We also talk about stuff in a horizontal continuum. In our culture—and many others—you’ve got expressions for positive attributes like “the right answer,” or “right-hand man” and expressions for things that are clumsy or bad, like “two left feet.” This left-right dichotomy is even more stringent in some cultures. For example, in Ghana, you’re not allowed to point with your left hand, because the left hand is reserved for dirty things. In some Islamic cultures, you’re told to use your right foot to step into the mosque and your left foot to step into the toilet.

The majority of us are right-handed. Social psychologists have shown us that there’s a link between fluency [dexterity] and perceived goodness. We go through life interacting more fluently on the right with our dominant hand … If people conceptualize good and bad stuff on a left-right continuum in the way their language and culture tell them, everybody should think that right is good. Alternatively, if we have a mental metaphor based on asymmetries in the way we use our hands, then righties should think right is good, but lefties should think left is good—in spite of everything that language and culture are telling them.

Jacewicz: You’ve done a bunch of studies on handedness and bias. Could you walk through a few of them?

Casasanto: We started very simply with a set of questionnaires, where people saw pairs of alien creatures—one on the left side and one on the right side of the page—and we asked which alien in each pair looked more honest, or less intelligent, or more attractive. On average, righties attributed more positive qualities to the alien creatures they happened to see on the right, while lefties preferred the creatures they saw on the left.

We wanted to know whether you could observe this kind of pattern “in the wild.” One of the ways we went about this was analyzing spontaneous speech and gestures. We found a wonderful, already transcribed, large corpus of speech and gesture on the web in presidential debates. It just so happens, that in 2004 and 2008, the [candidates] in the presidential debates consisted of two lefties and two righties, crossed with political party. It was perfect. Obama’s a leftie, and McCain is a leftie. But Kerry is a rightie, and Bush is a rightie.

We parsed all of their speech into clauses and then sorted out whether each clause expressed a positive or negative idea, if we could tell. Then we looked at all of their hand gestures, and we wrote down if a gesture was performed with the right hand or the left hand. Overall, everybody gestures more with their dominant hand, but righties tend to gesture more during positive stuff with their right hand, lefties with their left hand.