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

How can visual illusions illustrate top down processes in perception? Contrast this with a visual illusion that can be explained through bottom up processes.

Extracts from this document...

Introduction

Caroline Hewitt

How can visual illusions illustrate top down processes in perception? Contrast this with a visual illusion that can be explained through bottom up processes.

        There are many suggestions to explain how visual illusions can be perceived.  These suggestions include physical illusions, bottom up illusions and top down illusions.   An example of a physical illusion is how a straight stick when placed in water appears bent.  Here the illusion has occurred before the light has entered the eye and so is a physical illusion.  Bottom up and top down illusions however involve the processing after the light has entered the eye.  Bottom up processes are processes which take information into the eye and then make judgements about the nature of the visual world based solely on this information.  Hering who suggested that it was the innate ability of the visual system that led to how things were perceived illustrates this. Top down processing however involves using prior knowledge and experience about the structure of the world to influence how something is perceived.  Helmholtz who felt that the perception of a stimulus was based on visual experience illustrated this.  The following illusions show examples of how both processes can be used to explain perceptions.

...read more.

Middle

        However bottom up processing is also used to perceive visual illusions.  Examples of this include the Herman Grid (figure 4) and Mach Bands (figure 6).  Firstly the Herman Grid which is simply a grid consisting of twenty-five black squares intersected by white lines.  However when looking at this grid black smudges seem to appear in the intersection of the white lines. This however doesn’t occur at the intersection that is being fixated upon.  This illusion can be explained through bottom up processes whereby judgements are made solely on the information that enters the eye and knowledge of the world has no effect.  Figure illustrates how the Herman Grid can be explained.  It shows how when a receptive field that is over-excitatory is aligned with an intersection there will be a larger amount of inhibition than when the receptive field is centred in the space between two squares.  This results in the ganglion cells registering there being less light in the intersections compared to the other areas between the squares.  This shows how the illusion is physiological and so does not rely on any previous experience or knowledge thus showing how the illusion can be explained through bottom up processing.  Similarly

...read more.

Conclusion

Therefore despite the more obvious explanations stated in the first four examples there are also alternative explanations which can involve the use of both bottom up and top down processes combined to perceive an illusion.  And so as it is hard to provide an adequate and clear-cut explanation for an illusion and these explanations remain different for each illusion, the perception of illusion becomes subjective.


References

S Coren, L M Ward & J T Enns 2004 Sensation and Perception 6th edn

W N Dember & J S Warm 1979 Psychology of Perception 2nd edn

Purves & Andrews 1997 The Perception of Transparent Three Dimensional Objects Proc. Natl. Acad. Sci. USA Vol 94

Mach Bands 1965 Quantitative Studies on Neural Networks in the Retina Holden Day

M W Eysenck 2004 Principles of Cognitive Psychology 2nd edn Psychology Press

Bruner, J. S., Postman, L., & Rodrigues, J. (1951). Expectations and the Perception of Colour. American Journal of Psychology, Vol 64

...read more.

This student written piece of work is one of many that can be found in our GCSE Number Stairs, Grids and Sequences 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 GCSE Number Stairs, Grids and Sequences essays

  1. Boxes made in the shape of a cube are easy to stack to make ...

    So the equation for this shape is: B= 1/2 N2 + 1/2 N To check this formula I will try it on the next shape in the series: B= 0.5 x 62 +0.5 x 6 B=21 My formula is correct.

  2. For my investigation I will be finding out patterns and differences in a number ...

    I have set them out in a table and gradually as I go along I will fill in all the blanks boxes and even add a 6x6 column and a 7x7 column. Prediction My prediction for my 6x6 and 7x7 is that they will both be a multiple of 10.

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