JasonAnderson illusions

Visual Illusions: 

Visual Illusions Playing with Perspective CS99D Final Project By: Jason Anderson Professor Marc Levoy

William Hogarth: 

William Hogarth 1754 - "Whoever makes a DESIGN without the knowledge of PERSPECTIVE will be liable to such Absurdities as are shown in this Frontispiece."      Source: W. Hogarth, 1697-1764 Trustees of the British Museum.

Theories of Geometrical Illusions: 

Theories of Geometrical Illusions Eye-movement  perceived length Perspective cues Transactionalist approach Adaptation-level theory

Eye-Movement Theory: 

Eye-Movement Theory Line length  eye movement Testable, but usually fails – initial perception, eyes are stable Finding an index of eye movements a problem

Müller-Lyer Lines: 

Müller-Lyer Lines Eye-movement theory: Arrowheads influence extent of eye movements

Perspective Cues: 

Perspective Cues Pictures converted in our brain from 2-dimensional drawings to represent 3-dimensional scenes Different level of explanation – does not propose a mechanism for perception Well established, although some ‘loopholes’ have been found

Müller-Lyer Lines Revisited: 

Müller-Lyer Lines Revisited The same illusion through perspective cues Oculomotor Macropsia/Micropsia

Transactionalist Theory: 

Transactionalist Theory The world is a product of perception, not a cause of it Hamlet: Do you see yonder cloud that’s almost in shape of a camel? Polonius: By the Mass, and ‘tis like a camel indeed. Hamlet: Methinks it is like a weasel Polonius: It is backed like a weasel Hamlet: Or like a whale? Polonius: Very like a whale Hamlet (Act III, Scene II) Change our way of looking  Perception will change Old Man

Adaptation-Level Theory: 

Adaptation-Level Theory Helson, 1964 – “spatial pooling” Green & Stacey, 1966 applied to illusions Past stimulation  current stimulation “stored norms” “Top-down processing” Some flaws – Ames room

Depth Cues on a Flat Surface: 

Depth Cues on a Flat Surface 1967, R.L. Gregory – all pictures are “impossible objects” Conflicting depth cues in the content of the picture with the flat surface on which it is presented

Retinal Disparity: 

Retinal Disparity No retinal disparity on a flat surface As a viewer of an image, we choose to suppress the cue of retinal disparity Source: http://frank.mtsu.edu/~pyskip/splec6.htm

The Acceptance of Perspective: 

The Acceptance of Perspective We have come to accept that although we are seeing a flat surface, that the objects on it represent 3 dimensional concepts Pictorial cues: interposition (occlusion), relative size, linear perspective & texture gradients Ambiguous dimensional cues can lend themselves to be great visual illusions

Depth Ambiguity: 

Depth Ambiguity Because of the way everything we see is projected onto the retina, there is a great deal of ambiguity

Wundt’s crosses: 

Wundt’s crosses Hering (1879) & Wundt (1898) Most ambiguous of all figures Infinite number of interpretations, but perceptual system tries to settle with a ‘best’ one

Sanford’s figure: 

Sanford’s figure Sanford, 1903 Although there may be an obvious ‘best’ interpretation, once can easily be persuaded to accept an alternate one!

Of Ambiguous Figures and Depth Reversals: 

Of Ambiguous Figures and Depth Reversals Necker cube Mach Book

Of Ambiguous Figures & Depth Reversals 2: 

Of Ambiguous Figures & Depth Reversals 2 Not enough information in the image to make a decision as to the “best” interpretation Taken advantage of to create “impossible” figures

The ‘freemish’ crate: 

The ‘freemish’ crate Cochran’s photo of his ‘freemish’ crate (1966).

How did he do that???: 

How did he do that??? Any guesses?

Viewing from a single, special perspective: 

Viewing from a single, special perspective Viewing the image from a misleading perspective Viewing from another angle wrecks the effect Monocular viewing required Occlusion

Misleading depth cues: 

Misleading depth cues Stage scenery – gives impression of greater depth The Ames Room

The Ames Room: 

The Ames Room

Of Giants and Dwarves?: 

Of Giants and Dwarves? Of course not! But how?

What’s going on here?: 

What’s going on here? Adelbert Ames, Jr. (1946) – concept by Helmoltz Special viewpoint – monocular Floor, ceiling, some walls, & windows are trapezoidal Inclined floor Appears as a normal cubic room

So how does it work?: 

So how does it work? Peephole removes stereopsis Forms an identical image of a cubic room on your retina Both corners of the room subtend the same visual angle to your eye – appear equidistant Seckel & Klarke: Past experiences not relevant

But what about the people?: 

But what about the people? A split between perception & expectation Apparent cubic perspective overrides sense of size constancy Stanford psychologist Robert Shepherd – use background & relationship to the horizon to judge size

Retinal Size != Apparent Size: 

Retinal Size != Apparent Size Distance cues: relative size of elements, separation, density, clarity, background

But is the Ames Room necessary?: 

But is the Ames Room necessary? Seckel and Klarke: only charm An apparent horizontal path is all that’s necessary Richard Gregory: same effect, ambiguous background

The Moon Illusion: 

The Moon Illusion Perceived distance, visual angle, & linear size != physical values Illusion from comparison of perceived values at the horizon & at the zenith Subtends .5º in the eye no matter what Not atmospheric Illusion disappears in a “mooning position” 

Theories: 

Theories Apparent distance theory – appears farther away  larger Size-distance paradox Distance, visual angle, & linear size illusions work together Oculomotor micropsia / macropsia  visual angle Distance cues  macropsia for horizon moon

The Mystery Spot: 

The Mystery Spot Tilted house No visible horizon – assumed horizon with internal reference frame of house Your body is on a tilt as well – enhances effects as much as 3x Application to pilots

A new perspective on seeing: 

A new perspective on seeing Many theories, none are all-encompassing yet New ways to see things – become more aware of space through witnessing these illusions Perspective is a powerful tool – in ‘imitating’ reality, it can also deceive Seeing is believing  Perceiving is believing