In the mid-sixties, John Robson and Christina Enroth-Cugell, without realizing what they were doing, set off a virtual revolution in the study of the visual system. They were trying to apply the methods of linear systems analysis (which were already being used to describe the optics of the eye and the psychophysical performance of the human visual system) to the properties of retinal ganglion cells in the cat. Their idea was to stimulate the retina with patterns of stripes and to look at the way that the signals from the center and the antagonistic surround of the respective field of each ganglion cell (first described by Stephen Kuffier) interact to generate the cell's responses. Many of the ganglion cells behaved themselves very nicely and John and Christina got into the habit (they now say) of calling them I (interesting) cells. However. to their annoyance, the majority of neurons they recorded had nasty, nonlinear properties that couldn't be predicted on the basis of simple summ4tion of light within the center and the surround. These uncoop­ erative ganglion cells, which Enroth-Cugell and Robson at first called D (dull) cells, produced transient bursts of impulses every time the distribution of light falling on the receptive field was changed, even if the total light flux was unaltered.

I. The Classification of Retinal Ganglion Cells.- 1. From the Beginning: Ganglion Cell Classification to 1966.- 1.1. Conduction Velocity Groupings in the Optic Nerve.- 1.2. Receptive Field Studies of Retinal Ganglion Cells.- 1.2.1. Parametric Analyses of Receptive Fields.- 1.2.2. Feature Extraction Analyses of Receptive Fields.- 1.3. Morphological Classifications of Ganglion Cells.- 1.4. Function or Phylogeny as a Basis for Ganglion Cell Classifications?.- 2. The Y/X/W Classification of Cat Retinal Ganglion Cells.- 2.1. The Development of the Y/X/W Classification.- 2.1.1. Description of the X/Y Difference.- 2.1.2. Conduction Velocity Correlates of X and Y Cells.- 2.1.3. The W-Cell Grouping.- 2.1.4. Morphological Classes of Cat Ganglion Cells.- 2.2. The Y/X/W Classification: Categories and Taxa.- 2.2.1. Evidence for Choice of Categories.- 2.2.2. Evidence for Choice of Taxa.- 2.3. The Interpretation of Variation: A Central Problem in Cell Classification.- 2.3.1. "Single" and "Multiple" Interpretations of Variation.- 2.3.2. Sources of Variation in the Properties of Ganglion Cells.- 2.3.3. A Multiple Interpretation of Variation in the Properties of Ganglion Cells.- 2.4. A Two-Group (XY/W) Classification of Cat Retinal Ganglion Cells.- 2.5. Two Notes on the Classification of Nerve Cells.- 2.5.1. Incommensurable Classifications.- 2.5.2. Mixed Classifications: The Best of Both Approaches?.- 3. Ganglion Cell Classification in Other Species.- 3.1. In the Monkey.- 3.1.1. Conduction Velocity Groupings.- 3.1.2. Physiological Classifications: Parametric and Feature Extraction.- 3.1.3. The W-like System of Ganglion Cells.- 3.1.4. Morphological Classifications.- 3.1.5. Summary.- 3.2. In the Rat.- 3.2.1. Conduction Velocity Groupings.- 3.2.2. Receptive Field Correlates: Is There an X-like Group?.- 3.2.3. Morphological Classifications.- 3.2.4. Summary.- 3.3. In the Rabbit.- 3.3.1. Conduction Velocity Groupings.- 3.3.2. The Feature Extraction Classification of Rabbit Ganglion Cells.- 3.3.3. More Parametric Analyses.- 3.3.4. Summary.- 3.4. In Other Mammals: Tree Shrew, Goat, and Ground Squirrel.- 3.4.1. Tree Shrew.- 3.4.2. Goat and Ground Squirrel.- 3.5. In Nonmammals: Frog, Toad, Pigeon, Eel, and Mudpuppy.- 3.5.1. Frog and Toad.- 3.5.2. Pigeon.- 3.5.3. Eel and Mudpuppy.- II. On the Methodology of Classification.- 4. Toward Certainty, Objectivity, or Testability? Two Notes on Alternative Methodologies of Classification.- 4.1. Alternative Methodologies of Classification: Their Basis in the Concerns of Classifiers.- 4.1.1. Nominalism and Realism.- 4.1.2. Different Realist Approaches: Toward Certainty, Objectivity, or Testability.- 4.1.3. Summary.