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C:\Vision\17Performance Pt 1A.Wpd PROCESSES IN BIOLOGICAL VISION: including, ELECTROCHEMISTRY OF THE NEURON This material is excerpted from the full β-version of the text. The final printed version will be more concise due to further editing and economical constraints. A Table of Contents and an index are located at the end of this paper. James T. Fulton Vision Concepts [email protected] April 30, 2017 Copyright 2003 James T. Fulton Performance Descriptors 17- 1 [xxx reconfirm all Section references to or in 17.2.2, etc. ] [xxx reword references to constant quantum efficiency ] 17 Performance descriptors of Vision1 Probably more error has crept into the subject of colour vision from inexact description of experimental conditions and the nature of the stimuli employed than from any other cause. Sir John Parsons, 1915 Because of the amount of color artwork in this chapter, it has been necessary to divide it into three parts for distribution over the INTERNET. PART 1A: INTRO, LUMINANCE & NEW CHROMATICITY DIAGRAM PART 1B: EXTENSIONS TO THE NEW CHROMATICITY DIAGRAM PART 2: TEMPORAL AND SPATIAL DESCRIPTORS OF VISION PART 1A: INTRO. LUMINANCE & CHROMINANCE The press of work on other parts of the manuscript may delay the final cleanup of this PART but it is too valuable to delay its release for comment. Any comments are welcome at [email protected]. 17.1 Introduction This Chapter and Chapter 16 form a pair. While the last Chapter developed equations that are applicable to any animal, this Chapter will concentrate on the most highly developed performance descriptors, those applicable to the human. The visual system is considerably more capable, more flexible and more complex than reflected in even the scientific literature. To understand the operation of the visual system has required the development of a considerably more advanced model of the visual system than previously available. This model has defined many of the operating modes of the visual system for the first time. It has also indicated that considerably more sophisticated instrumentation is required than was used in the past. Discussions of the shortcomings of the instrumentation and many of the current theories based on inductive reasoning and floating models used in vision research were originally included in the main body of this Chapter. This material has now been moved to Chapter 19. The material stresses the many degrees of freedom that have not been adequately controlled in most experiments. It also stresses the inadequacies of the theory of vision adopted by the C.I.E. based almost entirely on the inductive approach2. This approach did not call for rigorous experiments to verify the theory. This chapter will concentrate on the descriptors of vision that can be formulated from the electrophysiology of the actual system as presented earlier in this work. While much of this electrophysiology has developed and can be confirmed using psychophysical experiments, it is extremely difficult to develop precise descriptors based on psychophysics alone. This is due to the very large number of uncontrolled variables encountered in the experiments reported in the literature. Section 17.8 of this chapter provides a discussion of this problem. It also provides an initial experimental framework that can be used to pars the description of an experiment provided by the author of a 1Released April 30, 2017 2[CIE-- Commission Internationale de l’Eclairage or International Commission on Illumination; responsible for standards in this area. Most well known for the CIE Chromaticity Diagram of 1924 (2 degree Standard Observer), the CIE Photopic Observer Curve of 1924 (2 degree Standard Observer) and the CIE Scotopic Observer curve of 1951 (2 degree Standard Observer) The Science of Color says they were adopted to aid in color measurement (i.e., not for use in color research) 2 Processes in Biological Vision published paper. More usefully, it can be used to define their future experiments and report their results more precisely. The primary descriptors are; the luminance, chrominance and temporal performance descriptors. A brief discussion of a combined luminance/chrominance descriptor solid will be presented; however, this concept is shown to have limited utility. The noise limiting and spatial performance descriptors of vision will only be discussed briefly in this document. Stochastic noise plays a remarkably small role in vision. Many of the major descriptors are compatible with other members of the animal kingdom format-wise but require different scales. Using the temporal descriptors with other animals is primarily a matter of incorporating the appropriate time constants. The first known theoretical derivation of the waveforms found in the Electroretinogram will be presented here. After-images, a primarily temporal effect, are based on the state of adaptation of the various chromatic photodetection channels, the performance of the vascular system and the background illumination during the after image. After images will be discussed in Chapter 18. To appreciate this Chapter, the