perception: how we see

2. Once upon a time, there was atalented sculptor who producedbeautiful works of art.But when it came time to stepback and share his work with theadmiring public, a strangeforgetfulness would take charge.The sculptor would look at thestatue and forget that it was hiscreation.He saw the statue as simply outthere rather than as a creativeproduct.2 3. When it comes to seeing, we allbehave like this sculptor.We shape our perceptions, thenpromptly forget our role increating them. We consider themas stuff that happens to be outthere, not as something wecreate.We are aware of what we see but not of how we see.Sculpting sandcastles of realityhappens without our permissionor awareness.3 4. The eye is not a camera.Perception is all about survival; it cares not for documentingwhat is really out there. Vision is a survival tool, not arecording device.It doesnt matter if we see things wrong, as long as we seewhat we need to survive. 4 5. 1. Seeing MovementThe setting sun is a giant optical illusion. We know thesun isnt actually sinking into the ocean, yet that is whatwe see. How could we be so wrong about something sobig and so common? 6. To see, we use shortcuts, or best guesses. Whenwere not sure which object is moving and which isstationary, we guess the small object is the one moving.This guess is not a conscious decision; it just happens.We see the small sun moving into the large horizon itseems so obvious. The fact that this guess is wrongdoes not threaten our survival. Its an acceptableerror. 6 7. You sit in a parked train or airplane. You look out the window and seemovement. Are you moving or is it the train on the next track or theplane parked next to you? You feel a twinge of uncertainty becauseyou have no size comparison on which to base your educated guess.This brief feeling of uncertainty is a peek into your normally hiddenvisual processing -- your subliminal sculpting. 7 8. Consider the toad. It also makeseducated guesses aboutmovement. Like humans, itsguesses are also meant for survival.To a toad, food equals movement.Put a pet toad in a cage and kindlyprovide it with dead flies and it mightstarve to death. To the toad, if itdoesnt move, its not food. Thats aperceptual shortcut that works forthe toads survival most of the time.Lets take a look at some othershortcuts we humans use to sculptour visual word.8 9. 2. Seeing Colors We think of color as something out there, as a property in things. We say the stop sign IS red, the sunflower IS yellow. But color is not a thing in objects; its a visual effect a creation of our visual sculpting. Treating color as a thing that objects have is a toad-like shortcut that works for us most of the time.We use context to judge both movement and color.This context typically remains invisible to the seer. 9 10. The colors in the tiles In the two rectangles above are identical but theydont look that way. The yellow and blue backgrounds influence ourprocess of color creation. Context (an objects surround) influences ourperception. 10 11. The orange and red squares within in thediamonds to the right are the same red.The yellowish-green and bluish greensquares within the diamonds to the rightare the same green.But our eyes do not see them as thesame. We see colors in terms of whatsurrounds them. 11 12. Next time you look at a nighttime sky, ask yourself, isthe moon really white? Or is that whiteness a resultof context and your visual sculpting? 12 13. Light reflected off a surface changes constantly. Sunlight, afluorescent bulb, or a shadow each changes what a surfacereflects. Yet (within limits) we perceive the color of the object tobe the same. We call this visual shortcut color constancy. Ifobjects kept changing color on us, the world would be quiteconfusing. But color constancy sometimes leads to mis-perceptions. 13 14. The squares labeled A and B above are the same shade of gray. Sinceyou mistakenly assume your eyes document the world you might say Ais darker than B. This judgment is based on a visual shortcut you usethat usually works, but not here. Your eyes dont fail you. Its yourinterpretation that leads to a false conclusion. You see your14interpretation. 15. The visual shortcut we use is to guess that if something is lighter in colorthan what surrounds it, it is probably of a light color in absolute terms. Inother words, its light, not merely lighter. Another perceptual shortcutwe use is to assume that something in a shadow is lighter than it appears.These assumptions work well but they mislead us in this image. Why dontyou simply avoid these shortcuts? You cant not use them because yourenot aware that you do use them. 15 16. The typical human retina has three cones that detect blue, green and red.So, humans are trichromats, we see three (tri) colors (chroma). The braincombines variations of these three colors into about a million different hues.A small percentage of the worlds women have a genetic mutation givingthem a fourth photoreceptor that enables them to distinguish among colorsthat look identical to most of us. To these tetrachromats, most of us mustseem somewhat color blind. 16 17. About eight percent of the worlds men are color blind. This does not mean they see no color. A more accurate term is color vision deficiency. Most of them inherit two red or two green cones along with the standard blue cone, making it impossible for them to distinguish between red and green peppers, tell how well-done a steak is, pick out matching clothes, or see red lines painted on grass marking a hazard.Why men? Because color vision deficiency is carried by the X chromosome. Women are carriers ofthis defective chromosome, but need two defective x chromosomes to be affected. Only .5% ofwomen are color blind. So a color blind male will not pass the gene to his children. But acolorblind woman will pass that trait to all her sons. 17 18. Most people who are color blind are not aware theysee differently until they talk to others who speak ofhues they cannot see. If everyone were color blind,we would never know it. The inability to see a number in the above circle is part of a typical test for color blindness. 