grey walter's robots

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doi: 10.1098/rsta.2003.1260, 2085-21213612003Phil. Trans. R. Soc. Lond. A

Grey WalterExploration and high adventure: the legacy of

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10.1098/rsta.2003.1260

Exploration and high adventure:the legacy of Grey Walter

B y O w e n H o l l a n d

Department of Computer Science, University of Essex,Wivenhoe Park, Colchester CO4 3SQ, UK ([email protected])

Published online 20 August 2003

Although many people feel themselves to be familiar with Grey Walters ideas, andwith the design principles of his tortoises, most of the published sources are lackingin detail. This paper gathers together images and written material from a variety of published and unpublished sources to set both the man and his work in a richer con-text than has been possible for many decades. Grey Walter emerges as a fascinatingand far-seeing gure whose work has not dated, perhaps because it was explicitlybased on similar principles to those used today in biologically inspired robotics.

Keywords: cybernetics; biological inspiration; robotics

1. IntroductionThere can be no doubt that some of the ideas pioneered by W. Grey Walter (1910{1977) have inuenced the eld of biologically inspired robotics down to the presentday. The other papers in this issue show how the power of the approach is revealedby both the present state of the art, and the promise of future developments. Thispaper looks backwards rather than forwards; it is an examination of Grey Waltersoriginal work in the context of his life and times, and uses a selection of contemporaryimages and documents to place his achievements against a richer background thanhas previously been possible. Even a few years ago, little was known of his robotics

work beyond what had been published in two papers in Scientic American (Walter1950a , 1951) and in his book The living brain (Walter 1953 a ). However, the recentrevival of interest in his work and in the early years of the cybernetic movement inBritain has led to the discovery of some fascinating and illuminating material, andit is probably only in the last few years that we have been in a position to make aninformed assessment of his true contribution. Some of the material presented in thispaper has already been published elsewhere; it is included here in order to give a fulland rounded view of Walters work in the context of the theme of this collection.

Perhaps the best approach is to begin with a brief biography, illustrated with some

of the recently uncovered material. (For a more detailed account of his life and career,see Hayward (2001 b).) William Grey Walter, always known as `Grey, was born in1910, in Kansas City, the only child of Karl Walter (a British journalist, then editorof the Kansas City Star ) and Margaret Hardy, an American journalist. The family

One contribution of 16 to a Theme `Biologically inspired robotics.

Phil. Trans. R. Soc. Lond. A (2003) 361 , 2085{21212085

c 2003 The Royal Society

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The legacy of Grey Walter 2087

in epileptics between seizures. As well as these studies of brain disease Itried to make some sense of the variations in alpha rhythms and in orderto quantify frequency measurements I invented and built the rst on-linefrequency analyser. . . . The operational proof of this instrument is thatwith it I discovered the complexity of the ne structure of alpha rhythms

and demonstrated their relation to individual dierences in mentality andimagery. I also showed that (it was wrong to speak of) `driving the alpharhythms with icker|the alpha components remained in the spectrumand the icker-evoked ones added to them. This was an important discov-ery. . . it demonstrated the widespread eects of visual stimulation, fromwhich emerged the discovery of photic activation in epilepsy and the con-cept of certain epileptic seizures as due to coupling or synchronisation of previously uncoupled systems. The identication of quasi-harmonic com-ponents in the inter-seizure EEG of epileptics (by frequency analysis) wasthe clue to this concept.

At this period also (1943{6) I discovered and named theta rhythms. . .and this term also has been accepted, although sometimes I think mis-used. . . . [In] some of the records (of experiments on conditioned reexes)I noticed a slow potential change in certain conditions when the subjectwas severely penalised for a wrong decision. . . . I began to look for thisslow change more carefully. . . . It took a long time, several hundred longpolygraphic records and innumerable control studies to establish beyondany doubt that in all normal human brains the frontal cortex developsa potential change of about 20 microvolts following a signal (sensory orinternal) which is signicantly related to the expectancy of a subsequentevent with which the person is in some way engaged. This is the Contin-gent Negative Variation (CNV) or Expectancy Wave which is now beingstudied intensively in many laboratories all over the world. . .

I have not referred to the various technical innovations and adaptationsthat I have been involved in during the last 20 years. These were originaland productive but were joint eorts with my friends and colleagues. . . .

