Tempted by a plate of cookies on the buffet table? Chances are, the goodies are a little farther away than you think they are. But your faulty estimation may give you a little added nudge to head over to the table and have one. (Or two.)

In research published in the January 2010 issue of the journal Psychological Science, psychology professor David Dunning and Emily Balcetis, Ph.D. '06 (now an assistant professor of psychology at New York University), found that when an object is desirable, we perceive it to be closer than it actually is. A $100 bill, for example, may appear just within reach -- while a letter from the IRS, if it were placed at exactly the same distance, may appear farther away.

The phenomenon could be part of an adaptive mechanism that gives us added incentive to pursue the things we want and discourages us from expending energy on things we don't.

In the study, the researchers first tested the effect of thirst (a physical desire) on distance perception. They asked 90 undergraduates -- half of whom had just eaten a serving of pretzels and half who hadn't -- to estimate the distance between themselves and a bottle of water. On average, the thirsty group judged the water to be 25 inches away, while the non-thirsty group estimated the distance at 28 inches.

To test the effect on social desires, the researchers then asked two groups of students to judge their distance from objects that had social value (a $100 bill that could be won or a form with positive feedback) and objects that had no value or negative value (a $100 bill that belonged to someone else or a form with critical feedback). Because mood has been shown in previous research to affect aspects of perception, the participants also completed a mood assessment exercise.

As in the first experiment, the desirable objects were thought to be closer than the undesirable ones. Mood, however, showed no effect on distance perception.

In a final set of experiments, the researchers tested whether the results were due to actual differences in perception, or instead to differences in the thought processes that go into reporting the perception.

Instead of asking participants to estimate inches to an object, they asked participants to toss a beanbag as close as possible to it or to walk a set distance toward or away from it. In both cases, the participants acted as though the desirable objects were closer.

The finding makes sense from an evolutionary perspective, said Dunning. "We know that things that are closer are more motivating than things that are farther away. So if you wanted to motivate an organism to go and pick up that thing that's really good for it or that it desires, you'd want an organism that would see that thing as closer."

Understanding how desire and other factors influence perception is also important in everyday life, he said. The way we perceive changes in our health can influence what kind of medical care we seek, for example. "Also interpersonal relationships -- if you're in a marriage, how loud do you think your spouse is yelling at you? Is that a smile or is that a smirk? There are a lot of ways perception might guide people toward a more pleasant or a less pleasant road."

The research was supported by the National Science Foundation and the National Institute of Mental Health.