Visual Perception

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 Color , and others point out that vision using Rod Cell s uses different physical detectors on the retina from Cone Cell s. 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 brain receives ninety percent of its information from the eyes also. 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 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.

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.

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’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 – 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 {Link without Title} for an non-mathematical tutorial.

Gestalt

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 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 Style s, Gender , occupation, age, Values , Attitudes , motivation, religious beliefs, economic status, education, habits, etc.

REFERENCES

Berkeley G (1709/1975) Philosophical works including works on vision. (Ayers, MR ed)London:
Eveyman/J.M. Dent.

Mamassian, P., Landy, M. S. and Maloney, L. T. (2002). Bayesian Modelling of Visual Perception. In R. Rao, B. Olshausen and M. Lewicki (Eds.) Probabilistic Models of the Brain: Perception and Neural Function (pp. 13-36). Cambridge, MA: MIT Press.

Purves D, Lotto RB, Williams SM, Nundy S, Yang Z (2001) Why we see things the way we do:
evidence for a wholly empirical strategy of vision. Phil Trans Roy Soc London B-Bio Sci
356:285-297.

Purves D, Lotto RB (2003) Why We See What We Do: An Empirical Theory of Vision. Sunderland
MA: Sinauer Associates.

Purves D, Williams MS, Nundy S, Lotto RB (2004) Perceiving the intensity of light. Psychological
Rev. Vol 111: 142-158.

Howe, Catherine Q., Purves, Dale (2005) Perceiving Geometry: Geometrical Illusions Explained by
Natural Scene Statistics. New York, NY: Springer Publishing.

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

SEE ALSO

Types of visual perception

Information About

Visual Perception