figure-ground reversal

n. The capacity of the human sensory system to change focus within a perceptual field so that first one part or object and then another seems to stand out distinctly against the rest of the field, which seems homogeneous and less important. Thus if we are looking at a farm, we first might notice the barn, which stands out, and then switch focus so that we are seeing a cow clearly, in which case the barn seems less distinct and perceptually important.