Vision Science during Renaissance

From Wikivision

Introduction

Renaissance was a period of European rebirth that lasted roughly from 14th through the 17th century. New ideas developed by Islamic scientists and philosophers were very influential in bringing Europe out of its dark ages. Renaissance scientists used ancient Greek and Roman ideas on vision as well more recent ideas of Muslim scholars, especially Alhazen's ideas of optics and scientific method, to develop their own theories. The rise of rational thinking and the use scientific method was the key to the success of these Renaissance thinkers. The following sections describe theories developed by various European scholars during the Renaissance period on vision.

Kepler (1571 A.D. - 1630 A.D.)

Kepler, the great astronomer, also contributed to theory of vision and optics. Being very religious, Kepler believed light was the essence of God. For Kepler, light was something that connected the spiritual world with the material world. Kepler also attempted to relate light with the soul. He believed that light is associated with life through soul. He though that God added light to the material world so humans could interact with God not only spiritually but also physically. And it was the eye that interacts with the spiritual essence of light.

Kepler's greatest contribution to vision science was on function of the lens. Kepler was the first person to propose the idea that the lens focuses images onto the retina. This idea would later be proved correct by Descartes. ^[1]

Leonardo da Vinci (1452 A.D. - 1519 A.D.)

Leonardo's demonstration of refraction by cornea.

Leonardo's success in vision science lies in the fact that he was a good observer. One of his major achievements was to show that light passing through a tiny hole forms an inverted image. Leonard made a small hole in a heavy paper and in a dark room observed an image cast on the wall from light passing through the small hole. He noticed the images was inverted. This was a landmark experiment at the time as it showed that the idea that light travels in straight lines is accurate. This allowed Leonardo to conjecture that the pinhole could be a simple model for the eye. In the eye, the pupil could serve the purpose of the pinhole and the back part of the eye could serve as a screen or wall where the image is projected. And the eye's pinhole was even better than a paper pinhole because the pupil was not static but instead could contract or expand and hence regulate the amount of light that goes into the eye. Leonardo observed this phenomena carefully, observing that the size of pupil is smaller during daytime and larger during nighttime. ^[2]

Descartes (1596 A.D. - 1650 A.D)

Although Descartes spent most of his career developing philosophical ideas, he made a hugely significant contribution to vision by proving Kepler's idea that the lens focuses image onto the retina. In an experiment, Descartes surgically removed the eye from an ox and scraped the eye's retina to make it transparent. He then decided to hold the ox eye in front of the window so that the eye was looking outside the window. To Descartes' surprise, he saw an inverted image of the outside world projected onto the retina! Hence, not only did Descartes prove Kepler right but also discovered that the lens forms an inverted image onto the retina.

Newton (1643 A.D. - 1727 A.D)

Artist's conception of Newton separating sunlight into color components.

Newton's contributions to optics, and perhaps to science in general, were of greater importance than any other scientist before him because it enabled humanity to think about light and vision in a completely new and clearer way. His book Optiks was one the most revolutionary books published in history and still enlightens modern science. His most famous discovery in optics is that white light (coming from the sun) is composed of several different colors, which could be separated into individual colors if white light is passed through a prism. This discovery was not only a more thorough explanation of refraction but also shed light on how various colors are produced by different objects. Newton decided to investigate further on color. He observed that color light does not change its properties when reflects, refracts, or is transmitted through different objects. This led Newton to develop his theory of color, which states that the color of objects depends upon their interaction with colored light, and that objects themselves do not generate color.

Newton embarked on a completely new journey in the field of optics when he first proposed the idea of wave-particle duality of light. Newton realized that light was such a phenomenon that only considering it as a wave or only considering it as particles could not explain all of its characteristics. To Newton, light could be considered as composed of particles (now called photons) as its particle nature explained how particles of light could be refracted by accelerating towards the denser medium as they moved from a less dense to a more dense medium. At the same time, light could be made of waves because Newton could explain the idea of diffraction better using waves. Newton had already entered the realms of quantum mechanics and even though quantum mechanism does not agree with Newton's ideas, Newton was the one who gave a birth to this field. Newton's ideas would later greatly influence future ideas on interaction of light and eyes and their implications for visual processing. ^[3]

References

1. ↑ Lindberg, David, C. The Genesis of Kepler's Theory of Light: Light Metaphysics from Plotinus to Kepler. Osiris. 2nd Series, Vol. 2, (1986).
2. ↑ Ackerman, James, S. Leonardo's Eye. Journal of the Warburg and Courtauld Institutes. Vol. 41, (1978).
3. ↑ Shapiro, Alan, E. The Evolving Structure of Newton's Theory of White Light and Color. Isis. Vol. 71, No. 2, (Jun., 1980),