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Perception: How We See

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Perception: How We See

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Explore how we see. Discover that our world of perception is not about documenting reality -- it's all about survival. We do not so much "picture" what's out there as we create a world of perception.

Explore how we see. Discover that our world of perception is not about documenting reality -- it's all about survival. We do not so much "picture" what's out there as we create a world of perception.


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Perception: How We See

  1. 1. Perception: How We See See Yourself Seeing Copyright ©2012 by Jeffrey Schrank 1 COPYRIGHT 2011 JEFFREY SCHRANK
  2. 2. Once upon a time, there was a talented sculptor who produced beautiful works of art. But when it came time to step back and share his work with the admiring public, a strange forgetfulness would take charge. The sculptor would look at the statue and “forget” that it was his creation. He saw the statue as simply “out there” rather than as a creative product. 2
  3. 3. When it comes to seeing, we all behave like this sculptor. We shape our perceptions, then promptly “forget” our role in creating them. We consider them as “stuff” that happens to be out there, not as something we create. We are aware of what we see – but not of how we see. Sculpting sandcastles of reality happens without our permission or awareness. 3
  4. 4. The eye is not a camera. Perception is all about survival; it cares not for documenting what is “really out there.” Vision is a survival tool, not a recording device. It doesn’t matter if we see things “wrong,” as long as we see what we need to survive. 4
  5. 5. 1. Seeing Movement The setting sun is a giant optical illusion. We know the sun isn’t actually sinking into the ocean, yet that is what we see. How could we be so wrong about something so big and so common?
  6. 6. To see, we use “shortcuts,” or “best guesses.” When we’re not sure which object is moving and which is stationary, 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 – it seems so obvious. The fact that this “guess” is wrong does not threaten our survival. It’s an “acceptable error.” 6
  7. 7. You sit in a parked train or airplane. You look out the window and see movement. Are you moving or is it the train on the next track or the plane parked next to you? You feel a twinge of uncertainty because you have no size comparison on which to base your educated guess. This brief feeling of uncertainty is a peek into your normally hidden visual processing -- your subliminal sculpting. 7
  8. 8. Consider the toad. It also makes “educated guesses” about movement. Like humans, its “guesses” are also meant for survival. To a toad, food equals movement. Put a pet toad in a cage and kindly provide it with dead flies and it might starve to death. To the toad, if it doesn’t move, it’s not food. That’s a perceptual shortcut that works for the toad’s survival – most of the time. Let’s take a look at some other shortcuts we humans use to sculpt our visual word. 8
  9. 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; it’s 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. 10. The colors in the tiles In the two rectangles above are identical – but they don’t look that way. The yellow and blue backgrounds influence our process of color creation. Context (an object’s surround) influences our perception. 10
  11. 11. The orange and red squares within in the diamonds to the right are the same red. The yellowish-green and bluish green squares within the diamonds to the right are the same green. But our eyes do not see them as the same. We see colors in terms of what surrounds them. 11
  12. 12. Next time you look at a nighttime sky, ask yourself, “is the moon really white?” Or is that whiteness a result of context and your visual sculpting? 12
  13. 13. Light reflected off a surface changes constantly. Sunlight, a fluorescent bulb, or a shadow each changes what a surface reflects. Yet (within limits) we perceive the color of the object to be the same. We call this visual shortcut “color constancy.” If objects kept changing color on us, the world would be quite confusing. But color constancy sometimes leads to mis- perceptions. 13
  14. 14. The squares labeled “A” and “B” above are the same shade of gray. Since you mistakenly assume your eyes “document the world” you might say “A” is darker than “B.” This judgment is based on a visual shortcut you use that usually works, but not here. Your eyes don’t fail you. It’s your “interpretation” that leads to a false conclusion. You see your 14 interpretation.
