Visual perception

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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.

Main article: Visual system

The Eye

Our eyes are our bodies' most highly developed sensory organs.^{[How to reference and link to summary or text]} 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.

The retina

Human eyes

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.

Main article: Biochemistry of the retina

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.

The neuropsychology of vision

Tthe remaining stages of visual perception occurring in the optic nerve, the lateral geniculate nucleus, and the visual cortex of the brain.

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.

The visual dorsal stream (green) and ventral stream (purple) are shown. Much of the human cerebral cortex is involved in vision.

Main article: Neuropsychology of visual perception

Areas of study in visual perception

Main article: Visual object processing

Main article: Shape processing

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.

The development of visual perception

Visual perception develops through interaction with the environment and is a developmental process

Main article: Development of visual perception

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.

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.

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.

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 have guided the study of how people perceive visual components as organized patterns or wholes, instead of many separate 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 – the objects closest together are more likely to form a group.
• Similarity – objects similar in size or shape are more likely to form a group.
• Closure – our brains add missing components to complete a larger pattern.
• Symmetry – symmetrical items are more likely to group together.
• Common fate – items moving in the same direction are more likely to group together.
• Continuity – once a pattern is formed, it is more likely to continue even if the elements are redistributed.

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, beliefs, etc.

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.

Development of visual perception

Main article: Development of visual perception

See also

Types of visual perception

• Black and white vision
• Color vision
• Object perception
• Motion perception
• Depth perception
• Multimodal perception

Disorders/Dysfunctions

See aberration in optical systems but this needs rewriting for the eye

• Achromatopsia
• Astigmatism
• Chromatic aberration
• Color blindness
• Scotopic Sensitivity Syndrome
• Spherical aberration

Journals

• Vision research

Related Disciplines

• Psychophysics
• Neuroscience
• Cognitive Science
• Optometry
• Ophthalmology

Other

• Acquired vision
• Attentional blink
• Binocular rivalry and Multistable perception
• Blindsight
• Brightness and Contrast
• Color, Color circle, and Color vision
• Consciousness and visual qualia
• Corrective lens
• Entoptic phenomenon
• Eye tracking
• Eye dominance
• 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 skills
• Visual stimulus
• Visual tectum
• Visual threshold

Key texts

Books

• Farah, M. J. & RatcliffG. (1994)(Eds.), The Neuropsychology of High-level Vision. Hillsdale, N. J.: Erlbaum. ISBN 0805809112
• Humphreys, G. W. (1992) (Ed.) Understanding vision: An inter-disciplinary approach. Oxford: Blackwells.
• Spillman, L., and Werner, J.(1990) (Eds.) Visual Perception: The Neurophysiological Foundations, New York: Academic Press.

Additional material

Books

• Rudolph Arnheim (1954). Art and Visual Perception: A Psychology of the Creative Eye. Berkeley: University of California Press.
• Lothar Kleine-Horst (2001). Empiristic Theory of Visual Gestalt Perception. Hierarchy and Interactions of Visual Functions. Koeln: Enane. ISBN 3-928955-42X
• Barlow H, Blakemore C (1990/1991) Images and Understanding, Cambridge, UK, Cambridge University Press.
• Helmholtz Hermann Von (2000), reprinted from 1865/1866 edition, The Treatise On Physiolological Optics, Thoemmes Continuum.
• Kleine-Horst Lothar (2001). Empiristic Theory of Visual Gestalt Perception. Hierarchy and Interactions of Visual Functions. Koeln: Enane. ISBN 3-928955-42X
• Palmer Stephen E., (1999) Vision Science: Photons To Phenomenology, Bradford Books.
• Purves D, Lotto B, (2003) Why We See What We Do: An Empirical Theory of Vision, Sunderland, MA: Sinauer Associates.
• Rodieck RW, (1998) The First Steps In Seeing, Sunderland, MA: Sinauer Associates.

Papers

• Google Scholar

External links

• Empiristic theory of visual gestalt perception
• Visual Perception 3 - Cultural and Environmental Factors
• Gestalt Laws
• Visual Perception 4 - Individual Differences, Purposes and Needs
• VisionSimulations.com | Vision simulators for various diseases and conditions of the eye
• Summary of Kosslyn et al.'s theory of high-level vision
• The Organization of the Retina and Visual System
• San Diego Vision Group

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