Gregory used the Hollow-Face illusion (also known as Hollow-Mask illusion) as an example of an optical illusion to explain how expectations can affect how we perceive objects. In this case how the observer perceives a concave mask of a face which appears as a normal convex face. While a convex face will appear to look in a single direction, and a flat face which can appear to follow the moving viewer, a hollow face can appear to move its eyes faster than the viewer: looking forward when the viewer is directly ahead, but looking at an extreme angle when the viewer is only at a moderate angle. According to Richard Gregory this illusion shows the strong visual bias for the participants favouring to see a hollow mask as a normal convex face. This is a key example of how perception can act as a top-down process for visual knowledge. This bias of seeing faces as convex which the
Gregory used the Hollow-Face illusion (also known as Hollow-Mask illusion) as an example of an optical illusion to explain how expectations can affect how we perceive objects. In this case how the observer perceives a concave mask of a face which appears as a normal convex face. While a convex face will appear to look in a single direction, and a flat face which can appear to follow the moving viewer, a hollow face can appear to move its eyes faster than the viewer: looking forward when the viewer is directly ahead, but looking at an extreme angle when the viewer is only at a moderate angle. According to Richard Gregory this illusion shows the strong visual bias for the participants favouring to see a hollow mask as a normal convex face. This is a key example of how perception can act as a top-down process for visual knowledge. This bias of seeing faces as convex which the