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The terminus of the projection originating in the eye is the enormous sheet of cells in the back of the brain known as the striate cortex. The retina is projected systematically onto the cortex, with hundreds of cells to process the output of each incoming fiber. Striate cells have several characteristics such as binocularity, directional selectivity, and much more narrow orientation and spatial frequency selectivity. This chapter discusses the nature of striate processing, in particular, the anatomy of the striate cortex and the physiology of the striate cortex.

This chapter presents two lengthy papers entitled “Plasticity of Ocular Dominance Columns in Monkey Striate Cortex”, and “The Development of Ocular Dominance Columns in Normal and Visually Deprived Monkeys”. The chief finding of the first paper tackles the effects of early eye removal or monocular lid closure on the ocular dominance stripes in layer IVC. Deprivation in the first few weeks of life resulted in a change in the relative sizes of the two sets of stripes, with a shrinkage of stripes receiving input from the deprived eye and a corresponding expansion of those with input from the normal eye. The main purpose of the second paper was to examine the normal postnatal development of ocular dominance columns in the striate cortex of the macaque monkey and to determine how this developmental process was influenced by the monocular lid-suture.

In the absence of striate cortex, it is in no sense completely deprived of visual information, although it may be reduced quantitatively. This chapter examines how the residual information is processed qualitatively, and whether any particular pathways or their targets, or interactions with other targets or further projections, have a responsibility for any particular visual attribute. Further, this chapter explores whether the absence of striate cortex eliminates any particular attribute and, in particular, whether it eliminates visual awareness. A detailed assessment of the visual system is presented, including the retina, to relate various subtypes of residual capacity to the known or putative properties of specific subparts of the extra-striate visual pathways and cortical areas. Two questions are also addressed regarding the ‘blind’ aspect of blindsight by the chapter.

This chapter presents a 1968 paper entitled “Receptive Fields and Functional Architecture of Monkey Striate Cortex”. This paper represented a first attempt to survey physiologically the monkey striate cortex. It was discovered that there was a tendency for cells to be grouped according to symmetry of responses to movement. A horizontal organization corresponding to the cortical layering can also be discerned. The cortex was seen as a system organized vertically and horizontally in entirely different ways. In the vertical system, stimulus dimensions such as retinal position, line orientation, and ocular dominance, were mapped in sets of superimposed but independent mosaics. The horizontal system segregated cells in layers by hierarchical orders, the lowest orders located in and near layer IV, the higher orders in the upper and lower layers.

This chapter presents a paper entitled “Laminar and Columnar Distribution of Geniculo—Cortical Fibers in the Macaque Monkey”. This paper demonstrated the ocular dominance columns anatomically. Small lesions were made in single layers or pairs of layers in the lateral geniculate body, and the striate cortex was later examined with a Fink—Heimer modification of the Nauta method. It shows that the long narrow stripes of alternating left-eye and right-eye input to layer IV were an anatomical counterpart of the physiologically observed ocular dominance columns. Because of this segregation of inputs, cells of layer IV were almost invariably influenced by one eye only. A cell above or below layer IV would be dominated by the eye supplying the nearest IVth layer stripe but would generally receive a subsidiary input from the other eye by diagonal connections from the nearest stripes supplied by that eye.

The existence of perceptual completion is well documented by a wealth of psychophysical studies, perhaps only rivaled by the many different interpretations of the underlying mechanisms. This chapter argues that some forms of completion are likely implemented early in the visual system. It reviews experimental data showing completion-like properties across the blind spot representation in the striate cortex of monkeys. This property seems to be based on interpolation of spatially collinear stimuli. Experimental evidence is presented for interpolation not restricted to natural scotomata like the blind spot. Additionally, the chapter presents findings of spatial interpolation from striate cortex cells of the opossum, a more primitive mammal.

This chapter examines the role of the primary visual cortex in visual processing. It describes evidence on the nature of the neuronal responses in the primary visual cortex and the processing streams that lead to the primary visual cortex, and discusses some of their computational properties and the computational processes by which they arise. The chapter suggests that there seem to be partially separated neural pathways within the striate cortex that imply a segregation of the processing channels into three functionally distinct pathways, which includes a stereopsis and motion pathway, a colour pathway, and a form pathway.

