Advances in Photoreception: Proceedings of a Symposium on Frontiers of Visual Science

Description

One of a continuing series on Frontiers of Visual Science, this short volume contains papers presented at a recent symposium. These papers describe techniques for assessing the structure and function of photoreception, both in isolation and in aggregation as the "receptor mosaic" of the retina. Also described are dynamic and spatial sampling properties of photoreceptors, with an emphasis on techniques of measurement and associated models of retinal function. This volume should be of interest to basic vision scientists, clinical ophthalmologists, workers in human factors, and computer scientists curious about the visual apparatus of biological systems. Advances in Photoreception PREFACE CONTENTS INTRODUCTION Optical and Molecular Design of Rods Introduction Green Rod Green Color Not Caused by Visual Pigment Alone Myoids Are Waveguides Green Rod Function Green Rods May Be Color Receptors Are Individual Fat Rods Samplers? Transduction Is Response Recovery Mediated Initially by Cyclase Activation? Disagreement Regarding Role of PDE Inactivation Light Response Recovery Because of PDE Activation? Conclusion Acknowledgments References COLOR AND WAVELENGTH SPECIFICITY OF RECEPTORS Cone Visual Pigments in Monkeys and Humans Long- to Middle-Wave Pigments Old World Monkeys and Humans New World Monkeys Spectral Location of Pigments Short-Wave Cones Old World Monkeys and Humans New World Monkeys Spectral Location of Pigments Acknowledgment References Photosensitivity of Primate Photoreceptors Methods Results Spectral Sensitivity Color Matching Luminosity Bleaching Cross Section Acknowledgments References TRANSDUCTION, ADAPTATION, AND DISEASE PROCESSES The ERG and Sites and Mechanisms of Retinal Disease, Adaptation, and Development Introduction Inferring the Site of Adaptation from ERG Data A Model of the ERG A Model of Adaptation of the Rod Receptor Using A-Wave Data to Estimate Ka and Am Assessing the Approach Retinal Disease and ERG Changes Development and ERG Changes Summary Acknowledgments References Phototransduction in Vertebrate Rods: The Electrophysiological Approach to the cGMP Cascade Theory Introduction The Nature of Phototransduction Two Fundamental Constraints Light-Sensitive Conductance Internal Messenger Hypothesis Calcium as Internal Messenger Cyclic GMP as Internal Messenger The cGMP Cascade: A Biochemical Sketch Formal Theory Photocurrent Velocity and Delay Saturation Theoretical Account of Velocity Saturation Theoretical Account of Delay Saturation and Translation Summary References Partitioning Visual Processes Identifying and Sequencing Operations Method and Rationale Illustrative Results Basic Partitions Losses Preceding the Nonlinear Stage Losses Following the Nonlinear Stage A Test for Serial Filter Model Spatial Antagonism Preceding the Nonlinearity Spatiotemporal Filters Cumulative Spatial Filtering Summary of Results Optics (Stages 1 to 3) Phenomena Related to Light Absorption (Stages 4 to 11) Neural Processes Preceding the Nonlinear Process The Nonlinearity Processes Following the Nonlinear Stage Generalizing the Approach Relations to Anatomy and Physiology Locus of the Nonlinearity Form of the Nonlinear Process On Metaphor in Vision Acknowledgments References SPATIAL EFFECTS OF PHOTORECEPTOR MOSAIC The Distribution of Cones in the Primate Retina Tissue Preparation Cone Density Image Sampling Ganglion/Foveal Cell Ratio References The Photoreceptor Mosaic as an Image Sampling Device Shannon's Theorem Sampling Parameters of the Foveal Cone Mosaic Image Recovery from Irregular Samples: Yen's Theorem Extrafoveal Image Sampling Acknowledgements References The Invisible Cone Mosaic Cone Spacing Cone Diameter Sampling by the Three Cone Mosaics References