Many people believe that liars won’t look you in the eye. Liars are aware of this piece of folklore as much as anyone else, with the result that they tend to over-compensate by making excessive eye contact. Liars are shifty-eyed, but this has nothing to do with whether they’re ashamed to meet your gaze. This kind of eye shift is also different from the eye-slide with which a child or inexperienced liar evades your gaze because he has the unconscious fear that by some magical process you’ll see into his mind if your eyes meet. What we’re picking up on is a much smaller eye movement away from the listener’s face and back again, which occurs in less than two seconds. This eye toggling has to do with the computational load of lying, not with shame or guilt. You ask a question: One or two seconds before the liar answers, his eyes go back and forth in what we call a series of lateral saccades, often preceded by blinking. His eyes toggle because his brain is very busy—far busier, in fact, than it has any right to be if he were telling the truth. Because lying is so complicated and involves so many reconciliations with past facts and future implications, it involves more parts of the brain than simply telling the truth. When a person activates different brain regions their eyes often (but not invariably) shift gaze to one side or the other. You can try this for yourself, noting where your gaze goes when you think of the answers to these two different kinds of questions. What is the name of the main city in Jamaica? In the house where you grew up, how many doors were there between your bedroom and the kitchen? Both are memory questions, but to get the answers we have to activate different regions of your brain. The first is a question about words and employs the dominant side of the brain (the right side in almost all right-handers and in most left-handers too). The second question can only be answered by an imaginary tour, courtesy of your non-dominant parietal lobe. Most people will shift the direction of their eyes to the side opposite to the side of the brain they’re activating. The eye toggle, as an indicator that a shift in being made to activate a different area of the brain, is a rough and ready sign that the brain is changing gears. Telling the truth is easy. It’s neatly packaged, ready to go, in the memory banks of the liar’s temporal lobes. Why then, if he’s telling the truth, does he need to shift activation to other parts of his brain? It’s possible the memory task is a hard one, though entirely innocent and even trivial, such as: Who sat at your table for lunch on Tuesday last week? But lie detection depends on figuring out anomalies, and the question is: Why does he need to activate these other parts of his brain—unless he’s doing something far more complicated than telling the simple truth, something that’s eating up processing capacity—like lying? On the principle that it’s hard to chew gum and lie at the same time, it’s good to watch for eye toggles when the brain’s capacity is already stretched, such as asking crucial questions when someone is performing a household task such as chopping carrots or changing a light bulb. Forensic psychiatrist Paul Lucas makes use of this principle at a crucial moment in The Interview Room.
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