Chapter 7

Chapter summary

The visual system can be divided into three major components: the retina, the visual pathway, and the visual cortex. The retina is a layered network of cells lining the inner surface of each eye. Photoreceptor cells (rods and cones) in the outer layer respond to light, and ganglion cells in the inner layer carry this neural activity along the visual pathway to the brain. Different ganglion cell classes (midget, parasol, and bistratified) convey different kinds of information about the image. A neural relay in the visual pathway (lateral geniculate nucleus, LGN) modulates incoming responses on the way to the cortex.

Cells in the cortical receiving area for vision (V1 or striate cortex) respond selectively to stimulus orientation, movement direction, colour, and binocular disparity. Cells in secondary areas have larger receptive fields and more complex responses than striate cells. There is a broad division between two parallel streams of processing in later areas. One stream includes a series of ventral areas, and the other passes through more dorsal areas. The ventral stream is thought to specialize in the analysis of spatial pattern and form; the dorsal stream seems to be important for visually guided action and navigation, though its function is still debated.