User:LittleHow/Aubert illusion

Aubert illusion (or effect) is the rotation experienced in darkness of the subjective sense of the visual vertical when lying horizontally in the direction of body or head tilt. It is tested by people adjusting a luminous line to what they take to be vertical when either their head or body is tilted. It is arises from the conflict between somaesthetic and vestibular sensation of of the line of gravity (graviception). It occurs to a reduce degree even in the present of light. The effect is abolished after lesions of the posterolateral thalamus.

There is an opposite illusion when the visual environment is tilted with an apparent downward direction that is different to that of gravity see Rod-and-frame illusion

It was first noted by Hermann Rudolph Aubert in 1861.