One walks a few meters away from the two heads and observes what happens to them. The most conspicuous thing is the right head.
It seems as if the right head is turning and his eyes are following us. The left one seems to look straight ahead.
Further viewsof the exhibit "Rotating Head"
Further informationson the exhibit "Rotating Head"
The difference between these two heads lies in the fact that the left head is a relief arched outwards and the right head is a relief arched inwards. Passing the two faces also changes the perspective from which we look at them. Depending on the direction from which we look at the inwardly curved relief, certain parts of the face are hidden - in contrast to the left relief. The brain misinterprets this fact and interprets it as the turning of the head.
This effect works particularly well with the two heads, because the image of a face is very familiar to our brain and is frequently called up. With other hollow forms, which are not as familiar to us as a face, this effect does not emerge as strongly. Turning the head upside down would be enough. This unusual impression makes the human brain more aware of the inner curvature of the face and will not fall for the deception.