Constancy phenomena are processes of correction in vision and an essential precondition for constructing an orderly image of reality. Constancy in this sense is the ability to recognise constant objects, even when their size, shape, reflectivity and colour or the surroundings change. These include, among other factors, changes in distance, spatial position or lighting.
What all of these have in common is that objects retain their colour, shape, size and brightness despite changing conditions in terms of surroundings and lighting.
The perception of the brightness of the grey field depends on the surroundings; in a bright surrounding, an identical grey appears darker than in a dark surrounding.
Good to know: Based on long experience, the observer does not evaluate shadows as colour-changing.
Spatial form can be recognised purely on the basis of shadow progressions.
The example of a hemisphere on a plane demonstrates how the incidence of light and the progression of shadows influence the perceived shape:
The positioning of the light incidence from above determines the spatial impression.
When the image is rotated, elevation and depression change positions.
