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Description
Click on the image to display it full size. In a dim room with the monitor backlighting low, gently pivot or rock your monitor at about 3 or 4 Hz. I see the interior boundary as moving with respect to the high contrast exterior boundaries. If the image is printed, it is easier to shake and the effect is even stronger. The illusion is strongest in low ambient light (mesopic vision conditions) and/or low image luminance conditions.

I don't know why this illusion occurs, but it appears to be related to timing differences in visual detection of high and low contrast edges and lines.

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There are no restrictions on use of this image. Claiming to be the originator or owner, explicitly or implicitly, is bad karma . A link (if appropriate), a note to markdow30@gmail.com, and credit are appreciated but not required.

Description
Click on the image to display it full size. In a dim room with the monitor backlighting low, gently pivot or rock your monitor at about 3 or 4 Hz. I see the interior boundary as moving with respect to the high contrast exterior boundaries. If the image is printed, it is easier to shake and the effect is even stronger. The illusion is strongest in low ambient light (mesopic vision conditions) and/or low image luminance conditions.

I don't know why this illusion occurs, but it appears to be related to timing differences in visual detection of high and low contrast edges and lines.

----------------------
There are no restrictions on use of this image. Claiming to be the originator or owner, explicitly or implicitly, is bad karma . A link (if appropriate), a note to markdow30@gmail.com, and credit are appreciated but not required.