Visual Illusions: Their Causes, Characteristics and Applications

Part 1

Produced by Bryan Ness and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive.)

VISUAL ILLUSIONS

THEIR CAUSES, CHARACTERISTICS AND APPLICATIONS

BY M. LUCKIESH

DIRECTOR OF APPLIED SCIENCE, NELA RESEARCH LABORATORIES, NATIONAL LAMP WORKS OF GENERAL ELECTRIC CO.

AUTHOR OF "COLOR AND ITS APPLICATIONS," "LIGHT AND SHADE AND THEIR APPLICATIONS," "THE LIGHTING ART," "THE LANGUAGE OF COLOR," "ARTIFICIAL LIGHT--ITS INFLUENCE UPON CIVILIZATION," "LIGHTING THE HOME," ETC.

100 ILLUSTRATIONS

NEW YORK D. VAN NOSTRAND COMPANY EIGHT WARREN STREET 1922

COPYRIGHT, 1922, BY D. VAN NOSTRAND COMPANY

PREFACE

Eventually one of the results of application to the analysis and measurement of the phenomena of light, color, lighting, and vision is a firmly entrenched conviction of the inadequacy of physical measurements as a means for representing what is perceived. Physical measurements have supplied much of the foundation of knowledge and it is not a reflection upon their great usefulness to state that often they differ from the results of intellectual appraisal through the visual sense. In other words, there are numberless so-called visual illusions which must be taken into account. All are of interest; many can be utilized; and some must be suppressed.

Scientific literature yields a great many valuable discussions from theoretical and experimental viewpoints but much of the material is controversial. The practical aspects of visual illusions have been quite generally passed by and, inasmuch as there does not appear to be a volume available which treats the subject in a condensed manner but with a broad scope, this small volume is contributed toward filling the gap.

The extreme complexity of the subject is recognized, but an attempt toward simplicity of treatment has been made by confining the discussion chiefly to static visual illusions, by suppressing minor details, and by subordinating theory. In other words, the intent has been to emphasize experimental facts. Even these are so numerous that only the merest glimpses of various aspects can be given in order to limit the text to a small volume. Some theoretical aspects of the subject are still extremely controversial, so they are introduced only occasionally and then chiefly for the purpose of illustrating the complexities and the trends of attempted explanations. Space does not even admit many qualifications which may be necessary in order to escape criticism entirely.

The visual illusions discussed are chiefly of the static type, although a few others have been introduced. Some of the latter border upon motion, others upon hallucinations, and still others produced by external optical media are illusions only by extension of the term. These exceptions are included for the purpose of providing glimpses into the borderlands.

It is hoped that this condensed discussion, which is ambitious only in scope, will be of interest to the general reader, to painters, decorators, and architects, to lighting experts, and to all interested in light, color, and vision. It is an essential supplement to certain previous works.

M. LUCKIESH

November, 1920.

CONTENTS

CHAPTER PAGE

I. Introduction 1

II. The eye 13

III. Vision 29

IV. Some types of geometrical illusions 44

V. Equivocal figures 64

VI. The influence of angles 76

VII. Illusions of depth and of distance 102

VIII. Irradiation and brightness-contrast 114

IX. Color 124

Part 2

X. Lighting 144

XI. Nature 164

XII. Painting and decoration 179

XIII. Architecture 195

XIV. Mirror Magic 205

XV. Camouflage 210

LIST OF ILLUSTRATIONS

FIGURE PAGE

1. Principal parts of the eye 14

2. Stereoscopic pictures for combining by converging or diverging the optical axes 41

3. Stereoscopic pictures 41

4. The vertical line appears longer than the equal horizontal line in each case 46

5. The vertical dimension is equal to the horizontal one, but the former appears greater 47

6. The divided or filled space on the left appears longer than the equal space on the right 49

7. The three lines are of equal length 50

8. The distance between the two circles on the left is equal to the distance between the outside edges of the two circles on the right 50

9. Three squares of equal dimensions which appear different in area and dimension 51

10. The vertical distance between the upper circle and the left-hand one of the group is equal to the overall length of the group of three circles 52

