Motion & perception / 1929 / 1935
Barber pole
Diagonal stripes move sideways but seem to travel upward.
TRY THIS
Press Play. Follow the stripes inside the elongated viewing window. Their apparent direction is influenced by where they end at its edges.
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History, evidence & image credit
THE IMAGE IN THIS ARCHIVE
The original uploader was Rokers at English Wikipedia.
Original file & attribution · CC BY-SA 3.0
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.
Download imageFrequently asked questions
What is Barber pole?
Diagonal stripes move sideways but seem to travel upward.
What should I look for in Barber pole?
Press Play. Follow the stripes inside the elongated viewing window. Their apparent direction is influenced by where they end at its edges.
What explains Barber pole?
A small view of a moving diagonal edge gives incomplete information about its true direction. Endpoints at the aperture boundary provide extra cues. An elongated window can bias the integrated motion toward its longer axis.
Another way to see it
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Peripheral drift
Jocelyn Faubert & Andrew M. Herbert
Still gradients seem to drift at the edge of vision.
Moving image