Visual Neuroscience - Perceptions of Light & Shadows

Perceptions of Light & Shadows

Recently, scientists have conducted experiments challenging the hierarchal process of visual perception of lightness. These experiments have suggested that the perception of lightness is derived from a much higher level of cognition involving the interpretation of illuminations and shadows rather than the process occurring at a basic single unit level. This idea is best explained by examining two different versions of two common visual illustrations. The first set of illustrations cause a phenomenon known as the induction effect. The image consists of two identical gray squares, surrounded by black and white respectively. The result is that the perception of the gray on the white is darker than the gray on the black. The traditional way of explaining this is through lateral inhibition. A cell with a receptive field in the gray square surrounded by the white receives more of the lateral inhibition and thus it does not fire as often and appears darker. The second set of illustrations explain the Craik-O' Brien-Cornsweet illusion. This includes a sharp transition from black to white in the middle then fading to medium gray on the other side. The other two diagrams exhibit the same two effects but with a much greater intensity. This is due to the shapes in the illustrations being 3-dimensional causing the human mind to interpret the seemingly darker areas as shadows. This was first introduced by Ernst Mach in the 1866.