Origins and objectives of computational diversity in sensory populations

Populations of sensory neurons are not homogeneous. Even neighboring neurons located in the same brain area can process identical stimuli in significantly different ways. Retinal ganglion cells (RGCs) are a prominent example of such heterogeneity — they exhibit diverse properties whose computational role and purpose remain mysterious. In this review, we explore normative theories of neural computation that attempt to explain the origins and role of functional variability in the retina. We first express a general mathematical formulation of normative theories of neural computation and identify components of these theories that can explain the heterogeneity of sensory populations. We then organize existing theoretical studies of retinal coding according to the factors they highlight as explanations of the computational diversity in the retina — the beginning of the visual hierarchy.