Although Dr. William Grey Walter is most known for his Turtle robots, he is a neurophysiologist first. So it's better to study his researches in fields of neural system before we move on to his studies in robots. I found wiki lists two chapters for Dr. W.Grey Walter: Brain Waves and Robots. Here I will add other materials from the google.

He is regarded as the pioneer of cybernetics. So we need to check up more about cybernetics. In 1948, Norbert Wiener described cybernetics as “the scientific study of control and communication in the animal and the machine.” Another interesting thing is that a core concept of cybernetics is self replication, came from von Neumann's cellular automata.

Dr. W.Grey was born in Kansas City, Missouri, in 1910. He's educated mostly in Britain. He made a self-introduction in the book titled “Discussions on Child Development” from which we can see how he was influenced by the Pavlovian Theories in his early studies. Dr. W.Grey carried out long time researches to improve the technologies of electroencephalography(EEG), or the brain waves, for measuring electrical activity in the brain. During this period, he “devoted a number of years to the study of organic lesions of the nervous system, to relearn neuroanatomy and apply it to” some studies. By these efforts, he made some important discoveries about the high speed alpha waves and slow delta waves. He also demonstrated the use of delta waves to locate brain tumors.

Also in this book, Dr. W.Grey described the children project he was engaged in before. From that time, he combined his interests in the physiology of nervous system to the influence of environment on children and how children grew up. Later he extended this “nervous system/environment influence/children development” studies to further thinking. He wrote “and I have attempted particularly to quantify methods of study, to develop men and machines able to make objective and concrete appreciation of the problems which we encounter in this sort of work”. This would lead to our cybernetics scientist Dr. Grey.

In 1951, Dr. Grey displayed his `tortoises' at the Festival of Britain. These robots were designed to show the interaction of two sensory systems: a light-sensitive and a touch-sensitive control mechanisms. One vacuum tube was used to simulate two interconnected neurons. These simple amplifier circuits connected two sensors to two motors. The first sensor was a photocell and it was connected to the drive and steering motors. The second sensor was a contact switch that indicated that the turtle’s “shell” had bumped into something; this sent the vacuum-tube amplifiers into oscillation and changed the robot’s direction. This circuitry allowed the turtles to wander a room and return to a hutch to recharge their batteries.

From the simple neural circuitry, several sophisticated behaviors arose. Under normal operation, the steering motor turned slowly with the drive motor at half speed. This scanned the photocell and produced an arcing motion. When the photocell detected a bright-enough light, the turning stopped and the robot headed towards it. This demonstrated simple phototropic(light attracted) behavior. Once the light detected by the photocell became too bright, though, the steering motor began turning; this demonstrated photophobic(light avoiding) behavior. If the shell struck an object, then the system would oscillate until it successfully avoided the object. The robot could adjust its behavior according to the information it got from its “event-window”.

Although the original intention was to study the basis of simple reflex actions and to test his theory on complex behavior arising from neural interconnections, Dr. Grey's successful experiments with these robots had great influences on the birth of science of cybernetics. His two papers, “An Imitation of Life” in 1950, “A Machine that Learns” in 1951 and his book “The Living Brain” in 1963 were widely read and studied.

The technique he used are reflected in today’s reactive and biologically-inspired robots such as those based on the B.E.A.M philosophy. Here the acronym BEAM is standing for: Biology, Electronics, Aesthetics, Mechanics. Biology means we look the nature for inspirations, to solve our problems; Electronics is the technology for us to get our creations work; Aesthetics means that something “looks cool” rather than something crappy though they may work; Mechanics is an intelligent design such as your robot can get around without optical or touch switches.