Neurophysiological Aspects of Color Vision in Primates : Comparative Studies on Simian Retinal Ganglion Cells and the Human Visual System

"To explain all nature is too difficult a task for anyone man or even for anyone age. Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things ... " Sir Isaac Newton (1642-1727) This book describes and discusses some new aspects of col­ or vision in primates which have emerged from a series of experiments conducted over the past 8 years both on single ganglion cells in monkey retina and on the visually evoked cortical potential in man: corresponding psychophysical mechanisms of human perception will be considered as well. An attempt will be made to better understand the basic mechanisms of color vision using a more comprehensive approach which takes into account new mechanisms found in single cells and relates them to those found valid for the entire visual system. The processing of color signals was followed up from the retina to the visual cortex and to the percepq.tal centers, as far as the available techniques permitted.

1 Introduction.- 1.1 Color Vision Theories. Historical Aspects.- Trichromatic Vision; Color-Opponency; Photopigments.- 1.2 Electrophysiological Studies Related to Color Vision.- Recordings from Cell Populations: Electroretinogram; Visually Evoked Cortical Potential.- Single Cell Studies, Anatomy and Electrophysiology: Receptors; Horizontal Cells; Bipolar Cells; Amacrine Cells; Biplexiform Cells; Ganglion Cells (Early Data).- 2 Methods.- 2.1 Methods of Single Cell Recording in Rhesus Monkeys.- Preparation; Stimulation; Recording and Evaluation Procedure.- 2.2 Identification of Cone Inputs in Retinal Ganglion Cells.- 3 Types of Retinal Ganglion Cells and Their Distribution.- 3.1 Introductory Remarks.- Tonic Cells; Phasic Cells; X-Y Classification.- 3.2 The Concept of Color-Opponency.- Color-Opponent Responses; “On” and “Off”; The Neutral Point; Spatial Organization; The Cone Interaction.- 3.3 The Various Types of Color-Opponent Cells.- Incidence of the Main Types; Comparison Between Spectrally Different Types: Receptive Field Structure; Response Profiles; Spectral Sensitivity Functions.- 3.4 Variations in Color-Opponency.- Dependence Upon Spatial Variables; Fluctuations in the Neutral Point; A Scale of Color-Opponency; Color-Opponency Varies with Retinal Eccentricity.- 3.5 Spectrally Non-Opponent Ganglion Cells.- Spectrally Non-Opponent Tonic Ganglion Cells; Phasic Ganglion Cells; Rare Cell Types.- 3.6 Distribution of Classes of Ganglion Cells Across the Retina.- 3.7 A Simplified Classification Procedure.- 3.8 Résumé: Some Implications for the Understanding of the Visual System’s Function.- Red-Green Versus Blue-Yellow Opponency; On the Neutral Point; How Can Variations in Color-Opponency Improve Color Discrimination? Color Coding in the Retinal Periphery; The Consequences for the Circuitry of the Retinocortical Pathway: A Model; Anatomical Considerations; Brightness, Whiteness, and Color Contrast.- 4 Special Properties of Blue-Sensitive Ganglion Cells.- 4.1 Some Recent Electrophysiological and Psychophysical Data on the Blue-Sensitive Cone System.- 4.2 Chromatic Adaptation and Spectral Sensitivity.- Response Profiles; Action Spectra; Intensity-Response Functions.- 4.3 Paradoxical Phenomena Occurring During Light and Dark Adaptation in Blue-Sensitive Ganglion Cells.- Sensitization; Transient Desensitization; Psychophysical Correlates.- 4.4 A Model Describing the Interaction Between Cone Mechanisms in Blue-Sensitive, Color-Opponent Ganglion Cells.- 4.4.1 Forward Versus Backward Inhibition: Two Models.- General Circuitry; The Anatomy of the Feedback.- 4.4.2 Implications of the Backward-Inhibition Model in Terms of Membrane Properties, Ionic Action and Transmitters.- The Prerequisites; The Function in the Light Adapted and Non-Adapted State as well as Immediately After the Termination of Yellow Adaptation; The Dynamics; The Transmitter.- 4.4.3 The Limitations of the Model: Feedback onto the Receptor or onto the Bipolar Cell?.