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