Intention

An afterimage refers to an image that remains in your vision even after you are no longer exposed to the original stimulus. There are two types of afterimages: negative and positive.
Negative afterimages occur when our photoreceptors in our retina, known as rods and cons, adapt to overstimulation and lose sensitivity. More specifically, the microsaccades, or small eye movements that shift overstimulating images to new areas of the retina, are reduced when we fixate on a stimulus. The photoreceptors that are constantly exposed to this stimulus thus exhaust their supply of photopigment, decreasing signals to the brain. Thus, when we look away from the stimulus, the photoreceptors surrounding the adapted photoreceptors strongly signal opponent cells in the lateral geniculate nucleus, which is involved in color vision, causing the negative version of the stimulus to persist in our vision.
Positive afterimages, on the other hand, retain the same color as the original image. The scientific reason for this phenomenon is not well understood, but is possibly reflective of persisting activity in the brain when photoreceptors continue sending neural impulses to the occipital lobe. Positive afterimages mostly occur with very bright stimuli, and are often, interestingly, followed by a negative afterimage. This adaptation reflects our occipital lobe's attempt to keep vision consistent in dynamic lighting, similar to color balancing in photography.      

Examples in the World

Afterimages are constantly pervasive in our vision, although we often they are subtle enough that we don't notice them in our everyday lives. Perhaps the clearest demonstration of a negative afterimage occurs after fixating on a negative image, such as the one below:

If we stare at the dot on the woman's nose for 30 to 60 seconds, and then flicker our eyes to a plain surface such as the gray box below and blink quickly and repeatedly: 

We should see a full color representation of the original image as our brains/retinas process the negative image. 
Other common experiences with negative afterimages occur when walking indoors after a bright, snowy day, which causes everything indoors to appear dark, or fixating on a red object, which causes blue splotches in our vision. 

An abnormally persistent afterimage is a common symptom for individuals with eye diseases such as visual snow. Visual snow sufferers usually experience  symptoms such as: "persistent afterimages and trails following moving lights or images (palinopsia); photophobia; photopsia (temporary dark spots or bright flashes appearing in the field of vision); halos or starbursts around bright lights; grainy or 'snowy' vision (night vision seems especially affected); flickering or pulsating of vision (often aggravated at high altitude); bright blue or purple 'swirling' phenomena appearing in the field of vision when in the dark with eyes closed." The image below documents a familiar view for individuals who experience visual snow: 

According to some, these symptoms are also experienced by individuals who use LSD or other drugs and is categorized as  Hallucinogen Persisting Perception Disorder (HPPD), which is believed to be caused by toxic insults to certain serotonergic receptors. 

As children, we often stared at a light for a prolonged amount of time, only to turn off the light immediately afterward to experience the positive afterimage, the persisting floating blob in front of our eyes. This often occurs with the sun, one of the most common sources of positive afterimages. Positive afterimages also occur with common objects, although their effect is much more subtle, and thus overlooked, such as the effect below: 

Examples in Media/Art

In contemporary art, Olafur Eliasson is an eccentric artist who studies modes of perception, particularly concerning space and time. His exhibitions which focus on movement, color, and light, often invite the viewer to collaborate in the creative process, as it is the viewer's subjective perception and mediation of the work that activates it, prompting a new awareness of our own methods of interpreting the world.

Below is Intangible afterimage star (2008), in which six spotlights project blue, yellow, magenta, green, and turquoise geometric shapes that constantly intersect and layer. As the intense projections fade in and out, complimentary afterimages briefly linger on the viewer's retina and appear to multiply the color compositions, combing with the actual image to create a magical effect. It is notable that film is only partially produced by the spotlights' projection, and the viewer's participation is only internal.

Afterimages have also been used outside of contemporary art, such as in the "See No Evil" campaign by Amnesty International. This campaign features a series of billboards which initially depict seemingly unrelated black shapes. However, if we focus on the red cross for 30 to 60 seconds then look at a plain surface, we should be able to see the negative afterimage of the black shape, which should form the faces of various leaders from the United States, China, Russia, North Korea and Iran. 

In this campaign, Amnesty International challenges viewers to look beyond the respectability associated with national office. The ambiguity of the question, “See no evil?” asks if we are blind to atrocity, or perhaps if these leaders are blind to it. 

Reflection

Through this project, I was able to discover the scientific explanation for the common afterimages that I experienced since childhood. In addition, I stumbled across various forums for undiagnosed vision disorders and was able to read the accounts of several sufferers of such diseases, further aiding their cause of bringing awareness to the commonality of such symptoms. I also explored the various uses of afterimages in contemporary art and political activism in ways that I had never even imagined. Overall, I was in awe by the complex way our brains process our surroundings and the creative methods which we utilize some of the discrepancies between our reality and our interpretation of our reality. 
If I were to create my own media art using my new knowledge of afterimages, I would create images such as those of Artists Anonymous, shown below: 

These works address the existing physical and philosophical controversies surrounding 'painting' and 'photography'. Employing a negative colour-reversal look, they bring painting and photography into direct contact with one another. The interesting concept of paintings on canvases derived from photographic sources) and photographs that look like paintings deliberately questions the positive and negative and dismisses the common workflow of an original painted canvas and subsequent photograph. The overall effect is a fusion of information which seems opposed to today's commodified contemporary art meltdown.
These ideas are very similar to the concept I was attempting to recreate in my previous project, "Last Watch," in which I attempt to break down the wall between original and innovative by using varying color palettes. However, I would love to expand my efforts to incorporate elements of color-reversal and afterimages.    

  In the spirit of Halloween, the image below demonstrates Yorick's Skull, a great example of a negative afterimage effect: