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vol I chap 3 sect 1

Volume I: Motion

Previous: 2.3. Knowledge domains for understanding.

3. Detecting signals in the eye and creating maps in the brain.

Introduction.

What can be seen with our eyes and located in our brains?

This Chapter refers to the process of viewing that occurs when the tracks of bundles of light rays are concentrated in the human eye. We also consider the processes of creating mental maps for positioning and orientation.

Learning objectives of Chapter 3.

After this Chapter you should be able to:

• Describe the Nobel Prizes in Medicine awarded in 1911, 1967 and 1981 concerning visual systems and processes.

• Describe the Nobel Lectures corresponding to the 2014 Nobel Prize in Medicine awarded for discovering a positioning system in the brain.

• Identify the cognitive procedures (Inquiring, Training, Comprehension, and Metacognition) in the description of the perihelion precession of the planet Mercury.

Description of content of Chapter 3.

Section 3.1. Understanding the mechanisms of vision.

We comment on three Nobel Prizes in Physiology or Medicine: to Allvar Gullstrand in 1911 “for his work on the dioptrics of the eye” [Dioptrics is the study of the refraction of light, especially by lenses.], to Ragnar Granit, Haldan Keffer Hartline and George Wald in 1967 “for their discoveries concerning the primary physiological and chemical visual processes in the eye”, and to David H. Hubel and Torsten N. Wiesel in 1981 “for their discoveries concerning information processing in the visual system”.

Section 3.2. Existence of a mental Global Positioning System (GPS).

We consider the 2014 Nobel Prize in Physiology or Medicine awarded to John O’Keefe, May-Britt Moser and Edvard I. Moser “for their discoveries of cells that constitute a positioning system in the brain”. Their investigations have served to understand the working conditions of a sort of mental GPS (Global Positioning System) used for visualization, memorization, and learning.

Section 3.3. Cognitive procedures for creating scientific knowledge.

We consider the process Cognitive procedures for creating scientific knowledge (Inquiring, Training, Comprehension, and Metacognition) and apply it to the description of the motion of the planet Mercury around the Sun.

3.1. Understanding the mechanisms of vision.

On vision and the study of Optics.

Intelligence comes from Latin intus legere: to read inside. We need eyes to read, to see and understand shapes and meanings. Human eyes function like windows to observe the external world, communication channels for transmitting messages and interpretation screens to receive and process electromagnetic signals in a range of frequencies limited by ultraviolet and infrared radiations. We see because external stimuli are transformed into internal images. The sense of vision implies control of light in motion.

Eyes are the first element in the chain eye-optic nerve-brain: the receiver, the transmitter, and the interpreter. This chain makes possible to distinguish, understand and employ representations of information and interpretations of knowledge about optical properties of objects. From the point of view of embryology eyes and brains come from the same type of cells.

The study of Optics, as a branch of Physics, deals with three aspects of light: geometrical optics concerns propagation in straight lines, reflection, and refraction; physical optics refers to interference, diffraction and polarization, and quantum optics considers the behavior of photons and their interactions with different materials.

In what follows we analyze three Nobel Prizes in Physiology or Medicine recognizing important contributions to the study of vision: the Prizes awarded in 1911 to Allvar Gullstrand, in 1967 to Ragnar Granit, Haldan Keffer Hartline and George Wald, and in 1981 to David H. Hubel and Torsten N. Wiesel. For each one of these six laureates we analyze two kinds of publications available in the web page of the Nobel Foundation: a full quotation of the document called WORK that explains the main contributions of each laureate and the description of their Nobel Lectures that we concentrate in two boxes: the first one dedicated to Accepted knowledge or questions under discussion in laureate´s time and the second one regarding Laureate´s contributions or explanations.

1911 Medicine Nobel Prize awarded to Gullstrand.

WORK: "Our vision is based on the eye’s lens breaking up light from the outside world and converting it into an image at the back of the eye. From here, photosensitive retinal cells convert the light into nerve impulses that eventually become visual images. Calculating the path rays of light take through the eye and how an image is created is very complicated because the eye’s lens consists of different layers that refract light to different degrees. Moreover, the lens also changes shape. However, Allvar Gullstrand (1862-1930) succeeded in doing just that in the 1890s using advanced mathematics."

