A Hole in the Head Page 5

  4. Von Staden, 1989; Dobson, 1926–1927, Gross 1998a.

  5. Gross, 1995.

  6. Gross, 1995.

  7. Lloyd, 1975; Longrigg, 1993; Gross, 1998a; Freeman, 1954.

  8. Plato, 1920.

  9. Tielman, 1996, 2002.

  10. Tielman, 1996, 2002.

  11. Tielman, 1996, 2002; Bowersock, 1969.

  12. Nutton, 1984; Wilson, 1972; Sarton, 1959; Galen, 1978–1984.

  13. Sarton, 1954.

  14. Sarton, 1954; Wilson, 1972.

  15. Sigerist, 1961; Guthrie, 1945; Walsh, 1934, 1935, 1936, 1937, 1939.

  16. Sarton, 1954; Wilson, 1972; Walsh, 1934, 1935, 1936, 1937, 1939. Galen (1988), in a work relatively recently translated from Arabic, On the Examinations by which the Best Physicians Are Recognized, described the exam he took to get the position at the gladiator school in Pergamon: “A high priest followed this method (of choosing physicians) when I returned to our city from places which I had set out to visit. Although I had not yet completed thirty years of my age he entrusted me with the treatment of all the wounded (men) among those who had fought duels in combat. . . . I performed many anatomical demonstrations before the spectators: I made an incision in the abdomen of an ape and exposed its intestines: then called upon the physicians who were present to replace them back and to make the necessary abdominal sutures—but none of them dared to do this. We ourselves then treated the ape, displaying our skill, manual training, and dexterity. Furthermore, we deliberately severed many large veins, thus allowing the blood to run freely, and called upon the Elders of the physicians to provide treatment, but they had nothing to offer. We then provided treatment, making it clear to the intellectuals who were present that those physicians who possessed skills like mine should be in charge of the wounded. That man was delighted when he put me in charge of the wounded. . . . With the exception of two, none of the wounded in my charge died, whereas sixteen individuals had died under my predecessor. Later, another high priest put me in charge of the wounded and in doing so he was even more fortunate. None of the patients under my care died even though each suffered grave and multiple wounds.” This was actually written much later in Galen’s life than when he got the position in Pergamon and is typical of his grandiose and inflated self-advertisement.

  17. Sarton, 1954.

  18. Bowersock, 1969.

  19. Bowersock, 1969; Sarton, 1954; Wilson, 1972; Nutton, 1984.

  20. Sarton, 1954; Wilson, 1972; Walsh, 1934, 1935, 1936, 1937, 1939; Nutton, 1984.

  21. Singer, 1957; Temkin, 1973.

  22. Singer, 1957; Temkin, 1973; Siegel, 1968.

  23. Galen, 1962; Goss, 1966; Smith, 1971.

  24. Singer, 1957; Smith, 1971; Woolam, 1958; Rocca, 2003b.

  25. Galen, 1968; Temkin, 1973.

  26. Galen, 1962; Goss, 1966; Spillane, 1981; Siegel, 1973.

  27. Galen, 1962.

  28. Galen, 1978–1984.

  29. Galen, 1968.

  30. Gross, 1998a.

  31. Lloyd, 1975; Longrigg, 1993; Gross, 1998a; Freeman, 1954; Hippocrates, 1950; von Staden, 1989; Dobson, 1926–1927; Gross 1995, 1998a.

  32. Plato, 1920; Tielman, 1996, 2002.

  33. Galen, 1978–1984.

  34. Galen, 1979, 1968, 1962; Farrington, 1932.

  35. Galen, 1979.

  36. Galen, 1968.

  37. Walzer, 1929.

  38. Bastholm, 1950.

  39. Galen, 1968.

  40. Galen, 1968.

  41. Galen, 1968.

  42. Galen, 1968.

  43. Walsh, 1926.

  44. Galen, 1978–1984.

  45. Gross, 1997b, figure 7.

  46. Farrington, 1932.

  47. Nutton, 2002.

  48. Nutton, 1995.

  49. Rocca, 2003.

  50. Gross, 1995.

  51. Avicenna, 1930.

  52. Schlomoh, 1953.

  53. Burton, 1885. The colorful Captain Sir Richard Burton himself. Given its racy nature this translation, The Book of the Thousand Nights and a Night, was a privately printed edition available only by subscription. Some of his other translations of Eastern erotica, such as The Scented Garden, which Burton called “a manual of erotology,” were burned by his widow (Lovell, 1998). The later work should be distinguished from his translation of another erotic classic, The Perfumed Garden (Burton, 1886), that was again published privately.

