Visual perception
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In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. The resulting perception is also known as eyesight, sight or vision. The various components involved in vision are known as the visual system.
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[edit] Human Visual System
[edit] The Eye
Our eyes are our bodies' most highly developed sensory organs.[citation needed] Light rays enter the eye by first crossing the clear cornea. Nearly two-thirds of the eye's focusing power occurs along the front surface. A normal cornea should have a round contour like a soup spoon, allowing the eye to create a single focused image.
[edit] The retina
The visual system is highly efficient in providing a rapid assimilation of information from the environment to help guide our actions. The act of seeing starts when the cornea and lens focus an image of the outside world onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals.
The lens of the eye focuses light on the photoreceptive cells of the retina, which detect the photons of light via the visual cycle and respond by producing neural impulses.Light is absorbed by photopigment into two classes of receptors, rods and cones. There are approximately one hundred million rods and five million cones in the human retina. The rods are active under scotopic, or dim lighting, and the cones are active under photopic, or daylight settings. There are two opponent colour systems; blue-yellow and red-green. The three streams (luminance, B-Y and R-G) are initially processed in parallel. The retina contains three different types of cones each with visual pigments of differing peak spectral sensitivity, Red: (560nm), green (530 nm) and blue (430 nm). Both the red and green pigments are encoded on the x chromosome, and the blue con pigment is found on chromosome seven.
[edit] The brain
After light passes through the cornea it then moves through the lens to the retina. Signals from the retina are processed in a hierarchical fashion by different parts of the brain, such as the lateral geniculate nucleus, and the primary and secondary visual cortex of the brain.
[edit] Theoretical perspectives in the study of visual perception
The major problem in visual perception is that what people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Thus people interested in perception have long struggled to explain what visual processing does to create what we actually see.
[edit] 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.
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.
The unconscious inference hypothesis has recently been revived in so-called Bayesian studies of visual perception. Proponents of this approach consider that the visual system performs some form of Bayesian inference to derive a perception from sensory data. Models based on this idea have been used to describe various visual subsystems, such as the perception of motion or the perception of depth. An introduction can be found in Mamassian, Landy & Maloney (2002). See here [1] for a non-mathematical tutorial on these general ideas.
[edit] Gestalt theory
Gestalt psychologists working primarily in the 1930s and 1940s raised many of the research questions that are studied by vision scientists today.
The Gestalt Laws of Organization (or Pragnanz) have guided the study of how people perceive visual components as organized patterns or wholes, instead of many different parts. Gestalt is a German word that translates to "configuration or pattern". According to this theory, there are six main factors that determine how we group things according to visual perception: Proximity, Similarity, Closure, Symmetry, Common fate and Continuity.
The major problem with the Gestalt laws (and the Gestalt school generally) is that they are descriptive not explanatory. For example, one cannot explain how humans see continuous contours by simply stating that the brain "prefers good continuity". Computational models of vision have had more success in explaining visual phenomena[1] and have largely superseded Gestalt theory.
[edit] See also
[edit] Directly related articles
[edit] Types of visual perception
[edit] Disorders/Dysfunctions
[edit] Related Disciplines
[edit] Other
- Acquired vision
- Attentional blink
- Binocular rivalry and Multistable perception
- Blindsight
- Brightness and Contrast
- Consciousness and visual qualia
- Corrective lens
- Entoptic phenomenon
- Eye tracking
- Face perception
- Flicker fusion and the Persistence of vision
- Glasses
- Visual threshold
- Night vision
- Optic flow
- Optical illusion
- Peripheral vision
- Perspective (visual)
- Phi phenomenon
- Philosophy of perception
- Phosphenes
- Photoreceptor
- Pattern recognition and Computer vision
- Primary sensory cortex
- Repetition blindness
- Visual perception in dreams
- Vestibulo-ocular reflex
- Visual acuity
- Visual aid
- Visual cortex
- Visual deprivation
- Visual feedback
- Visual field
- Visual fixation
- Visual pathway
- Visual photosensitivity
- Visual phototransduction
- Visual pigment
- Visual stimulus
- Visual tectum
[edit] External links
- Empiristic theory of visual gestalt perception
- Visual Perception 3 - Cultural and Environmental Factors
- Visual Perception 4 - Individual Differences, Purposes and Needs
- Gestalt Laws
- Summary of Kosslyn et al.'s theory of high-level vision
- The Organization of the Retina and Visual System
- Dr Trippy's Sensorium A website dedicated to the study of the human sensorium and organisational behaviour
