did you know?

the ames room illusion
The Ames Room shows that we maintain shape constancy (of the
room) at the expense of size constancy.
The room is constructed in a trapezoidal shape, but made to
appear square when observed through a peephole. It is necessary
to prevent the use of both eyes, so that the strongest (binocular)
depth cues do not work. The rear wall actually runs from right to
left, away from the viewer. The far-left corner is twice as far from
the peephole as the far-right corner. To add to the illusion, the
ceiling is not parallel to the floor. It slopes upwards from right
to left, while the floor slopes downwards from right to left, so
that the height of the room at far left is double that at far right.
When a person walks from the left corner to the right corner, the
observer maintains shape constancy, but cannot also maintain size
constancy—so the person appears to be growing rapidly in size.
review 6.4
1 Describe the Ponzo Illusion.
2 Draw some of your own Müller-Lyer illusions and
try them out on your fellow students.
3 Do these visual clues apply to all humans? If not why not?
4 Explain why the Ames Room Illusion occurs.
5 Why does the person who is viewed through the peep-hole
appear to grow and shrink before your eyes?
6 Go to www.illusionworks.com. Create a PowerPoint
presentation of one other illusion and explain why this occurs.
7 M.C. Escher is a famous lithographic artist who created many
impossible figures. Perfom an Internet search for M.C. Escher
and prepare a presentation on his work.
6.5 investigate
Visual illusions
1 How do visual illusions occur?
2 There are two theories to explain the Müller-Lyer Illusion. Choose one
of these theories and briefly outline the key points.
3 How does the Ames Room work? Describe the construction and how
this influences what is seen when looking through the peephole.
4 Using the Internet, search ‘visual illusions’ and create a PowerPoint
presentation of the illusions you have found to share with the class.
Make sure that you define ‘Visual Illusions’ at the beginning of your
presentation and create at least 10 slides.
fig 6.26>> The Ames Room is not really rectangular,
but because of our lifetime of experience with
rectangular rooms, we perceive it to be bounded by
right-angles. In fact the ‘smaller’ person is simply twice
as far from the observer as the ‘larger’ person. The
shape of the room is shown below.
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