Vision in Limulus Haldan Keffer Hartline One of the scientists who took advantage of this remarkable animal was H. Keffer Hartline. He was able to isolate and study the activity of single nerve fibers as they relayed signals from single ommatidia to the brain in Limulus. It was his work in clarifying how ommatidia interact with each other, however, that led to understanding the mechanisms of lateral inhibition and won him the Nobel Prize.
Lateral inhibition is a process that animals, including humans, use to better distinguish borders.
When you look at the ocean horizon the ocean appears darker at the horizon, at the boundary between sea and sky. This apparent difference in light intensity is not actually there but is created by our visual receptors and is known as lateral inhibition. This process increases contrast and results in a sharpening of vision. In fact, computers sharpen images by almost the same process process. What this means is that the signals coming from the outside are actually altered before being sent to the brain so that what we see isn't necessarily there.