Visual perception

Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it. The resulting perception is known as eyesight, 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 the "black and white" vision system and the color one, pointing out that they use completely different sets of photoreceptors (respectively rod cells and cone cells). Some argue that perception of depth also constitutes a distinct sense, but others persuasively argue that depth is just one of many pieces of information extracted from several visual cues (it is based on the stereoscopic effect of having two eyes, the relative size of objects, motion, etc). Many people are also able to perceive the polarization of light.

The visual system

Human eyes

The eye is a light-sensitive organ that is the first component of the visual system. Humans rely heavily on their vision - blindness has an enormous impact on their lives. The eye's retina turns light into neural impulses and even performs the first stages of processing on those signals, with the remaining stages of visual perception occurring in the optic nerve, the lateral geniculate nucleus, and the visual cortex of the brain.

A recent University of Pennsylvania study calculated the approximate bandwidth of human retinas as 8.75 megabits per second, whereas guinea pig retinas transfer at 875 kilobits. [1]

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 seeing a door. The retina receives an image of a brown rectangle, with a little white thing sticking out, the visual perception system references past experience and the context it is working in (this shape is embedded in the wall of a house), and decides that what it is seeing is a door, and not, say, a big piece of paper, a stain, or a strangely shaped animal. Doing this requires taking into account for the fact that this same door seen from a different angle would be a different shape, and in a different light would appear as a different color. The simplicity of this example may seem strange at first, but that is because our visual systems work so easily and well for us that we rarely appreciate how incredibly hard the problems are that it solves so effortlessly (with occasional mistakes, see below).

Theoretical perspectives in the study of visual perception

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.

Vision's general goal is to identify, reasonably accurately, the features of our environment: roughly, what objects are present and moving where. It receives a lot of information that is irrelevant to this task, that it needs to sort through and discard: illumination patterns, viewing position, etc. Those are confounding variables. Call S = (F, C) the scene, with F the features we’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's could correspond to the same S. There are many reasons for this, but one of them is that the retina is 2 dimensional, and so it loses a lot of information in perceiving a 3-dimensional world.

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 – 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.

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 percept 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 [2] for a non-mathematical tutorial.

Gestalt theory

Gestalt psychologists have 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.

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.

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 dependent 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, habits, etc.

References

• Arnheim Rudolph (1954). Art and Visual Perception: A Psychology of the Creative Eye. Berkeley: University of California Press.
• Kleine-Horst Lothar (2001). Empiristic Theory of Visual Gestalt Perception. Hierarchy and Interactions of Visual Functions. Koeln: Enane. ISBN 3-928955-42X

See also

Types of visual perception

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

Disorders/Dysfunctions

• Achromatopsia
• Color blindness
• Scotopic Sensitivity Syndrome

Related Disciplines

• Psychophysics
• Neuroscience
• Cognitive Science
• Optometry
• Ophthalmology

Other

• 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
• Face perception
• Flicker fusion and the Persistence of vision
• Glasses
• Visual threshold
• Night vision
• Optic flow
• Optical illusion
• Peripheral vision
• 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

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
• Achieve Publications Offers solutions for children and adults with learning disabilities or dysylexia
• LD Support Offers answers to FAQs for learning disabled and gifted students