  15. 15. The visual shortcut we use is to “guess” that if something is lighter in color than what surrounds it, it is probably of a light color in absolute terms. In other words, it’s “light,” not merely “lighter.” Another perceptual shortcut we 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 don’t you simply avoid these shortcuts? You can’t “not use them” because you’re not aware that you “do use them.” 15
  16. 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 brain combines variations of these three colors into about a million different hues. A small percentage of the world’s women have a genetic mutation giving them a fourth photoreceptor that enables them to distinguish among colors that look identical to most of us. To these tetrachromats, most of us must seem somewhat color blind. 16
  17. 17. About eight percent of the world's 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 of this defective chromosome, but need two defective x chromosomes to be affected. Only .5% of women are color blind. So a color blind male will not pass the gene to his children. But a colorblind woman will pass that trait to all her sons. 17
  18. 18. Most people who are color blind are not aware they see differently until they talk to others who speak of hues 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. 19. 3. Seeing in 3-D Seeing the world in three dimensions is another of your sculpting creations. The fact that you have two eyes means each sees from a slightly different angle and distance. You knit the two images together to produce a single “3-D” image. You might become aware of your 3-D creation after a blow to the head or too much alcohol causes you to “see double.” The alcohol or blow interferes with your normal image-knitting. Seeing double is your default vision. 19
  20. 20. Hold a finger between your eyes and the monitor so it covers the lighthouse. View the lighthouse with only one eye. Close that eye and open 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 move even more. This “jumping” is caused by the fact that your eyes are separated horizontally, and present slightly different viewpoints. 20
  21. 21. One reason movies and TV have been flat for over a hundred years is that cameras have only one lens. They lack two images that can be “knitted together” to create depth. 3-D cameras have two lens (to better simulate our binocular visual system) each taking a slightly different picture so they can be “re- united” into a single 3-D image. 21
  22. 22. Your visual sculpting includes a lot of “editing” that you do without awareness. Consider your nose, for example. Close one eye. Notice that you see your nose. Now look through the other eye. The side of your nose is again in your field of vision. So why doesn’t your nose interfere with your ordinary vision? Your 3-D creation “edits out” awareness of your nose. You have the ability to make your nose vanish. Quite a trick. 22
  23. 23. …it’s merely a drawing -- lines on a surface. You “assemble” these lines into a three dimensional cube using a visual grammar whose rules are invisible to you. You can’t help but see a cube. 23
  24. 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 don’t get smaller after they take off, even if our eyes present them that way. What we finally “see” is not so much “what’s out there” as it is our interpretation of what’s out there. 24
  25. 25. You make “guesses” concerning size based on clues about distance. If you don’t know how far 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 film director can surround a small plastic model of a cruise ship with featureless ocean to make a believable giant ship. In sci-fi movies , a spaceship model only a few feet long can seem as large as a building. 25
  26. 26. “Sensation itself has no ‘markers’ for size and distance; these have to be learned on the basis of experience. Thus, it has been reported that if people who have lived their entire lives in dense 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 Anthropologist on Mars 26
  27. 27. A sunset again illustrates how we use context to judge size. At noon the sun appears a small disk -- there are no objects near it to help us judge size. But the setting sun turns the horizon into context. Only when the sun sets or rises do we see it as a gigantic ball of fire. 27
  28. 28. Look at the two shapes below. The left is clearly longer and narrower than the nearly square figure on the right. The two are actually identical, but your visual system does not present them to you that way. The part of your visual system that misleads you is not under your conscious control. You “see” your interpretation. 28
  29. 29. The red and blues lines are the same length. The illusion has been well studied since it was described by German psychiatrist Franz Carl Muller-Lyer in 1889. However, there is no universally accepted explanation for the apparent difference in the lengths of the two line segments. 29
  30. 30. Muller-Lyer attempted to explain the illusion he had discovered as follows: "the judgment not only takes the lines themselves, but also, unintentionally, some part of the space on either side.“ In other words, (a) context shapes perception, and (b) we are not aware of the influence of context. 30
  31. 31. The two long horizontal lines above are perfectly straight. They don’t bend in the middle one little bit. The visual habits that confuse us in optical illusions serve us well in everyday life. Optical illusions are not merely “neat tricks” that confuse the eye. They are illustrations that use unusual contexts to help us understand how we see. 31
  32. 32. A whiteout can cause a pilot, or people in a snowstorm t to lose track of apparent sizes and even confuse up from down. Whiteout is a visual lack of context – it illustrates how much our everyday vision depends on context. A helicopter pilot in whiteout might not be able to determine if these people are doll-sized figures in front of him or real people far away. 32