I have been very fortunate in being at the right place at the right

time with the right tools and the right people. I do claim, however, tohave helped to organise these coincidences. I founded the EEG Society in1943, organised the rst EEG Congress in 1947, and. . . the InternationalFederation of EEG Societies (of which I was President from 1953{57)and the EEG Journal in that year. . . I claim also that I have never goneseriously wrong in my descriptions, interpretations, inventions or conjec-tures. There are thousands of people working now as I was alone 30 yearsago, and I believe that in 10 years they will be working along the linesthat I am exploring now.

Walter (1967)

The work that mainly concerns us here|the design of the tortoises, and the inter-pretation of their behaviour|was carried out in 1948 and 1949. Although it loomslarge in our view, it is important to realize that it formed a very small part of hisintellectual output: only a single chapter in The living brain , and a handful of papers

Phil. Trans. R. Soc. Lond. A (2003)



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amongst the 174 recorded under his authorship in the BNI bibliography. This doesnot mean that he spent only a little time on the tortoises, or considered them unim-portant; the fact is that he was an extremely active person in very many ways, andhad a high work rate and an unusually wide range of interests.

Nicolas Walter described some aspects of his lifestyle and character as follows:

He was. . . involved in the peace movement before and after the war, beinga member of the Peace Pledge Union in the 1930s and of the Bristol Com-mittee of 100 in the 1960s; but he was never a pacist, and during thewar he was an enthusiastic ocer in the Bristol Home Guard. He wasa convinced trade unionist, and was a leading member of the Bristolbranch of the Association of Scientic Workers. He was a rm atheist,and frequently addressed humanist meetings. . . . He was interested. . . inthe paranormal, and he did some research on the neurological aspectsof altered states of consciousness and participated in conferences of theParapsychology Foundation. He was a uent speaker and writer in sev-eral languages, on general as well as technical subjects. . . . He relishedmaking broadcasts and giving talks; he was a frequent guest on the BBCtelevision Brains Trust during the 1950s and 1960s. . . . He also wrotemany articles; but he found it dicult to produce more sustained work,and both of his two books were actually written by his father from hisnotes and conversations. y He always looked much younger than his age,and he kept t at tennis, gliding, and skin-diving. He grew a beard in1948, when this was still very unfashionable, and he was fond of behaving

unconventionally and of wearing either very casual or very formal clothes.Walter (1990)

His disregard of conventionality extended into his private life, which was oftenscandalous by the ordinary standards of the day, though no more so than that of many in his circle. Did his lifestyle and character aect his career in any way? Thereare certainly grounds for suspecting that they did, although he always received duerecognition for his achievements from the EEG community. Hayward (2001 b) exam-ined Walters career in the context of the history of science, and noted that, in con-

trast to `the reserved and stately gures of Adrian and Sherrington, who dominatedneurophysiology, `Walter cultivated a more swashbuckling image as an emotionaladventurer (Hayward 2001 b, p. 616). After listing some of Walters personal andprofessional characteristics, he remarked,

Such eclectic and amboyant combinations. . . certainly estranged manyof his professional colleagues. . . . Despite his leading role in the clinicaland commercial development of the EEG during World War II, Waltersmaverick reputation ensured his continuing alienation from the scienticestablishment.

Hayward (2001 b, p. 616)

y The 1961 Penguin edition of his rst book, The living brain , carries the dedication: `To my father,with whom this book was happily written. His second book (Walter 1956 a ) was a science ction novel,published in the UK as Further outlook and in the US as The curve of the snowake .




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Figure 1. One of the earliest photographs of Elsie, probably dating from late 1949.The notice reads `Please do not feed these machines.

Some of his inuential contemporaries may have regarded him as `unsound; othersmay have objected to his `showmanship, and to what Shipton called his `. . . immensetalent for persuasive oratory. . . (Shipton 1977), which on occasion may have carriedhim beyond the facts. It is possible that the continuing ow of his scientic con-tributions might have brought some eventual ocial acknowledgement, but it wascut short by a tragic accident: as he travelled home on his motor scooter one dayin 1970, he collided with a runaway horse, and received serious head injuries. Afterweeks in a coma, he regained consciousness; he eventually made a good physicalrecovery, but it soon became clear that he was no longer able to work eectively, andthat his research career was at an end. Characteristically, he had never saved for hisretirement, but a small pension was arranged for him, and he nally retired in 1975.He died following a heart attack in 1977.