MLA style: Allvar Gullstrand – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1911/gullstrand/facts/

Nobel Lecture: How I Found the Mechanism of Intracapsular Accomodation.

MLA style: Allvar Gullstrand – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1911/gullstrand/lecture/

BOX 3.1: Accepted knowledge or questions under discussion in Gullstrand´s times.

  • To see at different distances the eye’s optical system changes the shape of the lens to modify its refractive index. This is a mechanism of accommodation that involves both the lens and the capsule that enclosed it.

  • The intracapsular mechanism of accommodation depends on the structure of the lens: an arrange of layers of coiled microscopic fibers. During accommodation these fibers must remain of constant volume because they are not very elastic; any change of shape of the lens would produce internal displacements of these individual fibers.

  • The laws governing optical image-formation in a heterogeneous medium with a continually varying refractive index as in the eye were completely unknown. The conventional mechanism in which focusing light rays issuing from one point in the object will produce a corresponding point in the image is not applicable here.

BOX 3.2: Gullstrand´s contributions or explanations.

  • Study the laws governing the focusing of light rays when the equations of surfaces of the eye´s lens cannot be expressed explicitly and do not strictly satisfy the rules of the Euclidean geometry but the ones of a differential one. Examples of these conditions are the following aberrations: when rays propagating in perpendicular planes have different focci (astigmatism), when rays spread out over some region of space rather than focused to a point (spherical aberration) or when objects appear to have a tail (coma error).

  • Understanding the problem of image-formation in heterogeneous media of continually variable refractive index and particularly the structure of the eye lens and the intracapsular accommodation mechanism. Two aspects required proper understanding: how the ray bundle is refracted in the eye and how the radiant emission is seen around light-points like fixed stars.

  • Knowledge about the structure of the cornea required more precise information about the shape and thickness of the lens surfaces as well as about how the convergence of light changes during passage through the heterogeneous medium.

1967 Medicine Nobel Prize awarded to Granit.

WORK: "Our vision works by the light around us being captured by a large number of light-sensitive cells located in the retinas at the back of our eyes. After a series of nerve switches and conversions of chemical and electrical signals, this results in visual impressions. Using very sophisticated electrodes, Ragnar Granit (1900-1991) was able to study the electrical impulses from the retina’s cells. In studies conducted from the 1930s to the 1950s, he demonstrated that there are different types of cones (the cells that enable color vision) and that these are sensitive to light of three different wavelengths."

MLA style: Ragnar Granit – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/granit/facts/

Nobel Lecture: The Development of Retinal Neurophysiology.

MLA style: Ragnar Granit – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/granit/lecture/

BOX 3.3: Accepted knowledge or questions under discussion in Granit´s times.

  • Retinal electrophysiology was initially studied by psychophysical methods that led to well established correlations between perceptions of color, luminosity, shape and form, and physically defined measurable entities accessible by powerful technological equipment.

  • In 1865 Frithiof Holmgren (1831-1897) at Uppsala, discovered the electrical response of the retina to light, using a primitive version of modern electroretinograms (ERG).

  • In 1894 Santiago Ramón y Cajal (1852-1934) described the retina as a "true nervous centre". Shared with Camillo Golgi, Ramón y Cajal received in 1906 the Medicine Nobel Prize "in recognition of their work on the structure of the nervous system".

BOX 3.4: Granit´s contributions or explanations.

  • It was impossible to understand on a purely photochemical basis the processes involved in light and dark adaptation registered by ERG. “I came to the conclusion that the light adapted eye makes more use of inhibition: impulses in the optic nerve might be stopped by light. The details of the visual image were elaborated by the interplay of excitation and inhibition in the nervous centre of the retina itself.” (Note: ERG means electroretinogram.)

  • Our microelectrode studies of the retina permitted isolation of single fibers in the optic nerve showing that there are two fundamental processes of opposite character in the retina.

  • In his book Sensory Mechanism of the Retina, Granit wrote in 1943 that "The accurate appreciation of contour, in particular, must be due to minute fluctuations of the eyeballs resulting in on- and off-effects as well as sudden inhibitions of the latter".

  • A trichromatic theory was proposed by Hecht as a mechanism of wavelength reception based on the existence of three types of cones in the eye having very close spectral distribution of sensitivity. “However, our experiments demonstrated that there had to be substances in the retina with-absorption spectra in different bands of wavelength widely apart. To test previous results, we start working with microelectrodes.”

  • “The mechanism of colour reception is organized by the peripheral visual apparatus, the number of colour-sensitive elements is relatively limited, and these elements represent widely different regions of the visible spectrum.”

1967 Medicine Nobel Prize awarded to Hartline.

WORK: "Our vision functions because light from the surrounding world is captured by many light-sensitive cells in the retina at the back of the eye. A series of reconnections and transformations of chemical and electrical signals finally result in visual impressions. In studies of the horseshoe crab around 1950, Keffer Hartline (1903-1983) analyzed how the primary signals from visual cells are processed in a network of nerve cells. Among other things, he showed that when a cell is stimulated, signals from surrounding cells are suppressed. This makes it easier to understand the concept of contrasts."

MLA style: Keffer Hartline – – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/hartline/facts/

Nobel Lecture: Visual Receptors and Retinal Interaction.

MLA style: Keffer Hartline – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/hartline/lecture/

BOX 3.5: Accepted knowledge or questions under discussion in Hartline´s times.

  • “The neuron is the functional as well as the structural unit of the nervous system. Neurophysiology studies developed and exploited methods for recording the activity of single neurons and sensory receptors. These studies laid the foundations for the unitary analysis of nervous function…

  • The experiments realized around 1930 on "horseshoe crabs" (Limulus polyphemus) were the first applications to an optic nerve of the technique consisting in isolating a single fiber.

  • As a result of the application of unitary analysis to the receptors and neurons of the visual system different oscillograms of the action potentials in a single nerve fiber represented the responses of retinal receptors stimulated by light.

BOX 3.6: Hartline´s contributions or explanations.

  • “When I first worked with Limulus, I thought that the receptor units acted independently of one another. But I soon noticed that extraneous lights in the laboratory, rather than increasing the rate of discharge of impulses from a receptor, often caused a decrease in its activity.”

  • “One role of inhibitory interaction is enhancement of contrast. … Since inhibition is stronger between close neighbors than between widely separated ones, steep intensity gradients in the retinal image-edges and contours-will be accentuated by contrast.”

  • “Vision itself is a dynamic process because new distributions of excitation are established, and readjustments of the inhibitory interactions are mediated over the retinal network. There is a dynamic interplay of excitation and inhibition.”

  • “The unitary analysis of visual function has yielded substantial knowledge about receptor properties, and about dynamic integrative mechanisms in the retina. The main results of these clarification efforts have been the following: (1) the codification process of impulses generated in the sensory cells when they respond to different intensities and duration of illumination on visual receptors and (2) the mechanisms associated to the perception of brightness, form, and motion.”

1967 Medicine Nobel Prize awarded to Wald.

WORK: "Our vision functions because light from the surrounding world is captured by many light-sensitive cells in the retina at the back of the eye. George Wald (1906-1997) found that vitamin A is an important component in rhodopsin, a light-sensitive substance in the retina, and explained in a series of studies from the 1930s to the 1960s how light causes rhodopsin to change form and be converted. This conversion gives rise to signals in a complicated network of nerve cells by which a number of reconnections and transformations occur before the signals eventually are transformed into visual impressions in the brain."

MLA style: George Wald – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/wald/facts/

Nobel Lecture: The Molecular Basis of Visual Excitation.

MLA style: George Wald – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1967/wald/lecture/

BOX 3.7: Accepted knowledge or questions under discussion in Wald´s times.

  • The book Quantitative Laws in Biological Chemistry, written by Svante Arrhenius in 1915, “offered the hope of translating accurate measurements on whole organisms into the simple kinetics and thermodynamics of chemical reactions in solution.”

  • “Selig Hecht applied his measurements and those of earlier workers to constructing a general conceptual model for the photoreceptor process.”

  • It has been known that dietary night blindness was a symptom of vitamin A deficiency: rats with such a deficiency synthesized less rhodopsin than normal animals. Rhodopsin is a protein; “rhodopsins of deep-sea fishes have spectra displaced to shorter wavelengths than those of surface forms.”