  3

  THE FIRE THAT COMES FROM THE EYE

  One of the earliest ideas about vision is that it depends on light that streams out of the eye and detects surrounding objects. This view was attacked in its own time and finally disproved over two thousand years later. Yet the idea of a beam leaving the eye persisted in beliefs both about the evil eye and the power of a lover’s gaze. It is still widely held among U.S. schoolchildren and adults. We consider the history and ramifications of ideas about the sources of vision.

  VISION: OUT OF THE EYE—EXTRAMISSION THEORIES

  One of the first neuroscientists we know of was the pre-Socratic Alcmaeon of Croton (ca. 450 BCE). He was the first to advocate the brain as the seat of sensation and cognition and the first to dissect parts of the visual system.1 Presumably after observing phosphenes resulting from a blow to the head, he noted, “The eye obviously has fire within it, for when one is struck this fire flashes out. Vision is due to the gleaming.”2

  This idea of vision depending on the “fire in the eye” was elaborated by Plato (427–347 BCE) in his cosmological (and rather anti-science) dialogue the Timaeus, which was enormously influential in the Middle Ages and beyond.3 Plato argued that visual fire streams out of the eye and combines with daylight to form a “single homogeneous body” which serves as an instrument for detecting and reporting visual objects:

  Such fire as has the property, not of burning, but of yielding a gentle light, they [the Gods] contrived should become the proper body of each day. For the pure fire within us is akin to this, and they caused it to flow through the eyes . . . Accordingly, whenever there is daylight round about, the visual current issues forth, like to like, and coalesces with the daylight and is formed into a single homogeneous body in a direct line with the eyes, in whatever quarter the stream issuing from within strikes upon any object it encounters outside. So the whole . . . is similarly affected and passes on the motions of anything it comes in contact with . . . throughout the whole body, to the soul, and thus causes the sensation we call seeing.4

  Theories of vision such as this one, which depend on something streaming out of the eye, are known as extramission theories. Later, the great mathematician Euclid (ca. 300 BCE), in his Optika, developed a rigorously and narrowly geometric extramission theory. In this theory, “Rectilinear rays proceeding from the eye diverge infinitely [and] those things are seen upon which the visual rays fall and those things are not seen upon which the visual rays do not fall.”5

  The astronomer and mathematician Ptolemy (127–148) carried Euclid’s extramission ideas further and combined them with Galen’s (129– ca. 213) work on the anatomy of the eye. Whereas Euclid had postulated discrete rays leaving the eye that became separated with increasing distance, Ptolemy argued that the visual rays formed a continuous bundle or cone.6

  VISION: INTO THE EYE—INTROMISSION THEORIES

  There was an almost equally old but different view of vision among the Greek Natural philosophers, namely that vision involves something entering the eye from the object seen, a class of visual theory known as intromission theory. The first intromission theories were those of the atomists such as Democritus (ca. 410 BCE) and Epicurus (ca. 341–270 BCE). They believed that isomorphic images (or eidola) streamed off objects and entered the eye, where they were sensed.7 As Epicurus put it,

  For particles are continually streaming off from the surface of bodies though no diminution of the bodies is observed . . . And those given off maintain their position and arrangement . . . it is by the entrance of something coming from external objects that we see shapes and think of th
em.8

  The later atomist poet Lucretius (ca. 95–55 BCE) had a similar view. He called the images coming from objects simulacra, and in his poem On the Nature of Things compared them to the skin cast off by cicadas and snakes and the membrane (caul) covering the head of a newborn calf.9

  In Aristotle (384–322 BCE) we find the first detailed discussion of vision. He argued that the atomist view is wrong because if objects put out copies of themselves, these would be objects themselves; but this is impossible because the copies would overlap on their way to the eye and two objects cannot be in the same place at the same time. The Alcmaeon-Plato extramission view is also inadequate because,