2. The tortoises and the public

It is now impossible to establish exactly when Walter began work on the tortoises, but

it was probably at some time in 1948. In a letter, Nicolas Walter recalled `. . . I stayedwith Grey and Vivian y for the last time during the school holidays in spring 1948,and although he talked a lot about his work he said nothing about making models, so

y Vivian Dovey was Grey Walters second wife. A colleague for many years, she was co-author withhim of eight papers on electroencephalography between 1944 and 1957.




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he must have started after that (Walter 1995). However, by late 1949, Grey Walterwas demonstrating Elmer and Elsie, the rst two tortoises, to the press, with all theshowmanship that some held against him. Figure 1, one of the earliest photographsfrom this period, is an excellent example of his style. Fortunately, the rst major pressstory, by Chapman Pincher in the Daily Express of 13 December 1949, is a model

of restrained and factual popular reporting, giving reasonably accurate technicaldetails of the robots construction and behavioural repertoire. It seems likely thatthe background information in the article is also correct: Elmer, the `prototype, isreported to have been built `more than a year ago, indicating a date of 1948; therobots were built in the `backroom laboratory of his house by Grey Walter, `helpedby his wife Vivian.

Other newspaper accounts were less accurate and more sensational:

Toys which feed themselves, sleep, think, walk, and do tricks like a domes-tic animal may go into Tommys Christmas stocking in 1950, said brainspecialist Dr. Grey Walter in Bristol last night. For two years he has beenexperimenting with toys containing an electric brain. . . . Dr. Walter saidthe toys possess the senses of sight, hunger, touch, and memory. Theycan walk about the room avoiding obstacles, stroll round the garden,climb stairs, and feed themselves by automatically recharging six-voltaccumulators from the light in the room. And they can dance a jig, go tosleep when tired, and give an electric shock if disturbed when they arenot playful. . . . Dr. Walter said: `There is no other machine like it in theworld. This hobby of making toys with brains is proving of great value

in the study of the human brain. The toy has only two cells. The humanbrain has ten thousand million. `But, said Dr. Walter, `most people getalong with using as few as possible.

Daily Mail , 17 November 1949

Walter had excellent contacts in the BBC, and in 1950 the tortoises were thesubject of a BBC television newsreel lm `Bristols robot tortoises have minds of theirown. The commentary (transcribed) was not calculated to appeal to his scienticpeers:

In a modest villa on the outskirts of Bristol lives Dr. Grey Walter, a neu-rologist, who makes robots as a hobby. They are small, and he doesntdress them up to look like men|he calls them tortoises. And so cun-ningly have their insides been designed that they respond to the stimuliof light and touch in a completely life-like manner. This model is namedElsie, and she sees out of a photo-electric cell which rotates about herbody. When light strikes the cell, driving and steering mechanisms sendher hurrying towards it. If she brushes against any objects in her path,contacts are operated which turn the steering away, and so automaticallyshe takes avoiding action. Mrs. Walters pet is Elmer, Elsies brother,in the darker vest. He works in exactly the same way. Dr. Walter saysthat his electronic toys work exactly as though they have a simple two-cell nervous system, and that, with more cells, they would be able to domany more tricks. Already Elsie has one up on Elmer: when her batteries




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begin to fail, she automatically runs home to her kennel for charging up,and in consequence can lead a much gayer life.

The newsreel, which survives, is probably the earliest (and possibly the only)existing lmed record of Elmer and Elsie. It is valuable in many ways. Shot in

Walters lounge, it shows the tortoises operating in the environment in which theywere developed, and gives many clues about their speed and sensory abilities. Theopening scene shows Walter in his workshop|a small study with a workbench and arack of tools. Elsie, her cover removed, is on the bench, and he is ostensibly makingsome adjustments. There is a good close-up of the operation of the worm drive to thesteering apparatus. He replaces Elsies shell, not without some diculty, and carriesher through to the lounge, where he puts her down on what appears to be a polishedwooden oor. Behind her is the hutch, or kennel, containing an immobile Elmer.Walter places a small waste bin in front of Elsie, and switches her on, with the clearintention that the avoidance behaviour should be triggered when she hits the wastebin. She begins to move in the typical cycloidal path, with her photocell rotatinganticlockwise and scanning the environment, but is very soon attracted towards asource of light to the left of the camera. (The position of the light can be deduced not just from Elsies behaviour but from the reections and shadows in the room.) Shehits the waste bin, pushing it aside, but close examination of the lm shows no signof any behavioural change; the obstacle may well have been too light to actuate theswitch mechanism. Walter moves the bin in front of Elsie again, but no behaviouralchange can be seen when the second collision occurs.

