What is the difference between positive and negative afterimages? How were you able to experience both phenomena during our virtual recitation?
The Correct Answer and Explanation is:
Correct Answer:
Positive afterimages retain the original colors and brightness of the stimulus and occur almost immediately after the stimulus is removed. Negative afterimages show reversed colors (complementary hues) and usually appear after a longer viewing period or when staring at a stimulus for a prolonged time.
Explanation:
Afterimages are visual illusions that occur after staring at an image for a period of time and then looking away. There are two types: positive and negative afterimages.
Positive afterimages occur very briefly (usually less than a second) after the stimulus is removed. They appear in the same color and brightness as the original image. This happens because the visual information lingers momentarily in the retina and visual cortex. For instance, if you briefly look at a bright flash or a camera flash, you might still see the same light shape immediately after, even though the light is gone.
In contrast, negative afterimages are more common and last longer. They occur when you stare at a bright or colorful image for an extended period, and then shift your gaze to a blank or neutral surface. The afterimage you see appears in opposite (complementary) colors. For example, if you stare at a red square, the afterimage will appear green. This happens due to photoreceptor fatigue in the retina. The cone cells that detect certain wavelengths (colors) become desensitized after prolonged stimulation, and the unstimulated cones then produce the opposite color response when the image is removed.
During our virtual recitation, both types of afterimages could be experienced through on-screen visual demonstrations. For example, when you quickly looked at a bright colored shape and then it disappeared, a positive afterimage momentarily appeared. In exercises where you were asked to stare at an image (such as a colored flag or symbol) for about 20–30 seconds and then look at a white screen, a negative afterimage appeared with reversed colors. These activities allowed you to directly experience the physiological basis of how your eyes and brain process and adapt to visual stimuli.