The input to the striate cortex (area V1) from the lateral geniculate nucleus is transformed to create orientation, direction, velocity, and spatial frequency selective neurons. Many area V1 cells receive a convergent input from the two eyes that contributes to stereoscopic depth perception. Feedback circuits from higher cortical areas modulate the responses of area V1 cells for higher level visual analysis. This chapter has six subsections. Section A discusses the general anatomy of the striate cortex. Section B deals with the functional properties of single cells in area V1. Section C examines the cytoarchitecture of the area. Section D examines the neural mechanisms that give rise to orientation and direction selectivities in area V1. Section E discusses feedback circuits to area V1. Section F provides a summary of the chapter.

This chapter discusses the anatomical and functional continuation of the three parallel visual pathways in cortical areas beyond the striate cortex. These partially segregated visual streams are the magnocellular system, the parvocellular-interblob system, and the parvocellular-blob system. The findings indicate that visual attentional mechanisms allow these processing streams to interact and the attentional effects are implemented via top-down feedback parallel interactions.

Many aspects of visual development over the first months of life can be understood in terms of visual function becoming increasingly dominated by cortical processes. More recent formulations have developed this idea in terms of cortical processes modulating continuing visual functions of subcortical structures and of differential development of distinct visual cortical streams and areas. One important source of evidence for visual cortical development is the development of capabilities that require the specific kinds of stimulus selectivity found in cortical neurons. These include selectivity for orientation, for directional motion selectivity, and binocular disparity. This chapter concentrates on three other lines of evidence; from the control of shifts in visual attention, from optokinetic responses in children with localized brain damage, and from sensitivity to ‘second-order’ stimuli that are presumed to require relatively elaborate cortical processing. These new kinds of evidence are consistent with the broad idea of increasing cortical dominance in the early months but also make clear that the developmental relationships between cortical and subcortical processing, and between cortical areas, are complex ones.

This chapter reviews the ability of neglect patients to navigate in three-dimensional space. It specifically addresses two questions about different navigational systems and about the nature of neglect. The first can be formulated as follows: since hemispatial neglect is a multimodal disorder, does it also produce an anisometry in environmental navigation when using either visual or nonvisual updating? The second question refers to the integration of visual and nonvisual information. Evidence shows that the integration of nonvisual information in processing a navigational space involves brain structures different from those involved in the interaction between multimodal information and the subjects' segmental responses. The studies reviewed so far suggest that brain-damaged patients, including patients with unilateral neglect, can process spatial information as well as normal controls when the entire body is moved. In addition, the lesion may be located either in the parietal lobe, disconnecting the pathway indirectly connecting the striate cortex with the parieto-insular vestibular cortex (PIVC) area, or in areas involved in the connection of the superior colliculus to the PIVC via the pulvinar and the thalamus.

Smooth pursuit consists of conjugate eye movements that allow both eyes to smoothly track a slowly moving object so that its image is kept on the foveae. For example, smooth pursuit eye movements are used when you track a child on a swing. Only animals with foveae make smooth pursuit eye movements. Rabbits, for instance, do not have foveae, and their eyes cannot track a small moving target. However, if a rabbit is placed inside a rotating drum painted on the inside with stripes so that the rabbit sees the entire visual field rotating en bloc, it will track the stripes optokinetically. Humans have both smooth pursuit and optokinetic eye movements, but pursuit predominates. When you track a small, moving object against a detailed stationary background, such as a bird flying against a background of leaves, the optokinetic system will try to hold your gaze on the stationary background, but it is overridden by pursuit. Pursuit works well at speeds up to about 70°/sec, but top athletes may generate pursuit as fast as 130°/sec. Pursuit responds slowly to unexpected changes—it takes about 100 msec to track a target that starts to move suddenly, and this is why we need the faster acting vestibulo-ocular reflex (VOR) to stabilize our eyes when our heads move. However, pursuit can detect patterns of motion and respond to predictable target motion in much less than 100 msec. Pursuit cannot be generated voluntarily without a suitable target. If you try to pursue an imaginary target moving across your visual field, you will make a series of saccades instead of pursuit. However, the target that evokes pursuit does not have to be visual; it may be auditory (e.g., a moving, beeping pager), proprioceptive (e.g., tracking your outstretched finger in the dark), tactile (e.g., an ant crawling on your arm in the dark), or cognitive (e.g., tracking a stroboscopic motion in which a series of light flashes in sequence, even though no actual motion occurs.