Over a shot of a smiling Vivian Walter, the commentary introduces Elmer as `MrsWalters pet, and Elmer and Elsie are seen moving closer together and eventuallycolliding several times. In this part of the lm, Elsie is moving twice as fast asin the previous part|the lm speed has obviously been doubled, presumably tosustain the viewers interest. Elmer moves at about the same speed as Elsie, buthis photocell scans in the opposite direction, a fact unrecorded in any of Walterswritings. After the fourth collision between the robots, Elsie stops moving for severalseconds; this must be a malfunction, as the electronic circuitry should not supportany such behavioural state. The lm then cuts to another sequence in which bothrobots are moving freely without colliding. The nal shot shows Elsie moving towards

the hutch in a straight line, with the commentary implying that this is how she `runshome to her kennel for charging up. The angle of the shot gives a good view of the charging system at the back of the hutch. The lm ends with Elsie apparentlycoming to rest in the hutch, but it is not clear whether she has really stopped, orwhether the last few frames of lm have been repeated. What is very clear, however,is that the light that is supposed to attract Elsie into the hutch is not lit, and so weare forced to the conclusion that the shot must have been staged, with the steeringhaving been centred and the steering motor disabled so that Elsie would steer astraight course after being lined up with the hutch. Although these observations tosome extent devalue the lm as a record of the tortoises performance, they give auseful insight into the unreliability and variability of the machines, and perhaps givesome support to the concerns of Walters detractors.

Helped by high levels of exposure through more popular post-war media such asillustrated magazines (e.g. Morley 1950; Walter 1950 b), the tortoises rapidly becamefamous, not just in the UK, but worldwide, and Walter received many requests for




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Figure 2. Grey Walters `personal tortoise from the 1951 batch,now on display in the Science Museum, London.

demonstrations. Their presence was also demanded at the 1951 Festival of Britain,the futuristic celebration of Britains recovery from the war years. Both activitiespresented problems: Elmer and Elsie had been cobbled together from wartime surpluscomponents and scrap materials|for example, their gearwheels were salvaged fromold gas meters and alarm clocks|and were in consequence chronically unreliable. Thesituation was saved when six more tortoises of an improved electrical and mechanical

design were built for Grey Walter in early 1951 by Mr W. J. `Bunny Warren, one of the talented BNI engineers recruited by Walter after the war. Elmer and Elsie appearto have been scrapped at about this time. Of the six 1951 tortoises, two are knownto have survived. One, the tortoise used by Walter for most of his demonstrationsafter 1951, went on display in the London Science Museum in 2000 (see gure 2),and the other has been on show in the MIT Museum since 2001.

Although Walter soon moved on to build other models, the tortoises managed toretain a high public prole for several years. Some of this was undoubtedly due toWalters continuing showmanship|for example, in 1955 he released them amongstthe audience at a British Association meeting (George 1956)|but much was due tothe success in 1953 of The living brain , which went into paperback in 1961, and wasreprinted in 1963 and again as late as 1968. A rather dierent view of the tortoises wasprovided by Pierre de Latils La pensee articiel le (de Latil 1953) later publishedin English as Thinking by machine (de Latil 1956). It is an account, an analysis,and even an attempt at a synthesis of the cybernetic movement, particularly as ithad developed in England and France. Grey Walters tortoises are central to it. Itcontains an extended report of an interview with Grey Walter that can be datedby its context to late 1950. Some of the technical information is not found in anyother published record, and is clear and accurate, but some of de Latils purportedeye-witness descriptions of the behaviour of the tortoises do not ring true, and wereprobably glossed from information provided by Walter. y Nevertheless, it provided

y One particularly puzzling aspect is that de Latil appears to think that it is possible for the tortoisesto nd a static equilibrium at some intermediate light level, and to rest there without moving, whereastheir electronic and mechanical design should always produce movement of one sort or another. He notes




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an independent and quasi-scholarly endorsement of the scientic signicance of thetortoises, along with more popular material: a photograph of the Walters watchingtheir nine-month-old child Timothy playing with a tortoise is captioned, Ìn theircountry home near Bristol, these parents have two children: one is electronic. VivianDovey and Grey Walter have two ospring: Timothy, a human baby and Elsie, the

tortoise, of coils and electronic valves (de Latil 1956).

