Visual Perception Illusions & Paradoxes d Priyadarshi Patnaik Associate ProfessorDepartment of Humanities & Social S iD fH ii S i l Sciences IIT Kharagpur
What about visuals?Many things which are visually communicated orperceived are biologically determinedBut many other things are learntVisuals communicate powerVisuals communicate emotionsVisuals communicate culture
The PanopticonJeremy Bentham (1785)Discipline and PunishParanoiaControlFearClose circuitEPR
In philosophy psychology and the cognitive philosophy, psychology,sciences, perception is the process of attainingawareness or understanding of sensoryinformation. The word "perception" comesfrom the Latin words perceptio percipio and means perceptio, percipio,"receiving, collecting, action of takingpossession,possession apprehension with the mind orsenses."
When external stimuli is transmitted to our brainthrough our senses – sensationDevoid of any definition, any interpretation,meaningThe simplest building blockBut then it is taken up by the mind and analyzedMemory is stirred up remembering used up,Sensation identified, matched, given a name,defined,defined interpreted and remembered for futureuse
Part of what we perceive comes through thesenses from the objects before us; another partalways comes out of our own head William J Willi James
Subjective perception Image credit: Mark R. Homes @ National Geographic Society
To resolve ambiguities and make sense of theworld, the brain also creates shapes fromincomplete data. dataThe i lTh triangle you saw was d l d b I li developed by Italianpsychologist Gaetano Kanizsa.
IllusionImage credit: Mark R. Homes @ National Geographic Society
Illusion created because of “size constancy size constancy”effect to be discussed a little later.
OrientationImage credit: Mark R. Homes @ National Geographic Society
According to noted neuroscientist V. VRamachandran of University of California, SanDiego,Diego the brain can make guesses based oninformation available and some simpleassumptionsPattern of shadowsLightLi h usually from top ll f
From the eye to the mind Retina 1 2 braineye 1: R l t ti 1 Relay station - LGN 2: Primary and more advanced area of visual cortex
Rods: Monochrome and in low lightCones: colour vision
AttentionThe perceptual process of selecting certaininputs for inclusion in our conscious experienceor awareness at any given time
Flash animationImage taken Flash Animation Software demo movie
FilteringWhy does focus shift?We filter, partly bl ki certain iW fil l blocking i inputs Limited Mental Capacity
Perception is taking in, filtering and interpretation tomake sense of the world. Memory and learning play animportant part, but so do certain innate organizationalabilities of the mind, highlighted by Gestaltpsychologists.The limits of my perception are the limits of my worldThe word is the world (since it takes us a step furtherand helps us cognize what we have perceived)
What we shall do nextForm perceptionColour perceptionDepthD h perception iThese will give us some idea of how and why wevisually perceive the many things that we do. yp y g
Gestalt (German) used to indicate the form- form-forming capabilities of the mind (Whole formapproach) and the belief that this holisticperception is innate to the mind
Figure-g ou dFigure-ground gu e M.C. Escher: Moebious with Birds
The visual system uses an innate binary division– the figure we look at and the ground which iseverything else and forms the backgroundThis relation is reversibleButB we cannot perceive the same thing as fi i h hi figureand ground at the same time – it requires amental switching l i hi
GestaltMax WertheimerKurt KoffkaWolfgang K hlW lf KohlerWe are surrounded by sounds and forms that donot have a sole meaning. At any moment, our g y ,perception is what gives it form and meaning.
What do we have here? Twelve lines 4 vertical 4 horizontal 4 oblong
The vase and the two facesA demonstration of multi-stability: popping back and forthbetween two or more unstable perceptions
Organization in form perception The whole is more than the sum of its h h fi parts
A Poem A Black CoatIt was a dark evening d k i Simple Life
Subjective Contour/Reification Image credit: Mark R. Homes @ National Geographic Society
Colour symbolismCultural differencesAge differenceClass differenceCl diffGender differenceTrend or current fashion
IllusionThere is an innate ambiguity in retinal input. For a g y pgiven retinal image, there are infinite number of threedimensional images available for interpretation. Usuallywe get the interpretation right. When we don’t, we have t th i t rpr t ti ri ht Wh d ’t han illusion.Some illusions arise because there are more than onepossible interpretations.An illusion is a distortion of the senses, revealing howthe brain normally organizes and interprets sensorystimulation.
Types ofAmbiguous illusions are pictures or objects that g p jelicit a perceptual switch between the alternativeinterpretations.Distorting illusions are characterized by distortionsof size, length, or curvature.Paradox illusions are generated by objects that areparadoxical or impossible. d i l i iblFictional illusions (Hallucinations) are defined asthe perception of objects that are g p p bj genuinely not there yto all but a single observer, such as those induced byschizophrenia or a hallucinogen.
Image source: Encyclopedia Britannica 2007 deluxe edition
Image source: Encyclopedia Britannica 2007 deluxe edition
Escher on Escher"In the horizontal center strip there are birds and fish Inequivalent to each other. We associate flying with sky,and so for each of the black birds the sky in which it isflying is formed by the four white fish which encircle it.Similarly swimming makes us think of water, and watertherefore the four black birds that surround a fish becomethe water in which it swims." swims
References and images Doors of Perceptionhttp://www.doorsofperception.com/doors The Joy of Perceptionhttp://www.yorku.ca/eye Perception Onlinehttp://www.pion.co.uk/perception “Perception.” E l p di Britannica 2007 Deluxe Edition. “P ti ” Encyclopedia B it i D l Editi Art and Visual Perception. Rudolf Arnheim, University of California Press, 1984. Mark Hardin’s A hi (www.artchive.com) M k H di ’ Artchive (www.artchive.com) hi Colour. Bettey Edwards, Tarcher/Penguin, 2004. Perception, Gestalt, Panopticon, etc ( p p (Wikipedia) p )