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Jeffrey B. Mulligan; The phantom spokes illusion. Journal of Vision 2012;12(9):1211. doi: https://doi.org/10.1167/12.9.1211.
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© ARVO (1962-2015); The Authors (2016-present)
When a regular array of small bright dots is rotated in the image plane, dark spoke-like bands are seen, which are aligned with the array. The spokes are only seen when the pattern is in motion, and have an ephemeral, shimmering appearance, similar the that seen in certain op art designs. This illusion was first observed by the author when handling a 2' x 4' sheet of diffusing plastic intended for a flourescent lighting fixture. For a sheet with square cells, a cross is seen aligned with grid, with a somewhat fainter cross appearing at 45 degrees to the grid. For a sheet with triangular cells, 6 spokes are seen. The effect can be seen equally well by rotating an LCD display monitor (e.g., a laptop screen) displaying a regular array of bright dots. The illusion can be explained by an early compressive nonlinearity, which depresses the average response in regions where the motion causes neighboring dots to follow a common path, relative to off-axis regions where the smeared dots fill the space uniformly. ~
Meeting abstract presented at VSS 2012
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