SNARC
Minsky and Edmonds built a net of probabilistic artificial neurons, of valves and potentiometers, that learned to run a maze.
Why it matters
Learning became a physical device rather than a description: a shared shaft turned the weights of the connections through magnetic clutches.
The SNARC was built in the summer of 1951 at the Harvard Psychological Laboratory, under a US Air Force contract. In each unit a potentiometer set the probability of passing a pulse on, and the unit's internal memory set how long its clutch stayed engaged on the reinforcement shaft, from half a second to ten seconds. A reward pulse turned up the potentiometers of units that had recently fired, a punishment pulse turned them down. The mazes had up to ten vertices. The net went on working with wires pulled out and valves removed. Forty neurons and money from the Office of Naval Research come only from Minsky's later account; in the thesis that office supports the thesis work itself.