pyllusion 0.0.10

A Parametric Framework to Generate Visual Illusions.

A Parametric Framework to Generate Visual Illusions using Python

Overview

Visual illusions are fascinating phenomena that have been used and studied by artists and scientists for centuries, leading to important discoveries about how conscious perception is generated by the brain. Instead of crafting them by hand, Pyllusion offers a framework to manipulate and generate illusions in a systematic way.

The parametric approach implemented in this software proposes to describe illusions using a set of parameters, such as for instance the difference and illusion strength. These two parameters can be modulated to independently impact either the objective difference of the core components of the illusion (e.g., the difference between the two segments in the Müller-Lyer illusion) or the intensity of the illusion effect (e.g., the angle of the “distractors” arrows).

Describing illusions using a set of parameters aims at fostering reproducible science, allowing neuroscientists to easily report, generate and manipulate similar stimuli regardless of the display format and software.

PsychoPy Integration

Pyllusion can be easily integrated into PsychoPy for running experiments as well!

Installation

pip install https://github.com/RealityBending/Pyllusion/zipball/master

Contribution

You have some ideas? Want to improve things, add new illusions, and help us shake people’s brain? Let us know, we would be very happy to have you on board :relaxed:.

Citation

You can cite the package as follows:

Makowski, D., Pham, T., Lau, Z. J. (2020). Pyllusion: A Parametric Framework to Generate Visual Illusions using Python. GitHub. 
Retrieved from https://github.com/RealityBending/Pyllusion

Features

Delboeuf Illusion

The Delboeuf illusion is an optical illusion of relative size perception, where circles of identical size appear as different because of their surrounding context. The illusion was named for the Belgian philosopher, mathematician, experimental psychologist, hypnotist, and psychophysicist Joseph Remi Leopold Delboeuf (1831–1896), who created it in 1865.

import pyllusion as ill

parameters = ill.delboeuf_parameters(illusion_strength=3)
ill.delboeuf_image(parameters)

Ebbinghaus Illusion

The Ebbinghaus illusion is an optical illusion of relative size perception, where circles of identical size appear as different because of their surrounding context (the right red circle appears as smaller). The illusion was named after its creator the German psychologist Hermann Ebbinghaus (1850–1909), though it got popularized by Edward B. Titchener in a 1901 textbook of experimental psychology.

parameters = ill.ebbinghaus_parameters(illusion_strength=2)
ill.ebbinghaus_image(parameters)

Müller-Lyer illusion Illusion

The Müller-Lyer illusion is an optical illusion causing the participant to perceive two segments as being of different length depending on the shape of the arrows. The illusion was named after its creator the erman sociologist Franz Carl Müller-Lyer (1857–1916) in 1889.

parameters = ill.mullerlyer_parameters(illusion_strength=30)
ill.mullerlyer_image(parameters)

Ponzo Illusion

The Ponzo illusion is an optical illusion of relative size perception, where horizontal lines of identical size appear as different because of their surrounding context (the top line appear as longer, as it is interepreted as being in the distance). The illusion was named after its creator the Italian psychologist Mario Ponzo (1882–1960) in 1911, who suggested that the human mind judges an object’s size based on its background.

parameters = ill.ponzo_parameters(illusion_strength=20)
ill.ponzo_image(parameters)

Vertical–horizontal Illusion

The vertical–horizontal illusion illustrates the tendency for observers to overestimate the length of a vertical line relative to a horizontal line of the same length (Shipley et al., 1949).

parameters = ill.verticalhorizontal_parameters(illusion_strength=90)
ill.verticalhorizontal_image(parameters)

Zöllner Illusion

The Zöllner illusion is an optical illusion, where horizontal lines are perceived as not parallel because of their background. It is named after its discoverer, the German astrophysicist Johann Karl Friedrich Zöllner in 1860.

parameters = ill.zollner_parameters(illusion_strength=75)
ill.zollner_image(parameters)

Rod and Frame Illusion

The Rod and frame illusion is an optical illusion causing the participant to perceive the rod to be oriented congruent with the orientation of the frame.

