FoundationalConceptsNeuroscience

lobe called visual area 1, or V1. Cells in V1 send axons to other nearby
regions of the cerebral cortex called V2, V3, V4, and V5 (Fig. 14.8). All
these visual areas are very highly interconnected, with axons con-
necting every one of the areas with every other, and with axons going
in both directions between any two areas. Many neurons in the visual
cortex also send axons back to the LGN—complex interconnectivity
runs in both directions.
Different visual areas may be distinguished by the functional
properties of their nerve cells. Many neurons in V1 respond to visual
stimuli having an edge of contrast oriented at a particular angle and
sometimes moving in a particular direction. That is, V1 cells respond
to edges of objects. Information about edges and how the edges are
oriented in space may be used to construct the overall shape of an ob-
ject. Many cells in V4 respond to specific colors and are less influenced
by things like shape and movement. And many cells in V5 respond to
movement and its speed and direction and are not so influenced by
things like shape and color.
Furthermore, each of these visual areas contains something like a
map of visual space. Light from objects in the external world (visual
space) is detected by photoreceptors in the retina such that objects
that appear nearby in visual space will stimulate photoreceptor cells
that are near to one another in the retina. This topographic relation-
ship between objects in external visual space is preserved all the way
through the retina to the LGN and into the visual cortex. Thus, cells in
V1 are organized in such a way that the receptive fields of neighboring
V1 cells respond to regions of visual space that are also nearby—there
is a kind of a map of visual space in V1. And these topographic maps
are preserved throughout the other cortical visual areas.