Vision

Introduction To Vision

Vision can be described as a feature in living beings thats allows them to see. Basically, the visual system is part of our nervous system which produces a vision into the eyes of organisms.

In psychology, visual perception is the ability to interpret information from visible light reaching the eyes. The resulting perception is also known as eyesight, sight or vision. The various physiological components involved in vision are referred to collectively as the visual system.



Visible Light

The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light.

Wavelengths visible to the eye also pass through the "optical window", the region of the electromagnetic spectrum which passes largely unattenuated through the Earth's atmosphere.The "visible window" is so called because it overlaps the human visible response spectrum; the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR and Long Wavelength are far beyond the human response region.

The eyes of many species perceive wavelengths different from the spectrum visible to the human eye. For example, many insects, such as bees, can see light in the ultraviolet, which is useful for finding nectar in flowers. For this reason, plant species whose life cycles are linked to insect pollination may owe their reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to our eyes.




Electro Magnetic Spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object.




Visual System

The visual system allows the human induviduals to recieve information from the environment.The eyes become able to see when the lens of the eye focuses an image of its surrounding 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 converter 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 and respond by producing neural impulses.These signals are processed by different parts of the brain, from the retina to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain.

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.



The Emission theory

The "emission theory" which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If we saw an object directly it was by 'means of rays' coming out of the eyes and again falling on the object. A refracted image was, however, seen by 'means of rays' as well, which came out of the eyes, traversed through the air, and after refraction, fell on the visible object which was sighted as the result of the movement of the rays from the eye. This theory was emphasised by scholars like Euclid and Ptolemy.



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 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.

One of the reasons why Gestalt laws have often been disregarded by cognitive psychologists is a lack of understanding the nature of peripheral vision. It is true that visual perception only takes place during fixations.

But during fixations not only the high definition foveal vision at the fixation point, but also the peripheral vision is functioning. Due to its lack of acuity and relative independence of eye position (due to its extreme wide angle) it is an image compressing system.

While foveal vision is very slow (only 3 to 4 high quality telescopic images per second), peripheral vision is very inaccurate but also very fast (up to 90 images per second - permitting to see the flicker of the European 50Hz TV images). Elements of the visual field are thus grouped automatically according to laws like Proximity, Similarity, Closure, Symmetry, Common fate and Continuity.