- Can the ERG Help to Solve the Problem? Hyperpolarizing versus Depolarizing Transmitter.- 4.4.4 Testing the Feedback Model.- A Membrane Circuitry; Computer Simulation of the Model.- 4.5 Résumé: What is Special About the Blue Cone Mechanism?.- 4.5.1 Properties of the B-Cone System: Summary.- 4.5.2 The New Model of Cone Interaction: Its Implications.- Linearity; How is Color Contrast Enhanced? The Model’s Possible Relation to Tritanopic Phenomena.- 4.5.3 Comments on the Retino-Cortical Pathway of the B-Cone Mechanism.- The “Yellow” Signal; The Westheimer Paradigm.- 5 Temporal Properties of Color-Opponent Ganglion Cells..- Flicker-Stimulation; Testing the “Channel” Hypothesis.- 5.1 Critical Flicker Frequencies (CFF) in Tonic and Phasic Ganglion Cells.- 5.2 Influence of Stimulation Frequency on the Spectral Sensitivity Function: Loss of Color-Opponency at Higher Flicker Rates.- The General Response Pattern; The Transition of the Action Spectra; The Paradox in the Ferry-Porter Law and the Gradual Change in Spectral Sensitivity.- 5.3 The Basic Mechanism: Phase-Shift Between Center and Surround Responses.- 5.4 Latency of Center and Surround Responses.- 5.5 The Processing of Luminous and Chromatic Flicker.- 5.6 Stimulus Duration Changes the Action Spectrum.- 5.7 Résumé: Possible Implication of the Transition Between Antagonism and Synergism in Color-Opponent Ganglion Cells.- 5.7.1 Hue and Brightness Can be Signalled via the Same Channel.- 5.7.2 Enhancement Occurs by Synergistic Action of Center and Surround.- Conditions Which Can Modify or Suppress the Enhancement Effect; The Vx-Function; The Brücke Bartley Effect, Brightness and Darkness Enhancement.- 5.7.3 The Fechner-Benham Top.- Attempt at an Explanation; What Could Be the Reason for Different Colors in the Fechner-Benham Illusion? Colors Induced by “Stationary” Black and White Patterns.- 5.7.4 The Loss of Color-Opponency.- Is it Linked to a Loss of Visual Acuity? Can it Provide an Advantage?.- 5.7.5 Possible Consequences for Cortical Processing of Color.- 6 The Spectral Properties of the Human Visual System as Revealed by Visually Evoked Cortical Potentials (VECP) and Psychophysical Investigations.- 6.1 Methods as Applied in Human Observers.- The Observers; Stimulation Technique; Recording and Evaluation Techniques.- 6.2 Rods and Cones.- Intensity-Amplitude Functions; Spectral Sensitivity; Rod and Cone VECP Evoked by Eccentric Stimulation.- 6.3 Fundamental Cone Functions.- 6.3.1 Trichromatic Observers.- Selective Chromatic Adaptation; Cone Signals; Spectral Sensitivity Functions; Comparisons with Sensory Measurements; Anomalous Trichromats.- 6.3.2 Dichromatic Observers.- Incidence; Spectral Sensitivity in the VECP; Comparison with Psychophysical Data.- 6.3.3 The Peculiarities of the Blue-Sensitive Mechanism in the VECP.- 6.3.4 Monochromatic Observers.- A Case Report.- 6.4 Color-Opponency in the VECP and in Psychophysical Measurements.- 6.4.1 Color-Opponency in Normal Color Vision.- Action Spectra.- 6.4.2 Color-Opponency in Congenital Color Vision Deficiencies.- 6.4.3 Acquired Color Vision Deficiencies.- 6.4.3.1 Acquired Red/Green Defects.- A Drug-Induced Loss of Color-Opponency; Case Report; The Implications of a Functional Loss.- 6.4.3.2 Acquired Blue/Yellow Defects.- A Drug Affecting the Blue Cone Mechanism; Transient Tritanopia Under AR-L 115 BS; Standing Potentials Under AR-L 115 BS; The Possible Site of Action; A Speculation Based on the Calcium Hypothesis.- 6.5 The Influence of Flicker Frequency on Spectral Sensitivity.- Electrophysiological Recordings in Man; Psychophysical Data; Flicker Studies in Normal Individuals as Compared with Flicker Responses in Protanopes and Deuteranopes.- 6.6 Conclusion: To What Extent Can Visually Evoked Cortical Potentials Reveal the Function of Individual Receptor Mechanisms?.- Rods and Cones; The Three Spectrally Different Cone Mechanisms; Color-Opponency in Psychophysical and Electrical Data; Congenital Color Vision Deficiencies; Flicker.- Epilogue.- Summary.- References.