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ILLUSIONS

This page contains demos in Java and C.

The Java demos require a Java version no older than 1.5. It is likely that this is already installed on your computer, in which case all you have to do is click on the button near each of the demos. If Java is not installed on your computer you will be promted to install it automatically. Alternatively, you can manually install Java from the Java website.

The C demos work only in Windows and require that you first download this: font file.
In order for the illusions to work the file above MUST be downloaded first.

Java demos C demos
Cylinders g08Tetrahedron.exe
Rama flicker g100NecRot.exe
Color mixing g39MacKay.exe
Random dot g108Pointillism.exe
Blind spot g22JuleszFF.exe
Necker cube
Reading g27stick.exe
After image g76Vanes.exe
Brown g86SterWaterfall.exe
Fading jpeg4FaceV.exe
Four Spheres
Motion 3D
Motion

                                                                    
   


 

The collection consists of 18 examples of visual phenomena (all are labeled “g except the final jpeg one). The other items (fv. and tms.) are not programs, but are ancillary to many examples, supplying fonts or bit-maps. To run a program (g or jpeg), just double click on it. Expect a slight delay, up to at most a minute.
The examples fall into several overlapping categories:
Color 26 (includes black-and-white), 66, 47, 49, 72.
Movement 19, 2, 27, 39, 76,
Stereopsis/depth 8, 22, 31, 45, 77, 79
Form jpeg4

*Many exhibit special effects related to ‘equiluminance’, in which the foreground and background are in a sense equal—loosely in brightness, but not in the sense of physical energy, but energy multiplied by the sensitivity of the measuring device--in this case, our eyes and brain. Generally I’ve chosen red for the information (writing, dots, etc.) and green for the background, and made the information variable from red to black by dragging the mouse.
*Others are bistable illusions ( 27, 19, 2, 77, 79 jepg4) in which some effect such as direction of movement, or a shape, will flip from one mode to another. This will happen every few seconds or tens of seconds, without your being able to control it, or with limited control.
*Some are anaglyphs, requiring red/green or red/blue glasses (it doesn’t matter which). These are meant to achieve the same results that free fusion does. They have the advantage of not being much of a challenge, and the disadvantage that one can’t vary colors, as in the case of showing that stereopsis degrades at equiluminance.
*Several show how depth can be achieved by the help of movement (g27, g2, g77 & g79.
*Many illustrate after-effects, presumably in the sense of fatiguing a particular system, so that following the stimulus its opponent system has the upper hand. These include color after images, presumably retinal (g49); waterfall (movement, g76, g39); the MacKay (g39) presumably an after-effect of stimulating cortical orientation selective cells, or movement-direction-selective cells, or both; and finally a stereo afterimage (g22, g31) that is subtle but nonetheless genuine—see if you can see it.

Some of these phenomena are well understood in physiological terms. The color ones are examples. The equiluminance ones illustrate the idea that color, on the one hand, and stereo and movement on the other, form to a large extent separate pathways in the CNS. This is hotly disputed, as are many “psychophysical” matters, especially those involving color. Our understanding of stereopsis is rapidly advancing. But effects like the Rama, g19, involving a kind of binding over large visual field areas, are not understood at all. The some applies to the Face-Vase illusion, and the examples involving many face-vases or Necker cubes.

I hope you enjoy these programs: they were fun to write, even on computers that crash on average once every half hour!