- 4.2. Three Stages in the Taxonomy of Animals.- 4.2.1. Aristotle's Taxonomy: Metaphysical Essentialism.- 4.2.2. Physical Typology.- 4.2.3. The Influence of the Theory of Evolution.- 5. Epistemological Background: Inductivism, Essentialism, Instrumentalism, Falsificationism, and Paradigms.- 5.1. Inductivism.- 5.2. Essentialism (Typology).- 5.3. Instrumentalism.- 5.4. Falsificationism.- 5.5. Paradigms and Revolutions.- 5.6. A Falsificationist Approach to the Classification of Neurons.- III. The Impact of Ganglion Cell Classification.- 6. On the Understanding of Visual Processing in the Diencephalon.- 6.1. The LGN of the Cat.- 6.1.1. Evidence of Parallel Processing in the LGN.- 6.1.2. The W-Cell Relay in the dLGN.- 6.1.3. The Medial Interlaminar Nucleus.- 6.1.4. The vLGN.- 6.1.5. The Lamination of the dLGN.- 6.1.6. Morphology of Relay Cells.- 6.1.7. Cortical Projections of Y-, X-, and W-Class Relay Cells.- 6.1.8. Corticogeniculate Projections.- 6.2. The LGN of Primates.- 6.2.1. X/Y Analysis of Parvo- and Magnocellular Laminae.- 6.2.2. Other Components of the LGN.- 6.2.3. Corticofugal Projections.- 6.2.4. Summary.- 6.3. Other Species.- 6.3.1. The LGN of the Rat.- 6.3.2. The LGN of the Tree Shrew.- 6.3.3. The LGN of the Mink.- 6.3.4. Summary.- 6.4. Qualifications to the Parallel Processing Model of the LGN.- 6.5. The Hypothalamus.- 6.6. The Pulvinar: Evidence for an Extrageniculate W-Cell Relay.- 7. On the Understanding of the Visual Centers of the Midbrain.- 7.1. The Midbrain/Forebrain Division of the Visual Pathways: By Branching or Grouping of Ganglion Cells?.- 7.2. The Superior Colliculus of the Cat.- 7.2.1. Early Evidence: Conduction Velocity Analysis of the Retinocollicular Projections.- 7.2.2. Receptive Field Correlates: Hoffmann's Three-Channel Model of the Retinocollicular Projection.- 7.2.3. The Influence of the Visual Cortex and of Visual Deprivation on the Superior Colliculus.- 7.2.4. Qualifications and Limitations.- 7.3. The Superior Colliculus of the Monkey.- 7.4. The Superior Colliculus of Other Species.- 7.4.1. The Rat.- 7.4.2. The Rabbit.- 7.4.3. The Hamster.- 7.4.4. The Opossum.- 7.4.5. Summary.- 7.5. Other Midbrain Centers.- 7.5.1. The Pretectal Nuclei and the Nucleus of the Optic Tract.- 7.5.2. Nuclei of the Accessory Optic Tract and Nucleus Raphe Dorsalis.- 8. On the Understanding of Visual Cortex.- 8.1. Cat Visual Cortex: Processing of Geniculate Input.- 8.1.1. Parallel Pathways to Different Cortical Areas.- 8.1.2. Parallel Organization of Area 17: Correlations between Afferent Input and Receptive Field Properties.- 8.1.3. Parallel Organization of Area 17: Analyses of Its Lamination.- 8.1.4. Corticofugal Projections of Areas 17, 18, and 19.- 8.2. Primate Visual Cortex: Processing of Geniculate Input.- 8.2.1. Parallel Organization of Area 17.- 8.2.2. Organization of the Prestriate Cortex.- 8.3. Cortical Afferents from Extrageniculate Sources.- 8.3.1. Sources of Extrageniculate Afferents in the Cat.- 8.3.2. Sources of Extrageniculate Afferents in the Monkey.- 8.3.3. Functional Significance of the "Second" Visual Pathway.- 8.4. Models of Neuronal Processing within the Striate Cortex: An Argument against Serial Processing.- 8.4.1. The Simple/Complex Model of Serial Intracortical Processing.- 8.4.2. Synaptic Latencies: A Second Line of Evidence for Serial Processing?.- 8.4.3. Summary.- 8.5. Future Work: The Importance of the Classification and Terminology Used for Cortical Cells.- 9. On the Understanding of Retinal Topography: A "Two-Axis" Model of Mammalian Retina.- 9.1. The Problem: The Variability of Retinal Topography.- 9.2. A Two-Axis Model of the Topography of Mammalian Retina.- 9.3. The Vertical Axis: The Nasotemporal Division of Retina.- 9.3.1. Historical Note: The Nasotemporal Division of Human Retina.- 9.3.2. The Nasotemporal Division of the Retina in the Monkey.- 9.3.3. The Nasotemporal Division of the Retina in the Common Cat.- 9.3.4. The Nasotemporal Division of the Retina in t…