18 19. 3. Seeing in 3-DSeeing the world in three dimensions isanother of your sculpting creations.The fact that you have two eyes meanseach sees from a slightly different angleand distance. You knit the two imagestogether to produce a single 3-D image.You might become aware of your 3-Dcreation after a blow to the head or toomuch alcohol causes you to see double.The alcohol or blow interferes with yournormal image-knitting.Seeing double is your default vision.19 20. Hold a finger between your eyes and the monitor so it covers thelighthouse. View the lighthouse with only one eye. Close that eye andopen the other. The lighthouse seems to move as you switch eyes.Try the same test with a more distant object, and it will appear to moveeven more. This jumping is caused by the fact that your eyes areseparated horizontally, and present slightly different viewpoints. 20 21. One reason movies and TV have been flat for over a hundred years isthat cameras have only one lens. They lack two images that can beknitted together to create depth.3-D cameras have two lens (to better simulate our binocular visualsystem) each taking a slightly different picture so they can be re-united into a single 3-D image. 21 22. Your visual sculpting includes a lot of editing that you do withoutawareness. Consider your nose, for example.Close one eye. Notice that you see your nose. Now look through theother eye. The side of your nose is again in your field of vision. So whydoesnt your nose interfere with your ordinary vision?Your 3-D creation edits out awareness of your nose. You have theability to make your nose vanish. Quite a trick.22 23. its merely a drawing -- lines on a surface. You assemble theselines into a three dimensional cube using a visual grammar whoserules are invisible to you. You cant help but see a cube. 23 24. 4. Size, Shape, Distance, and Height As objects move into the distance, they appear to become smaller. But we know the world around us does not grow and shrink as it did for Alice in Wonderland. We saw earlier that we possess a sense of color constancy. We also have a sense of size constancy. We know that planes dont get smaller after they take off, even if our eyes present them that way. What we finally see is not so much whats out there as it is our interpretation of whats out there.24 25. You make guesses concerning size based on clues about distance. If you dont know howfar away something is, you cannot determine its actual size visually.Moviemakers use the lack of distance cues to make you think a small object is large. A filmdirector can surround a small plastic model of a cruise ship with featureless ocean to makea believable giant ship. In sci-fi movies , a spaceship model only a few feet long can seemas large as a building.25 26. Sensation itself has no markers for size and distance; these have to be learned on the basisof experience. Thus, it has been reported that if people who have lived their entire lives indense rain forest, with a far point no more than a few feet away, are brought into a wide,empty landscape, they may reach out and try to touch the mountaintops with their hands;they have no concept of how far the mountains are. --Oliver Sacks in An Anthropologiston Mars 26 27. A sunset again illustrates how we use context to judge size.At noon the sun appears a small disk -- there are no objectsnear it to help us judge size. But the setting sun turns thehorizon into context. Only when the sun sets or rises do wesee it as a gigantic ball of fire. 27 28. Look at the two shapes below. The left is clearly longer and narrower thanthe nearly square figure on the right.The two are actually identical, but your visual system does not present themto you that way. The part of your visual system that misleads you is not underyour conscious control. You see your interpretation. 28 29. The red and blues lines are the same length.The illusion has been well studied since it was described by Germanpsychiatrist Franz Carl Muller-Lyer in 1889. However, there is nouniversally accepted explanation for the apparent difference in thelengths of the two line segments.29 30. Muller-Lyer attempted to explain the illusion he had discovered asfollows: "the judgment not only takes the lines themselves, butalso, unintentionally, some part of the space on either side. Inother words, (a) context shapes perception, and (b) we are notaware of the influence of context. 30 31. The two long horizontal lines above are perfectly straight. Theydont bend in the middle one little bit.The visual habits that confuse us in optical illusions serve us wellin everyday life. Optical illusions are not merely neat tricksthat confuse the eye. They are illustrations that use unusualcontexts to help us understand how we see. 31 32. A whiteout can cause a pilot, or people in a snowstorm t to lose track ofapparent sizes and even confuse up from down. Whiteout is a visuallack of context it illustrates how much our everyday vision depends oncontext. A helicopter pilot in whiteout might not be able to determineif these people are doll-sized figures in front of him or real people faraway.32 33. In scuba diving, the termblue water dive refers to adive without a reef, floor orany other visual reference.An inexperienced diver caneasily be caught in a blueout with no idea of up ordown. He could be sinkingstraight down but assumehe is going up.The ropes here help providevisual and tactile cues.Whiteouts and blue waterdives are rare situations, likethose clever opticalillusions.33 34. We seem to have a built in tendency to overestimateheights. When you look at the figure below the vertical lineappears longer than the horizontal even though both areidentical. 