Afterimage

An afterimage is a non-specific term that refers to an image continuing to appear in one's vision after the exposure to the original image has ceased. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. The remainder of this article refers to physiological afterimages. A common physiological afterimage is the dim area that seems to float before one's eyes after briefly looking into a light source, such as a camera flash.

Negative afterimages

Negative afterimages are caused when the eye's photoreceptors, primarily known as rods and cones, adapt to overstimulation and lose sensitivity. Newer evidence suggests there is cortical contribution as well. Normally, the overstimulating image is moved to a fresh area of the retina with small eye movements known as microsaccades. However, if the image is large or the eye remains too steady, these small movements are not enough to keep the image constantly moving to fresh parts of the retina. The photoreceptors that are constantly exposed to the same stimulus will eventually exhaust their supply of photopigment, resulting in a decrease in signal to the brain. This phenomenon can be seen when moving from a bright environment to a dim one, like walking indoors on a bright snowy day. These effects are accompanied by neural adaptations in the occipital lobe of the brain that function similar to color balance adjustments in photography. These adaptations attempt to keep vision consistent in dynamic lighting. Viewing a uniform background while these adaptations are still occurring will allow an individual to see the after image because localized areas of vision are still being processed by the brain using adaptations that are no longer needed.

Afterimage (song)

Afterimage is the second track from Rush's 1984 album Grace Under Pressure. The track was dedicated to Robbie Whelan, a friend of the band who worked as an assistant engineer on some of Rush's earlier albums, most notably Moving Pictures and Signals. The track deals with the loss of a friend and the emotional aftermath that follows.

The single was a Japan-only release. The opening lyric was quoted in the liner notes for Rush's 1998 live release, Different Stages, as a dedication to drummer Neil Peart's daughter and wife, who died in 1997 and 1998, respectively. The memoriam is as follows:

"Suddenly...you were gone...from all the lives you left your mark upon..."
In loving memory of Jackie and Selena

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References

Afterimage (Star Trek: Deep Space Nine)

"Afterimage" is the 153rd episode of the television series Star Trek: Deep Space Nine, the third episode of the seventh season. It was first broadcast on October 14, 1998.

Plot

In addition to coping with the memories of her symbiant's past lives, Ezri Dax must deal with the range of reactions her presence generates on Deep Space Nine. Her presence is not looked highly upon, as many people are unsure how to feel about Ezri. Worf has the worst reaction, even threatening fellow friends and officers. Garak, who is also not taking Ezri well, suffers problems of his own when acute claustrophobia, worse than ever, strikes him down.

At the end of the episode, Ezri leaves her position aboard the USS Destiny and becomes Deep Space Nine's official counselor. Because of her extensive Starfleet experience from her past lives, Ezri receives a promotion from ensign to lieutenant junior grade.

References