  33. 33. In scuba diving, the term “blue water dive” refers to a dive without a reef, floor or any other visual reference. An inexperienced diver can easily be caught in a “blue out” with no idea of up or down. He could be sinking straight down but assume he is going up. The ropes here help provide visual and tactile cues. Whiteouts and blue water dives are rare situations, like those clever optical illusions. 33
  34. 34. We seem to have a “built in” tendency to overestimate heights. When you look at the figure below the vertical line appears longer than the horizontal even though both are identical. 34
  35. 35. The Gateway Arch in St. Louis is as wide as it is tall. It stands 630 feet tall and 630 feet wide at its base. Most observers would report the arch is taller than it is wide. We give greater visual weight to verticals. 630 feet tall 630 feet wide 35
  36. 36. The visual shortcut of giving more “visual weight” to height might cause us to drink more. Prof. Brian Wansink at Cornell’s Food and Brand Lab asked bartenders to pour a drink into 10 oz. glasses that were either short, wide tumblers or tall, thin highball glasses. Even these experienced bartenders served 20% more liquid in the short wide glasses. He also found people who pour their own drinks from a self-serve machine will pour about 6% more liquid when given short, wide glasses than with a tall tumbler. But, those who poured more believed they had poured less, and those who poured less believed they had taken more. 36
  37. 37. Why do we over estimate height? Possibly because in our past, overestimating heights helped us survive. It is an “error” in our visual processing that proved useful. After all, to underestimate a height could prove fatal. Seeing is about survival. 37
  38. 38. 5. Filling in the Blanks If I “see it with my own eyes” it must be true. Part of our trust in the visual comes from the fact that seeing operates almost entirely below our level of conscious awareness. Since we are not aware of our role in creating what we see, we treat it as the gold standard to judge reality. “I saw it with my own eyes,” it must be true. We are unaware that what we see is shaped by our expectations and beliefs. 38
  39. 39. Some images confuse our visual processing. Stare at the pattern on this page. The image appears to move. But this is a still image. You interpret the image as having motion. You create the movement you see. 39
  40. 40. A similar perceptual illusion happens with the chemicals capsaicin and menthol. Capsaicin is the chemical that makes peppers hot. Menthol gives coolness to many skin creams. We perceive heat and cold, yet a thermometer will not register meaningful changes in skin temperature. The heat or coolness are in your interpretation of sensory data, not in the substance itself; much like the movement in the previous image was in your perception rather than the grid itself. We see, feel, hear, and taste All these pain relievers contain menthol as an active ingredient. interpretations, expectations, and beliefs. 40
  41. 41. An optic nerve contains about a million neural “wires” (called axons) connecting each retina to your brain. Each axon represents one “pixel” of your visual image. Each eye “sees” with the resolution of a one-megapixel camera. 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 visual experience is created by your “fill-in-the blanks “ interpretations. 41
  42. 42. We see a richly detailed reality even when our eyes capture very limited data. 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 feet from the screen. Now both appear clear and undistorted. You fill in the missing detail. This “filling in” helps explain why you might not see a difference in snapshots taken by a 3 megapixel camera compared to one with 7 megapixel resolution….or why 720 HDTV looks much like 1080. 42
  43. 43. A flipbook is a primitive form of movie. It is made of a series of drawings that, when flipped through rapidly, appear to move. The drawings show the same scene with only a minor change in each drawing. The reason we see movement in a flipbook or a movie is that we fill-in what we expect to happen between the still pictures. The movement is our own creation. 43
  44. 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 blanks exist. Perception requires energy – seeing requires a steady supply of calories. To conserve energy we use selective attention – a perceptual shortcut that works most of the time. We are surprisingly blind to what we do not pay attention to. You’ve played card games and looked at the picture cards thousands of time. So you know which of the four playing card kings shows only one eye – don’t you? Which suit of cards shows the one-eyed king? 44
  45. 45. If you could not identify the king of diamonds as the one-eyed king, it’s because you did not need to know. You look at playing cards just enough to see the suit and rank – that’s all you need to play cards. Remember, perception is not about documenting what’s there, its about using it for your own interests. Speaking of playing cards….here’s another illustration of perception. This one involves a bit of mind reading. 45
  46. 46. Above are six playing cards. Select one by staring at it for eight or more seconds to establish a solid visual image. Keep it clearly in your mind. 46
  47. 47. Don’t allow this screen to distract you. We use it to “read” your 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. 48. Did we get it right? If so, what does this teach about how you see? 48
  49. 49. It illustrates selective seeing. What counts is not so much what you see, as what you are aware of. We are aware only of what we pay attention to, while we ignore much of the visual data captured by our eyes. Like the one-eyed king, we see what we need and ignore the rest. If you wish, go back and try the experiment again. See if it works twice. Maybe it was a lucky guess. 49
