Scientists at the University of Southern California have pinned down the region of the brain responsible for a key survival trait: people’s ability to comprehend a scene, even one never previously encountered, in a fraction of a second.

The brain’s ability to understand a whole scene on the fly gives us an enormous edge on an organism that would have to look at objects one by one and slowly add them up, the scientists said.

To find out the “where” of this “scene-facilitation effect,” researchers flashed drawings of pairs of objects for just 1/20 of a second. Some of these objects were depicted as interacting, such as a hand grasping for a pen, and some were not, with the hand reaching away from the pen. Test subjects were asked to press a button if a label on the screen matched either one of the two objects, which it did on half of the presentations.

To accurately identify the responsible region of the brain, test subjects received transcranial magnetic stimulation, a treatment where electromagnetic currents alternately zap two regions of the brain (the lateral occipital cortex and the intraparietal sulcus), temporarily numbing each region and preventing it from providing assistance with the task.

The researchers found that zapping the lateral occipital cortex eliminated the scene-facilitation effect, while zapping the intraparietal sulcus did not.

Ref.: J. G. Kim, I. Biederman, C.H. Juan, The Benefit of Object Interactions Arises in the Lateral Occipital Cortex Independent of Attentional Modulation from the Intraparietal Sulcus: A Transcranial Magnetic Stimulation Study, Journal of Neuroscience, 2011; 31 (22): 8320 [DOI:10.1523/JNEUROSCI.6450-10.2011]