Visual illusions Flashcards
What are visual illusions?
When what we see does not correspond to what is physically present in the world
When what we see does not correspond to what is physically present in the world
This is known as…?
Visual illusions
What do illusions tell us about normal vision?
Illusions of the senses tell us the truth about perception
Illusions of the senses tell us the truth about perception
Who said this?
Purkinje
What are the 4 classifications of visual illusions?
1) Distortions
2) Ambiguous figures
3) Paradoxical figures
4) Fictions
Who proposed the 4 classifications of visual illusions?
Gregory
Give 3 examples of distortions.
- Muller-Lyer experiment
- Ponzo
- Poggendorff
Give 2 examples of ambiguous figures
- Necker cube
- Rubin vase
Give an example of paradoxical figures
Penrose impossible objects
Give an example of fictions
Kanizsa triangle
Describe the muller-lyer distortion illusion?
- Red and Blue straight lines of equal length
- Blue line with arrow head pointing downwards appears longer than red line with arrow pointing upwards
Why does the muller-lyer illusion occur?
Gregory (1966) explained Muller-Lyer illusion on basis of misapplied size constancy.
Fins on blue line make this look like part of the inside corner of a room.
Fins on red line make this look like part of the outside corner of a room.
Inside corner tend to look further away thus size- distance scaling causes this line to look longer.
Illusions have often been considered to be a…… phenomenon.
Negative
lllusion, itself, from Latin root word, “illudere” which means …….. (Coren, 1978).
“To mock”
What is perception?
Perception is the brain’s search for the best interpretation of the data that is being presented.
The brain’s search for the best interpretation of the data that is being presented.
This is known as…?
Perception
True or False?
Sometimes the “perceptual hypothesis” is incorrect and an illusion results (Gregory, 1997).
True
“The study of what are called illusions of the senses is a very prominent part of the senses; for just those cases which are not in accordance with reality are particularly instructive for the discovering the laws of those means and processes by which normal perception originates”
Who said this?
Helmholtz
Optical illusions mock our trust in our senses
What does this suggest?
Suggest that the eye is not a passive camera; perception is an active process that takes place in the brain.
We see lines with inward-facing arrows as outside corners therefore they appear….?
a. Closer
b. Further
a. Closer
We see lines with outward-facing arrows as inside corners therefore they appear….?
a. Closer
b. Further
b. Further
We see lines with outward-facing arrows as inside corners therefore they appear further away.
The brain perceives this as…?
a. Smaller
b. Larger
b. Larger
Is the muller-lyer distortion illusion cross-cultural?
No
Who is much less prone to the muller-lyer distortion illusion?
People who live in a natural environment i.e. without man-made rectangular building
The illusion of size is known as…?
Ponzo illusion
Which distortion is this?
See inward-facing arrows as outside corners looming towards us therefore closer. Outward arrows look further away but
because they are the same size brain thinks it is larger.
Muller-Lyer
Which distortion is this?
Two lines converge towards the ‘vanishing’ point – giving the impression that the line nearer the vanishing point is further away – thus appears larger
Ponzo illusion
Describe the Ponzo illusion
- Two lines converge towards the ‘vanishing’ point
- It gives the impression that the line nearer the vanishing point is further away
- Thus it appears larger
Why does the Ponzo illusion occur?
The effect of the Ponzo illusion is often attributed to linear perspective
The upper line looks longer because we interpret the converging sides as parallel lines receding into the distance
In this context, we interpret the upper line as though it were farther away, so we see it as longer.
Which distortion is this?
The setup for this illusion is a straight line that passes behind a rectangle.
Actual angle dilation: Our brains make small angles appear larger than they actually are (angle theory).
Poggendorff
Describe the Poggendorff distortion illusion
The setup for this illusion is a straight line that passes behind a rectangle.
Actual angle dilation: Our brains make small angles appear larger than they actually are (angle theory).
When the angle between the line and the box increases, the misperception of lining up the two lines decreases.
In the Poggendorff distortion illusion, when the angle between the line and the box increases, the misperception of lining up the two lines ….?
Decreases
Which distortion illusion is this?
The straight lines in the illusion appear to bow outwards in the centre. You may interpret the radiating lines in terms of depth, seeing the central spot as being further away than the edges.
Thus you believe that the heavy black lines must also be further away in the centre.
Herring
The Herring illusion is also similar to 2 other illusions. What are they?
- Wundt illusion
- Titchener illusion
Describe the Herring distortion illusion
- The straight lines in the illusion appear to bow out in the centre
- You may interpret the radiating lines in terms of depth, seeing the central spot as being further away than the edges.
- Thus you believe that the heavy black lines must also be further away in the centre.
Why does the Herring distortion illusion occur?
Because the heavy black lines are the same thickness at the centre as at the edges but are further away, your brain thinks they must be more widely spaced at the centre.
What is the Wundth illusion?
Equal but opposite effect to Hering
Equal but the opposite effect to Hering
What distortion illusion is this?
Wundth illusion
What is the Titchner (Ebbinghaus) Illusion?
Brain over emphasizes size differences in grouping and separating objects
Brain over emphasizes size differences in grouping and separating objects
What distortion illusion is this?
Titchner (Ebbinghaus) Illusion
What do the distortion illusions of Muller-Lyer, Ponzo, Poggendoff, Wundt and Titchner tell us about perception?
Tells us that perception involves complex depth and size calculations that the brain is doing (correctly) all the time
The brain experiences an unfair situation of (2D/3D) drawings
2D
True or False?
