• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

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?

Extracts from this document...

Introduction

"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.

Middle

-- 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.

Conclusion

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.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our University Degree Cognitive Psychology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related University Degree Cognitive Psychology essays

  1. How can visual illusions illustrate top down processes in perception? Contrast this with a ...

    dark vertical band near the area where there is a strong gradient change in the color, when in fact none exists. This is supposedly due to 'lateral inhibition of the receptors in the eye' however it can also be attributed to the 'statistical strategy of visual perception' (Lotto, Williams, Purves, 1999).

  2. Are visual illusions due to low-level, so-called "bottom-up" processing, or are they aberrations of ...

    Psychologists trained monkeys to report the direction in which a display of dots moved while the researchers observed the response of individual neurones previously identified as feature detectors for movement of a particular speed and direction (Newsome, Britten, & Moushon, 1989).

  1. Perception - Object Recognition and Naming Project. This small scale study replicates an ...

    On satisfactory completion of the practice run subjects were asked to press the space bar and wait for the display of the 'fixation cross'. This was the focus point of which participants were asked to gaze upon and wait for the presentation of each line drawing.

  2. The effect of context, and the relationship of cue and target, in word recognition ...

    Completing this answer sheet, participants were given an explanation of the experiment, and were free to leave. Results For each subject, a total score for each item type (HiHi, HiLo, LoHi and LoLo types) was calculated separately. Means and standard deviations of scores for each item type is given in

  1. Compare and contrast theories of perception which emphasize top-down processing against those which emphasize ...

    This is highlighted with the Penrose Triangle (Fig 3). Fig 3: Penrose Triangle (Pike & Edgar, 2005) Whilst we understand that this figure is impossible to construct when we attend to each corner we perceive it as a three dimensional possibility.

  2. Describe and evaluate the Gestalt laws of perceptual organization.

    point out ?the laws...have withstood the test of time. In fact, not one of them has been refuted, and no new ones have been added?. A final point concerning the Gestalt laws of perceptual organization is that, whilst they are detailed in description, the explanation is often lacking. In fact, the Gestaltists have been criticised for over-simplifying a very complex process by not providing sufficient supporting evidence.

  1. An Evaluation of the theories of viewpoint-invariant and viewpoint- dependent approaches of three dimensional ...

    (Tarr & Bulthoff 1995) Many image-based theorists posit that much of the research findings that support viewpoint-invariant recognition maybe questionable as, they state, lack ecological validity in that they don?t account for everyday recognition/not typical to real world recognition.

  2. Using evidence drawn from Chapter 2 explain how theory of mind may have evolved ...

    Another possible reason could be that the relationship between the nutritional value of the lunch and the level of distractibility are spurious which, even when possible, would have in this study a very low chance to be the case. Q1, (h)

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work