William Russell Levick. 5 December 1931—5 May 2022

William R. Levick was one of Australia’s most distinguished neuroscientists, making fundamental contributions to our understanding of the neural circuitry of the retina and the visual pathways. Levick’s mastery of the extracellular, single-unit recording technology of his era elucidated the visual function of parallel networks of mammalian retinal neurons, each network transmitting via the optic nerve a unique rendering of the retinal image formed by the eye’s optical system. His physiological analysis revealed the presence of complex processing at the earliest stages of the visual pathway, thus overturning the prevailing view that complex visual analysis begins in the brain. His best-known example is the discovery of a class of retinal ganglion cells that detect moving objects and identify their direction of motion in the visual environment. Another seminal line of investigation revealed the irreducible fluctuations of light quanta as a fundamental limit to visual sensitivity and the reliable encoding of visual information by retinal neurons. Levick’s legacy as a consummate experimental physiologist rests on his attention to detail, mastery of medical physiology needed for maintenance of first-class animal preparations, innovative resourcefulness in creating custom laboratory apparatus and sheer intellect for the design, conduct and assessment of experiments.