The fact-check log

1. An illusion is a misrepresentation of a “real” sensory stimulus: an interpretation that contradicts objective “reality” as defined by general agreement. Britannica Scholars: illusion

2. An illusion is distinguished from a hallucination, which seems to originate without an external source of stimulation. Britannica Scholars: illusion

3. Neither an illusion nor a hallucination is necessarily a sign of psychiatric disturbance, and both are regularly reported by virtually everyone. Britannica Scholars: illusion

4. Many common visual illusions are perceptual: they result from the brain’s processing of ambiguous or unusual visual information. Britannica Scholars: illusion

5. Perception, in humans, is the process whereby sensory stimulation is translated into organized experience. Britannica Scholars: perception

6. In the language of Gestalt psychologists, immediate human experience is of organized wholes, not of collections of elements. Britannica Scholars: perception

7. The figure-ground illusion is commonly experienced in the illustration of a white vase whose outline is created by two black profiles. Britannica Scholars: illusion

8. At any moment you can see either the white vase, in the centre, as the figure, or the black profiles on each side, in which case the white is seen as the ground. Britannica Scholars: illusion

9. The fluctuations of figure and ground may occur even without conscious effort. Britannica Scholars: illusion

10. Seeing one aspect usually excludes seeing the other. Britannica Scholars: illusion

11. In the figure-and-ground illustration, the vase appears against the dark background, or two framed silhouettes of heads are seen against the white background. Britannica Students: illusion

12. Britannica Students treats the vase-and-faces figure as an example of object reversibility, an illusion also encountered in the Necker cube. Britannica Students: illusion

13. One Gestalt principle is the figure-ground relationship: we tend to segment our visual world into figure and ground. OpenStax Psychology 2e

14. Figure is the object or person that is the focus of the visual field, while the ground is the background. OpenStax Psychology 2e

15. The figure-ground relationship explains why the same image can be perceived either as a vase or as a pair of faces. OpenStax Psychology 2e

16. Gestalt psychology grew from the work of Max Wertheimer and his assistants Wolfgang Köhler and Kurt Koffka in the early twentieth century. OpenStax Psychology 2e

17. The word gestalt literally means form or pattern, but its use reflects the idea that the whole is different from the sum of its parts. OpenStax Psychology 2e

18. On first looking at a drawing of this sort, you will probably immediately see a meaningful picture. Britannica Scholars: perception

19. After continued gazing, the initial percept may abruptly be replaced by another. Britannica Scholars: perception

20. Thereafter, the two percepts should alternate with the passage of time. Britannica Scholars: perception

21. Some people first see a vase, whereas others first see two profiles. Britannica Scholars: perception

22. Another example of ambiguity and object reversibility is the Necker cube, which may seem to flip-flop. Britannica Scholars: illusion

23. If you view a Necker cube for a prolonged time, you may perceive a sudden reversal, typically every three to five seconds, between the two cube orientations. Michael Bach: Necker cube

24. Can you “hold” one orientation? Normally this is not possible. After about ten seconds or so, it will flip again. Michael Bach: Necker cube

25. L. A. Necker was a Swiss mineralogist. He discovered the reversals by accident when looking at the drawing of a cube-like crystal. Michael Bach: Necker cube

26. Necker published an account of the phenomenon in 1832. Michael Bach: Necker cube

27. The percept of a three-dimensional wireframe cube is already an interpretation, performed on the two-dimensional visual input of a flat line image. Michael Bach: Necker cube

28. Many interpretations of that flat image are possible, but the usual choice is a cube, and both orientations are about equally likely. Michael Bach: Necker cube

29. Some studies have suggested that younger people tend to perceive these reversals more readily than do their elders. Britannica Scholars: illusion

30. Britannica Students puts it as a rule: young people see the reversals more readily than do those who are more mature. Britannica Students: illusion

31. Look at the hollow, negative version of a face mask and it immediately switches back into a positive, normal-looking face; you cannot hold the hollow view. Michael Bach: hollow face

32. Information about the three-dimensional world is lost when it is projected onto our two-dimensional retinas, and some retinal images can be interpreted in more than one way. Michael Bach: hollow face

33. If we cannot rely on shadows, there is nothing in the image that can tell us whether a face is really hollow or normal. Michael Bach: hollow face

34. Faces have a special relevance for us: throughout life we try to “read” faces, and when both a hollow and a normal reading are equally likely, the balance tips toward a normal face. Michael Bach: hollow face

35. Optical illusions do not reveal your personality. There is no reliable scientific data that which variant you see, or whether you see an illusion at all, can be used to deduce it. Michael Bach: optical illusions

36. There is some influence of age, though you do not need an illusion to know your age. Michael Bach: optical illusions

37. For many illusions, a percentage of people with perfectly normal vision do not see them, mostly for reasons currently unknown. Michael Bach: optical illusions

38. In July 1915 Edgar Rubin, a 28-year-old Dane, defended a doctoral thesis titled Synsoplevede Figurer (Visually experienced figures) at the University of Copenhagen. Pind, The Psychologist (BPS)

39. It was in this work that Rubin first elucidated the figure–ground distinction, now a staple of introductory psychology textbooks. Pind, The Psychologist (BPS)

40. It was also in that thesis that he presented his celebrated illustration. Pind, The Psychologist (BPS)

41. In the dissertation Rubin compared “areal figures”, such as the classic vase, with line or stroke figures drawn with a pencil. Pind, The Psychologist (BPS)

42. The vase-and-faces figure was first published in Rubin’s doctoral thesis, Synsoplevede figurer, in 1915. The Illusions Index: Rubin’s vase

43. The Illusions Index credits the figure to Edgar John Rubin (1886–1951), a Danish psychologist and philosopher. The Illusions Index: Rubin’s vase

44. Edgar Rubin was born in Copenhagen in 1886. Pind, The Psychologist (BPS)

45. He became Professor of Psychology at the University of Copenhagen in 1922, and held the post until his death in 1951. Pind, The Psychologist (BPS)

46. Max Wertheimer, Wolfgang Köhler and Kurt Koffka, pioneers of the Gestalt movement, eagerly embraced Rubin’s study, which featured prominently in Koffka’s 1935 Principles of Gestalt Psychology. Pind, The Psychologist (BPS)

47. Rubin was never happy with being counted as one of the Gestalt psychologists. He admired their descriptive psychology but was sceptical of their wide-ranging theories. Pind, The Psychologist (BPS)

Notes