George Wald won the 1967 Nobel Prize in Medicine jointly with Ragner Granit and Halden Keffer Hartline "for their discoveries concerning the primary physiological and chemical visual processes in the eye". George Wald began exploring vision under Hecht, with a focus on understanding what was happening on a molecular level. Wald was the first to discover vitamin A in the retina. In his Nobel lecture he describes how all visual pigment has a retina bound to a type of protein called an opsin that exists in on the outer parts of the rods for eyes in vertebrates, and in rhabdomeres, the counterparts for rods, in invertebrates. These proteins are also important in the cones and variants of them have peak responses at different frequencies.