  • Light bleaches visual pigments by making less dark certain regions on a surface. Light of certain frequencies produces isomerization, a chemical process that transforms the atomic arrangements of molecular structures.

BOX 3.8: Wald´s contributions or explanations.

  • “In the retina a substance called opsin regulates, among other things, how much visual pigment is synthesized. …With the different opsins go differences in absorption spectrum, stability, the kinetics of bleaching and regeneration, and other properties.”

  • The human cones are the receptors of color vision. Normal human color vision is trivariant; it involves three types of cones, each with its own visual pigment…

  • A microspectrophotometer can register the differences in the spectra of the visual pigments in single parafoveal rods and cones of human and monkey retinas.

  • “Normal human vision requires the synthesis of four different opsins: one in the rods, to make rhodopsin, and three in the cones, for the color-vision pigments. Each of these must be specified by a different gene.”

  • “…..some of the most significant aspects of the photoreceptor process come from its being laid out in two dimensions: on the molecular level, in two-dimensional arrays of oriented molecules, the membranes that compose the photoreceptor organelles; and on the cellular level, in the single layer of receptor cells that composes the retinal mosaic.”

1981 Medicine Nobel Prize awarded to Hubel.

WORK: "Our vision works by the light around us being captured by a large number of light-sensitive cells located in the retinas at the back of our eyes. The light is converted into signals that are sent to the brain and there converted into visual impressions. David Hubel (1926-2013) and Torsten Wiesel clarified how this process works during the 1960s: In the cerebral cortex signals are analyzed in sequence by cells with the specific tasks of interpreting contrasts, patterns, and movements. They also showed that this ability develops in children during the initial period after birth."

MLA style: David H. Hubel – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1981/hubel/facts/

Nobel Lecture: Evolution of ideas on the primary visual cortex, 1955-1978: a biased historical account.

  • INTRODUCTION
  • HIERARCHY OF VISUAL CELLS
  • HYPERCOMPLEX CELLS
  • ARCHITECTURE
  • ORIENTATION COLUMNS
  • OCULAR DOMINANCE COLUMNS
  • RELATIONSHIP BETWEEN COLUMNS, MAGNIFICATION AND FIELD SIZE

MLA style: David H. Hubel – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1981/hubel/lecture/

BOX 3.9: Accepted knowledge or questions under discussion in Hubel´s times.

  • “Kuffler had described two types of retinal ganglion cells, which he called “on-center” and “off-center”. The receptive field of each type was made up of two mutually antagonistic regions, a center and a surround, one excitatory and the other inhibitory…Kuffler’s center-surround receptive fields thus began to explain why the appearance of objects depends so little on the intensity of the light source.”

BOX 3.10: Hubel´s contributions or explanations.

  • “By the early 1960s our research had extended into different but overlapping areas: working out of response properties (i.e. receptive fields) of single cells; grouping of cells according to function into layers and columns, studied by track reconstructions; experiments in which single-cell recording was combined with experimental anatomy; working out detailed pathways by making microelectrode lesions that were far smaller than conventional lesions to make lesions in single layers of the lateral geniculate body; studies of newborn animals’ postnatal development, and the effects of distorting normal sensory experience in young animals.”

  • “More interesting to us than the mere binocularity was the similarity of a given cell’s receptive fields in the two eyes, in size, complexity, orientation and position. Presumably this forms the basis of the fusion of the images in the two eyes.”

BOX 3.11: David H. Hubel. Other resources.

MLA style: David H. Hubel – Other resources. NobelPrize.org. Nobel Prize Outreach AB 2023. Thu. 16 Mar 2023. https://www.nobelprize.org/prizes/medicine/1981/hubel/other-resources/

Links to other sites: A Nobel Partnership: Hubel & Wiesel https://braintour.harvard.edu/archives/portfolio-items/hubel-and-wiesel

Hubel & Wiesel Come to Harvard.

"Hubel and Wiesel recorded electrical activity from individual neurons in the brains of cats. They used a slide projector to show specific patterns to the cats and noted that specific patterns stimulated activity in specific parts of the brain. Such single-neuron recordings were an innovation at the time, enabled by Hubel’s earlier invention of a special recording electrode. They systematically created a map of the visual cortex with these experiments. The original film projector, light filters and slides, are held at the Warren Anatomical Museum at the Countway Library of Medicine."

