Photon detection

Photon detection can be considered the most elementary retinal computation, but achieving exquisite sensitivity to dim lights using the hardware of biology is no simple task; it requires specializations from molecules to circuits to behavior. Amazingly, our ability to detect light approaches the physical limits set by its quantization into discrete photons. This is one of the most extraordinary examples in biology of evolution's power to optimize computation. As one of the best-studied retinal computations, much is known about the components of photon detection from the level of the molecules involved in phototransduction up to the neurons and synapses of the downstream circuit. Decades of behavioral studies, including some brilliant classical works, have made quantitative links between photons captured by the retina and perception. This chapter will review the signal and noise sources for photon detection at several processing stages in the retina and discuss the neural mechanisms that enable the signal to be amplified and detected over the noise. I will bookend this discussion of neural mechanisms with accounts of the behavioral literature in both humans and animal models.