3. Science and the tortoises

The rst scientic publication dealing with the tortoises is the Scientic American paper of May 1950, entitled Àn imitation of life (Walter 1950 a ). Although the papercontains eight stylized sketches illustrating the tortoises behaviour (drawn by theartist Bernarda Bryson Shahn), it gives only the briefest textual description of theconstructional and electronic details of the robots, and it is not possible to work

out exactly how each type of behaviour is generated. A follow-up paper in Scientic American in August 1951, entitled À machine that learns (Walter 1951), discussesthe addition to a tortoise of a hardware learning mechanism (the conditioned reexanalogue (CORA)). It includes a time exposure photograph of a tortoise with atorch mounted on its shell nding and entering the brightly lit hutch; the streak of light left by the torch enables the robots trajectory to be seen. However, the majorcontemporary published source of information on the tortoises is The living brain (Walter 1953 a ). Until recently, these three publications were all that were generallyavailable by Walter, but the discovery and release of other contemporary materialsand artefacts has lled in many gaps left by these original sources (e.g. Holland 1996,2003).

There appear to have been three distinct sources of scientic inspiration for thetortoises: the presence in post-war Britain of a well-developed cybernetic movementlargely independent of the better-known American strand associated with Wiener;Grey Walters principled interest in building physical working models to test hypothe-ses; and his theories about brain function. Each of these will be examined in turn.

(a ) The British cybernetic movement

It is not generally realized that the development of cybernetics around Wiener inthe US was paralleled by an independent stream of similar ideas in the UK (de Latil1956; Cordeschi 1987; Hayward 2001 a ; Pickering 2002). The growth of the Wienerschool was essentially centred around his 1948 book Cybernetics (Wiener 1948). Inthe UK, things were rather dierent; the driving force was a London-based diningclub, the Ratio Club (Hayward 2001 a ). It was founded by the neurologist JohnBates in 1949, and met regularly for several years, nally being dissolved in 1958.Membership was by invitation only, and Batess original idea, as set out in a letter toGrey Walter (Bates 1949), was that the club should consist of àbout fteen peoplewho had Wieners ideas before Wieners book appeared. In fact they found 20 suchof Elmer: `. . . his electronic system found its equilibrium not for a precisely dened light intensity, butfor quite a wide range. Thus, he was perfectly happy quietly ruminating under an arm-chair (de Latil1956, pp. 213, 214). Even more mysteriously, he then quotes Walter on Elmer: `His reexes are reallylacking, he is quite lifeless. For days on end he doesnt stir from under the furniture; I must liven himup a bit and make him more intelligent. Because, you see, if an individual is intelligent he has to paythe price of a certain degree of accompanying irritability (de Latil 1956, p. 214).




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people, including Ross Ashby, Horace Barlow, Donald Mackay, Philip Woodward,Alan Turing, Jack Good and A. M. Uttley. The groups attitude towards Wiener isnicely summed up by Bates in the draft of a paper on cybernetics intended for theBritish Medical Journal :

Those who have been inuenced by these ideas so far, would not acknow-ledge any particular indebtedness to Wiener, for although he was the rstto collect them together under one cover, they had been common know-ledge to many workers in biology who had contacts with various types of engineering during the war.

Bates (1952)

Grey Walters own account of the genesis of the tortoises in The living brain empha-sizes the intellectual independence of the British tradition:

The rst notion of constructing a free goal-seeking mechanism goes backto a wartime talk with the psychologist, Kenneth Craik, whose untimelydeath was one of the greatest losses Cambridge has suered in years.When he was engaged on a war job for the Government, he came to getthe help of our automatic analyser with some very complicated curveshe had obtained, curves relating to the aiming errors of air gunners.Goal-seeking missiles were literally much in the air in those days; so, inour minds, were scanning mechanisms. Long before the home study wasturned into a workshop, the two ideas, goal-seeking and scanning, had

combined as the essential mechanical conception of a working model thatwould behave like a very simple animal.

