Visual processing

The Vision can be defined as the procedure of discovering from images what is present in the world and where it is. In humans it is anticipated that almost half of the cerebral cortex is implicated in vision, more than is devoted to any other single function. This involves that vision is the most complex task which the brain executes.

The brain uses a 2-dimensional shifting pattern of light intensity values on the two retinas to form a representation of the form of an object, its movement color, and position in 3-dimensional space. Each of the visual channels (i.e., color, form, movement, and depth perception) is handled concurrently by different pathways. This is known as the parallel processing. (It contrasts with the serial processing in which a task is segmented into various subroutines which are executed sequentially.) The parallel processing has the benefit of speed. The last visual representation is a unified percept in which all the channels are combined. How the brain does this is unsure and is known as the binding problem that applies to all sensory modalities.

The visual system abstracts the key features from retinal images and this includes considerable data compression. Therefore the visual processing gives higher weight to areas of the visual world which are changing in time (movement) and space (contrast) than those which are constant. The Visual perception needs the existence of internal representations of the visual world that permit the brain to make hypotheses about what the retinal image is. The Internal representations account for the fact that vision permits pattern completion; it can create a whole percept even whenever the raw sensory data is incomplete or corrupted by the noise, and generalization, the capability to recognize objects from a wide range of vantage points and contexts. Some internal representations are identified during development and are immutable, but most probably depend on early learning. The Mental images of objects are thought to be manifestations of the internal representations of the objects and can be manipulated by most people in predictable manners. Whenever an irresolvable mismatch takes place between the sensory input and the internal representation the outcome is a visual illusion.

The Perceptual constancy is a key property of vision. The Visual perception can be invariant more than wide differences in the properties of the retinal image. For illustration, with size constancy, the familiar objects do not reduce in size in proportion to the reduction of the retinal image, but looks larger than they must. The Color constancy preserves the colors of objects in the face of alterations in the wavelength composition of the light source. The Perceptual constancy allows successful object recognition under a wide range of ambient conditions.