  In general it is unreasonable to suppose that seeing occurs by something issuing from the eye; that the ray of vision reaches as far as the stars, or it goes to a certain point and there coalesces with the object as some [Plato] think.10

  Instead, Aristotle developed a rather complicated intromission theory. He assumed that a transparent medium, something like the modern ether, is found in air and water and is necessary for vision. Light is the state of this transparent medium. The color of an object (black and white are types of colors) moves the transparent medium and since the medium is continuous between the object and the eye, movement of the medium is sensed by the eye, yielding visual sensation.11

  ALHAZEN’S SYNTHESIS

  In Europe, soon after the deaths of Ptolemy and Galen, interest in studying the natural world declined and then virtually disappeared. Scientific inquiry gradually shifted to Islamic centers of learning, first in Baghdad and then in Cairo and Coérdoba. Translation of Greek scientific works into Arabic began in the eighth century, and by the end of the ninth century, the achievements of Greek science were being actively discussed and often extended.12

  The nature of vision and light were of great interest to Islamic scientists. Some natural philosophers such as Al-Kindi (ca. 801–866) defended and expanded Euclid’s extramission views. Others such as Avicenna (Ibn Sina, 980–1037), probably the most important Arab natural philosopher, mounted an assault on extramission and built on Aristotle’s theories of vision.13 The primary achievement of Islamic visual science was to merge the two strains of Greek visual theory and eliminate the inadequacies of each. The architect of this synthesis was Ibn al-Haytham (965–1040), known in the West as Alhazen.14 When translated into Latin in the beginning of the thirteenth century Alhazen’s Book of Optics (De Aspectibus) dominated physiological optics in Europe for the 200 years until Kepler (1571–1630).

  Alhazen’s achievement had two parts. The first was to destroy extra-mission theory forever (at least among optical scientists) with a series of irrefutable arguments. For example, he pointed out that bright light produces pain in the eye and that when we look at the heavens it would hardly be possible for the eye to put out enough material to fill the space up to the stars. The second and more original contribution was to introduce a fundamentally new type of intromission theory that incorporated Euclid’s rays and the visual cone of Ptolemy’s extramission theory. Alhazen argued that although every point on a visible object sends light in every direction, only one ray from each point falls on the eye perpendicularly. All the others fall obliquely, are refracted and thereby weakened to virtual ineffectiveness. The sensitive part of the eye (the crystalline humor or lens, following Galen) responds only to the perpendicular rays and these form a cone with the visual field as the base and the center of the eye as the vertex (figure 3.1).15

  Thus Alhazen not only eliminated extramission theory but also built a new intromission theory using the geometric ideas of Euclid and Ptolemy and the anatomico-physiologic ideas of Galen. His theory became “enormously influential” and became the basis of most of the subsequent work in optics in Europe between the thirteenth and seventeenth centuries. Indeed it led directly to Kepler’s theory of the retinal image (1611) and modern visual science.16

  THE FIRE IN THE EYE IS QUENCHED

  Deformation phosphenes, the “fire in the eye” caused by pressure to the eyeball, continued to be observed after Alcmaeon and to demand explanation. Aristotle, having rejected the idea of light emitted from the eye, decided that phosphenes were due to “self-reflection” within the eye. Much later, Kepler still believed that pressure on the eye produced light. Since he realized that the retina was the sensitive surface he assumed that deformation of the eyeball produced sparks which stimulated the retina. He decided that the sparks were produced by mechanical irritation of the iris because “light can not possibly have its seat in the lens or vitreous body because then it would disturb the process of vision.”17

  Unlike Kepler, Descartes (1596–1650) rejected the idea of a physical light in the eye. Rather he suggested a blow on the eye produced vision in the same way he thought that light did, namely by moving the small fibers of the optic nerve. Newton (1642–1727) also thought that pressure on the eye, rather than producing light, mimicked the action of light on the retina:

  Do not these colors arise from such motions, excited in the bottom of the eye by the pressure and motion of the finger, as, at other times are excited there by light for causing vision?

  Figure 3.1

  Alhazen’s intromission theory of vision, which combines elements of earlier intromission and extramission theories. Only the rays from the object that fall perpendicular to the surface of the crystalline humor (Galen’s term for our “lens”) are sensed (Lindberg, 1992).

