| | 134 Visual Phenomena & Optical Illusionsby Michael Bach (G+)[other language: Deutsch] |
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Some History / What’s new
Optical illusions don't “trick the eye” nor “fool the brain”, nor reveal that “our brain sucks”, … but are fascinating!
They also teach us about our visual perception, and its limitations. My selection emphazises beauty and interactive experiments; I also attempt explanations of the underlying visual mechanisms where possible.
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»Optical illusion« sounds pejorative, as if exposing a malfunction of the visual system. Rather, I view these phenomena as highlighting particular good adaptations of our visual system to experience with standard viewing situations. These experiences are based on normal visual experiences, and thus under unusual contexts can lead to inappropriate interpretations of a visual scene (=“Bayesian interpretation of perception”).
If you are not a vision scientist, you might find my explanations too highbrow. That is not on purpose, but vision research simply is not trivial, like any science. So, if the explanation seems gibberish, simply enjoy the phenomenon 😉.
More here: Bach & Poloschek (2006) Optical Illusions Primer; on the programming: Bach (2014, PDF).
Can illusions reveal something about my personality?
No. The web is full of claims that your personality (right- or left brain dominated, intro- vs. extroverted, or whatever) can be deduced from your ability to see some certain illusion or not. However, there is no reliable scientific data that suggests this. That's just click-baiting BS. There is some influence of age, though – but you don't need illusions to know your age… So: Don’t let it irk you if you don’t see all the phenomena described. For many illusions, there is a percentage of people with perfectly normal vision who just don’t see it, mostly for reasons currently unknown.
Motion & Time
- »Stepping feet« illusion 1 – strong, beautiful and (relatively) easy to understand
- Motion Induced Blindness – an illusion of disappearing dots
- Stereokinetic Phenomenon – an optical illusion of 3D from motion (aka »kinetic depth effect«)
- Motion silences hue changes – winner of the illusion contest 2011
- »Rotating Snakes« Illusion – with a new explanatory twist
- Snake ad lib – optimising this motion illusion
- “Rotating Snakes” – with luminance control
- Pinna-Brelstaff Illusion
- Pinna-Brelstaff Illusion #2
- Motion Aftereffect – also known as »waterfall effect«
- Spiral Motion Aftereffect – more effective for some
- Kinegram (“Scanimation”) – akin to a flip book
- Roget's Palisade Illusion
- Spoke Illusion – a motion illusion + an unexpected (?) aftereffect
- Wagon-wheel effect – closely related to stroboscopic artifacts
- Wagon-wheel with colours
- Stroboscopic Artifacts – making a teaching point out of a nuisance
- Sigma Motion – an optical illusion due to an interaction of image dynamics and eye movements
- Spine Drift illusion – more on eye movements, involuntary ones
- Eye Jitter – and even more on involuntary eye movements
- Biological Motion – for me the most beautiful class of visual illusions
- Flash-lag Effect – moving and stationary objects perceived at different times
- Ramp Aftereffect – an aftereffect in time
- Enigma (Isia Leviant)
- Freezing Rotation Illusion – a “Best Illusion of the Year” winner
- Reverse Phi Motion – something for the specialist
- »Stepping feet« illusion 2 – circular version of »Stepping feet 1«, weaker
- Motion Binding
- Tusi Motion
- Breathing Square
- Missing-fundamental motion inversion
- Frequency-doubling illusion
- »Kaleidoscope Motion« Illusion
- Ternus Display
- Stroboscopic alternative motion
- “Pigeon Neck” illusion
- “Psychokinematic” objects
- Dotted Lines motion illusion
Luminance & Contrast
- Hermann’s Grid – fleeting luminance illusions
- Hermann’s Grid bent – a new twist, refuting the classical explanation
- Scintillating Grid – strong fleeting luminance illusions
- 12 Vanishing Dots – No variation of the above
- Translational Moiré Patterns
- Rotatory Moiré Patterns
- Pulfrich effect – luminance turning time into displacement → stereo
- Induced grating – classical brightness contrast
- Shaded-diamond illusion – more brightness contrast
- Craik-O’Brien-Cornsweet – collaboration of retina & cortex
- Wertheimer-Koffka-Ring – pitting Gestalt vs. lateral inhibition
- Mach Bands
- Simultaneous Contrast – here dynamic
- Pyramid Illusion – Vasarely revealed
- Munker-White Illusion – contrary to lateral inhibition
- Adelson’s »Corrugated Plaid« – context affecting brightness
- Adelson’s »Checker Shadow« illusion – more context affecting brightness
- Saccadic Suppression – eye movements interact with visibility
- Contour Adaptation – a new case of contrast gain control
- Contrast Constancy – demonstrating space-average-based contrast gain control
- Contrast Gain Control – demonstrating temporal contrast gain control
- Lazy Shadow – Interaction of luminance & time
- Visual Acuity ↔ Hyperacuity
Colour
- Hinton's »Lilac Chaser« – a strong aftereffect, colours move which aren't really there
- Watercolor Illusion – long-range colour induction
- Context affects colour – different eyes?
