Overview
Inspired by Professor Alain Goriely's Gresham College lecture, "The Deceived Brain: Coding and Illusions," this interactive viewer explores the fascinating world of optical illusions. As the ancient Greek philosopher Epicharmus of Kos noted, "The mind sees and the mind hears. The rest is blind and deaf." Our perception is not a direct reflection of physical reality; it's a construction of the brain. This simulation allows you to see this principle in action.
Here, you can manipulate classic geometric illusions to understand how context (modifiers) can radically alter our perception of simple shapes (objects) in terms of their size, orientation, and even existence.
How to Use
Choose Illusion: Use the dropdown menu to select from a variety of classic illusions, including Müller-Lyer, Hering, Poggendorff, Kanizsa Triangle, and Ebbinghaus.
Adjust Parameters: Use the sliders that appear for each illusion to change its properties, such as the length of lines, angles, or the size of surrounding elements. Observe how the strength of the illusion changes.
Reality Check: Click this button to toggle an overlay that shows the "true" physical state of the objects. For example, it will reveal that two lines in the Müller-Lyer illusion are, in fact, the same length, or highlight the alignment in the Poggendorff illusion.
Play Demo: Press this button to start an automatic tour through all the illusions, demonstrating how their parameters affect perception.
Audio: Toggle on for subtle auditory feedback as you interact with the sliders.
The Mathematical Theory in Brief
Professor Goriely proposed a mathematical framework to model these illusions, drawing inspiration from art theory and neuroscience.
Completion (Kanizsa): Our visual system follows a "law of good continuation," preferring to see the smoothest possible path. It completes missing information by constructing curves that minimize changes in curvature (a concept described by the Elastica equation).
Orientation (Hering, Zöllner): The perception of a line's orientation is "pulled" or "pushed" by the orientation of nearby lines. This is modeled as a "torque" that bends the perceived line. This effect is strongest for acute angles. The Hering illusion shows lines radiating from a center point, making straight horizontal lines appear to bow outward. Its counterpart, the Wundt illusion (achieved by moving the convergence slider), shows the opposite effect where lines converge at the edges, making straight lines appear to bow inward.
Size (Müller-Lyer, Ebbinghaus): The perceived size or position of an object is influenced by its surroundings. The model suggests our brain is pulled towards a "center of mass" of the surrounding visual elements, distorting our judgment of length and distance.
Alignment (Poggendorff): The Poggendorff illusion demonstrates how our perception of alignment is disrupted when a straight line is interrupted by an intervening shape (such as a bar), causing us to misjudge the continuation of the line. This effect is thought to arise from the brain's tendency to process angles and occlusions in context.
Future Directions
This viewer currently focuses on geometric illusions related to completion, orientation, size, and alignment. The world of illusions is vast and includes fascinating effects related to color (e.g., color constancy), motion (e.g., the spinning dancer), and more complex cognitive phenomena. Future updates may incorporate these other categories to provide a more comprehensive look at how our brains construct reality.