reader must recognize the previously poorly documented fact that the human visual system is fundamentally tetrachromatic. As shown in Chapter 5, the fundamental photochemistry of all biological vision is tetrachromatic. Goldsmith has also pointed out that virtually all vertebrate vision is tetrachromatic3, at least as some time during the species lifetime. Chapter 11 shows how the signaling architecture of the visual system is designed to exploit this tetrachromatic capability. Less capable visual system appear to have evolved as an adaptation to a specific habitat. In the case of humans, and other large chordates, ultraviolet sensitivity has been lost as a traded-off with physical size. The tetrachromatic capability of the retina of humans is easily demonstrated in the case of aphakic eyes. The retina in such an eye exhibits the precise tetrachromatic sensitivity function predicted by this theory. As a result of its growth in physical size, the lens of the human eye exhibits an optical density of 3.5 in the ultraviolet spectrum between 325 and 395 nm. Because of this absorption by the lens, the human visual system can be considered a degenerate tetrachromatic system. More specifically, it could be described as a ultraviolet blocked tetrachromatic system. Less specifically, it could be described as a long wavelength trichromatic system. The use of the term tetrachromatic in this Chapter does not include the proposed variants on human vision described by Gavrik4 or similar variants suggested in women due to a genetic mutation5. In both cases, the authors suggest the presence of a fourth chromophore in the region between the normal M– and L– channel photoreceptors. However, the proposal is based on psychophysical testing and does not include any electro-physical or other physiological. data.. 17.1.1 Baseline human visual system required to understand this chapter 17.1.1.1 Historical Background Beginning in the very early 1900's, significant effort was expended in attempting to characterize the performance of the human eye. These efforts can be described in terms of three areas; the luminance response, the chrominance 3Goldsmith, T. (1990) Optimization, constraint, and history in the evolution of eyes. Quart. Rev. Biol. vol. 65, no. 9, pp 281-322 4Gavrik, V. (2002) Tetrachromacy of human vision: spectral channels and primary colors SPIE Proc vol 2241, pp 315-318 5Greenwood, V. (2012) Super human vison Discover Special Issue, Jul/Aug pp 29-31 Performance Descriptors 17- 3 response, and the temporal response of the eye. Much of the effort was concentrated in the first two areas. Because of the complexity of the visual system and the lack of a model, debate raged in the vision community with regard to the adequacy of many workers efforts. This led to considerable social difficulty and historically interesting statements by many leaders and groups of leaders of the day. Several of these positions were incorporated into official documents because of the positions occupied by some of these leaders in the scientific societies. By the 1950's, the leadership had changed but the official text, The Science of Color, of the Committee on Colorimetry of the Optical Society of America, L. A. Jones Chairman, took a number of very defensive positions. As an example, on page 242-243, it stated under the heading “Data independent of all theories of color vision. Theories of color vision purport to explain the phenomenon in terms of retinal structure and function, nerve action, and cerebral projection. Color-mixture data on which are based computations of color specifications are independent of all theories.” Unfortunately, most of their work is based on a theoretical foundation which employs linear addition of spectral component data using the human eye as a null detector and mixing illuminants on an energy basis instead of a photon flux basis. These assumptions lead to problems with both the r-g-b system and the x-y-z system of color description. A major difficulty in the literature is nomenclature. Nearly all languages have a limited to very limited vocabulary associated with the parameters of vision. The limitation is a particular problem with regard to color. This has led to many attempts by scientists to use the same word in many different contexts, usually without specific definition, in their papers. The result has been considerable confusion. A specific example has arisen in the literature during the 1990's with regard to a 2-dimensional representation of a color space represented by hue and saturation and a 3- dimensional color space represented by either lightness (or brightness) and hue and saturation. Whereas the bulk of the literature defines color separately from lightness, several authors discussing a 3-dimensional representation, that has traditionally been called a color solid, have chosen to use a contraction and also call the 3-dimensional representation a color space. In this way, they implicitly define color as a perceived sensation resulting from a visual excitation that is defined in terms of lightness, hue and saturation,.
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