Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Reading the following paragraph:

After staring at the red and blue shamrock, you saw a green and yellow afterimage. Opponent-process theory proposes that as you stared at the red and blue shamrock, you were using the red and blue portions of the opponent-process cells. After a period of 60 to 90 seconds of continuous staring, you expended these cells' capacity to fire action potentials. In a sense, you temporarily "wore out" the red and blue portions of these cells. Then you looked at a blank sheet of white paper. Under normal conditions, the while light would excite all of the opponent-process cells. Recall that white light contains all colors of light. But, given the exhausted state of your opponent-process cells, only parts of them were capable of firing action potentials. In this example, the green and yellow parts of the cells were ready to fire. The light reflected off of the white paper could excite only the yellow and green parts of the cells, so you saw a green and yellow shamrock.

(Ellen Pastorino & Susann Doyle-Portillo, What Is Psychology? Essentials, 2010)

I've been wondering:

Can the negative afterimage appear only if there is light or is it possible in darkness?

In other words does the red color make the ganglion continue working even when there is no image and the afterimage appears green or is more light required in order for the afterimage to appear?

share|improve this question

Glutamate release from photoreceptors is inhibited by incident photons (ref). During photobleaching, assume that the effect of an incident photon drops to zero. The implication then is that if all light is removed subsequent to selective photobleaching, there will be no difference in activation between bleached photoreceptors and unbleached photoreceptors. This observation suggests that no afterimage will be visible in darkness.

But there might be rebound effects or other effects of light adaptation that will result in a perceivable afterimage in darkness. Certainly there are hallucinatory visual patterns than can be generated cortically, suggesting that a cortical afterimage could be generated in darkness.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.