Reading Assignment
• Read chapter by Pinker for Wed. of next week.
Shape from Shading
Investigating Perception
• Perception is mysterious
• So how do we go about understanding how it works?
Investigating Perception
• What is Science?
Investigating Perception
• What is Science?
• Science is a method for understanding how nature works
Science
• What isn’t Science?
• Headlines on www.reuters.com Science Page:
– Juan Strengthens Into Hurricane, Misses Bermuda
Science
• What isn’t Science?
• Headlines on www.reuters.com Science Page:
– Juan Strengthens Into Hurricane, Misses Bermuda
– Japan's Mt Fuji Shows Subsidence, No Eruption Danger
Science
• What isn’t Science?
• Headlines on www.reuters.com Science Page:
– Juan Strengthens Into Hurricane, Misses Bermuda
– Japan's Mt Fuji Shows Subsidence, No Eruption Danger
– Official Report: French Heat-Wave Death Toll 15,000
Science
• What isn’t Science?
• Headlines on www.reuters.com Science Page:
– Juan Strengthens Into Hurricane, Misses Bermuda
– Japan's Mt Fuji Shows Subsidence, No Eruption Danger
– Official Report: French Heat-Wave Death Toll 15,000
– Man Questioned in Australia Over Mutilated Whale Carcass
Science
• Science is like a set of procedures:
Identify a question
Science
• Science is like a set of procedures:
Identify a question
Make a Hypothesis
Science
• Science is like a set of procedures:
Identify a question
Make a Hypothesis
Make a Prediction
Science
• Science is like a set of procedures:
Identify a question
Make a Hypothesis
Make a Prediction
Test It
Science
• Science is like a set of procedures:
Identify a question
Make a Hypothesis
Make a Prediction
Test ItPrediction holds
Prediction Fails
Example: The horizontal-vertical illusion
Example: The horizontal-vertical illusion
• Question:
• Hypothesis:
• Prediction:
• Test:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis:
• Prediction:
• Test:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction:
• Test:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction: Stabilized image should eliminate the illusion
• Test:
Example: The horizontal-vertical illusion
• Question: Why does the vertical line seem longer?
• Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently
• Prediction: Stabilized image should eliminate the illusion
• Test: Illusion is still present in afterimage!
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”
– implicit is that the brain shrinks things that are perceived as near and expands things that are perceived as far away
Size Constancy
• Brain shrinks things that are near and expands things that are far
The Ponzo Illusion:
Size Constancy
• The lines of perspective in the Ponzo Illusion make the top line appear farther away
• Why isn’t it this simple for the Muller-Lyer Illusion ?
Size Constancy
• The lines of perspective in the Ponzo Illusion make the top line appear farther away
• Why isn’t it this simple for the Muller-Lyer Illusion ?
– Because the Muller-Lyer figure looks flat !
Paradox of Pictures
• What does Gregory find so paradoxical about pictures?
QuickTime™ and aH.263 decompressorare needed to see this picture.
Paradox of Pictures
• What does Gregory find so paradoxical about pictures?
• What does he do to remove the paradox so that the Muller-Lyer figure no longer looks flat?
Paradox of Pictures
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?
• How did Gregory test that?
Removing the Background
• Perceived size and perceived distance are tightly related
Size Constancy in Motion
• What does Gregory wonder about size constancy and motion?
• How does he test that?
Size Constancy in Motion
• Gregory finds that motion does invoke size constancy in certain cases:
Size Constancy in Motion
• Gregory finds that motion does invoke size constancy in certain cases:– only when observer is accelerating
Science Works at Different Scales
• What’s the “Big Picture” theory, amid the more specific hypothesis? (hint: look in the first paragraph)
Science Works at Different Scales
• What’s the “Big Picture” theory, amid the more specific hypothesis? (hint: look in the first paragraph)
• That illusions occur because of perceptual mechanisms evolved to handle vision under normal circumstances
Science Works at Different Scales
• What is Gregory’s theory about how the brain accomplishes this?
Science Works at Different Scales
• What is Gregory’s theory about how the brain accomplishes this?
“it is as though the brain entertains alternative hypotheses of what object the eye’s image may be representing”
Next Time
• More on seeing in 3D
• Read chapter by Pinker for Wed. next week