A popular modern philosophical view is that the brain cannot contain images so our sense of space must be due to the actual space occupied by physical things. However, as René Descartes noticed, perceptual space has a projective geometry, things within it appear as if they are viewed from a point. The phenomenon of perspective was closely studied by artists and architects in the Renaissance, who relied mainly on the 11th century polymath, Alhazen (Ibn al-Haytham), who affirmed the visibility of perceptual space in geometric structuring projections.[14][15] Mathematicians now know of many types of projective geometry such as complex Minkowski space that might describe the layout of things in perception (see Peters (2000)) and it has also emerged that parts of the brain contain patterns of electrical activity that correspond closely to the layout of the retinal image (this is known as retinotopy).