Fig. 10.

Summary of the bilateral representation of visual space and the specificity of horizontal and callosal connections in the tree shrew. A, Map of visual space modified from one first presented by Kaas et al. (1972) to reflect the ipsilateral visual field representation revealed by optical imaging. The dorsal portion of V1 is shown for both left and right visual cortex. Rostral is toward the top of the page. The thick black lines form the border of V1, and the thin black lines in each hemisphere indicate isoelevation and isoazimuth lines within the map of visual space. The dark gray andlight gray regions beneath the map of visual space simulate vertical and horizontal orientation preference domains, respectively. The small dark gray circles in each hemisphere indicate the location of cells that would be likely to provide input to the site in left cortex indicated by the larger gray circle. The intrinsic inputs, in left cortex, are nonspecific at short distances, but at longer distances they originate mainly from sites along the vertical axis in the map of visual space and whose orientation preference is near vertical. The callosal input originates from a much smaller region of the opposite hemisphere and comes from regions that have both vertical and horizontal orientation preference.B, Visual field depiction of input received via horizontal connections. The dark gray rectangle in the background indicates the receptive field of a cell located where thelarge gray circle is found in the left cortex. Theopen rectangles indicate the receptive field locations of the cells that would provide input to this cell via horizontal connections. These inputs have receptive fields that span a total distance of ∼30^ο of visual space. The cell receives input from many other cells with overlapping receptive fields that can be of any orientation and from other cells that have nonoverlapping receptive fields and whose receptive fields are displaced along a vertical line in visual space and have an orientation preference near 90^ο. C, Visual field depiction of input received via callosal connections. The inputs received from callosal connections have receptive fields confined to a much smaller region of visual space, and they include a wide range of orientation preferences.