Seeing Negative Aftereffects

Three fields appear in the first two Figures below. The left field is labeled ' Low Intensity' and the right field is labeled 'High Intensity.'

Viewing on an LCD or plasma monitor reduces the difference between the two fields on a light intensity dimension more than would be the case if you were viewing on a CRT monitor or in print.

Stare at the marker in the middle of a center field for 30 seconds and then quickly change your fixation to the marker in the right field. You are likely to experience a negative color aftereffect. Repeat the procedure by fixating on the marker in a center field and then shift your gazed to the marker in the left field. The strength of the color aftereffect that you experience is likely to be less when you shift your gaze to the low intensity field. You will not likely reduce the intensity to 0, but will approximate 0 more closely that when you are looking at the high intensity field. If you reduce the intensity reaching your eyes close enough to 0 while you look at the low intensity field, the aftereffect will not appear or be less vivid than when you look at the high intensity field.

When you see the aftereffect while gazing at the high intensity field, note that the afterimage moves as you move your eyes. This effect provides one indication that the afterimages are retinal in origin.

You can also repeat the procedure, but use one eye for viewing the middle field and the other to test for an afterimage in the high intensity field. That the color aftereffect does not transfer across eyes provides additional evidence that the effect is based in the bleaching of photopigments in the retina.

You can decrease the apparent size of the afterimage by moving closer to the high intensity field or increase the apparent size by moving further away or gazing at a distant wall surface. The change in apparent size demonstrates Emmert's Law.

You can experience the constant involuntary movements of your eyes, which people typically do not experience, by inducing an aftereffect and the shifting your gaze to an edge of the high intensity field. Try to keep your eyes steadily fixating on the edge. You may note the small shifts in the afterimage that occur as your eyes move involuntarily as the extraocular muscles fire slightly out of phase in relation to one another.












The decay of stimulus intensity from a stimulus used to induce a negative aftereffect tends to be rapid in that it a funciton of your rapid movement of your fixation. The intensity decay for an aftereffect inducing stimulus is shown below as is the slower decay from a tube type television.




Five curves are presented below.

Three curves show physical properties (appear black):
  1. Induction Stimulus Intensity -- a measure of the amount of light from the stimulus used to induce the aftereffect
  2. High Intensity View Field -- amount of light reflected from the field viewed following the induction
  3. 0 Intensity View Field -- amount of light reflected from the field viewed following the induction
Two curves show people's percepts (appear red):
  1. AE (aftereffect) using a High Intensity Viewing Field -- the 'brightness' or vividness appears above 0 -- aftereffect reported
  2. AE (aftereffect) using a 0 Intensity Viewing Field -- the 'brightness' or vividness appears at 0 -- no aftereffect reported





Can you explain why the negative aftereffects appear when people look at a high intensity field after the induction, but the aftereffects do not appear if people look at a 0 intensity surface after the induction? (Hint: Our sensory and perceptual systems function well relationally and not absolutely. You need to do some thinking about relative bleaching and relative stimulation in order to answer the question.)