  50. 50. Here are the cards presented in both screens. Note that the face cards in the second screen contain none of the same cards as in the first. Chances are you concentrated so hard on the card that you DID pick you never “attended to” the cards you didn’t pick. This visual shortcut is called attentional blindness. The “selection cards” The “answer cards” 50
  51. 51. An experiment observed students walking across a campus square. Some walked in pairs, some alone, while others talked on a cell phone. Each was observed while a clown on a unicycle approached and circled them. Students walking in pairs were most likely to see the clown. Surprisingly, half the students talking on cell phones missed the clown completely. The researchers concluded that cell phones contribute to attentional blindness. 51
  52. 52. In another experiment, volunteers were asked to follow a jogger at a fixed distance and count how many times the jogger touched his hat. About a minute into the run, three students stage a fight slightly off to the side of the jogging path. Researcher Chris Chabris explains, “we had two students beating up a third, punching him and kicking him and throwing him to the ground." Only forty percent of the subjects noticed the fight, even in broad daylight. At night the figure dropped to one-third. The subjects were attending to the task of counting hat touches, so the nearby mayhem was invisible. 52
  53. 53. You imagine your eyes gliding around, soaking in detailed images. In reality, your eyes 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 of any eye movement. Seeing consists of eyes “jumping” in rapid succession from one focus to another. Your brain edits out the jumps and presents only the information gained from each “jump target.” You sense a detail-rich, stable-seeming picture of the world “out there.” Eyesight is jumpy. Awareness is smooth. Start Moving your eyes keeps the world stable. To see this for yourself, try looking into a mirror…… 53
  54. 54. Look in a mirror. Move your eyes back and forth, looking first at your left eye, then at your right eye, then at your left eye again. Someone watching you can see your eyes move – they shift from left to right. But surprise, you don’t see your own eyes move. You see yourself staring straight ahead. 54
  55. 55. We call peripheral vision “seeing out of the corner of the eye,” but no such “corner” exists. Peripheral vision is created by eye movements. To experience this, focus on the red dot below. The surrounding circle will vanish -- 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 the 55 refrigerator is always on.
  56. 56. 6. Seeing Me: Self-Blindness You can sense a difference between how you imagine yourself and how you look to others. You sense this difference when you see video of yourself or hear a recording of your voice. We think “is that really how I look or sound?” We are designed to be a bit “self-blind.” We devote far less visual attention to ourselves than to others. This makes sense in terms of seeing as survival. We judge others based on what we see, but ourselves based on what we think and feel. We have a built-in perceptual double standard. Being somewhat “self-blind” is part of our nature. The only problem is we are not aware of our self-blindness, so we keep bumping into ourselves. 56
  57. 57. We see ourselves, “through a glass darkly.” To help understand how we see, consider that we cannot see our own faces. For 99.99% of human history, not one single human ever saw his or her own face. Our ancestors saw reflections, first in ponds then much later in the amazing invention called a mirror. But a reflection is not a face. Reflections are reversed right to left. The image you see in the mirror is not the way you appear to others. This very basic fact of human existence teaches us something about how we see. 57
  58. 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 simply another baby in some untouchable space? At around six months, babies interact with the mirror image but treat the reflection as a plaything. At around age one they think of searching behind the mirror for the playmate. In one research study, 65% of babies demonstrated recognition of their mirror images by age two. Research suggests that babies realize they are seeing themselves sometime during the second year. 58
  59. 59. Someone asks you to smile for a photo. You can’t see yourself smile, so you say “cheese” or try to imitate what you think a smile looks like. It invariably comes off looking “fake” because it is not driven by emotion, and because you have so little experience in seeing yourself smile – you can’t see your face. A genuine smile is nearly impossible to fake. You need to feel an emotion that “makes you” smile. 59
  60. 60. When you open your eyes tomorrow morning, realize you are seeing a world you spent a lifetime learning to see. It is a world you create through constant, demanding, yet invisible work. You see with your brain. That brain sits in total darkness. It can’t see anything. It receives electrical signals, but that’s all. No pictures. No light. No colors. It has no screen to serve as a viewfinder. You the sculptor create colors, dimensions, brightness, and all the awesome beauty of the visual world. Take time to enjoy your amazing creation. 60

Notas do Editor

  • Most people have a favorite way to resolve this “am I moving?” question. Some try to detect vibrations from moving wheels. Others close one eye and sight along the edge of a window. It takes some effort to determine if you are moving or not.
  • The nene, the state bird of Hawaii, have the opposite problem. They are nearly extinct, often becoming road kill as they stand in the middle of a highway. They might be a victim of their evolutionary past that did not encounter large, fast moving objects. They fail to perceive cars as dangerous.
  • Tiles from University of Massachusetts, Lowell Psychology Dept. David T. Landigan, Ph.D.
  • This file is licensed under the Creative Commons Attribution 2.0 Generic license.
