ILLUSIONS

What are they?

What can we learn from them?

D.J. Aks 11/10/09Proseminar Lecture for Z. Pylyshyn, RUCCs

Photo credit: Andy Goldsworthy

ILLUSIONS

Correspondence Problem

Appearance vs. Reality

ILLUSIONS

Discrepancy between…

physical & perceptual stimulus

Mueller-Lyer Illusion

ILLUSIONSDiscrepancy between

physical & perceptual stimulus

Poggendorff Illusion

ILLUSIONSDiscrepancy between

2D & 3D info

Andy Goldsworthy

Experiments & Illusions

http://aks.rutgers.edu/…illusions/Pogg/HalfCircDrag.html

ILLUSIONS

Discrepancy between….?

2D & 3D info

ILLUSIONS

Discrepancy between….?

2D depiction of 3D infoi.e., conflicting perspective of parts of object

• SIZE CONSTANCY - the stability of perceived size despite changes in objective distance and retinal image size.

• CONSTANCY SCALING -

• Our mind adjusts retinal size to correct for registered viewing distance

= Size Distance Scaling

• SIZE CONSTANCY - the stability of perceived size despite changes in objective distance and retinal image size.

• CONSTANCY SCALING -

• MOON ILLUSION - moon appears larger near the horizon than when high in the sky

• Depth cues (on land) give impression that moon is at a "far" distance.--

Thus, we ‘expect’ a far object (moon) to appear small on the retina - but when it does not, the mind compensates and we see the object (moon) as large

Size-contrast

Violation of assumptions

• We tend to assume:

• 1) overhead lighting• SHADING

• 2) regularity of..• SHAPE

Shading&

Structure

Rodin

ILLUSIONS THAT VIOLATE

ASSUMPTIONS Overhead lighting• SHADING - we perceive convex shape when top is lit

& concave when lit at bottom

ILLUSIONS THAT VIOLATE

ASSUMPTIONS

Overhead lighting

• SHADING - we perceive convex shape when top is lit & concave when lit at bottom

ILLUSIONS THAT VIOLATE

ASSUMPTIONS

Overhead lighting & Shading

ILLUSIONS THAT VIOLATE

ASSUMPTIONS SHAPE & SIZE CONSTANCY - apparent shape of an

object remains constant despite changes in the shape of the retinal image -

– REGULAR SHAPES

– AMES ROOM

ILLUSIONS THAT VIOLATE

ASSUMPTIONS SHAPE & SIZE CONSTANCY

– REGULAR SHAPES– AMES ROOM ILLUSION

Occlusion & Shape Perception

Does shape of occluder drive shape percept of ‘occludee’?How about orientation of edges w/in occluder shapes?

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Camouflage & Occlusion

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Occlusion & Shape Perception

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Motion & Shape Perception

Kinetic Depth Effect

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Motion & Shape Perception

Johansson

Neuronal Interactions, Attention & Eye-movements

Visual-Auditory Integration

Sound localization & ventriloquism

Kevin Johnson on David Letterman

http://www.youtube.com/watch?v=DnNBgIKOvr4

Experiments & Illusions

http://aks.rutgers.edu/…illusions/Pogg/HalfCircDrag.html