Introduction
Perception is one of the aspects of cognitive psychology. Vision encompasses the eye gathering raw sensations which fall onto the retina and the eventual perception of the sensation in terms of shape, color, motion as well as different dimensions of objects. It is described that vision begins with the whole body during movement, of the eyes, the head or the entire body, as the body seeks to acquire information at depth (Stafford & Webb, 2005). In some cases, decisions on eye or body movement precede conscious recognition and thus vision can be said to be interactive and it is composed of feedback loops both in the early and late visual perception.
It is recognized that there is no orderly path of processing raw visual signal and often the brain processes and uses information as soon as it reaches it without waiting for all the information to be available. This forms part of early processing of visual information and when the perception is processed to the point of consciousness, it becomes possible to conceptualize the whole object instead of just seeing the aspects of vision (e.g. color, shapes) that are available to the eye. At conscious perception, it results that some objects are more conspicuous than others (Stafford & Webb, 2005). This paper examines how the eye senses signals from the outside world and sends these to the brain’s visual cortex and the resultant processing of visual signals into meaningful information.
The retina
The retina is located at the back of the eye and acts as a sensory surface as it bears the photoreceptors which not only detect light from outside but also covert the light into electrical signals. The eye is protected by the white, which itself is the continuation of the dura mater which covers the central nervous system. The retina is in fact taken to be “a piece of the brain that has grown into the eye” (PhysOrg.com, 2006, para 2). Upon detecting light, the retina goes ahead to process neural signals where the electrical signals are carried by the ganglion cells into other parts of the brain. The early visual processing is performed within the retina by other nerve cells while the optic nerve which is composed of the axons of the ganglions among other support cells conduct aggregated signals into the brain for further processing (PhysOrg.com, 2006). The photoreceptors are distributed considerably in the retina with the fovea (which is the center of the eye) having no signal aggregation onto a single cell. At the fovea, there is a high resolution and the uncompressed signal is taken to the optic nerve together with other signals from other photoreceptor cells. The optic nerve which conducts information to the brain from the eye is of a size that makes it make a hole in the field of vision as it quits the eyeball and this hole is called the blind spot. The human retina transmits the visual data to the brain at a very high speed which is estimated to be 10 million bits per second (PhysOrg.com, 2006).
Hemispheres as mirror images of each other
Just before the optic nerves enter the brain, an optic chiasm is formed by meeting and splitting of the optic nerves of each eye. Mirror images of the two hemispheres are created where the right hemisphere is linked to the right halves of the retina. On the other hand, the left hemisphere is linked to the left halves of the retina. The importance of this change of events is to remove confusion by enabling only one hemisphere to make a comparison of the same scene as perceived by both eyes. Otherwise, it would be impossible to have access information that is necessary for processing the depth of the perception. From the optic chiasm, the visual message is transmitted into the visual cortex at the back of the brain where comprehensive visual processing occurs (Stafford & Webb, 2005). It is important to note that nerves that have a connection to the temple side of the retina do not change their path to the visual cortex and their path is considered to be relatively simple. This is in contrast to nerves with a connection to the nasal side of the retina which requires a cross over to occur at the center of the brain and later the formation of the optic chiasma. These differences are used to explain why certain conditions affect some certain areas of vision only (Morgan, 2008).
Visual discrimination
As earlier mentioned, photoreceptors are in different densities in the retina with the fovea being highly packed and there has highest resolution. The peripheral vision has a lesser resolution but it the photoreceptors can still differentiate various kinds of light. The peripheral vision is therefore more capable of recognizing brightness than color. Color discrimination is best done at the fovea since this is where virtually all photoreceptors with color discrimination capability are located (Stafford & Webb, 2005).
Before getting to the visual cortex, the information is relayed via a lateral geniculate nucleus (LGN) which acts as a stop in each of the hemispheres. Grouping of similar colors and same orientation takes place at the visual cortex and the lateral occipital complex aids in grouping the similarities. A contrast with the background is also enabled. Then follows cognition of the generated objects and any other feature that is found after processing visual information is added to the existing data and depth of information is enhanced. The cortex does late visual processing and the cortex is able to make out visual information that can be related with language, emotions as well as memory, thus incorporating the whole brain in vision (Stafford & Webb, 2005).
Conclusion
The visual world is perceived by the eye and the brain through a complex visual processing system. The system involves the sensing of light from outside by the photoreceptors in the retina and consequential transmission of the light to the visual cortex of the brain via the optic nerve. The retina performs early visual processing while the cortex performs late visual processing and eventually makes sense of the perceived signals. The fovea is important in discriminating color and eventual vision due to highly-packed photoreceptors. It is evident that the visual system is a complex one involving not only the brain but also the eyes as primary receptors, the head and the entire body. The environment is also part of the vision system and also important is the fact that the visual processing system is undoubtedly a complex one
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