Starter
On the sheet, next to the image
write what type of Monocular
depth cues are shown.
Learning Objectives
• To understand and evaluate Gregory’s theory
of illusions.
• To understand the experimental method.
Success Criteria
• To present an evaluation of Gregory’s theory.
• To write a definition of the Muller-Lyer
experiment
Gregory’s Theory of Illusions
• To understand this theory
you need to make sure you
clearly understand
– Size Constancy.
– Monocular Depth Cues.
– Binocular Depth Cues.
Depth Cues
• REMEMBER: When we judge
an object to be far away, we
scale it up because distant
objects make small images on
the retina.
• Nearby objects are scaled
down because they make a
large image on the retina.
• This is how we maintain the
relative size of objects
regardless of their distance
from us.
Gregory’s Theory of Illusions
• Look back to Linear
perspective: What is it?
• Linear Perspective is a
depth cue.
• It is the apparent meeting
of a set of parallel lines in
the distance.
• Distortion illusions often
include angled lines.
Gregory’s Theory of Illusions
• Look at the radiating lines
of the Hering illusion to the
right.
• According to Gregory, we
interpret the patterns in
illusions as if they were
depth cues. We then apply
size constancy scaling and
distort our perception.
• Copy down the above point
into your book, Title:
Gregory’s theory.
Hering Illusion
• Stick the image
of the Hering
Illusion in your
book, in the
centre of the top
of your page,
giving it a title.
The Hering Illusion
• If the radiating lines act as
linear perspective cues then we
would use constancy scaling as if
the scene really had depth.
• The person who appear ‘furthest
away; would be scaled up so they
look bigger.
• The person who appears closest
would be scaled down, and look
smaller.
• This is exactly what we see.
• Now label this on your picture.
Gregory’s Theory of Illusions
• Basically: the
interpretation of depth
cues can cause us to
experience illusions, for
example the Ponzo
illusion (left) and Hering
illusion. (draw images)
The Muller-Lyer Illusion
• Investigate the Muller-Lyer
the
• illusion,
Write a answering
brief explanation
of
following
questions
in your
the Muller-lyer
illusion
books, in FULL sentences:
– Which depth cues does the
• Basically:
(draw image) linear
Muller-Lyer illusion play on?
perspective and constancy
– Explain
how these
cues
scaling
cause
us todepth
perceive
‘normally’
andthan
theshould
left work
line as
shorter
theexplain
righthow
line.they affect the
illusion.
Evaluating Gregory’s theory
• Prepare an argument
evaluating Gregory’s
theory.
• You must include both
sides of the argument
(for and against) and
include a conclusion.
Learning Objectives
• To understand and evaluate Gregory’s theory
of illusions.
• To understand the experimental method.
Success Criteria
• To present an evaluation of Gregory’s theory.
• To write a definition of the Muller-Lyer
experiment
Plenary
• Is this inside or outside the book,
explain how Gregory’s theory would
explain this distortion illusion.
It could be either, Gregory
would say that the angled
lines are interpreted as a
three dimensional figure. The
Angled lines could point
forwards or backwards.