- Colour Fan – more aftereffects
- Benham’s Top – colour from spatio-temporal patterns
- Benham’s Top “unrolled”
- Colour Assimilation
- Neon Colour Spreading
- White (?) Xmas – a seasonal variant of White's illusion
- Munker Illusion
- Structure from motion – fails at equiluminance
- Loss of countour in colour
- Gestalt loss in equilumance
- Equiluminance: Heterochromatic flicker fustion & minimum motion
- Colour mixing – additive and multiplicative
- Colour matching – a game
- Colour Phi
- Dress-Color enigma
- Red Strawberries that are not red – strong demo of colour constancy
- McCollough Effect – an aftereffect that can last months
Geometric- & Angle Illusions
- Skye’s Oblique Grating – No Café Wall variant
- Tilted Table – a cute Zöllner variant
- Hering Illusion – and other angular interactions
- Poggendorff Illusion – a classical geometric optical illusion with a new twist
- Disjointed Arch Illusion – a strong Poggendorff variant
- Fraser’s Spiral
- Tilt Illusion
- »Café Wall« Illusion
- Triangle Puzzle – a puzzle, but an illusion too
- Checker Bulge
- Jastrow Illusion – a classic, unexplained
Space, 3D & Size Constancy
- Müller-Lyer Illusion – test your bisection accuracy
- Moon illusion
- T-illusion
- Sine Illusion
- Schäffel's Luminance Looming
- Shepard’s “Turning the Tables”
- Shepard’s “Subterranean Terror”
- Reverspective – reverse perspective
- Necker Cube – the mother of reversible figures
- Missing Corner Cube – a cube with multiple ambiguities
- Ames Window
- Ambiguous Sillouette Illusion
- Frankfurter Illusion – binocular rivalry & supression
- Anamorphosis
- Leaning Towers Illusion
Cognitive- / Gestalt Effects
- Blind Spot – intelligent fill-in
- Darwin Illusion – the afterimage creates a recognisable Gestalt
- Blur & picture content – spatial filtering (or high frequency masking)
- Hidden message – blur & figure-ground discrimination
- Kanizsa’s Triangle – depends on context
- Blotted letters – Gestalt completion
- Hidden Figures – Dalmatian Dog with 2 helpers
- Hidden Bird – more camouflage
- Hidden object in brick wall
- Rotation – changes the interpretation
- Impossible Objects – draw your own impossible object
- Hallucii – An “impossible” movie
- Impossible waterfall – Another Escher inspiration
- Numerosity adaptation
- Delboeuf Illusion – with an application to eating
- Ebbinghaus Illusion
- Dynamic Ebbinghaus Illusion
Specialties with faces
- Rotating face mask – hollow faces
- Find the Face (in the Beans) – a picture puzzle
- The face on Mars – imaginations of perception
- Church or chicken?
- The »Thatcher Illusion« – inverted faces lose their emotional message
- »Ghostly Gaze« Illusion
- Dr. Angry and Mr. Smile – two messages in two spatial frequency bands
- The Lincoln Effect
Auditory Illusions
- Shepard Tone
- Motion-Bounce Illusion – sound influencing perception of motion (crossmodally)
Some sources
My bread-and-butter job Klinik für Augenheilkunde, Universität Freiburg
My involvement with our local art society
Thanks to Inga who created new artwork (2005-04) for the ‘eyes’. More from the Bach Family: Maren, Oliver. Occasionally I update my PlusOne Blog.
