Define a visual illusion .

A visual illusion is a perception that does not match physical reality — what we see conflicts with what is actually there, because the brain has misinterpreted the visual information.

Why do visual illusions happen?

The perceptual system applies its usual rules — depth cues, constancies and past experience — to an image where those rules do not fit , so it draws the wrong conclusion .

Ambiguity occurs when a single image can be interpreted in two different ways and contains equal evidence for both , so the brain cannot settle on one interpretation.

Give two examples of ambiguous visual illusions.

Rubin’s vase and the Necker cube .

True or False? In an ambiguous image, the viewer can see both interpretations at the same time.

False. Perception flips between the two — the viewer can see one or the other , but not both at once .

In an ambiguous figure, the second interpretation appears when the viewer shifts their .

In an ambiguous figure, the second interpretation appears when the viewer shifts their focus .

Why do misinterpreted depth cue illusions occur?

The brain applies depth cues to a flat image as if it were a real 3-D scene , and then misapplies size constancy .

In the Ponzo illusion , what do the two converging lines act as?

They act as a depth cue — linear perspective . The brain reads the narrowing lines as parallel lines receding into the distance , like railway tracks.

In the Ponzo illusion , why is the upper line perceived as longer?

The brain reasons that the upper line is further away but produces the same-sized retinal image as the lower one — so it must actually be bigger .

True or False? In the Ponzo illusion , the depth cue itself is faulty .

False. The depth cue is genuine and the rule is normally correct . The illusion happens because the cue is misinterpreted in a 2-D image where there is no real depth.

Define fiction , as an explanation for visual illusions.

Fiction is a type of visual illusion in which we perceive a figure that is not actually present — the brain creates something that has not been drawn .

How does the Kanizsa triangle create its illusion?

Three black circles with wedges cut out and three V shapes are arranged so that the brain perceives a white triangle lying over them — with clear edges, often appearing brighter than the background — yet no triangle has been drawn .

Why does the brain create a figure in a fiction illusion?

Because the arrangement of shapes is most easily explained by assuming another object is sitting on top of them , blocking part of them from view — so the brain ‘fills in’ that object .

Define illusory contours .

Illusory contours are edges we perceive even though there is no line or change in colour on the page.

Define size constancy .

Size constancy is the tendency to perceive an object as staying the same size even though the image it projects onto the retina changes as its distance from us changes.

How does the brain achieve size constancy ?

It combines the size of the retinal image with depth cues . If the image is small but the cues say ‘ far away ’, the brain scales the perceived size up to compensate.

Name two illusions in which the brain misapplies size constancy .

The Ponzo illusion and the Müller-Lyer illusion. In both, misleading depth cues make the brain apply size constancy where it is not needed , so identical objects appear to be different sizes .

How does the Ames room create its illusion?

The room’s odd shape removes the normal depth cues , so the brain assumes both people are the same distance away and perceives one as a giant and one as tiny .

Which explanation accounts for the Ponzo illusion ?

The Ponzo illusion is a misinterpreted depth cue , in which size constancy is then misapplied.

In the Ponzo illusion , why is the upper line perceived as longer?

It sits where the ‘tracks’ are narrowest , so the brain assumes it is further away . As it produces the same-sized retinal image as the lower line, the brain concludes it must really be bigger .

How did Gregory explain the Müller-Lyer illusion ?

Using our experience of a built environment : the outward-fin line resembles the inside corner of a room (a far edge), the inward-fin line the outside corner of a building (a near edge). The brain assumes the outward-fin line is further away and scales it up , so it appears longer .

True or False? In the Müller-Lyer illusion , the two vertical lines really are different lengths.

False. The two lines are identical — only the fins differ.

Which explanation accounts for Rubin’s vase and the Necker cube ?

Both are examples of ambiguity .

What can be perceived in Rubin’s vase ?

Either a vase — the central shape — or two faces in profile looking at each other, which are the outer shapes.

In Rubin’s vase the brain cannot decide which part of the image is the figure and which is the .

In Rubin’s vase the brain cannot decide which part of the image is the figure and which is the ground .

When perception flips in Rubin’s vase , what actually changes?

Nothing about the image changes — only the brain’s interpretation of it.

Why can the Necker cube be interpreted in two ways?

It is a wire-frame drawing with no shading, no hidden lines and no depth cues to show which face is nearer, so it is equally consistent with two different 3-D cubes .

What are the two ways of seeing the Necker cube ?

The lower-left square as the front face, so the cube is viewed from above ; or the upper-right square as the front face, so the cube is viewed from below .

Define the Ames Room .

The Ames Room is built as a trapezoid : the back wall slants away so that one back corner is much further from the viewer than the other, with the floor and ceiling sloping to match.

The Ames Room is viewed through a peephole with eye, which removes the binocular depth cues.

The Ames Room is viewed through a peephole with one eye, which removes the binocular depth cues.

Why does one person in the Ames Room appear to be a giant and the other tiny?

The brain assumes both are the same distance away , so it does not apply size constancy to the much smaller retinal image of the person in the far corner. If they swap places , they appear to change size .

How is the Kanizsa triangle constructed, and what does the brain do?

Three black circles with wedges cut out and three V shapes are arranged so the gaps line up . The brain decides the simplest explanation is a white triangle lying on top , so it ‘fills it in’ .

True or False? The Kanizsa triangle is an example of ambiguity .

False. It is an example of fiction — we perceive a figure that has not been drawn .

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Visual Illusions (AQA GCSE Psychology): Flashcards

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FrontExplanations for Visual Illusions
Define a visual illusion.

