Positive and Negative Afterimages

Positive and Negative Afterimages Theories Cognitive Psychology Print Positive and Negative Afterimages By Kendra Cherry facebook twitter Kendra Cherry, MS, is an author, educational consultant, and speaker focused on helping students learn about psychology. Learn about our editorial policy Kendra Cherry Updated on January 25, 2020 Brigitte Smith / Moment / Getty Images More in Theories Cognitive Psychology Behavioral Psychology Developmental Psychology Personality Psychology Social Psychology Biological Psychology Psychosocial Psychology An afterimage is a type of optical illusion in which an image continues to appear briefly even after exposure to the actual image has ended. You have probably noticed this effect a number of times. If you have ever stared for a long time at a fixed point and then suddenly shifted your gaze somewhere else, then you probably noticed a brief afterimage effect in which you continued to see the original stimulus. Learn more about what afterimages are and why they happen. Types of Afterimages There are two major types of afterimages: positive afterimages and negative afterimages. In some instances, the colors of the original stimulus are retained. This is known as a positive afterimage. In other cases, the colors may be reversed. This is known as a negative afterimage.?? There are a number of situations that can increase the likelihood of experiencing an afterimage: Brief exposure to a very bright stimulus, particularly when the surrounding conditions are much darker than the stimulus. Glancing at the bright midday sun or the glare of bright headlights at night are two instances that might produce this type of afterimage. This brief exposure to an intense source often produces a positive afterimage.Prolonged exposure to a colored stimulus, even if the surrounding conditions are equally well-lit. Staring at an image in a book for 60 seconds or so before turning to stare at a blank, light-colored wall can produce this type of afterimage. This prolonged exposure to a colored stimulus often results in a negative afterimage. Positive Afterimages In a positive afterimage, the colors of the original image are maintained. Essentially, the afterimage looks the same as the original image. You can experience a positive afterimage yourself by staring at a very brightly lit scene for a period of time and then closing your eyes. For the briefest of moments, you will continue to see the original scene in the same colors and brightness. The exact mechanisms behind positive afterimages are not well understood, although researchers believe that the phenomenon might be related to retinal inertia.?? The original image stimulates nerve impulses, and these impulses continue for a small window of time after you close your eyes or look away from the scene. The cells in the retina take some time to respond to light, and once the cells have been excited it takes some time for that response to cease. While positive afterimages happen quite frequently, we are generally unaware of them because they are so brief, often lasting as little as 500 milliseconds.?? Negative Afterimages In a negative afterimage, the colors you see are inverted from the original image. For example, if you stare for a long time at a red image, you will see a green afterimage. The appearance of negative afterimages can be explained by the opponent-process theory of color vision.?? How exactly does this process work? You can see an example of how the opponent-process works by trying the following activity. Draw an image of a red shamrock outlined in blue on a white piece of paper. Stare at the image for about one minute before shifting your gaze immediately to a white sheet of paper or a blank screen. After staring at the shamrock, you probably experienced a green and yellow afterimage for a very brief moment of time. According to the opponent-process theory of color vision, staring at the original red and blue image involved using the red and blue parts of the opponent-process cells.?? After that minute of extended staring, the ability of these cells to fire action potential was exhausted. In other words, you briefly wore out those red-blue cells. When you shifted your focus to a blank, white screen, those cells were still unable to fire and only the green/yellow opponent-process cells continued to fire action potentials. Since the light reflecting off your screen could only activate those green and yellow cells, you experienced a brief afterimage in green and yellow rather than in red and blue. You can also see an example of negative afterimages at work in an interesting visual illusion in the negative photo illusion. In this illusion, your brain and visual system essentially create a negative of an already negative image, resulting in a realistic, full-color afterimage. A Word From Verywell Afterimages can be an interesting visual phenomenon to observe. They can also be an important tool for helping researchers better understand how color vision and the visual perceptual system work.