Neuronal Operations in the Visual Cortex

The invitation by the editors of the series "studies of brain function" to contribute a monograph on the visual cortex gives me the opportunity to present in a concentrated manner much of the work I have done on the visual cortical areas of cat and monkey. However, the field of visual cortical physi­ ology is so active and so diverse that the presentation of only my own work would have given a very incomplete view of visual cortical functioning. Therefore this monograph also reviews most of the studies carried out on the subject in the last two decades. Where possible I have tried not only to describe the cortical machinery but also its possible functional purpose regarding vision. In doing this I have expressed my personal views rather than just reviewing the experimental facts. Much of the work presented in this monograph has been supported by the National Research Council of Belgium and the Research Council of the Catholic University of Leuven. I express my gratitude to them. I have en­ joyed collaborating in these studies with P. O. Bishop, H. Kato, H. Kennedy, K. P. Hoffmann, H. Maes, J. Duysens, E. Vandenbussche, and H. van der Glas. I am much indebted to all those who have commented on earlier versions of this monograph: J. Allman, H. Barlow, J. BuBier, M. Callens, J. Duysens, O. J. Griisser, P. Heggelund, H. Kennedy, L. C. Orban and L. Palmer.

1 The Visual System of Cat and Monkey Compared.- 1.1 The Basic Layout of the Visual System in Cat, Owl Monkey, and Rhesus Monkey.- 1.1.1 The Retina.- 1.1.2 The Optic Chiasm and Optic Tract.- 1.1.3 The Dorsal Lateral Geniculate Nucleus (dLGN).- 1.1.4 Visual Cortex.- 1.1.5 Pulvinar.- 1.1.6 Callosal Connections.- 1.2 Quantitative Aspects of the Retino-Geniculo-Cortical Projections.- 1.2.1 The Overall Numbers of Cells in the Visual Pathway.- 1.2.2 Distribution of Retinal Cell Populations.- 1.2.3 Magnification Factors.- 1.3 Conclusion.- 2 The Visual Cortical Areas of the Cat.- 2.1 Description of the Visual Cortical Areas.- 2.1.1 Area 17: The Prototype of Visual Cortical Areas.- 2.1.2 Areas 18 and 19.- 2.1.3 The Lateral Suprasylvian Areas.- 2.1.4 Areas 20 and 21.- 2.1.5 Additional Visual Areas?.- 2.2 The Levels of Processing in the Visual Cortical System of the Cat.- 2.3 Additional Observations on the Retinotopic Organization in the Primary Complex.- 2.3.1 Variability of the 3 Cortical Maps.- 2.3.2 RF Scatter.- 2.3.3 The 17–18 Border and the Question of the Naso-Temporal Overlap.- 2.3.4 The 18–19 Border and the Question of the Visual Field Islands.- 2.4 Conclusion.- 3 Afferent Projections to Areas 17, 18, 19 of the Cat: Evidence for Parallel Input.- 3.1 The Relay of Retinal Afferents: The Dorsal Lateral Geniculate Nuclear Complex.- 3.2 The Geniculocortical Projection.- 3.3 Functional Streams in the Retino-Geniculocortical Projection.- 3.3.1 Functional Properties of Retinal and Geniculate X, Y, W Cells.- 3.3.2 Correlation with Retinal Morphology.- 3.3.3 Separation of Functional Streams at LGN Level.- 3.3.4 Correlation with LGN Morphological Types.- 3.3.5 Distribution of Functional Streams in dLGN Nuclear Complex.- 3.3.6 Input to Different Areas of Primary Visual Complex.- 3.4 Physiological Identification of the Functional Type of Afferents to Areas 17, 18 and 19.- 3.5 The Termination of Geniculate Afferents in the Visual Cortex.- 3.6 Other Subcortical Afferents: Pulvinar-Lateralis Posterior Complex, Intralaminar Nuclei, Claustrum, and Brainstem.- 3.7 The Ipsilateral Corticocortical Connections.- 3.8 The Connections Through the Corpus Callosum.- 3.9 Conclusion.- 4 Receptive Field Organization in Areas 17, 18 and 19 of the Cat.- 4.1 Twenty Years with the Simple-Complex-Hypercomplex Scheme.- 4.2 Criteria for Classifying Cortical RFs.- 4.2.1 The ON―OFF Overlap or the Parcellation of the RF into Subregions.- 4.2.2 Position Test.- 4.2.3 RF Dimensions.- 4.2.4 End-Stopping or the Hypercomplex Property.- 4.3 The A, B, C, S Scheme.- 4.3.1 Properties and Distribution of Cell Types.- 4.3.2 The S and A Families.- 4.3.3 Responses to Other Stimuli.- 4.4 Correspondence of the A, B, C, S Scheme with Other Classification Schemes.- 4.5 Conclusion.- 5 Parameter Specificity of Visual Cortical Cells and Coding of Visual Parameters.- 5.1 The Tuned Cells as Bandpass Filters: The Multichannel Representation of a Parameter.- 5.2 Are All Tuned Cells Simple (Passive) Bandpass Filters or Are Some of Them Active Filters?.