when you look at a bright source of light for a few second then look away to find out the shape of the light source is somehow "imprinted" on the part of your eye and you can see it when you look at somewhere darker. Is there a term for this? What causes it?
Also why is it that when you blink hard repeatedly it gets more noticeable?
Then you can lie down and look at some edge of the shape. Then you notice your eye slowly accelerate to the direction of the image you were looking at. How does that happen?
cheers.

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And so it was, however late . . .

It's called an afterimage. Your retina adapts to the presence of a bright light, so that when you look away you see a negative image of the bright light source.
Blinking hard (by which I'm guessing you mean screwing your eyes tight shut) increases the pressure inside your eyes transiently and makes your retina fire off randomly and more vigorously, so it might well intensify the afterimage: it's not something I've encountered, though.
Trying to look towards the edge of the afterimage doesn't work, because the image shifts with your eye. So you get a spurious impression of movement as the afterimage seemingly dodges your efforts to look at it directly.

Grant Hutchison

The blinking effect he is referring to, Grant, is not the pressure-induced variety. As the afterimage fades, you can bring it back somewhat by blinking. I presume what is happening is that the afterimage produces a steady response from the retina. Steady responses fade because of fatigue of the retina and/or visual cortex. Blinking provides change and perhaps wakes up the relevant circuits.

This illusion here I believe demonstrates retinal fatigue and recovery:

Cchek out tihs cool oaitcpl ioillusn.

It's a strange thing about the eyes, but they cannot detect an unchanging pattern--the eyes move constantly (saccades) to work around this. (if not for that, anything you stared at would disappear) You can actually consciously slow down saccades (but not stop them) by staring at something (and if you stare hard at something, stuff in the "corner of the eye" sometimes fades and disappears as a result, but as soon as you move the eye, it's back). It's enough to cause retinal cells to saturate. When you look elsewhere, you see the "inverse" of the image (e.g. if you looked at something green, the green cones would saturate, and thus not pick up light so efficiently, meaning red and blue cones dominate what you look at, leaving a magenta afterimage).

Blinking--I've noticed that but not read an explanation--I figure it has something to do, as JD said, giving the eyes a slight rest.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

Does blinking, perhaps, produce a partially darkened background that allows the afterimage to stand out?

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