Explanations for Visual Illusions (AQA GCSE Psychology)
Revision Note
Written by: Claire Neeson
Reviewed by: Lucy Vinson
Ambiguity
A visual illusion occurs when a human being’s perceptual system attempts to make sense of their physical environment using visual cues and constancies to interpret the visual field
Ambiguity occurs when one image can be viewed/interpreted in two different ways to give two separate meanings
An ambiguous figure is one which may appear to show a specific image when viewed for the first time
It is only when the viewer shifts their perspective of the image that they can see that another image is also depicted as well as the first one
Ambiguous Figure Diagram
Can you make out both an old woman looking down and a young woman turning her face away in this ambiguous image?
Misinterpreted depth cues
Human beings have learned to interpret depth cues using size constancy which in turn means that a person/object who is viewed from far away appears to be smaller than their actual size
Due to this interpretation of depth it is possible to ‘fool’ the brain into believing that differences in size occur when objects are placed at points which signal ‘far away’ i.e. higher up the image
The brain understands that parallel lines converge when viewed from afar but if two identically-sized objects are placed across those lines at different points, the brain sees the higher object as larger than the lower object
Misinterpreted Depth Cues Diagram
A variation of the Ponzo illusion to show misinterpreted depth cues. The red figures are the same size but the nearer figure appears smaller than the figure further away.
Fiction
Fiction is a term used to describe visual illusions that lead to the perception of a figure that is not actually present in the image as it has been drawn
The configuration of the lines and shapes of the image suggest another ‘fictional’ or hidden image within the original image
Fiction illusions tend to use illusory contours which trace the shape of another image submerged or hiding within the original image which are very difficult/almost impossible to ignore
Fiction Example Diagram
A visual illusion using ‘fiction’ - can you see a cube when in fact no cube has been drawn?
Size constancy
Size constancy is part of one of the visual illusions already covered on this page: misinterpreted depth cues
The human brain knows that objects/people far away in the visual field are not as small as they appear
Human beings understand that objects/people appear to be growing larger as they move towards the viewer - they are not getting bigger as they approach (which would be quite scary!)
Size constancy occurs when an observer is familiar with an object or person so that the object or person appears to have a constant size when viewed from various distances
Size Constancy Diagram
The leaning tower of Pisa is being kept upright by these tourists…or is it?
Worked Example
Here are some examples of questions you might be asked on this topic - for AO1 and AO2.
AO1: You need to demonstrate knowledge and understanding of key concepts, ideas, theories and research.
AO2: You need to apply your knowledge and understanding, usually referring to the ‘stem’ in order to do so (the stem is the example given before the question)
AO3: You need to analyse and evaluate key concepts, ideas, theories and research.
After each featured question there is a ‘model’ answer i.e. one which would achieve top marks in the exam.
AO1:
Question: Which one of the following visual illusions can be explained as the brain suggesting an image which is not there:
A Size constancy
B Fiction
C Ambiguity
D Misinterpreted depth cues [1]
Model answer:
The answer is B, Fiction
AO2:
Professor Duckrabbbit has conducted research into ambiguous visual illusions, asking 60 people whether they could see an old woman or a young woman in an ambiguous image. The results are shown in the table below:
Number of people who saw an old woman | 49 |
Number of people who saw a young woman | 11 |
Question: Calculate the percentage of people who saw an old woman. State your answer using two significant figures and show your workings. [3]
Model answer:
For 3 marks:
82% as this is the result of 49 x 100 divided by 60 = 81.66
To ‘two significant figures’ means that you should round up/down to give the two most meaningful figures in the score i.e. because 81.66 is over 81.5 then you round this up to 82
Examiner Tips and Tricks
Decimal places are not the same as significant figures - if you were asked to calculate ‘to two decimal places’ your answer, for the worked example above. would be 81.66% as this is two places after the decimal point.
This sort of Maths question is often asked in exams so make sure you’ve done your prep!
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