The Delboeuf illusion makes one dot appear larger than the other. But they're the same size. Your brain is misled by comparing the dots to the surrounding circles. Washiucho/Wikimedia Commons hide caption toggle caption Washiucho/Wikimedia Commons The Salt Deception Diet: How Optical Illusions Can Trick Your Appetite January 28, 2012 Everything from the size of your plate to the color of your food may be telling you to eat more than you actually need. The good news is you can use psychology to your advantage, if you learn a few tricks of the trade.