Walter (1953 a , p. 125)

Walters own view of Wiener can be seen in a letter to Professor Adrian in 1947:

We had a visit yesterday from a Professor Wiener, from Boston. I methim over there last winter and nd his views somewhat dicult to absorb,but he represents quite a large group in the States, including McCulloch

and Rosenblueth. These people are thinking on very much the same linesas Kenneth Craik did, but with much less sparkle and humour.Walter (1947)

Other members of the Ratio Club also acknowledged their indebtedness to Craik,and in fact when the name of the club was under discussion in the early meetings,one proposal was that it should be called the Craik Club.

(b) Working models

Although the production and use of physical working models of biological systemsis now commonplace, it is rare to read a justication of the procedure. However,when the rst eorts at what Craik called the `synthetic method (Craik, cited inCordeschi (2002)) appeared in the rst half of the twentieth century, each attemptusually included a discussion of its legitimacy and usefulness. (For an excellent recent




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of responses he thought sucient for any conceivable individual entity `. . . Even weremany millions of permutations excluded as being lethal or ineective. . . (Walter1953a , p. 120). But how might dierent patterns of interconnection give rise to dif-ferent observable behaviours? He gained some insight into this problem by reasoningas follows:

. . . how many ways of behaviour would be possible for a creature with abrain having only two cells? Behaviour would depend on the activity of one or both of these cells|call them A and B. If (1) neither is active,there would be no action to be observed; if (2) A is active, behaviour of type a would be observed; if (3) B is active, behaviour of type b; if (4) Aand B are both active, but independently, there would be behaviour of both types a and b, mixed together; if (5) A is `driving B, type b wouldbe observed, but subordinate to A; if (6) B is `driving A, type a wouldbe subordinate to B; if (7) A and B are `driving each other, behaviourwill alternate between type a and type b. The internal states of such asystem in these seven modes may be represented symbolically as

0; A; B; A + B ; A ! B; A B; A $ B

with behaviour types,

0; a; b; a + b ; b(fA) ; a(fB) ; ababab : : : :

From the above it will be seen that the rst four ways of behaviourwould be identiable by simple observation, without interfering with thesystem, whereas the last three could only be identied by operating onthe system|by, as it were, dissecting out the arrows.

Walter (1953 a , p. 119)

(He rst presented a shorter version of these arguments, using only six modes of behaviour, in the 1950 Scientic American paper.)

The tortoises can therefore be seen on one level as Walters attempt to see whether

a simple working model with a few behaviour-producing elements, capable of beinginterconnected in many ways, could be made to produce a relatively large number of behaviour patterns. However, he was not just concerned with behaviour in general,but with a set of behaviours that could be said to be characteristic and denitiveof living beings, and in particular of animals. It was this audacity, and his apparentsuccess in achieving his aims, that lifted the tortoises from being mere testbeds forthe verication of a neurophysiological speculation to becoming icons of technologicalprogress in the post-war British revival.

The two key sources for tracing Walters thoughts about the imitation of life are the1950 Scientic American article, and ch. 5 of The living brain , from 1953. They dierin a very interesting way. In 1950 he presented the tortoise enterprise as being aninvestigation of what could be achieved using a small number of behaviour-generatingelements capable of being connected in a relatively large number of dierent permuta-tions. He merely noted some of the ways in which the tortoises behaviour resembledthat of animals, and remarked:




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Figure 3. A labelled diagram of Elsie with her shell removed.

These machines are perhaps the simplest that can be said to resembleanimals. Crude though they are, they give an eerie impression of pur-posefulness, independence, and spontaneity.

Walter (1950 a )

By 1953 he had a long list of the qualities required to pass the test of having imitated

life:Not in looks, but in action, the model must resemble an animal. There-fore, it must have these or some measure of these attributes: explo-ration, curiosity, free-will in the sense of unpredictability, goal-seeking,self-regulation, avoidance of dilemmas, foresight, memory, learning, for-getting, association of ideas, form recognition, and the elements of socialaccommodation. Such is life.

Walter (1953 a , pp. 120, 121)

Of the thirteen attributes in the new list, six (from foresight to form recognition) arethose derived from the learning machine CORA, and so are not really properties of the tortoises alone.

