For decades, photoreceptors have been an outstanding model system for elucidating basic
principles in sensory transduction and biochemistry and for understanding many facets of
neuronal cell biology. In recent years, new knowledge of the kinetics of signaling and the
large-scale movements of proteins underlying signaling has led to a deeper appreciation of
the photoreceptor's unique challenge in mediating the first steps in vision over a wide range
of light intensities.