  These and other speculations were offered as possible alternatives to fire in the eye as explanations for the phenomenon of phosphenes. However, the first experimental refutation of fire or light in the eye came in 1719 from the Italian anatomist Giovanni Morgagni (1682–1771). His experiment was very simple indeed. He pushed his eye to produce phosphenes and had his assistant look into his (Morgagni’s) to see whether any light came out. He found:

  Even when [the assistant] observed extremely carefully and very bright light appeared to me [Morgagni] he could never observe any light by himself.

  Georg Langguth (1711–1782), professor of anatomy and botany at the University of Wittenberg, extended Morgagni’s observations. To find out whether light is generated in the eye he pushed his eye in the dark and, with a mirror, tried to see if light came out of his eye. Then, he wrote,

  A friend, who became curious about these phenomena . . . visited me in the dark room. I briefly explained to him what I was doing. The doors were closed and I asked him to observe my eyes very closely. While I was perceiving the small light [the phosphenes], he was not able to observe any small flashes or oscillating light. Thereafter, he performed the same experiment on himself . . . I could never discover any light leaving his eyes.

  Thereafter, Morgagni and Langguth’s experimental disproof of light in the eye was generally accepted, although their names gradually dropped out of the textbooks. For a modern view of the neural bases of deformation phosphenes see box 3.1. For some drawings of deformation phosphenes see figure 3.2.

  Box 3.1

  Neural Mechanism of Phosphene Formation

  If phosphenes are not caused by a “fire in the eye,” what are they caused by? Otto Grusser and his colleagues (1989) in Berlin studied the effect of eyeball deformation in the cat on the activity of retinal ganglion cells. They found that deformation caused a marked increase in the activity of retinal ganglion on-cells and a marked decrease in the activity of off-cells. Such a pattern of activity is certainly consistent with a phosphene-like perceptual effect. Grusser and colleagues suggested that the deformation caused retinal stretch, which in turn caused an increase in the surface of horizontal cells, which, he suggests, should depolarize them. Horizontal cell depolarization should indeed cause an increase in excitation of the on-ganglion cells and an increase in the inhibition of off-ganglion cells, the result they observed.

  PERSISTENCE OF EXTRAMISSION VIEWS

  In spite of the decline of extramission theories under the widespread influence of Alhazen’s De Aspectibus, and their disappearance among
visual scientists after Kepler’s demonstration of the inversion of the retinal image, extramission views remained and are still widely held. Extramission views may be found in at least four main arenas. The first is the widespread belief in the “evil eye.” The second is in a long tradition in love poetry. Third and most surprisingly, strong extramission beliefs have been demonstrated in a high proportion of schoolchildren and college students in the United States. Finally, most people believe they can feel someone staring at them.

  The Evil Eye

  The evil eye approached and the storm sent no rain . . . the milk was no longer plentiful . . . the vigor of men was restrained. (Sumerian incantation, ca. 4000 BCE)

  A glance of the Medusa turned men to stone.

  Figure 3.2

  (a–c) Development of deformation phosphenes after pressure on the right temporal eyeball at different intervals and (d) after release. (e) simultaneous bilateral indentation of both temporal eyeballs produces a patterned and flickering phosphene (Grusser and Hagner, 1990). Reprinted with kind permission from Springer Science + Business Media.

  Simon ben Johai and Rabbi Jochanan could with their looks transform people into a heap of stones. (Talmud)

  Almost would the infidels strike thee down with their very looks when they hear the warning of the Koran. (Koran)

  Witches may kill by their looks. (G. Mackenzie, Laws and Customs of Scotland, 1674)

  A survey in 1962 at American University Hospital in Beirut indicated that 81% of 379 Armenian, Maronite Christian, and Sunni Muslim mothers sampled believed the evil eye affected their infant’s health.

  The foregoing are all examples of the “evil eye,” the belief that there are individuals whose glance can produce harm, disease, or death.18 Fear of the evil eye may be one of the oldest and most widespread superstitions. Freud called it “the most uncanny and universal.” It is ubiquitous among cultures of Semitic and Indo-European origin and those that have come under their influence. The evil eye is usually the envious eye, and thus is often directed against the innocence of babies, the beauty of women, and the wealth of the powerful and is often attributed to the outcast, the ugly, and the other.19