Diese beiden Optischen Täuschungen sind wirklich mal verdammt gut und haben mich echt mal überrascht. Einfach mal ein paar Sekunden auf den Mittelpunkt gucken.
So das war der erste. Beim zweiten ist es zwar der gleiche Effekt, nur ohne das Drehen.
Hier eine Erklärung auf Englisch:
The lilac chaser illusion combines three simple, well-known effects:
When a visual event occurs briefly at one place in the visual field, and then a similar event occurs at an adjacent place in the same visual field, we perceive movement from the first place to the second. This is called apparent movement or beta movement, because no actual movement has occurred. Apparent movement is the basis of moving neon signs, film, and video. We see movement because such displays stimulate receptors (called Reichardt detectors) in our brains that encode movement.The visual events in lilac chaser initially are the disappearances of the lilac disks. The visual events then become the appearances of green afterimages (see next).
When a lilac stimulus that is presented to a particular region of the visual field for a long time (say 10 seconds or so) disappears, a green afterimage will appear. The afterimage lasts only a short time, and in this case is effaced by the reappearance of the lilac stimulus. The afterimage is a simple consequence of adaptation of the rods and cones of the retina. Color and brightness are encoded by the ratios of activities in three types of cones (and also the rods under mesopic conditions). The cones stimulated by lilac get “tired”. When the stimulus disappears, the tiredness of some of the cones means that the ratios evoked by the grey background are the same as if a green stimulus had been presented to these cones when they are fresh. Adaptation of rods and cones begins immediately when they are stimulated, so afterimages also start to grow. We normally do not notice them because we move our eyes about three times a second, so the image of a stimulus constantly falls on new, fresh, unadapted rods and cones. In lilac chaser, we keep our eyes still, so the afterimages grow and are revealed when the stimulus disappears.
When a blurry stimulus is presented to a region of the visual field away from where we are fixating, and we keep our eyes still, that stimulus will disappear even though it is still physically presented. This is called Troxler’s fading. It occurs because although our eyes move a little when we are fixating a point, away from that point (in peripheral vision) the movements are not large enough to shift the lilac disks to new neurons of the visual system. Their afterimages essentially cancel the original images, so that all one sees of the lilac disks is grey, except for the gap where the green afterimage appears.
These effects combine to yield the remarkable sight of a green spot running around in a circle on a grey background when only stationary, flashing lilac spots have been presented. Occasionally it seems as though the green afterimage has eaten up the lilac disks, this resemblance to Pac-Man accounting for the illusion’s alternative name.
– Lilac Chaser