34 35. The Gateway Arch in St. Louis is as wide as it is tall. It stands 630 feet tall and630 feet wide at its base. Most observers would report the arch is taller thanit is wide. We give greater visual weight to verticals. 630 feet tall 630 feet wide 35 36. The visual shortcut of giving more visualweight to height might cause us to drinkmore.Prof. Brian Wansink at Cornells Food andBrand Lab asked bartenders to pour adrink into 10 oz. glasses that were eithershort, wide tumblers or tall, thin highballglasses. Even these experiencedbartenders served 20% more liquid in theshort wide glasses.He also found people who pour theirown drinks from a self-serve machinewill pour about 6% more liquid whengiven short, wide glasses than with a talltumbler. But, those who poured morebelieved they had poured less, and thosewho poured less believed they had takenmore.36 37. Why do we over estimate height? Possibly becausein our past, overestimating heights helped ussurvive. It is an error in our visual processing thatproved useful. After all, to underestimate a heightcould prove fatal. Seeing is about survival.37 38. 5. Filling in the BlanksIf I see it with my own eyes it must be true. Part of our trust inthe visual comes from the fact that seeing operates almost entirelybelow our level of conscious awareness.Since we are not aware of our role in creating what we see, wetreat it as the gold standard to judge reality. I saw it with my owneyes, it must be true. We are unaware that what we see is shaped by our expectationsand beliefs.38 39. Some images confuse our visual processing. Stare at thepattern on this page. The image appears to move. But this isa still image. You interpret the image as having motion. Youcreate the movement you see. 39 40. A similar perceptual illusionhappens with the chemicalscapsaicin and menthol. Capsaicinis the chemical that makespeppers hot. Menthol givescoolness to many skin creams.We perceive heat and cold, yet athermometer will not registermeaningful changes in skintemperature. The heat or coolnessare in your interpretation ofsensory data, not in the substanceitself; much like the movement inthe previous image was in yourperception rather than the griditself.We see, feel, hear, and tasteAll these pain relievers contain menthol as an active ingredient.interpretations, expectations, andbeliefs. 40 41. An optic nerve contains about a million neural wires (called axons)connecting each retina to your brain. Each axon represents one pixel ofyour visual image. Each eye sees with the resolution of a one-megapixelcamera. So your vision is less detailed than a cheap camera or cell phone.The picture here is a simulation of an actual image on your retina.But you perceive the world as rich and detailed. The richness of your visualexperience is created by your fill-in-the blanks interpretations. 41 42. We see a richly detailed reality even when our eyes capture very limiteddata. When viewed up close, the face on the left clearly has more detail,(more pixels) than the face on the right. But step back ten or more feetfrom the screen. Now both appear clear and undistorted. You fill in themissing detail.This filling in helps explain why you might not see a difference insnapshots taken by a 3 megapixel camera compared to one with 7megapixel resolution.or why 720 HDTV looks much like 1080.42 43. A flipbook is a primitive form of movie. It is made of a seriesof drawings that, when flipped through rapidly, appear tomove. The drawings show the same scene with only a minorchange in each drawing.The reason we see movement in a flipbook or a movie isthat we fill-in what we expect to happen between the stillpictures. The movement is our own creation.43 44. Perception is an ongoing process of fill-in-the-blanks. We are not aware we play fill-in-the-blanks. In fact, we are not even aware the blanksexist.Perception requires energy seeing requires asteady supply of calories. To conserve energy weuse selective attention a perceptual shortcut thatworks most of the time. We are surprisingly blindto what we do not pay attention to.Youve played card games and looked at thepicture cards thousands of time. So you knowwhich of the four playing card kings shows onlyone eye dont you?Which suit of cards shows the one-eyed king? 44 45. If you could not identify the king of diamonds as the one-eyed king,its because you did not need to know. You look at playing cards justenough to see the suit and rank thats all you need to play cards.Remember, perception is not about documenting whats there, itsabout using it for your own interests.Speaking of playing cards.heres another illustration of perception.This one involves a bit of mind reading.45 46. Above are six playing cards. Select one by staring at itfor eight or more seconds to establish a solid visualimage. Keep it clearly in your mind. 46 47. Dont allow this screen to distract you. We use it to readyour mind. Keep the visual image of the card in your mind. We have now read your mind and removed the card you chose. Look at the next screen and see if the card we discarded was indeed the one you selected.47 48. Did we get it right? If so, what does thisteach about how you see? 48 49. It illustrates selective seeing. What counts isnot so much what you see, as what you areaware of. We are aware only of what we payattention to, while we ignore much of thevisual data captured by our eyes.Like the one-eyed king, we see what we needand ignore the rest. If you wish, go back andtry the experiment again. See if it works twice.Maybe it was a lucky guess. 