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Our visual system does not give a true representation of the external world. Why do we not see an exact representation of the external world and what role does prior knowledge play in perception?

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"Our visual system does not give a true representation of the external world". Why do we not see an exact representation of the external world and what role does prior knowledge play in perception? 1) Describe vision Investigation of any physiological system is always an extremely complex task; the visual pathway is here no exception. However, in the past twenty years a lot of conclusive studies have been made in this area which now forms the basis of a firmer fundamental understanding of the processing of visual information from the retina through the cortex. Perception is a very interesting part of the body to study because everything we know from the external world must first come through our senses. This information will be received as sensations arriving at sense organs in the body, such as the eyes, the nose and the ears. This information will be assed on to the brain and the central nervous system (CNS) with the help of sensory receptors which detect the physical properties of the world around us, such as light and sound. Hubel (1988) As our first contact with the external visual world is through our senses it is important to understand the physical make up of the eye and the visual pathways in the brain. Visual System The visual system interprets information from visible light to build a representation of the world that is surrounded by our body. With light we mean a narrow band of electromagnetic spectrum which has a wavelength of between 380 and 760 nanometres and is visible to humans. ...read more.


-- Whereas direct perception theorists believe that cues are picked up directly from the visual array, constructivist would suggest that they are learned through past experiences with objects around us. Some of the so called 'cues' are overlapping which means that when one object blocks the view of an other the blocked object is perceived to be further away. Another cue is linear perspective where parallel lines, such as those at the side of the road or a railway appear to converge in the distance. A different one is called relative size where objects in the distance seem smaller than they actually are, therefore smaller objects are perceived to be further away. Also shadowing plays an important part. As light usually travels in straight lines, which means that surfaces where the sun shines on will appear to be relatively bright and surfaces away from the light source will be in shadow. Bruce (1996) Constructivist theories believe that successful perception requires not only intelligence but also at the ability to combine sensory information with knowledge based on previous experience. Another very important part of the visual system is called adaptation which is the ability of the visual system of contrast processing. In order to be able to see clearly it is important to have visual acuity which means the capacity to discern fine details. Visual contrast refers to the difference in brightness levels between adjoining areas. Pinel (1999) Brightness and colour are important characteristics of human vision, but we also need to be able to detect contours in order to be able to recognise objects in our perceptual world. ...read more.


Many colour illusions are due to physical causes, because of the poor spectral resolution of the eye, and also differences in illuminates and pigments. The figure above was introduced by Kanitza, an Italian psychologist. Everyone sees a white triangle in front of the three black disks and inverted triangle. However, the white triangle actually does not exist. The contours of this triangle are illusory contours created by our brain. The illusory triangle looks brighter than the background. This is a result of brightness contrast caused by the black disks being partially occluded by the corners of the illusory triangle. The reason, why the illusory triangle looks brighter as a whole and not only as its corners is that the brain fills in a uniform surface with certain brightness. All this evidence shows that our visual system does not give a true representation of the external world. Our brain function tells us what to do and fills in the gap that might not be seen by the visual system. Prior knowledge plays an important part as Gibson (1966) stated in his research and not to forget the cues we have to bear in mind when trying to explain the visual pathways. Both theories the direct theory and the constructivist theory have been influential in describing vision. We need both to receive a three dimensional accuracy of the world and what is happening around us. We do not only relay on what we pick up directly from the visual array that surrounds us but we also rely on visual stimulus and also on stored knowledge in a problem solving approach to perception. ...read more.

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