Plasticity & Critical Periods.

"Hubel and Wiesel demonstrated that some neurons were only responsive to information that came from a single eye, a phenomenon they referred to as “ocular dominance”. Intriguingly, neurons that are tuned to a particular eye cluster together in anatomical columns in the visual cortex of the brain. They called these “ocular dominance columns”. They also measured how distinct neurons respond to distinct visual features, such as the orientation of a line projected on a screen, or specific patterns of lines. These experiments were instrumental to our understanding of visual processing."

"This precise organization called to question the role that experience plays in the development of the visual system. In a series of papers, Hubel and Wiesel showed that blocking visual input from one eye during the first few months of life dramatically altered the organization of the columns. When an eye of an adult cat was deprived of input, the organization of the ocular dominance columns did not change. Hubel and Wiesel concluded that such plasticity is limited to early life, and called this a ‘critical period’ of visual cortex development. The discovery of critical periods demonstrated how experience shapes the developing brain’s circuitry, thus perception of the external world. This finding applies across all sensory systems, and even has been shown to be present in the development of social behavior and language acquisition. This critical period of visual plasticity forms the basis for medical interventions in strabismus and amblyopia in children."

1981 Medicine Nobel Prize awarded to Wiesel.

WORK: "Our vision works by the light around us being captured by a large number of light-sensitive cells located in the retinas at the back of our eyes. The light is converted into signals that are sent to the brain and there converted into visual impressions. Torsten Wiesel (1924) and David Hubel clarified how this process works during the 1960s: In the cerebral cortex signals are analyzed in sequence by cells with the specific tasks of interpreting contrasts, patterns, and movements. They also showed that this ability develops in children during the initial period after birth."

MLA style: Torsten N. Wiesel – Facts. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1981/wiesel/facts/

Nobel Lecture: The postnatal development of the visual cortex and the influence of environment.

  • INTRODUCTION
  • MONOCULAR DEPRIVATION
  • THE CRITICAL PERIOD
  • RECOVERY FROM DEPRIVATION
  • NORMAL DEVELOPMENT

MLA style: Torsten N. Wiesel – Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2023. Sat. 11 Mar 2023. https://www.nobelprize.org/prizes/medicine/1981/wiesel/lecture/

BOX 3.12: Wiesel´s contributions or explanations.

• “In the early sixties, having begun to describe the physiology of cells in the adult cat visual cortex, David Hubel and I decided to investigate how the highly specific response properties of cortical cells emerged during postnatal development. We were also interested in examining the role of visual experience in normal development. “

… • “Our initial findings were that kittens with one eye occluded by lid suture during the first three months of life were blind in the deprived eye, and that in the striate cortex the majority of the cells responded only to stimulation of the normal eye.”

… • “From another series of experiments, we found that the properties of orientation specificity and binocularity developed through innate mechanisms. This result, taken together with the monocular deprivation experiment, indicated that neural connections present early in life can be modified by visual experience.”

… • “Further advances in our understanding of the nature of and mechanism underlying the deprivation phenomena depended on working out some of the functional architecture of the visual cortex. This was done through further physiological experiments in the normal animal and by using newly developed anatomical methods.”

… • “The binocular deprivation and strabismus experiments support the notion that competition, rather than disuse, is the main cause of the observed changes…. The difference between normal and deprived animals is that under normal conditions a cell receives input synchronously from the two eyes, whereas in monocularly deprived, strabismic, or binocularly deprived animals the two eyes do not act together….In addition to providing insight into the mechanisms of development and plasticity in the visual cortex, the strabismus experiments may be of direct clinical relevance.”

… • “Innate mechanisms endow the visual system with highly specific connections, but visual experience early in life is necessary for their maintenance and full development. Deprivation experiments demonstrate that neural connections can be modulated by environmental influences during a critical period of postnatal development. We have studied this process in detail in one set of functional properties of the nervous system, but it may well be those other aspects of brain function, such as language, complex perceptual tasks, learning, memory and personality, have different programs of development. Such sensitivity of the nervous system to the effects of experience may represent the fundamental mechanism by which the organism adapts to its environment during the period of growth and development.”

Next: 3.2. Generation of a mental Global Positioning System (GPS).