Figure-ground (perception)

In visual perception, figure-ground is a type of perceptual organization in vision that involves assignment of edges to regions for purposes of shape determination, determination of depth across an edge, and the allocation of visual attention [Palmer, S.E. (1999). "Vision Science: Photons to Phenomenology". Cambridge, MA: MIT Press. (see chapter 6)] . Figure-ground is a critical process in perception because of its profound consequences for shape perception. It is a common textbook topic in general psychology and perception courses. The Gestalt psychologist Edgar Rubin is credited with popularizing the issue of figure-ground organization and it is therefore often associated with Gestalt Psychology more broadly.

Figure-ground organization is probably best known by the faces-vase drawing that Rubin described [Rubin, E. (1921) "Visuell Wahrgenommmene". Kobenhaven: Glydenalske boghandel.] [ Rubin, E. (2001). Figure and Ground. In Yantis, S.(Ed.), "Visual Perception". (pp. 225-229). Philadelphia, Psychology Press] . This drawing exemplifies one of the key aspects of figure-ground organization, edge-assignment and its effect on shape perception. Notice in the faces/vase drawing below, the perceived shape depends critically on the direction in which the border (edge) between the black and white regions is assigned. If the two curvy edges between the black and white regions are assigned inward then the central white region is seen as a vase shape in front of a black background. No faces are perceived in this case. On the other hand, if the edges are assigned outwards, then the two black profile faces are perceived on a white background and no vase shape is perceived.

Figure-ground is used extensively to help artists and designers in composition of a 2D piece. In its basic sense, it refers to a cognitive ability to separate elements based upon contrast, that is, dark and light, black and white. Many times this definition is expanded from a simple perception based on contrast to include abstract (i.e. non-visual) concepts such as melody/harmony, subject/background and positive/negative space.

The famous optical illusion image depicting both a vase and two profiles of a human face (the Rubin vase) is often used to illustrate the concept of figure ground: Depending on whether the white or black color is seen as the figure (forefront) or the ground (background) the brain will interpret the picture as two different images, and it may be difficult (or even, according to gestalt psychological theory, impossible) to perceive both meaningful images simultaneously. There is a tendency to switch rapidly between both 'readings' of the image.

The Flag of Canada has also been cited as an example of figure-ground reversal, in which the background edges of the maple leaf can also be seen as two faces arguing. [ [http://books.google.com/books?id=l-tHZfp8C5YC&pg=PA27&lpg=PA27&dq=jacques+jack+canadian+flag+illusion&source=web&ots=5_yke7kncg&sig=qVutzvuB1xebgfukWuXgPVisfcg "Can You Believe Your Eyes?"] ]

Figure-ground reversal may also be used an intentional visual design technique in which an existing image's foreground and background colours are purposely swapped to create a new image.

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