The Hering illusion was discovered by Ewald Hering, a German physiologist, in 1861. When two straight and parallel lines are presented in front of radial background (like the spokes of a bicycle), the lines appear as if they were bowed outwards.

A different framework suggests that the Hering illusion (and several other geometric illusions) are caused by temporal delays with which the visual system must cope.

In this framework, the visual system extrapolates current information to “perceive the present”: instead of providing a conscious image of how the world was ~100 ms in the past (when signals first struck the retina), the visual system estimates how the world is likely to look in the next moment. In the case of the Hering illusion, the radial lines trick the visual system into thinking it is moving forward. Since we are not actually moving and the figure is static, we misperceive the straight lines as curved—as they would appear in the next moment.

It is possible that both frameworks are compatible. The Hering illusion can also be induced by a background of optic flow (imagine dots flowing out from the center of a screen, as seen during warp speed on Star Trek).

Importantly, the bowing direction is the same whether the flow moves inward or outward. This result is consistent with a role for networks of visual orientation-tuned neurons (e.g., simple cells in primary visual cortex) in the spatial warping.

In this framework, under the common condition of forward ego-motion, it is possible that spatial warping counteracts the disadvantage of neural latencies. However, it also demonstrates that any spatial warping that counteracts neural delays is not a precise, on-the-fly computation, but instead a heuristic achieved by a simple mechanism that succeeds under normal circumstances.

A variant is the Wundt Illusion.

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