8/12/2019 Visual Illusion Notes

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Distortion of visual perceptions by illusions A visual illusion is a misinterpretation of real sensory information.

Even when we know what we are looking at is an illusion, and evenunderstand why the illusion occurs, the illusion still persists.

Psychologists have enhanced their understanding of illusions by looking atinstances when the illusion fails to occur.

The Muller-Lyer Illusion is a visual illusion in which one of the two lines ofequal length, each of which has opposite shaped ends, in incorrectlyperceived as being longer than the other.

Psychologists have four explanations as to why we see the illusion:

Biological perspective:

Focusses on the biological/physiological influences on behaviour and mental processes including the brainnervous system, the endocrine system, the immune system and genetics.

Eye-movement theory: because the feather end line is overall longer (see B line) than the arrow head line (see A line) the amount of eye movement needed to view the line is more. Therefore we perceive the feather end lineas the longer line.

The eye movement theory was rejected when further studies showed that the illusion persisted even when therewere no eye movement at all.

Other possible theories includeo Specific brain areas are involved which may influence our perceptiono Inborn (genetic) tendency to misperceive simple geometric patterns when they are viewed in 2D form

(as opposed to 3D)

Behavioural perspective:

http://www.google.com.au/url?sa=i&rct=j&q=muller+lyer&source=images&cd=&cad=rja&docid=0caKEtg6JKCmTM&tbnid=Ak5lPqydCYnDZM:&ved=0CAUQjRw&url=http://www.wpclipart.com/signs_symbol/optical_illusions/Muller_Lyer_illusion.png.html&ei=FJD5Uom2OcjvlAWqmYGgCg&bvm=bv.61190604,d.dGI&psig=AFQjCNGmvKU7AvOfw6Demb9VKLtqX1GCrg&ust=1392172808032276http://www.google.com.au/url?sa=i&rct=j&q=muller+lyer&source=images&cd=&cad=rja&docid=0caKEtg6JKCmTM&tbnid=Ak5lPqydCYnDZM:&ved=0CAUQjRw&url=http://www.wpclipart.com/signs_symbol/optical_illusions/Muller_Lyer_illusion.png.html&ei=FJD5Uom2OcjvlAWqmYGgCg&bvm=bv.61190604,d.dGI&psig=AFQjCNGmvKU7AvOfw6Demb9VKLtqX1GCrg&ust=1392172808032276

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Focusses on how behaviour is acquired or modified by environmental consequences such as rewards andpunishments.

Carpeted World Hypothesis: our past experience with the 3D world has led us to use angles and lines to judgedepth and distance. As a consequence the arrow-headed line looks like a nearer, outside edged corner and thefeather-headed line looks like a further away inside corner. Consequently the two lines appear to be at differentdistances. When an individual looks at the Muller-Lyer illusion the brain overrides any perception that the linesare the same length and the individual perceive the lines feather-tailed line as being longer.

Socio-cultural perspective:

Focuses on the roles for social and cultural influences on human behaviour and mental processes.o The following results from studies suggest an environmental influenceo Zulu African groups (who live in round houses/no corners) are less likely to perceive the illusion.o White American children are more likely to perceive the illusions compared to Zambian childreno Zambian children who live in urban areas are more likely to perceive the illusion compared to Zambian

children who live in rural area. Conflicting studies have found that it is not the environment, but rather other factors such as education, training

or raceo Little to no difference found between Aboriginal groups who live in carpeted and non-carpeted areas. o Little to no difference between Aboriginal and European Australians

No specific socio-cultural explanation, but socio-cultural factors and personal experience obviously play a role inperceiving the illusion.

Cognitive perspective:

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8/12/2019 Visual Illusion Notes

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Focuses on how we acquire, process, remember and use information about ourselves and the world around us Misapplication of size constancy: we make the (mental) assumption that the lines are of different distance away.

This leads us to make an interpretation that when two lines appear to be at different distances and cast retinalimages of equal size, then the line that appears the furthest away (feather-tailed) must be longer.

Correct Application of sizeconstancy

Misapplication of sizeconstancy

Size constantcy: recognisingthat objects actual remainsthe same even though theimage cast on the retina

changes.

Here the man is getting further away. Though the

image of the man that is castof the retina is getting

smaller, we are aware the the person themselves are not

shrinking.

When the two lines are presented, we make themental assumption thatthey must be different

distances away from eachother.

When images cast thesame size image on theretina (like the top half

pictures) we can see that itmakes it look like oneman/monster is quitebigger than the other

man/monster.

We apply the same principle to the Muller-Lyer

lines the feather-endedline is assumed to be

further away and thereforebigger than the arrow-ended line which we

mentally assume as beingcloser to us.

Limitation of this theory include:o The illusion working equally as well when he lines are horizontal rather than verticalo Other variations of the illusion which used different ends are also equally effective.

(the feather/arrow like ends are not necessary to produce the illusion)

http://www.google.com.au/url?sa=i&rct=j&q=size+constancy&source=images&cd=&cad=rja&docid=wqwgXUuA75lH6M&tbnid=_bps_0ozYRK7ZM:&ved=0CAUQjRw&url=http://www.ottobw.dds.nl/filosofie/perspect.htm&ei=t4_6UrClGpGakgXImoDgAw&bvm=bv.61190604,d.dGI&psig=AFQjCNFoLCKIQSLWcLmxPp-lh6dGZP17cQ&ust=1392238789219971http://www.google.com.au/url?sa=i&rct=j&q=size+constancy&source=images&cd=&cad=rja&docid=wqwgXUuA75lH6M&tbnid=_bps_0ozYRK7ZM:&ved=0CAUQjRw&url=http://www.ottobw.dds.nl/filosofie/perspect.htm&ei=t4_6UrClGpGakgXImoDgAw&bvm=bv.61190604,d.dGI&psig=AFQjCNFoLCKIQSLWcLmxPp-lh6dGZP17cQ&ust=1392238789219971http://www.google.com.au/url?sa=i&rct=j&q=size+constancy&source=images&cd=&cad=rja&docid=wqwgXUuA75lH6M&tbnid=_bps_0ozYRK7ZM:&ved=0CAUQjRw&url=http://www.ottobw.dds.nl/filosofie/perspect.htm&ei=t4_6UrClGpGakgXImoDgAw&bvm=bv.61190604,d.dGI&psig=AFQjCNFoLCKIQSLWcLmxPp-lh6dGZP17cQ&ust=1392238789219971http://www.google.com.au/url?sa=i&rct=j&q=size+constancy&source=images&cd=&cad=rja&docid=wqwgXUuA75lH6M&tbnid=_bps_0ozYRK7ZM:&ved=0CAUQjRw&url=http://www.ottobw.dds.nl/filosofie/perspect.htm&ei=t4_6UrClGpGakgXImoDgAw&bvm=bv.61190604,d.dGI&psig=AFQjCNFoLCKIQSLWcLmxPp-lh6dGZP17cQ&ust=1392238789219971http://www.google.com.au/url?sa=i&rct=j&q=size+constancy&source=images&cd=&cad=rja&docid=wqwgXUuA75lH6M&tbnid=_bps_0ozYRK7ZM:&ved=0CAUQjRw&url=http://www.ottobw.dds.nl/filosofie/perspect.htm&ei=t4_6UrClGpGakgXImoDgAw&bvm=bv.61190604,d.dGI&psig=AFQjCNFoLCKIQSLWcLmxPp-lh6dGZP17cQ&ust=1392238789219971