Visual Illusions

Visual IllusionsVisual IllusionsDefinitionIllusions occur when what we see does not correspond to what is physically present in the world

Brightness After EffectBrightness After Effect

Please Stare for a whilePlease Stare for a while

Colour After EffectColour After Effect

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Please Stare for a whilePlease Stare for a while

Negative Colour After ImagesNegative Colour After Images

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Motion ContrastMotion Contrast

The Zöllner Illusion (Orientation Contrast)The Zöllner Illusion

(Orientation Contrast)

The Zöllner Illusion (Orientation Contrast)The Zöllner Illusion

(Orientation Contrast)

Object size is inferred from perceived distance and retinal image size

If 2 objects have the same retinal image size (i.e., are the same real size), the object appearing further away is seen as larger

Size-Distance RelationshipSize-Distance Relationship

Size-Distance RelationshipSize-Distance Relationship

The Ponzo IllusionThe Ponzo Illusion

Gregory’s theory

The visual system makes hypotheses about distance to objects based on evidence in the image. Interpretation of size follows.

Müller-Lyer IllusionMüller-Lyer Illusion

Müller-Lyer IllusionMüller-Lyer Illusion

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Objectively equal in separation, perceptually different

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Müller-Lyer IllusionMüller-Lyer Illusion

Perceptually equal in separation, objectively 30% different

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Perspective cues set up false interpretations of distance

Müller-Lyer IllusionMüller-Lyer Illusion

Ames RoomAmes Room

Ames roomAmes room

Ames room sets up false distance cues

Objects that are different distances appear the same distance

Reversible Figure and GroundReversible Figure and Ground

Necker cubeNecker cube

Look at the red dot…

It can be either on a near corner or a far corner

Ambiguous figuresAmbiguous figures

Old woman looking down/young woman looking away

Ambiguous figuresAmbiguous figures

Ambiguous figuresAmbiguous figures

Rabbit

Ambiguous figuresAmbiguous figures

Duck

How many dolphins?How many dolphins?

Penrose TrianglePenrose Triangle

Escher’s printsEscher’s prints

The brain cannot compute 3-D structure from all parts at once, each part looks plausible in isolation

Escher’s printsEscher’s prints

The Thatcher IllusionThe Thatcher Illusion

This is the same stimuli but 1 looks more strange than other