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Machina Speculatrix

W. Grey Walter, a British physiologist, in 1950 and 1951, published two Scientific American articles describing his wonderful Machina Speculatrix (fondly known as Grey Walter's "turtle").

Walter's turtles represent a milestone in the conception and design of intelligent machines, and a second generation turtle is preserved at the Smithsonian Institution. Walter Grey's turtles have inspired Rodney Brooks amongst many others in their quest for building intelligent machines. Walter Freeman has referred to Grey Walter as "Godfather of truly intelligent machines".

A turtle's brain was built with two valves, two mechanical relays, and two capacitors. On the movement side, a turtle was equipped with three wheels and two motors. One motor powered the front wheel whereas other helped steer the front wheel. On the sense side, a turtle had two receptors. One internal "touch" receptor provided the ability to detect if it had hit an obstacle or an incline -- in which case it would stop, back up, and try to navigate around the obstacle. Other external receptor was a photocell. A turtle searched for "moderate level illumination" of where the precise threshold changed with the amount of charge left in its batteries. It was housed in a brightly lit hutch which it found aversive when its batteries were charged and attractive when the batteries were running out. A turtle had an internal status light that went on when it was turning. If it saw its own light in a mirror or a light of another turtle, it would engage in a remarkable turning and backing behavior.


  1. Walter J Freeman, W.Grey Walter: Biographical Essay. Encyclopedia of Cognitive Science(2003) 4: 537-539.
  2. Michael Gasperi's Machina Speculatrix page.
  3. W. Grey Walter, The Living Brain, W. W. Norton, New York, 1963.
  4. W. Grey Walter, An Imitation of Life, Scientific American, pp. 42-45. May 1950.
  5. W. Grey Walter, A Machine that Learns, Scientific American, pp. 60-63, Aug 1951.


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