Ponzo Illusion

The Ponzo Illusion demonstrates how our perception of size is influenced by background context. Two identical horizontal lines appear different in length when placed between converging lines that mimic perspective, with the top line seeming longer.

1. Draw or project two converging lines, similar to railroad tracks meeting at a vanishing point.
2. Place two identical horizontal lines across the converging lines, one near the top and one lower down.
3. Ask observers which line appears longer.
4. Reveal that the two horizontal lines are exactly the same length.

Ponzo Illusion - learningscienceisfun:

The Ponzo Illusion | What is the Ponzo Illusion | What does the Ponzo Illusion Tell Us - Contact Lens King:

📄 What Is The Ponzo Illusion And How Does It Work? - Jagran Josh: https://www.jagranjosh.com/general-knowledge/what-is-the-ponzo-illusion-and-how-does-it-work-1660197760-1

• Change the angle of convergence of the background lines to test how strongly the illusion works.
• Use different colors or line thicknesses for the horizontal bars.
• Replace straight converging lines with other perspective cues, such as a drawn road or hallway.
• Allow observers to adjust one line until they believe the lengths match, then measure the difference.

• Ensure projection or printed materials are clearly visible to avoid eye strain.
• If using drawing tools, handle rulers and sharp implements safely.

• Why does the upper line appear longer even though both are the same size? (Because the brain interprets the converging lines as perspective, making the upper line seem farther away and therefore larger.)
• How does this illusion illustrate the concept of size constancy? (The brain adjusts perceived size based on assumed distance.)
• Would the illusion still work if the converging lines were parallel? (No, without perspective cues the effect is much weaker.)
• What real-world situations might this illusion relate to? (Judging distance and size in photography, architecture, or everyday perspective viewing.)