  • File created by Adrian Pingstone, based on the original created by Edward H. Adelson
  • Note: Although 15% of the world’s women are tetrachromats, only about 2-3% have the cones close to the middle between the basic red and green cones to give them what could be considered “super color awareness.” Proving which women have this color “super power” is difficult. For more information on tetrachromatic color vision see TETRACHROMATIC COLOR VISIONBy Kimberly A. Jameson in The Oxford Companion to Consciousness. Also search the Internet on the term tetrachromatic color vision.
  • For an excellent description and a series of tests relating to color blindess see: http://www.healthytimesblog.com/2011/04/facts-about-color-blindness/
  • What is Double Vision? (Binocular Diplopia)To experience how much difference the binocular vision system makes, try catching a ball with one eye closed. Our visual system is based on input from two eyes spaced about two inches apart. Each eye sees the world from a slightly different perspective, and your brain uses the difference to calculate distance and create a 3-D world. You need glasses to watch a 3-D movie so that your eyes are fed different images. The screen displays two images (it looks blurry without the glasses) , and the glasses cause one of the images to enter one eye and the other to enter the other eye. You could think of 3-D movies as a kind of controlled double vision.About 5-10% of the population has little or no stereo vision and are often not aware of their lack. They may discover their 2-D vision only upon examination by an ophthalmologist or optometrist. (from The Mind’s Eye, by Oliver Sacks.) For an interesting study of the discovery of how we create three dimensions, see the chapter “Stereo Sue” in Mind’s Eye.
  • Camera image by Koperczak. Public domain.
  • Emmert's Law states that objects that generate retinal images of the same size will look different in physical size (linear size) if they appear to be located at different distances. Specifically, the perceived linear size of an object increases as its perceived distance from the observer increases. This makes intuitive sense: an object of constant size will project progressively smaller retinal images as its distance from the observer increases. Similarly, if the retinal images of two different objects at different distances are the same, the physical size of the object that is farther away must be larger than the one that is closer.Cruise ship photo by Alistair young. Creative Commons 2.0. Space station is public domain.
  • Illusion attributed to Roger Shepherd.
  • White out on the Ekström Shelf Ice, Weddell Sea, Antarctica, HannesGrobe/AWI. This file is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license
  • Image: NOAA
  • Call this bias the “church steeple effect.” A church steeple is architecture designed to maximize its “uplifting” effect.
  • Journal of Consumer Research, December 2003. Mindless Eating by Brian Wansink. Also interview in Nutrition Action Healthletter, May 2011.Glasses from Crate and Barrel catalog.
  • Note: If you look at this image from an angle, the illusion of movement is lessened.
  • Note: Even though these three skin creams all contain the same active ingredient (3-10% menthol) it is not clear if they should make you feel coolness or heat. One hedges its expectations with the name “IcyHot.” Blind testing of these creams on the skin yields ambiguous results as to heat or cold, but most report coolness.
  • By Anton (Own work) [GFDL (www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons.
  • Picture and idea from,The Tinkerbell Effect: Motion Perception and Illusion by Frank Durgin. Journal of Consciousness Studies, 9, No. 5–6, 2002,
  • Hyman, I., Boss, S., Wise, B., McKenzie, K., & Caggiano, J. (2010). Did you see the unicycling clown?: Inattentional blindness while walking and talking on a cell phone. Applied Cognitive Psychology, 24, 597-607. 
  • From: Why Seeing (The Unexpected) Is Often Not Believing, NPR 8/6/11. Study by Chris Chabris from Union College and Daniel Simons from the University of Illinois.Photo by Infrogmation (talk) of New Orleans. Creative Commons Attribution 3.0 Unported license.
  • Above description based on:From Eye, Brain, and Vision by David Hubel.Referenced at hubel.med.harvard.edu/book/b20.htmImage: Eye movements during the first 2 seconds of viewing a picture. based on data by Yarbus, A. L. (1967). Eye movements and vision, Plenum Press, New YorkIm Auge des Lesers, Transmedia Verlag, Stäubli AG, Zürich 2006. Hans-Werner Hunziker. Creative Commons attribution 3.
  • File #: 1901772
  • From A Brief Tour of Consciousnessby V.S. Ramachandran: “..the goal of vision is to do as little processing or computation as is necessary for the job on hand….”
  • “Mirror Self-Image Reactions Before Age Two,” Deulah Amsterdam in Developmental Psychobiology (1972). See also Michael Lewis’s Social Cognition and the Acquistion of Self (1979) and Jerome Kagan’sNature of the Child (1984).
  • Photo: Hamed Saber. Creative Commons attribution 2.0 generic license.