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Light and dark rectangular blocks moving across alternating black and white vertical stripes.
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Motion & perception / 2001 / 2003

Stepping feet

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Smoothly moving blocks seem to stop and start.

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Press Play and compare the two blocks against the stripes. Their apparent alternating steps can occur even when they move smoothly at the same speed.

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History, evidence & image credit

THE IMAGE IN THIS ARCHIVE

Rinuraeni

Original file & attribution · CC BY-SA 4.0

Original image downloaded from Wikimedia Commons; the downloaded file is unchanged. Gallery previews may be resized or converted to WebP; animated previews show the first frame.

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Frequently asked questions

What is Stepping feet?

Smoothly moving blocks seem to stop and start.

What should I look for in Stepping feet?

Press Play and compare the two blocks against the stripes. Their apparent alternating steps can occur even when they move smoothly at the same speed.

What explains Stepping feet?

The contrast at a moving block’s leading and trailing edges changes as it crosses the stripes. Motion signals become weaker or stronger, altering apparent speed despite steady physical movement.

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Stepping feet