Transcript 2320Lecture12.pptx

Midterm 2 is March 11th and 12th
Read Land article for March 5th
Illusions related to depth
perception
• Misperceptions of size
• Misperceptions of location
Muller - Lyer Illusion
Muller-Lyer Illusion
• What theory does Gregory take up?
Muller-Lyer Illusion
• What theory does Gregory take up?
– Thiery / Woodworth : Muller-Lyer figure
“suggests perspective”
Muller-Lyer Illusion
• What theory does Gregory take up?
– Thiery / Woodworth : Muller-Lyer figure
“suggests perspective”
– Is there something about the presence of
pictorial depth cues in an image that
distorts size?
Depth Cues and Size
Distortion
The Ponzo Illusion:
Depth Cues and Size
Distortion
The Ponzo Illusion:
Depth Cues and Size
Distortion
• The illusion of depth in an image seems
to distort the perception of size in the
image
• This is due to misapplication of Size Constancy
Pictures are Weird
• What does Gregory find paradoxical
about pictures?
Pictures are Weird
• What does Gregory find paradoxical
about pictures?
Pictures convey depth yet also appear flat
Why?
The Apparatus
• When you view a picture there are
some depth cues telling you to perceive
depth, but other cues telling you that the
image is on a flat surface
• …the surface matters!
Pictorial Depth Cues
• Retinal image size
Pictorial Depth Cues
• Retinal image size
The Apparatus
• What does he do to remove the paradox
so that the Muller-Lyer figure no longer
looks flat?
• Remove the background surface
The Apparatus
Removing the Background
• With background removed, Muller-Lyer
figure actually looks 3D
• What prediction can you make about
how the perceived size and the
perceived distance of the center line are
related?
Removing the Background
• With background removed, Muller-Lyer
figure actually looks 3D
• What prediction can you make about
how the perceived size and the
perceived distance of the center line are
related?
When the centre line appears close,it should also appear small
When the centre line appears far, it should also appear large
Removing the Background
• How did Gregory test that?
The Apparatus
Removing the Background
• Perceived size and perceived distance are tightly
related
• inward arrowheads make line look closer/ outward
arrowheads make line look farther
Misperception of Depth Drives Other Illusions
• Ames Room view from
above
Now on to Magic Eye
Stereograms
Stereograms
Divider
Left Eye
Right Eye
•Right eye sees face to the
left; left eye sees face to the
right therefore:
faces present crossed
disparity to the brain
•Face appears in front of
square
Autostereograms
• Optically separate images aren’t
needed
Autostereograms
• Optically separate images aren’t
needed
• WARNING! Tricky stuff coming in the
next slides
Autostereograms
• Optically separate images aren’t
needed
• WARNING! Tricky stuff coming in the
next slides
• Keep the definitions of convergence and
disparity separate.
Autostereograms
What would happen if you remove the
divider of a stereoscope?
•Convergence is on a point
at the same distance as the
images
•Boxes and faces are on the
horopter
•How many boxes would you
see?
boxes and faces are on the horopter
Autostereograms
Now cross your eyes:
•right-eye line of sight crosses lefteye line of sight in front of image
(crossed convergence)
•each retina is now pointed at the
opposite box
•How many boxes would you see?
crossed convergence
•What would happen to the face?
Autostereograms
•There would be three boxes
•middle box: right eye sees face
shifted to right; left eye sees face
shifted to left therefore:
uncrossed disparity
crossed convergence
•Face in the middle box appears
behind square
Autostereograms
• What would happen if you moved the
faces within the box?
• What would happen if you viewed this
with uncrossed convergence?