Visual perception

Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it as the perception known as sight or naked eye vision. Vision has a specific sensory system, the visual system.

There is disagreement as to whether or not this constitutes one, two or even three distinct senses. Some people make a distinction between "black and white" vision and the perception of colour, and others point out that vision using rod cells uses different physical detectors on the retina from cone cells. Some argue that the perception of depth also constitutes a sense, but others argue that this is really cognition (that is, post-sensory) function derived from having stereoscopic vision (two eyes) and is not a sensory perception as such. Many people are also able to perceive the polarization of light.

The visual system
The eye is the light-sensitive organ that is the first component of the visual system. The eye's retina performs the first stages of visual perception processing, with the remaining stages of visual perception occurring in the optic nerve, the lateral geniculate nucleus, and the visual cortex of the brain.

Sources of information
To perform its task, visual perception takes into account not only patterns of illumination on the retina, but also our other senses and our past experiences. Consider the task of bird sighting (an instance of object recognition): to be able to identify a bird against a background of tree and brushes, one needs prior exposure to general properties of the bird category. From past experiences, we expect birds to have a certain shape, color, etc. Hearing a sound that is characteristic of birds, a song for example, will help us locate one: information from the other senses is used in visual perception. In this case, locational information from the auditory domain is used.

Individual and group differences in visual perception
Most of the general processes of visual perception have been shown to be universal, as opposed to being dependant on culture, although there are specific instances where cultural variability appears to come into play.

It has also been shown that certain individual differences such as impairment of sight and spatial skills can also affect our visual perception. There are also other factors that influence how we perceive things such as personality, cognitive styles, gender, occupation, age, values, attitudes, motivation, religious beliefs, economic status, education and habits.

Unconscious inference
Hermann von Helmholtz is often credited with the founding of the scientific study of visual perception. Helmholtz held vision to be a form of unconscious inference: vision is a matter of deriving a probable interpretation for incomplete data.

The general goal of vision is to identify, as accurately as possible, the features of our environment: roughly, what objects are present where. Other features are irrelevant to this task : illumination patterns, viewing position, etc. Those are confounding variables. Call S = (F,C) the scene, with F the features we&#8217;re interested in and C the confounding variables. S determines I, the pattern of illumination on the retina, which is all the information our visual system has on the current scene. The task is to find S given I. This problem is under-constrained: many different S correspond to the same I, and many I could correspond to the same S. One of the reasons is that much information is lost when a 3-dimensional world is collapsed into a 2-dimensional array.

To see why, consider the figure of a circle such as this one: O. It could correspond to an infinity of ellipses viewed at a certain slant. But we always interpret it as a circle viewed on the frontal plane &#8211; the explanation we infer from the data for this particular stimulus.

Inference requires prior assumptions about the world: two well-known assumptions that we make in processing visual information are that light comes from above, and that objects are viewed from above and not below. The study of visual illusions (cases when the inference process goes wrong) has yielded a lot of insight into what sort of assumptions the visual system makes.

Gestalt
Psychologists of the Gestalt school have raised a large part of the research questions that still preoccupy vision scientists today.

The so-called Gestalt Laws of Organisation have broadened the study of how people perceive objects to be organized patterns or wholes, instead of collections of many separate parts. Gestalt is a German word that translates to "configuration or pattern". According to this theory, there are four main factors that determine how we group things according to visual perception.


 * Proximity – Depending on how close object are to one other, we tend to group the ones closest to each other as a group.
 * Similarity – If objects are similar in shape or size to one another we tend to group them together.
 * Closure – How we complete a pattern because of how the items are grouped together even though the pattern is not complete.
 * Simplicity – How we group items according to symmetry, regularity, and smoothness.

Ecological psychology
Psychologist James J. Gibson developed a theoretical perspective on vision that is radically different from that of Helmholtz. Gibson considers that enough visual perception is available in normal environments to allow for veridical perception (accurate perception of the world). Gibson replaces inference with information pickup. Although most researchers today feel closer to Helmholtz's unconscious inference theory, Gibson has done much in identifying what sort of information is available to the visual system.

Types of visual perception

 * Black and white vision
 * Color vision
 * Gestalt perception
 * Motion perception

Disorders/Dysfuntions

 * Achromatopsia
 * Color blindness
 * Scotopic Sensitivity Syndrome