Form perception
From Wikipedia, the free encyclopedia
Form perception is the recognition of visual elements of objects, specifically those to do with shapes, patterns and previously identified important characteristics. An object is perceived by the retina as a two-dimensional image,[1] but the image can vary for the same object in terms of the context with which it is viewed, the apparent size of the object, the angle from which it is viewed, how illuminated it is, as well as where it resides in the field of vision.[2] Despite the fact that each instance of observing an object leads to a unique retinal response pattern, the visual processing in the brain is capable of recognizing these experiences as analogous, allowing invariant object recognition.[3] Visual processing occurs in a hierarchy with the lowest levels recognizing lines and contours, and slightly higher levels performing tasks such as completing boundaries and recognizing contour combinations. The highest levels integrate the perceived information to recognize an entire object.[4] Essentially object recognition is the ability to assign labels to objects in order to categorize and identify them, thus distinguishing one object from another.[3] During visual processing information is not created, but rather reformatted in a way that draws out the most detailed information of the stimulus.[3]
Form perception is a demanding task for the brain because a retina has a significant blind spot and retinal veins that obstruct light from reaching cells that detect light, or photoreceptor cells. The brain handles the blind spots through boundary processes, includes perceptual grouping, boundary completion, and figure-ground separation, and through surface processing, including compensation for variable illumination (“discounting the illuminant”), and filling blank areas with the surviving illuminant-discounted signals.[5]
In addition to photoreceptors, the eye requires a properly functioning lens, retina, and an undamaged optic nerve to recognize form. Light travels through the lens, hits the retina, activates the appropriate photoreceptors, depending on available light, which convert the light into an electrical signal that travels along the optic nerve to the lateral geniculate nucleus of the thalamus and then to the primary visual cortex. In the cortex, the adult brain processes information such as lines, orientation, and color. These inputs are integrated in the occipito-temporal cortex where a representation of the object as a whole is created. Visual information continues to be processed in the posterior parietal cortex, also known as the dorsal stream, where the representation of an object’s shape is formed using motion-based cues. It is believed that simultaneously information is processed in the anterior temporal cortex, also known as the ventral stream, where object recognition, identification and naming occur. In the process of recognizing an object, both the dorsal and ventral streams are active, but the ventral stream is more important in discriminating between and recognizing objects. The dorsal stream contributes to object recognition only when two objects have similar shapes and the images are degraded. Observed latency in activation of different parts of the brain supports the idea of hierarchal processing of visual stimuli, with object representations progressing from simple to complex.[5]
Development
By five months of age infants are capable of using line junction information to perceive three-D images, including depth and shape, like adults are able.[6] However, there are differences between younger infants and adults in the ability to use motion and color cues to discriminate between two objects.[7] Visual information then continues to be processed in the posterior parietal cortex, also known as the dorsal stream, where the representation of an objects shape is formed using motion-based cues.[7] The identification of differences between the infant and adult brain make it clear that there is either functional reorganization of the infant’s cortex or simply age related differences in which the breed impulses have been observed in infants. Although the infant brain is not identical to the adult brain, it is similar with areas of specialization and a hierarchy of processing.[7] However, adult abilities to perceive form from stationary viewing are not fully understood.[8]