- 5.3 Cells with Thresholds as High-Pass Filters: Single or Multichannel Representation of a Parameter.- 5.4 Conclusion.- 6 Influence of Luminance and Contrast on Cat Visual Cortical Neurons.- 6.1 Contrast-Response Curves Obtained with Sinusoidal Gratings.- 6.2 Contrast-Response Curves Obtained with Slits.- 6.3 The Extreme Contrast Sensitivity at the 18–19 Border.- 6.4 Influence of Contrast and Luminance on Other Response Properties.- 6.5 Conclusion.- 7 Coding of Spatial Parameters by Cat Visual Cortical Neurons: Influence of Stimulus Orientation, Length, Width, and Spatial Frequency.- 7.1 Orientation Tuning of Cortical Cells.- 7.1.1 Definitions and Criteria.- 7.1.2 Quantitative Determinations: Orientation-Response Curves.- 7.1.3 Qualitative Determination: Hand-Plotting.- 7.1.4 Distribution of Preferred Orientations.- 7.1.5 Orientation Columns.- 7.1.6 Conclusion.- 7.2 Influence of Stimulus Length on Cortical Cells.- 7.3 Selectivity of Cortical Neurons for Spatial Frequency and Stimulus Width.- 7.3.1 Selectivity for Spatial Frequency.- 7.3.2 Spatial Frequency and Coding of Stimulus Dimensions.- 7.3.3 Linearity of Cortical Cells.- 7.3.4 The Visual Cortex as a Fourier Analyzer.- 7.3.5 Spatial Frequency: Conclusion.- 7.4 Spatial Parameters: Conclusion.- 8 Coding of Spatio-Temporal Parameters by Cat Visual Cortical Neurons: Influence of Stimulus Velocity Direction and Amplitude of Movement.- 8.1 Influence of Stimulus Velocity.- 8.2 Influence of the Direction of Movement.- 8.3 Influence of Stimulus Movement Amplitude.- 8.4 Conclusion.- 9 Binocular Interactions in Cat Visual Cortical Cells and Coding of Parameters Involved in Static and Dynamic Depth Perception.- 9.1 The Binocularity of Cortical Cells and the Ocular Dominance Scheme.- 9.2 Position Disparity Tuning Curves and the Coding of Static Depth.- 9.3 Orientation Disparity, Another Mechanism for Static Depth Discrimination?.- 9.4 Neuronal Mechanisms Underlying Dynamic Depth Perception (Motion in Depth).- 9.5 Conclusion.- 10 The Output of the Cat Visual Cortex.- 10.1 The Projections of Layer V to the Superior Colliculus, Pons, Pretectum, and Pulvinar-LP Complex.- 10.2 The Projections of Layer VI to the dLGN and the Claustrum.- 10.3 The Commissural Projections.- 10.4 The Associative Corticocortical Projections.- 10.5 Conclusion.- 11 Correlation Between Geniculate Afferents and Visual Cortical Response Properties in the Cat.- 11.1 Electrical Stimulation of the Visual Pathways.- 11.2 The Question of ON or OFF Cell Input to Cortical S Cells.- 11.3 Other Attempts to Identify the LGN Input to Cortical Cells.- 11.4 Conclusion.- 12 Intracortical Mechanisms Underlying Properties of Cat Visual Cortical Cells.- 12.1 The Role of Intracortical Inhibition.- 12.1.1 Orientation Selectivity.- 12.1.2 Direction Selectivity.- 12.1.3 End-Stopping.- 12.1.4 Ocular Dominance.- 12.1.5 Velocity Upper Cut-Off.- 12.1.6 Absence of Response to Two-Dimensional Noise.- 12.2 Properties of the Intracortical Inhibitions.- 12.3 The Structural Counterpart of Inhibitions.- 12.4 Conclusion.- 13 Non-Visual Influences on Cat Visual Cortex.- 13.1 Non-Visual Sensory Inputs to the Visual Cortex.- 13.2 Influence of Eye Movements on Visual Cortical Cells.- 13.3 The Influence of Sleep and Anesthesia.- 14 Response Properties of Monkey Striate Neurons.- 14.1 Retinotopic Organization of Area 17.- 14.2 The Input-Output Relations of Monkey Striate Cortex.- 14.3 Receptive Field Organization and Size.- 14.4 Color Specificity in Monkey Striate Cortex.- 14.5 Influence of Light Intensity and Contrast on Monkey Striate Neurons.- 14.6 Influence of Spatial Parameters.- 14.7 Influence of Spatio-Temporal Parameters.- 14.8 Ocular Dominance Distribution and Depth Sensitivity.- 14.9 Columnar Organization and Functional Architecture of Striate Cortex.- 14.10 Correlation Between Response Properties and Afferent Input.- 14.11 Conclusion.- 15 Conclusion: Signification of Visual Cortical Function in Perception.- 15.1 Operating Principles in Cat Visual Cortex.- 15.1.1 Retinotopic Organization.- 15.1.2 Filtering.- 15.1.3 “Columnar” Organization.- 15.1.4 Distributed Processing in the Primary Complex.- 15.1.5 Changes with Eccentricity.- 15.1.6 Parallel Streams Within each Area.- 15.2 The Cat and Monkey Visual Cortex as a Model: The Question of the Relationship Between Animal Physiology and Human Visual Perception.- 15.3 The Role of the Primary Visual Cortex in Visual Perception: The Significance of Parameter Specificities for Object Recognition.- References.