It is dicult to avoid the conclusion that Walter drew up his 1953 list on thebasis of his interpretations of the observed behaviour of the tortoises, rather thanhaving designed the tortoises to display every characteristic in the list. The test of the successful imitation of life applied in the 1950 paper is much more relaxed andintuitive than the test implied in The living brain , and it is reasonable to supposethat his judgement of his success in 1950 was independent of the 1953 list. The

individual examples of tortoise behaviour are of course the same in both sources.

4. Tortoise mechanisms and functions

In order to understand how the tortoises worked, it is best to start with the mechan-ical design. Figure 3, from the archives of the BNI, is a conveniently labelled view




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Figure 4. The original circuit diagram for the 1951 batch of tortoises. It is clearer than theversion in The living brain , and is particularly useful because it also shows the component typesand values.

of Elsie with her shell removed. On the left, a single structure extends verticallydownwards from the photoelectric cell to the driving wheel; this structure is capableof being rotated in one direction only about its vertical axis by the steering motoracting via the steering gear. The driving wheel also rotates in one direction only whendriven by the driving motor. The two rear wheels, seen on the right, are not driven.The photoelectric cell is tted with a shroud which blocks the entry of light fromall directions except the front of the cell; the shroud and cell are aligned with thedriving wheel so that the direction in which light is sensed is always the directiontoward which the driving wheel is moving. When the shell is tted, it is hung onthe rubber touch contact mount. If the tortoise is on the level, and the shell is nottouching anything, the contact is open circuit, but if the shell is deected by gravity(when the tortoise is on a slope) or touch, the contact is closed. The headlamp is atorch bulb connected in series with the steering motor, so that it is lit only when the

steering motor is turned on. A hole in the shell allows the headlamp to be seen fromthe front when the shell is on.The circuit diagram shown in The living brain is unfortunately not very easy to

understand. Figure 4 shows a rather clearer version from the BNI archives whichdescribes the almost identical circuit used in the 1951 batch. The photoelectric cell(PEC) is on the extreme left; just above it is the touch contact. The two miniaturethermionic valves, or vacuum tubes, are represented by the two circular symbols inthe upper half of the diagram. Current ows through the valves from the upper atelectrodes (the anodes, or plates) to the lower looped electrodes (the cathodes). Thedotted lines within the symbols represent the control electrodes, which control thecurrent ow; the upper control electrode is known as the screen, and the lower asthe grid. The valves are arranged as a two-stage amplier. The input voltage to therst stage (the valve on the left) is determined by the amount of light falling on thephotoelectric cell; this voltage controls the current through the valve. The voltageproduced by this current is fed to the second stage, and controls the current through




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. . . the driving wheel is xed at whatever angle it was when the light wasseen, and the scanning of the horizon by the eye also stops of course.At the same time. . . the driving motor is turned up to full speed. Themodel stops looking slowly round and hurries toward the light. However,unless the light was seen when the eye happened to be facing straight

ahead, the angle at which the steering came to rest at the moment of sighting will deect the model gradually away from the light. When thedeection is so great that the activation level of the photo-cell falls belowthreshold, the Relay 2 opens again, the scanner starts up, the drive isreduced to half speed and the model is re-positioned, this time so thatthe light is more directly ahead. This process of progressive orientation isan important part of the behaviour mechanism. It is cumulative|everytime the model steers itself slightly o-beam the momentary operationof the steering-scanning mechanism brings it back more nearly on courseand it ends up with a heading on-beam. The process often looks clumsy,because the eye seems to veer away from the light and then the scannerhas to make nearly a whole rotation to bring it back, but inevitably witheach such operation the model gets itself into a better position to beardown directly on its goal. The aiming-error is steadily reduced as the goalis approached.

Walter (1960)

As the tortoise approaches a light, the intensity of light falling on the photoelectriccell will increase, and for a suciently bright light the current through RL1 willbecome low enough to cause RL1 to switch o. The current through RL2 will increase,but this will have no eect since RL2 is already on. The turning motor will thereforeoperate at half speed, and the drive motor will operate at full speed. This produceswhat Walter calls behaviour pattern N, for negative phototropism:

The result is that when the model gets `too close to a light it veerssmoothly away from it and avoids the fate of a moth in a candle. M.Speculatrix is moderate and restrained|it seeks an optimum light, nota maximum.

