Visual and Auditory Illusions

Ambiguous Figures

Rabbit / Duck

Young Woman/Old Woman 
  

One for academics: book or cleavage?

How many circles can you see in this picture? Focus on the cross and they'll start to appear!

  
 

 

Notice that when one triangle seems to point in a certain direction so do all those around it. 
  
  

Saw-Tooth Illusion 

  

An illusion similar to the Necker Cube. 
  

You may wish to read Fiona Macpherson (2006) "Ambiguous Figures and the Content of Experience", Nous, 40(1): 82-117, about experiences of ambiguous figures and their philosophical significance.

Shape Illusions  

   Muller-Lyer 
  
 
 
  Zollner Illusion 
  

 
  
Ebbinghaus Illusion

 

Impossible Figures 

  
Penrose Triangle 
  

  
Impossible Figure by Oscar Reutersvard 

 
  
  
Impossible Figure by Oscar Reutersvard 

  
 
Impossible Figure by Oscar Reutersvard

 
  Impossible Figure by Oscar Reutersvard 

  
  
 Impossible Figure by Oscar Reutersvard 

Many of Escher's pictures depict impossible figures, such as Belvedere.

These photos show a piece of wood that when looked at (or photographed) from the right angle appear to be of an impossible triangle.

These pictures show a sculpture in East Perth, Australia that, from the right angle, looks to be an impossible triangle.

To learn more about impossible figures you may wish to read Fiona Macpherson (forthcoming, 2009) "Impossible Figures", Sage Encyclopedia of Perception, edited by E. Bruce Goldstein, Thousand Oaks, CA: Sage Publications, Inc.

The Leaning Tower Illusion

© Kingdom, Yoonessi and Gheorghiu
(Winner of the 2007 Best Visual Illusion of the Year Contest)
The two images of the tower are identical although the one placed on the right looks to be leaning more.

Colour Contrast Effects 

The two central grey squares are the same colour. 

  
 

The two central green squares are the same colour. 

  

  
The two central pinkish squares are the same colour. 

 

The red colour is the same across this band. 

In this picture on the left the shades of colour that look to be different shades of blue and green are in fact the same shade. They look to be so different on account of the shades that surround them. You can see this clearly when all colours except the blue and the green have been blacked out, as is the case in the picture on the right.

The square marked A and the square marked B are the same shade of grey.
(Really! You can print out the image and put the squares physically together to check.)
  
  

Neon Colour Spreading and Similar Black and White Effects 

  
 Hermann Grid 

 
Scintillating Grid

 

Apparant Motion Effects

Please stop looking at the images if they cause you to feel dizzy or unwell.
These images were created by Akiyoshi Kitaoka.
The images are stationary and only appear to move.

"Boats" - The boats appear to move in a clockwise direction.

"Rollers" - the rollers appear to rotate in different directions.

"Rotating Snakes" - the circles appear to rotate in different directions.

Figures for Producing After-Images

 
By fixating on the bottom right corner of the yellow rectangle for 30 seconds or so and then looking at a white surface and blinking a few times, one can have an after-image of  the American flag in the correct colours.

An effect similar to after-images in certain respects, but perhaps even more vivid, can be got by first staring at the picture below and fixating on the centre spot for 30 seconds. Afterwards, roll the mouse over the picture and keep fixating on the centre spot (this is important). You seem to see the picture in colour even though it is really in black and white, as you can easily verify. These images are taken from John Sadowski and on one of his webapages he provides a tutorial on how to make such pictures.

Motion After-Effects

Fixate on the centre of the rotating spiral for 60 seconds and then look at a non-moving surface - preferably one with a pattern on it, such as the patter beside it. Note the illusion of movement when looking at the stationary pattern.

To see and read about the waterfall illusion and its connection with Scotland click here.

To see another demonstration of a motion after-effect similar to the waterfall illusion click here.

Change-Blindness

To find out about change-blindness and to test your own vision click here.

The Barber Pole Auditory Illusion
(also called Shepard Scales)

The tones below sound as if they are ever increasing or decreasing in pitch. However, this is only an illusion. The same sequence of notes, an octave, is simply being played over and over again. The illusion is an auditory equivalent of the apparently ever rising lines on a rotating barber's pole or the steps on Escher's lithograph 'Ascending and Descending'. The illusion is created because each note is composed of many pitch frequencies that are carefully crafted to create ambiguity and hence this illusion. See Shepard, R. N. (1964) "Circularity in Judgments of Relative Pitch", The Journal of the Acoustical Society of America, Vol. 36, No. 12, pp. 2346-2353.

Shepard tone rising Shepard tone falling

Echer's 'Ascending and Descending'