What Are Photoreceptors?
What Are Photoreceptors?
What Is Lateral Inhibition?
How Does The Hermann Grid Work?
How Do Mach Bands Work?
What Are Light Contrasts?
How Does White's Illusion Work?
The retina, the interior layer of the back part of the eyeball (as seen within the cross section image to the right), is composed of many cells. Among them are photoreceptors, which are responsible for detecting light and, therefore, enable us to see. These photoreceptors are arranged in certain ways to help us recognize different objects. Some photoreceptors are activated (and thereby sends signals to the brain) when they detect light, while others are activated when isthey do not detect light. The more light (or darkness) each cell detects, the more active they become.
These two types of photoreceptors usually encircle each other and are spread about throughout the retina (particularly toward the center).
The image below is a depiction of an extreme close-up to show how photoreceptors are arranged along the retina.
The lighter photoreceptors are the ones that activate in response to light while the others are the photoreceptors
that activate in the absence of light. As you can see, some of the dark photoreceptors encircle the lighter ones and vice versa. In
reality, however, these two types of photoreceptors look the same.
Each photoreceptor circle creates what is called a Receptive Field and connects to a cell that relays information from its connected photoreceptors to the brain.
The receptive fields with dark photoreceptors surrounding light photoreceptors are called
ON-Center while the others are called OFF-Center
depending on whether the center region becomes "on" or "off" in the presence of light.
The way in which receptive fields interact with each other and respond to different variations of light can affect how we see the world around us. Often, illusions can occur due to a process called Lateral Inhibition.