<Li> Third, and this is the technique most people will know, one can induce an afterimage, usually by an intense, brief flash, such as when one is photographed using a photographic flash . This causes an image to be bleached onto the retina by the strong response of the rods and cones . In all these cases, the stimulus fades away after a short time and disappears . </Li> <P> The Troxler effect is enhanced if the stimulus is small, is of low contrast (or "equiluminant"), or is blurred . The effect is enhanced the further the stimulus is away from the fixation point . </P> <P> Troxler's fading can occur without any extraordinary stabilization of the retinal image in peripheral vision because the neurons in the visual system beyond the rods and cones have large receptive fields . This means that the small, involuntary eye movements made when fixating on something fail to move the stimulus onto a new cell's receptive field, in effect giving unvarying stimulation . Further experimentation this century by Hsieh and Tse showed that at least some portion of the perceptual fading occurred in the brain, not in the eyes . </P>

When an image is stabilized on the retina after a brief period of time the image