Motion blur illusions — Move backward quite fast, away from the top-left corner of this image displaying black-and-white concentric circles, while remaining perpendicular to it, and you should see a blurred shape quite reminiscent of a ghost (here simulated using the motion-blur model presented in Gosselin & Lamontagne, 1997; this article also provides other examples of motion-blur illusions). 

Amblygrams — Amblygrams are a special type of motion-blur illusion. To create one, an image is deconvolved with a temporal filter, which typically renders it difficult to see under normal viewing conditions. The hidden image can then be revealed by applying the appropriate motion blur (Gosselin, 1999). Here, for example, the hidden image is an elephant, and the temporal filter is a biphasic impulse response described by Watson (1986). A faint image of the elephant can be revealed by tracking the tip of a moving pencil or finger from left to right across the amblygram.

Simulating letter-by-letter dyslexia — Fiset et al. (2006) proposed in that letter-by-letter dyslexic patients have lost the ability to use the optimal spatial-frequency band for parallel letter processing and word recognition, that they must rely on lower spatial frequencies for parallel processing, that these lower spatial frequencies produce confusions between visually similar letters, and that their compensatory letter-by-letter strategy allows them to extract higher spatial frequencies. In this image, which shows a boule de neige attributed to Dmitri Borgmann, with the optimal mid-range spatial frequencies filtered out, we simulate for a normal observer what reading would be like for a letter-by-letter dyslexic.

Illusions of Sex — Self-explanatory (created using the data from Dupuis-Roy et al., 2019)

Motion induced apparent movement —  In this video, the discs are flashed at periods that increase in regular steps from bottom to top. Eye-tracking the tip of a moving pencil or finger in front of the video, played in a loop, causes each stationary white disc to appear to move in the direction opposite to that of the eyes. The overall impression is similar to that of a meter needle rotating slightly around its base at the bottom. Under a variety of conditions, we have shown that this illusion is well predicted by the hypothesis that observers perceive apparent motion from the retinal projections of the flashed discs during smooth-pursuit eye movements, with no compensation from an extra-retinal signal (Gosselin & Faghel-Soubeyrand, 2017).

Random moiré  — Overlaying this image and this image printed on transparencies reveals a somewhat noisy image of an elephant (here simulated by applying an “AND” operator to the two transparencies). If the transparencies are slightly misaligned, their superposition looks like noise, as can be seen in this movie, which simulates the sliding of one transparency over the other. Given a hidden image (here, a two-tone elephant image), the two transparencies can be constructed as follows: (1) the first transparency is generated from independent random binary variables; (2) in the second transparency, each pixel corresponding to a white pixel in the hidden image has the same value as the corresponding pixel in the first transparency, whereas each pixel corresponding to a black pixel in the hidden image has the opposite value.