There is an “unfair” situation for the brain of 3D drawings which are (or are interpreted as) 2D representations
False
There is an “unfair” situation for the brain of 2D drawings which are (or are interpreted as) 3D representations
Describe the Necker cube ambiguous illusion
The cube appears to flip so that the red dot is sometimes inside, and sometimes outside the cube.
When you look at this 2D drawing, your brain automatically visualises it as a 3-D cube. But this drawing does not give enough information for your visual system to know exactly which face of the cube is at the front.
Which ambiguous illusion is this?
The cube appears to flip so that the red dot is sometimes inside, and sometimes outside the cube.
When you look at this 2D drawing, your brain automatically visualises it as a 3-D cube. But this drawing does not give enough information for your visual system to know exactly which face of the cube is at the front.
Necker cube
Why does the Necker cube ambiguous illusion occur?
Your visual system has a hypothesis that the cube is at one orientation, then for some reason suddenly another hypothesis is favoured and the cube flips.
Describe the Rubin vase ambiguous illusion
When you either see a vase or two faces facing each other because the drawing does not give enough information for your visual system to know exactly whether it is a vase or two faces
Which ambiguous illusion is this?
When you either see a vase or two faces facing each other because the drawing does not give enough information for your visual system to know exactly whether it is a vase or two faces
Rubin vase
What are paradoxical figures?
The triangle on your screen is 2D, yet your brain
automatically tries to picture it as a 3D object.
Which visual illusion is this?
The triangle on your screen is 2D, yet your brain
automatically tries to picture it as a 3D object.
Paradoxical figures
How do Paradoxical figure illusions occur?
- Most people’s visual systems make the false assumption that the triangle is in one plane
- It is not a triangle at all – in fact, one part of the ‘triangle’ actually sticks up into the air.
What do paradoxical figure illusions tell us about perception?
How our brains automatically try to make us see in 3D
After all, the image on your retina is flat, yet everything you see has depth.
Describe the Kanizsa triangle fiction illusion
When you see an outline of a triangle between 3 ‘pacman’ circles even though the outline is not physically drawn
Which illusion is this?
When you see an outline of a triangle between 3 ‘pacman’ circles even though the outline is not physically drawn
Kanizsa triangle
The unreal shapes in the Kanizsa triangle illusion are called ………… Schumann (1904)
Subjective contours
How does the Kanizsa triangle illusion occur?
- Usually, a near object looks brighter than a more distant one of the same colour
- Your brain interprets the illusory triangles as being closer than the circles
- This means you see them as being brighter than the things that you think are further away (the background)
The Ames room was based on who’s idea in the late 19th century?
Helmholtz
Describe the Ames room illusion
1) Two illusions
2) Firstly the room appears cubic when viewed monocularly from a special point, its true shape is trapezoidal
3) Secondly objects and people appear to grow or shrink as they travel from one corner of the room to the other
4) Causes two people of equal sizes to appear very different.
Which illusion is this?
1) Two illusions
2) Firstly the room appears cubic when viewed monocularly from a special point, its true shape is trapezoidal
3) Secondly objects and people appear to grow or shrink as they travel from one corner of the room to the other
4) Causes two people of equal sizes to appear very different.
Ames room
How does the Ames room illusion occur?
1) Individual standing on the left of the room has a much smaller visual angle than the individual on the right
2) We think that we are looking at a normal rectangular room, & our perception is that both individuals are at the same distance away
3) Given this assumption the individual with the larger visual angle appears taller
What are 2 unresolved and new visual illusions?
1) Moon illusion (size)
2) Ouchi illusion & Peripheral drift illusion (motion)
Describe the moon illusion
When moon is on the horizon it appears much larger than when it is directly overhead, at its zenith
Which illusion is this?
When the moon is on the horizon it appears much larger than when it is directly overhead, at its zenith
Moon illusion
How does the moon illusion occur, according to Kaufman and Rock (1962)?
1) Apparent distance theory
2) We see the sky as a flattened dome. It appears closer over our heads than near the horizon
3) The horizon moon looks larger because it appears further away.
What is forced interpretation?
Seeing things from only one perspective
Seeing things from only one perspective
This is known as…?
Forced interpretation
Describe the Ouchi illusion
The central disk seems to float above the checkered background when moving the eyes around while viewing the figure
Which illusion is this?
The central disk seems to float above the checkered background when moving the eyes around while viewing the figure
Ouchi illusion
How do Ouchi illusions occur?
Thought to be caused by eye movements.
1) Our eyes always move slightly even when we are fixated on something
2) Brain cancels out the movement/compensates for the movement
3) In the Ouchi Illusion the pattern is such that the compensation is not necessary/different effect on different orientations, therefore the brain interprets that it must be moving
How come we perceive Ouchi illusions in items that are in our peripheral vision and not items in our direct vision?
Peripheral drift
1) Even when fixated, our eyes make very small random movements
2) These are compensated for at the fovea, but not at the periphery
3) Normally not a problem but in special situations can cause the perception of movement
True or False?
Visual illusions are a phenomenon that points to the inadequacies of our visual and perceptual systems
False
Visual illusions are a phenomenon that allows us to become consciously aware of the intricate process that is always going on unconsciously
The visual world that we perceive is always being created by ……. and interpretations out of the sensory data it is receiving.
An active mind continuously searching for patterns
Why does the Ponzo illusion not work if the lines converge at the bottom rather than at the top?
When the lines converge at the bottom of the picture there is little sense to the perspective.
Apparent depth is diminished and the two lines appear essentially the same length.
