Ebbinghaus Illusion

Background

The Ebbinghaus illusion (also called Titchener circles) demonstrates that our perception of size is strongly influenced by surrounding context. A circle surrounded by large circles appears smaller than the same circle surrounded by small circles.

Why It Happens

The illusion is thought to arise from size contrast: the visual system judges size relative to nearby objects. Some researchers propose it reflects the operation of separate processing streams for perception vs. action (Aglioti et al., 1995), though this is debated.

Your Task

Two central circles are displayed, each surrounded by context circles of different sizes. Adjust the right central circle until it appears equal in size to the left central circle (the standard).

References

Ebbinghaus, H. (1902). Grundzüge der Psychologie. Leipzig: Veit.
Aglioti, S., DeSouza, J.F.X., & Goodale, M.A. (1995). Size-contrast illusions deceive the eye but not the hand. Current Biology, 5, 679–685.
Roberts, B., Harris, M.G., & Yates, T.A. (2005). The roles of inducer size and distance in the Ebbinghaus illusion. Perception, 34, 847–856.

You'll see two groups of circles. Each has a central circle surrounded by context circles.

The left central circle is the standard (fixed). The right central circle is adjustable.

Use the slider or ← → keys to adjust the right circle until both central circles appear equal in size.

Press Enter or click Confirm when satisfied. There are 18 trials.

Ebbinghaus Illusion

Your Results