11. Two equal semi-circles 53

12. Arcs of the same circle 53

13. Three incomplete but equal squares 53

14. Middle sections of the two lines are equal 54

15. An effect of contrasting areas (Baldwin's figure) 54

16. An illusion of contrast 55

17. Equal circles which appear unequal due to contrast (Ebbinghaus' figure) 56

18. Equal circles appearing unequal owing to contrasting concentric circles 56

19. Circles influenced by position within an angle 57

20. Contrasting angles 57

Part 3

21. Owing to perspective the right angles appear oblique and vice versa 58

22. Two equal diagonals which appear unequal 58

23. Apparent variations in the distance between two parallel lines 59

24. A striking illusion of perspective 60

25. Distortion of a square due to superposed lines 61

26. Distortion of a circle due to superposed lines 62

27. Illustrating fluctuation of attention 65

28. The grouping of the circles fluctuates 66

29. Crossed lines which may be interpreted in two ways 67

30. Reversible cubes 68

31. The reversible "open book" (after Mach) 69

32. A reversible tetrahedron 69

33. Reversible perspective of a group of rings or of a tube 70

34. Schröder's reversible staircase 70

35. Thiéry's figure 71

36. Illustrating certain influences upon the apparent direction of vision.

By covering all but the eyes the latter appear to be drawn alike in both sketches 73

37. Zöllner's illusion of direction 77

38. Parallel lines which do not appear so 79

39. Wundt's illusion of direction 79

40. Hering's illusion of direction 80

41. Simple effect of angles 81

42. The effect of two angles in tilting the horizontal lines 83

43. The effect of crossed lines upon their respective apparent directions 83

44. Another step toward the Zöllner illusion 84

45. The two diagonals would meet on the left vertical line 85

46. Poggendorff's illusion. Which oblique line on the right is the prolongation of the oblique line on the left? 85

47. A straight line appears to sag 86

Part 4

48. Distortions of contour due to contact with other contours 87

49. An illusion of direction 88

50. "Twisted-cord" illusion. These are straight cords 89

51. "Twisted-cord" illusion. These are concentric circles 89

52. A spiral when rotated appears to expand or contract, depending upon direction of rotation 90

53. Angles affect the apparent length of lines 91

54. The horizontal line appears to tilt downward toward the ends 92

55. The horizontal line appears to sag in the middle 92

56. The Müller-Lyer illusion 93

57. Combined influence of angles and contrasting lengths 95

58. Two equal oblique lines appear unequal because of their different positions 95

59. An illusion of area 96

60. Five equal areas showing the influence of contour upon judgment of area 97

61. Showing the effect of directing the attention 98

62. Simple apparatus for demonstrating the remarkable effects of contrasts in brightness and color 115

63. Illustrating brightness-contrast 117

64. An effect of brightness-contrast. Note the darkening of the intersections of the white strips 118

65. The phenomenon of irradiation 121

66. An excellent pattern for demonstrating color-contrast 126

67. By rotating this Mason (black and white) disk color-sensations are produced 133

68. For demonstrating retiring and advancing colors 137

69. By combining these stereoscopically the effect of metallic lustre (similar to graphite in this case) is obtained 141

70. A bas-relief lighted from above 146

71. An intaglio lighted from above 147

72. A bas-relief lighted from the left 148

73. An intaglio lighted from the left 149

74a. A disk (above) and a sphere (below) lighted from overhead 145

b. A disk and a sphere lighted by perfectly diffused light 145

Part 5

75. A concave hemispherical cup on the left and a convex hemisphere on the right lighted by a light-source of large angle such as a window 150

76. The same as Fig. 75, but lighted by a very small light-source 151

77. Apparent ending of a searchlight beam 161

78. An accurate tracing from a photograph (continual exposure) of the moon rising 171

79. Accurate tracings from a photograph (short exposures at intervals) of the sun setting 172

80. Explanation offered by Smith of the apparent enlargement of heavenly bodies near the horizon 174

81. Explanation of a common mirage 176

82. Illustrating the apparent distortion of a picture frame in which the grain of the wood is visible 190

83. Another example similar to Fig. 82 191

84. From actual photographs of the end-grain of a board 192

85. Exaggerated illusions in architecture 198

86. Illustrating the influence of visual angle upon apparent vertical height 199

87. Irradiation in architecture 200

88. Some simple geometrical-optical illusions in architecture 201

Continue reading Visual Illusions: Their Causes, Characteristics and Applications free in the Wunder reader →