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Physiological Depth Cues

– Convergence

Physiological Depth Cues

– Convergence– small angle of convergence = far away– large angle of convergence = near

– What two sensory systems is the brain integrating?

– What happens to images closer or farther away from fixation point?

Physiological Depth Cues

– Convergence and accommodation are reflexively linked

Under what circumstances might this be a problem?

Motion Depth Cues

– Motion1. Parallax

Motion Depth Cues

– Parallax

Motion Depth Cues

– Parallax– points at different locations

in the visual field move at different speeds depending on their distance from fixation

Motion Depth Cues

– Parallax

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More Depth Cues

• Pictorial Depth Cues

• Physiological Depth Cues

• Motion Parallax

• Stereoscopic Depth Cues

Binocular Disparity

• Your eyes have a different image on each retina– hold pen at arms length and fixate the spot

– how many pens do you see?– which pen matches which eye?

Binocular Disparity

• Your eyes have a different image on each retina– now fixate the pen

– how many spots do you see?– which spot matches which eye?

Binocular Disparity

• Binocular disparity is the difference between the two images

Binocular Disparity

• Binocular disparity is the difference between the two images

• Disparity depends on where the object is relative to the fixation point:– objects closer than fixation project images

that “cross”– objects farther than fixation project images

that do not “cross”

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:

Example: The horizontal-vertical illusion

• Question: Why does the vertical line seem longer?

• Hypothesis:

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:

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”

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

Pictures are Weird

• What does Gregory find ambiguous about pictures?

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Pictures are Weird

• What does Gregory find paradoxical about pictures?

The Apparatus

• What does he do to remove the paradox so that the Muller-Lyer figure no longer looks flat?

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?

• How did Gregory test that?

Removing the Background

• Perceived size and perceived distance are tightly related

Next Time

• Stereo vision

• Read Pinker for next Thursday