1. Visual Illusions

2. Don’t believe what you see
Visual perception directs our interactions with the environment
Before the brain can transform sensory information into meaningful perceptions, it must organise it into something that the brain can recognise
The brain must perceive things as distinct from their surroundings, see them as having a meaningful and constant form, and estimate how far they are away
This allows us to make sense of the world
BUT sometimes errors do occur…….

3. Is it all an illusion? https://www.youtube.com/watch?v=ynx6pb8 GVTA
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6. Don’t believe what you see…..
Visual Illusion:
A constant perceptual error in interpreting a real external stimulus
When we experience a visual illusion, the stimulus provides us with cues that mislead our perception
As a result, a mismatch between our perception and the reality of the actual stimulus occurs
Although perception of common stimuli is often described as unique, this is not the case with a visual illusion

9. With Visual Illusions…..
All individuals tend to be mislead in the same way
The stimulus can be misjudged by the:
Direction
Motion
Position
Length
Curvature

10. In contrast………
In hallucinations, people perceive (see, hear, taste smell) objects or events that have no external reality
That is hallucinations create stimuli that do not have a separate material existence
For example: A visual hallucination can generally be disproved by trying to experience the stimuli with another sense (trying to touch the wings of a giant hallucination of a butterfly)

12. Some things to think about…..
We know that illusions intentionally manipulate the cues we experienced in using to create a perception
But not all illusions can be explained to everyone’s satisfaction
What produces visual illusions include:
Size
Shape
Constancy
Habitual eye movements
Continuity
Perceptual habits

13. Which line is bigger?

14. Muller-Lyer Illusion
A visual illusion in which two lines of equal length- one capped with inward-pointing arrowheads, the other capped with outward- pointing arrowheads are perceived as being of different lengths

15. Muller-Lyer Illusion How is it created?
The illusion of differing lengths is created by the different figures at the end of each line.
How does it work?
It is based on our past experience of living in a three dimensional world where our buildings are basically square or rectangular shaped so that we have constantly been exposed to the edges and corners of buildings and rooms

16. Muller Lyer Illusion
It is believed that we see horizontal lines with the inward pointing arrowheads as being inside the corner of a room.
Compared to the outward pointing arrowheads representing the corner of the outer wall of a building
Because of the lines cast images of the same length the more “distant” line is perceived as being longer
This is also known as apparent distance hypothesis(Gregory & Wallace 1963), whereby an apparently more distant object that has the same size retinal image as an apparently nearer image will be perceived as the larger

17. Re-create the Muller Lyer Illusion
Students are to complete 2.12 of the activity manual
You are to complete all sections of this activity.
Note: that if you have made the apparatus before the end of the class ask your teacher if you can be excused to test this illusion on someone form another class. Students should only ask for permission in other classes if students are working individually

18. As a Class describe what you see and how this is an optical illusion

19. Ames Room Illusion Explained
Watch the following clip
Write down some key points
Go through key notes at the end of the clip as a class t8

20. Ames Room Illusion
An illusion caused by an intentionally distorted room, viewed through a peephole, disrupting perceptual constancies and misleading the viewer to perceive people changing size (shrinking or growing) as they cross the floor from one corner of the room to the corner directly opposite.

21. Ames Room Illusion The illusion was designed by Adelbert Ames (1934)
Besides now realising that the Ames Room is created by distorting the shape of regular sized room and using windows and flooring to match this shape
People who view the Ames room are asked to look through a peephole
This stops our binocular depth cues providing us with information about the depth and the distance of objects in the environment.

22. Ames Room Illusion
This explanation can be linked back to the “apparent distance hypothesis (Gregory & Wallace 1963).
If two objects (people) of the same size are introduced into the room, the object at the left hand corner comes in further away from the viewer then the object on the right hand side.
Yet because of the rooms distortion, both objects seem to be the same distance from the viewer

23. Which green line is longer in length?

24. Ponzo Illusion
An illusion where two horizontal lines of equal length are drawn inside two converging lines, but the line in the narrow section of the converging lines in perceived to be as longer dg 08

25. Ponzo Illusion Explained
This illusion is created by again by the apparent- distance hypothesis
In the image of the converging lines remind us of railway tracks we would see in our real 3D world.
The Ponzo illusion is a man made 2D drawing, but we use the depth perception principles we use in our 3D world to try and estimate the length of the horizontal lines
Our experience of using depth cues influences our perception of the top line as being further away because that is what we know from our “real life” experiences

26. Student Activities Activity 2.11- Build your own Ames Room
Check your understanding 3.9 questions 1-5 finish for homework