Neuroscientists shed light on how the brain responds to scenes and their mirror-image reversals

Picture a penny. You can probably recall its color (copper), which historical figure graces its front (Abraham Lincoln), and even the orientation of the portrait (profile, as opposed to straight on). But can you remember which way Lincoln is facing?

According to MIT research scientist Daniel D. Dilks, only about half of us get this right, meaning we're performing no better than if we had simply guessed. This well-known phenomenon suggests that left-right distinctions are irrelevant to object recognition; in other words, our brains perceive an object and its mirror image as one and the same.

On the other hand, when people look at scenes, it has long been thought that the brainis sensitive to left-right orientation, since this information is crucial for navigation. (A road curving to the right must be negotiated differently than one curving to the left.)

However, in a recent study at MIT's McGovern Institute for Brain Research, Dilks and his colleagues identified two parts of the brain that appear to be exceptions to this rule - including one that processes scenes without seeming to distinguish left from right. The results highlight the cognitive differences between perception and action.

The findings were published Aug. 3 in the Journal of Neuroscience; the paper's senior author is Nancy Kanwisher, the Walter A. Rosenblith professor of cognitive neuroscience, and the co-authors are McGovern Institute technical assistant Joshua B. Julian, graduate student Jonas Kubilius of Belgium's Katholieke Universiteit Leuven and professor Elizabeth Spelke of Harvard University.

The researchers started with ''a simple hypothesis,'' Dilks says: Areas of the brain thought to play a major role in object recognition would be indifferent to right and left, while those that respond to scenes would be sensitive to these distinctions.