Every now and then I experiment with making interesting images or visual illusions. This is all just for fun, though the results are often informative with respect to how the visual system works. I'm not current with the literature in this area, so I can provide no references to the original documentations of these effects. In all cases the images here are my own.
Sometimes it's very difficult to determine what an image depicts, just by looking at its individual elements. In this example, a collection of fuzzy black and white blobs form an easily interpretable scene. If you look at an individual blob, though, it's very hard to explain what it contributes to the overall percept. This example is similar to the classic "Dalmatian hidden in blobs" picture that many introductory vision books use.
People move their eyes about three times a second during typical tasks or behavior. Called saccades, these eye movements are frequently hard to consciously detect, at least for small amplitude movements. This image will flash at you every time you move your eyes; try staring at one spot without moving your eyes and then attend to different parts of the image. Most likely you'll be surprised how hard it is to keep your eyes still.
Color fill in happens when you stare at a patch of color and either gradually or suddenly the colors surrounding that patch change. Try staring at one patch with one eye open, and see what effect that has, then switch to another patch. It's important to not move your eyes as the effect requires some adaptation of the color receptors in your retina. It may take 30 seconds to see an effect for the first time.
example 1: easy
example 1: hard
example 3: very hard, fill in across large gaps
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(c) 2004 Alan Robinson (robinsoncogsci.ucsd.edu)