Warren McCulloch

American neurophysiologist who, with the young logician Walter PittsWalter Pitts, prop. n.: A largely self-taught American logician who, at about 20 and without a degree, co-invented with Warren McCulloch a simple logical model of a brain cell, the starting point of neural networks., wrote 'A Logical Calculus of the Ideas Immanent in Nervous Activity' (1943). The paper treated each neuron as an all-or-none switch that fires when enough excitatory inputs are active and no inhibitory input is, and showed that networks of such units can realize any expression of propositional logic. This McCulloch–Pitts neuronMcCulloch–Pitts neuron, n.: The first mathematical model of a brain cell as a simple on–off switch: it fires if enough of its inputs are on and no blocking input is. Networks of them can carry out logic. is the ancestor of the artificial neuronartificial neuron, n.: The basic building block of a neural network: a tiny calculator that multiplies each incoming number by a weight, adds them up, and passes the total through a simple function to decide its output. and of neural networksneural network, n.: A kind of computer program that learns a task from examples by tuning thousands to billions of connections between simple number-crunching units, an arrangement loosely inspired by nerve cells in the brain. generally, and influenced John von Neumann's design for stored-program computers. McCulloch chaired the Macy conferences (1946–1953) at which cyberneticscybernetics, n.: The study of how animals, machines and organizations steer themselves using feedback: sensing the result of an action and correcting course. It was both a parent and an early rival of AI. took shape, moved from the University of Illinois to the Research Laboratory of Electronics at MIT in 1952, and co-wrote 'What the Frog's Eye Tells the Frog's Brain' (1959), a landmark of visual neuroscience.