parameters = ill.rodframe_parameters(illusion_strength=11)
ill.rodframe_image(parameters)

Poggendorff Illusion

The Poggendorff illusion is an optical illusion that involves the misperception of the position of one segment of a transverse line that has been interrupted by the contour of an intervening structure. It is named after Johann Christian Poggendorff who discovered in Zöllner’s illusion after 1860. The magnitude of the illusion depends on the properties of the obscuring pattern and the nature of its borders.

parameters = ill.poggendorff_parameters(illusion_strength=-50)
ill.poggendorff_image(parameters)

Simultaneous Contrast illusion

A neutral gray target will appear lighter or darker than it does in isolation when compared to, respectively, a dark gray or light gray target. Simultaneous contrast, identified by Michel Eugène Chevreul, refers to the manner in which the colors of two different objects affect each other.

In the image here, the two inner rectangles are exactly the same shade of grey, but the upper one appears to be a lighter grey than the lower one due to the background provided by the outer rectangles.

parameters = ill.contrast_parameters(illusion_strength=-50)
ill.contrast_image(parameters)

White Illusion

White’s illusion is a brightness illusion in which rectangles of the same grey color are perceived of different luminance depending on their background.

parameters = ill.white_parameters(illusion_strength=100)
ill.white_image(parameters)

Kanizsa Square

The Kanizsa Square is an illusory contour illusion. See Keane et al., 2019.

• TO DO (consider helping!)

Autostereograms

Autostereograms are images made of a pattern that is horizontally repeated (with slight variations) which, when watched with the appropriate focus, will generate an illusion of depth.

For instance, in the image below, the autostereogram automatically adds a guide (you can disable it by setting guide=False), the two red dots. Look at them and relax your eyes until you see a new red dot between them two. Then, try focusing on this new red dot until it gets very sharp and until your eyes stabilize. You should then be able to perceive the letters 3D as carved in the figure

It can take a bit of time to “get there”, but once you are used to it, it’s a mind-blowing experience 🤯

ill.autostereogram(stimulus="3D", width=1600, height=900)

The function is highly customisable, and we can use a black and white image as a depth mask (in this case, the picture of a skull that you will see as emerging from the background), and customise the pattern used by providing another function (here, the image_circles() function to which we can provide additional arguments like blackwhite, the number of circles n, their size range and their transparency with alpha).

ill.autostereogram(stimulus="docs/img/depthmask.png",
                   pattern=ill.image_circles,
                   color="blackwhite",
                   alpha=0.75,
                   size_min=0.005,
                   size_max=0.03,
                   n=1000)

Pareidolia

Pareidolia is the tendency to incorrectly perceive of a stimulus as an object pattern or meaning known to the observer. Liu et al. (2014), in their study “Seeing Jesus in toast”, famously (the study got awarded an Ignobel prize) investigated the correlates of face pareidolia by blending images of faces with noise-like images.

Blending of images can be achieved:

ill.pareidolia(pattern="docs/img/snake.png", 
               n=[20, 300, 4000], 
               sd=[4, 2, 1], 
               weight=[3, 2, 1],
               alpha=80,
               blur=0.5)

Transparency From Motion (TFM)

In visual perception, the kinetic depth effect refers to the phenomenon whereby the three-dimensional structural form of an object can be perceived when the object is moving (Wallach & O’Connell, 1953; Mamassian & Wallace, 2010). One of its derivative is the Transparency-From-Motion illusion, consisting in the superposition of two dot clouds moving in different directions that results in the perception of two transparent layers (See ; Schütz, 2014; Wexler et al., 2015; Schütz & Mamassian, 2016 and http://lab-perception.org/demo/p/tfm for a demo).

parameters = ill.motiontransparency_parameters(angle=45)
images = ill.motiontransparency_images(parameters)

ill.images_to_gif(images, path="Transparency_From_Motion.gif", fps=parameters["FPS"])

Pinna illusion

See also Zeljic et al., 2021.

• TO DO (consider helping!)

References

Bertamini, M. (2017). Programming visual illusions for everyone. Springer.