Chapter 3 - The biological basis of vision: LGN, visual cortex and L+NL models

Abstract

In this chapter we will describe the layered structure, cell types and neural connections in the lateral geniculate nucleus and the visual cortex, with an emphasis on colour representation. We will also introduce linear+nonlinear (L+NL) models, which are arguably the most popular form of model not just for cell activity in the visual system but for visual perception as well. An important take-away message is that despite the enormous advances in the field, the most relevant questions about colour vision and its cortical representation remain open: which neurons encode colour, how does the cortex transform the cone signals, how shape and form are perceptually bound, and how do these neural signals correspond to colour perception. Another important message is that the parameters of L+NL models change with the image stimulus, and the effectiveness of these models decays considerably when they are tested on natural images. This has grave implications for our purposes, since in colour imaging many essential methodologies assume a L+NL form.