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Cards in this collection (34)

Define a visual illusion.
A visual illusion is a perception that does not match physical reality — what we see conflicts with what is actually there, because the brain has misinterpreted the visual information.
Why do visual illusions happen?
The perceptual system applies its usual rules — depth cues, constancies and past experience — to an image where those rules do not fit, so it draws the wrong conclusion.
Define ambiguity.
Ambiguity occurs when a single image can be interpreted in two different ways and contains equal evidence for both, so the brain cannot settle on one interpretation.
Give two examples of ambiguous visual illusions.
Rubin’s vase and the Necker cube.
True or False?
In an ambiguous image, the viewer can see both interpretations at the same time.
False.
Perception flips between the two — the viewer can see one or the other, but not both at once.
In an ambiguous figure, the second interpretation appears when the viewer shifts their .
In an ambiguous figure, the second interpretation appears when the viewer shifts their focus.
Why do misinterpreted depth cue illusions occur?
The brain applies depth cues to a flat image as if it were a real 3-D scene, and then misapplies size constancy.
In the Ponzo illusion, what do the two converging lines act as?
They act as a depth cue — linear perspective. The brain reads the narrowing lines as parallel lines receding into the distance, like railway tracks.
In the Ponzo illusion, why is the upper line perceived as longer?
The brain reasons that the upper line is further away but produces the same-sized retinal image as the lower one — so it must actually be bigger.
True or False?
In the Ponzo illusion, the depth cue itself is faulty.
False.
The depth cue is genuine and the rule is normally correct. The illusion happens because the cue is misinterpreted in a 2-D image where there is no real depth.
Define fiction, as an explanation for visual illusions.
Fiction is a type of visual illusion in which we perceive a figure that is not actually present — the brain creates something that has not been drawn.
Give an example of a fiction illusion.
The Kanizsa triangle.
How does the Kanizsa triangle create its illusion?
Three black circles with wedges cut out and three V shapes are arranged so that the brain perceives a white triangle lying over them — with clear edges, often appearing brighter than the background — yet no triangle has been drawn.
Why does the brain create a figure in a fiction illusion?
Because the arrangement of shapes is most easily explained by assuming another object is sitting on top of them, blocking part of them from view — so the brain ‘fills in’ that object.
Define illusory contours.
Illusory contours are edges we perceive even though there is no line or change in colour on the page.
Define size constancy.
Size constancy is the tendency to perceive an object as staying the same size even though the image it projects onto the retina changes as its distance from us changes.
How does the brain achieve size constancy?
It combines the size of the retinal image with depth cues. If the image is small but the cues say ‘far away’, the brain scales the perceived size up to compensate.
Name two illusions in which the brain misapplies size constancy.
The Ponzo illusion and the Müller-Lyer illusion. In both, misleading depth cues make the brain apply size constancy where it is not needed, so identical objects appear to be different sizes.
How does the Ames room create its illusion?
The room’s odd shape removes the normal depth cues, so the brain assumes both people are the same distance away and perceives one as a giant and one as tiny.
Which explanation accounts for the Ponzo illusion?
The Ponzo illusion is a misinterpreted depth cue, in which size constancy is then misapplied.
In the Ponzo illusion, why is the upper line perceived as longer?
It sits where the ‘tracks’ are narrowest, so the brain assumes it is further away. As it produces the same-sized retinal image as the lower line, the brain concludes it must really be bigger.
How did Gregory explain the Müller-Lyer illusion?
Using our experience of a built environment: the outward-fin line resembles the inside corner of a room (a far edge), the inward-fin line the outside corner of a building (a near edge). The brain assumes the outward-fin line is further away and scales it up, so it appears longer.
True or False?
In the Müller-Lyer illusion, the two vertical lines really are different lengths.
False.
The two lines are identical — only the fins differ.
Which explanation accounts for Rubin’s vase and the Necker cube?
Both are examples of ambiguity.
What can be perceived in Rubin’s vase?
Either a vase — the central shape — or two faces in profile looking at each other, which are the outer shapes.
In Rubin’s vase the brain cannot decide which part of the image is the figure and which is the .
In Rubin’s vase the brain cannot decide which part of the image is the figure and which is the ground.
When perception flips in Rubin’s vase, what actually changes?
Nothing about the image changes — only the brain’s interpretation of it.
Why can the Necker cube be interpreted in two ways?
It is a wire-frame drawing with no shading, no hidden lines and no depth cues to show which face is nearer, so it is equally consistent with two different 3-D cubes.
What are the two ways of seeing the Necker cube?
The lower-left square as the front face, so the cube is viewed from above; or the upper-right square as the front face, so the cube is viewed from below.
Define the Ames Room.
The Ames Room is built as a trapezoid: the back wall slants away so that one back corner is much further from the viewer than the other, with the floor and ceiling sloping to match.
The Ames Room is viewed through a peephole with eye, which removes the binocular depth cues.
The Ames Room is viewed through a peephole with one eye, which removes the binocular depth cues.
Why does one person in the Ames Room appear to be a giant and the other tiny?
The brain assumes both are the same distance away, so it does not apply size constancy to the much smaller retinal image of the person in the far corner. If they swap places, they appear to change size.
How is the Kanizsa triangle constructed, and what does the brain do?
Three black circles with wedges cut out and three V shapes are arranged so the gaps line up. The brain decides the simplest explanation is a white triangle lying on top, so it ‘fills it in’.
True or False?
The Kanizsa triangle is an example of ambiguity.
False.
It is an example of fiction — we perceive a figure that has not been drawn.

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