When a person views a familiar image, even having seen it just once before for a few seconds, something unique happens in the human brain.
Until recently, neuroscientists believed that vigorous activity in a visual part of the brain called the inferotemporal (IT) cortex meant the person was looking at something novel, like the face of a stranger or a never-before-seen painting. Less IT cortex activity, on the other hand, indicated familiarity.
In a new paper, researchers from the University of Pennsylvania propose a new theory, one in which the brain understands the level of activation expected from a sensory input and corrects for it, leaving behind the signal for familiarity. They call it sensory referenced suppression.