MOTION MOUNTAIN

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182 4 imagesandthe eye–optics F I G U R E 133 Top: a simplified cross section of the human eye; bottom: the comparison of the optical imaging for a healthy eye and for the most common eye problems, myopia, hyperopia and presbyopia (© NEI at NIH).
the eye and the brain: biological image acquisition and processing 183 Ref. 136 the eye and the brain are still unknown. Apart from rods and cones, human eyes also contain a third type of receptor.This receptortype,thephotosensitiveganglioncellorintrinsicallyphotosensitiveretinalganglion cell, has only been discovered in the early 1990s, sparking a whole new research field. Photosensitive ganglion cells are sensitive mainly to blue light, use melanopsin as photopigment and are extremely slow. They are connected to the suprachiasmatic nucleus in the brain, a small structure of the size of a grain of rice that controls our circadian hormonecycle.Forthisreasonyoushouldwalkalotoutside,wherealotofbluelightis available, in order to reset the body’s clock and get rid ofjet-lag.Photosensitive ganglion cells also produce the signals that control the diameter of the pupil. It is worth recalling that drawings such as the one of Figure 133 aresimplified.They do not show the structures in the transparent part of the eye, the vitreous body, such as the hyaloid canal, which plays an important role during the growth of the eye in the embryo stage. In fact, the growth of the eye inside the womb is even more amazing than its actual function – but this story is outside the scope of this text. Interestingly, the eye is the part that moves most frequently in the human body – more than the heart. It is estimated that the eye performs 200 million saccades every year – without counting the tiny eye movements.Therefore, the motion and lubrification mechanisms of the eye are especially involved. Human versus other eyes The human eye and many other animal eyes are better devices than most modern photographic or video cameras. Not only does it have more pixels than most cameras, it is also insensitive to pixel errors, to the blood vessels in front of the sensors. No camera covers the same range of intensity variation. No human-madecamerahasalenssystem of comparable quality or capabilities: the large viewing angle, the low field distortions – also due to the spherical shape of the retina – and the low chromatic aberrations. No technical autofocus system, image stabilizer or motion compensation system matches that of the eye. One limitation of the eye is its speed.The human eye produces an effective number of 30 images per second and up to 120 images per second under the most ideal conditions; dogs and birds achieve twice the basic rate and insects about ten times as much. Modern video cameras can produce more than 10 000 images per second. When developing the eye, evolution has traded speed for resolution. To achieve high resolution, the eye continuously performs small movements, called micronystagmus. In detail, the eye continuouslyoscillatesaroundthedirectionof vision with around 40 to50 Hz; it constantly averages an image pixel over 30 to 50 receptors, but the exact sharpening mechanism is not clear yet. This motion increases the effective number of pixels, avoids issues with dead pixels and also allows the rods and cones to recharge. All vertebrate eyes have rods, the pixel types that produce black and white images at night. Additionally, the retina of the human eye contains three types of cones, for the colours red, green and blue. As mentioned, much better eyes are found in birds, many reptiles and fish: they have four or more types of cones, built-in colour filters and an ultraviolet-transparent lens. The fourth type of conesand the special eye lens make the eyes of birds and reptiles sensitive to near-ultraviolet light; birds use their ultraviolet Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net
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ChristophSchiller MOTION MOUNTAIN t
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Editiovicesima octava. Proprietassc
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DieMenschenstärken,die Sachenklär
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8 preface PHYSICS: Describing motio
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10 preface Your donation to the cha
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12 contents Do we see what exists?
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Light, Charges and Brains Inourques
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16 1 electricity and fields F I G U
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18 1 electricityandfields F I G U R
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24 1 electricity and fields TA B L
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28 1 electricity and fields Challen
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30 1 electricity and fields If elec
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34 1 electricityandfields F I G U R
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42 1 electricity and fields Oersted
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44 1 electricity and fields Vol. IV
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48 1 electricity and fields Ref. 24
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50 1 electricity and fields Page 21
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52 1 electricity and fields Ref. 29
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Vol. IV, page 231 Chapter 2 THE DES
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Chapter 3 WHAT IS LIGHT? Ref. 57 Pa
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96 3 what is light? Electric field
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98 3 what is light? spark transmitt
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100 3 what is light? Ref. 59 Page 1
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102 3 what is light? primary infrar
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104 3 what is light? Page 84 gases
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106 3 what is light? Fre - Waveleng
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108 3 what is light? Challenge 110
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110 3 what is light? incoming light
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112 3 what is light? Ref. 70 Challe
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114 3 what is light? F I G U R E 69
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116 3 what is light? light Ref. 72
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118 3 what is light? light Challeng
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120 3 what is light? momentumLis gi
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130 3 what is light? v ph v So F I
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236 7 the story of the brain F I G
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238 7 the story of the brain Vol. V
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240 7 the story of the brain TA B L
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242 7 the story of the brain consci
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244 7 the story of the brain Ref. 2
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246 7 the story of the brain F I G
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248 7 the story of the brain Vol. I
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254 7 the story of the brain ∗∗
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Chapter 8 THOUGHT AND LANGUAGE Ref.
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260 8 thought and language Vol. VI,
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262 8 thought and language F I G U
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268 8 thought and language Vol. IV,
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270 8 thought and language . . 0 1
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274 8 thought and language ⊳ Ever
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276 8 thought and language F I G U
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Chapter 10 CLASSICAL PHYSICS IN A N
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322 10 classical physics in a nutsh
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328 a units, measurements and const
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342 challenge hints and solutions n
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360 challenge hints and solutions V
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362 bibliography 10 Thiseffect hasf
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364 bibliography 37 A discussionof
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366 bibliography M.B. van der Mark
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368 bibliography Vol. I, page 96 19
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370 bibliography S.W. McCuskey, F.C
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372 bibliography 119 A complete lis
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374 bibliography F I G U R E 178 Th
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376 bibliography in unserer Zeit33,
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378 bibliography private communicat
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382 bibliography Vol. IV, page 135
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384 bibliography and 304. 260 For a
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CREDITS Acknowledgements Many peopl
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NAME INDEX A Abbott A Abbott,T.A.37
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396 name index D Democritus Democri
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402 name index S Sheldon Sheldon, E
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404 name index Z Zybin Motion Mount
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406 subject index A units 328 Aplys
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408 subject index C classical class
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410 subject index E Earth Earth age
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412 subject index F finite finite 2
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414 subject index I infrared photog
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416 subject index L Lorentz Lorentz
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422 subject index S Scarabeus Scara
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424 subject index T table d’Unit
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426 subject index W Wien’s Wien
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