49 50. Here are the cards presented in both screens. Notethat the face cards in the second screen contain noneof the same cards as in the first. Chances are youconcentrated so hard on the card that you DID pickyou never attended to the cards you didnt pick.This visual shortcut is called attentional blindness. The selection cardsThe answer cards 50 51. An experiment observedstudents walking across acampus square. Somewalked in pairs, some alone,while others talked on a cellphone. Each was observedwhile a clown on a unicycleapproached and circled them.Students walking in pairswere most likely to see theclown. Surprisingly, half thestudents talking on cellphones missed the clowncompletely. The researchersconcluded that cell phonescontribute to attentionalblindness.51 52. In another experiment, volunteerswere asked to follow a jogger at afixed distance and count how manytimes the jogger touched his hat.About a minute into the run, threestudents stage a fight slightly off tothe side of the jogging path.Researcher Chris Chabris explains,we had two students beating up athird, punching him and kicking himand throwing him to the ground."Only forty percent of the subjectsnoticed the fight, even in broaddaylight. At night the figure droppedto one-third. The subjects wereattending to the task of counting hattouches, so the nearby mayhem wasinvisible.52 53. You imagine your eyes gliding around, soaking in detailed images. In reality, youreyes jump around and fix on what attracts you. During the jump (called a saccade,which is French for jerk"), the eyes move so rapidly that you are unconscious ofany eye movement. Seeing consists of eyes jumping in rapid succession from onefocus to another. Your brain edits out the jumps and presents only the informationgained from each jump target. You sense a detail-rich, stable-seeming picture ofthe world out there. Eyesight is jumpy. Awareness is smooth. StartMoving your eyes keeps the world stable. To see this for yourself, trylooking into a mirror 53 54. Look in a mirror. Move your eyes back and forth, lookingfirst at your left eye, then at your right eye, then at yourleft eye again. Someone watching you can see your eyesmove they shift from left to right.But surprise, you dont see yourown eyes move. You see yourselfstaringstraight ahead.54 55. We call peripheral vision seeing out of the corner of the eye, but no suchcorner exists. Peripheral vision is created by eye movements. Toexperience this, focus on the red dot below. The surrounding circle willvanish -- it might take 20 seconds or more. Visual awareness works a bit like a refrigerator light. When you see something out of the corner of your eye you quickly turn your attention to it and see it clearly. So you assume you see everything clearly. You assume the light in the55 refrigerator is always on. 56. 6. Seeing Me: Self-BlindnessYou can sense a difference between how you imagineyourself and how you look to others. You sense thisdifference when you see video of yourself or hear arecording of your voice. We think is that really how Ilook or sound? We are designed to be a bit self-blind.We devote far less visual attention to ourselves than toothers. This makes sense in terms of seeing as survival.We judge others based on what we see, but ourselvesbased on what we think and feel. We have a built-inperceptual double standard.Being somewhat self-blind is part of our nature. Theonly problem is we are not aware of our self-blindness,so we keep bumping into ourselves.56 57. We see ourselves, through a glass darkly.To help understand how we see, consider that wecannot see our own faces. For 99.99% of humanhistory, not one single human ever saw his or her ownface.Our ancestors saw reflections, first in ponds thenmuch later in the amazing invention called a mirror.But a reflection is not a face. Reflections are reversedright to left. The image you see in the mirror is notthe way you appear to others.This very basic fact of human existence teaches ussomething about how we see. 57 58. Our ability to see and read the faces of others is critical to our humanness.When a baby looks in a mirror, does it recognize the image as self or is it simplyanother baby in some untouchable space?At around six months, babies interact with the mirror image but treat thereflection as a plaything. At around age one they think of searching behind themirror for the playmate. In one research study, 65% of babies demonstratedrecognition of their mirror images by age two. Research suggests that babiesrealize they are seeing themselves sometime during the second year. 58 59. Someone asks you tosmile for a photo. Youcant see yourself smile,so you say cheese ortry to imitate what youthink a smile looks like.It invariably comes offlooking fake because itis not driven by emotion,and because you have solittle experience inseeing yourself smile you cant see your face.A genuine smile is nearlyimpossible to fake. Youneed to feel an emotionthat makes you smile.59 60. When you open your eyes tomorrowmorning, realize you are seeing a worldyou spent a lifetime learning to see. It is aworld you create through constant,demanding, yet invisible work.You see with your brain. That brain sits intotal darkness. It cant see anything. Itreceives electrical signals, but thats all. Nopictures. No light. No colors. It has noscreen to serve as a viewfinder. You thesculptor create colors, dimensions,brightness, and all the awesome beauty ofthe visual world.Take time to enjoy your amazing creation.60