Making Visual Illusions in R

• Lijia Yu (yu@lijiayu.net / GitHub / Twitter) A master candidate majoring in Bioinformatics at Beijing Institute of Genomics.

This article demonstrates how to make visual illusions with R. A visual illusion is a distortion of form, size or color in the visual field. In the animation package, functions vi.grid.illusion() and vi.lilac.chaser() can be used to produce visual illusions.

Scintillating grid illusion

vi.grid.illusion() function provides illustrations for the Scintillating grid illusion and Hermann grid illusion. They are two most common types of grid illusions.

You can see dark dots appear and disappear rapidly at random intersections.

library(animation)
vi.grid.illusion()

Hermann grid illusion

From Hermann grid illusion picture, you can see grey blobs disappear when looking directly at an intersection.

vi.grid.illusion(type = "h", lwd = 22, nrow = 5, ncol = 5, col = "white")

Lilac Chaser

We can draw a Lilac chaser with the function vi.lilac.chaser().

Stare at the center cross for a few (say 30) seconds to experience the illusion.

• A gap running around the circle of lilac discs;
• A green disc running around the circle of lilac discs in place of the gap;
• The green disc running around on the grey background, with the lilac discs having disappeared in sequence.

ani.options(nmax = 20)
par(mar = c(1, 1, 1, 1))
vi.lilac.chaser()

Note

Don’t worry if you can’t see all the phenomena described. For many illusions, there is a percentage of people with perfectly normal vision who just don’t see it, often for reasons currently unknown.

Further reading

You can see more illusions created by Kohske in R, which also illustrated the power of the grid package.