Walter (1960)

We can take issue with Walter here. In fact, the model will veer smoothly awayfrom the light only for a moment, because the shroud on the photoelectric cell makesits response highly directional; as soon as the turning motor has turned the spindleso that the sensor is no longer aligned with the light source, the model will revert tobehaviour pattern E. As it scans round, the sensor will once again become alignedwith the light, and behaviour pattern N will again be triggered, and so on. The modelcertainly avoids the moths fate, but it is clear that N is simply E with dierent motorspeeds, rather than the opposite of P, and is not really a negative phototropism.

If the shell makes contact with an obstacle, or if the gradient is suciently steep,the stick-and-ring touch contact will close. Via a capacitor, this connects the anodeof the valve in the second stage of the amplier to the grid of the valve in therst stage, and this phase-shifted feedback connection converts the circuit into anoscillator, with a period of around a second. This produces behaviour pattern O, forobstacle avoidance:




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2102 O. Holland

As arranged in M. Speculatrix, the oscillators [sic] recur about once asecond, and their eect is to open and close Relays 1 and 2 alternatelyas long as the skin is displaced. This makes the model butt, turn andrecoil continuously until it is clear of the obstacle. It may edge steadilyalong until it comes to an edge it can get round, it may shove the obstacle

to one side if it is movable, or if it gets into a tight corner it may endby swivelling right round and trying another approach. In any case it isvery pertinacious and it is also quite discerning, because as long as it isin trouble it will not respond to a light, however intense and attractive.It cannot, because as long as the skin is displacing the limit switch theampliers are completely preoccupied with sending signals back and forthto one another and are quite blind to outside information|an oscillatordoes not act as an amplier. When the model has cleared an obstacle andthe skin swings back to its normal position, the input{output circuit is

opened and after one more oscillation the ampliers resume their functionof transforming light signals into movements of the relays and the wholemodel.

Walter (1960)

In some of his writings, he made much of the persistence of the oscillation for onecycle after the obstacle had been cleared, often referring to it as a memory of theobstacle. De Latil was also impressed by this `. . . astonishing \memory" of the colli-sion with the obstacle (de Latil 1956, p. 220) but it is surely an overinterpretation.

Behaviour patterns E, P, N and O constitute the entire behavioural repertoireof the tortoise; all the reported complexity of tortoise behaviour is a result of thesequential activation of these behaviour patterns by the interaction between thetortoise and the environment.

5. Tortoise behaviour: the evidence

All that we seem to require now is conrmation that the behaviour described in x 4and in the published sources was actually produced by the tortoises at the time.

Again, the BNI archives have provided the crucial evidence, in the form of a set of time exposure photographs in which Elmer and Elsie, with lighted candles mountedon their shells, trace out their trajectories in various environmental arrangements.(It must have been necessary to shield each tortoises photocell from the light of thecandle it was carrying; under magnication, one of the photographs shows what lookslike a screen mounted just behind the photocell.) The photographs of single tortoisebehaviour are all of Elsie, who seems to have been rather more responsive thanElmer, perhaps because Elmer was the prototype (Pincher 1949). De Latil reportedthat on the day of his visit to Walters house in 1950

. . . Elsie was aicted with a very unstable, very feminine mood; her reg-ulating mechanism was hypersensitive. . . . Elmer, on the other hand, hadbeen given a very stable, very bourgeois character. . . .

de Latil (1956, p. 213)




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Figure 5. Elsie and Elmer, released at the top of the picture,interact with each other, and then head for the hutch.

The photographs were taken at Grey Walters house, probably in late 1949 or early1950. They may well have served as the basis for some of the drawings of trajectoriesin `An imitation of life. As a very valuable bonus, the BNI archives also yieldeda typescript entitled `Accomplishments of an artefact, consisting of descriptions of what seem to be several of the photographs, and of others that have unfortunatelybeen lost. The undated document seems to have been written to accompany somesort of display or exhibition of work at the BNI; it mentions The living brain , soit dates from 1953 or later. Although I have attributed the text to him (Walter1953b), it is impossible to be sure that Grey Walter was the author, but some of

the phrasing is very similar to his other work, and it seems likely that the documentmust at least have been approved by him. In what follows, the photographs will bematched with their apparent descriptions; as will be seen, the combination is muchmore informative than either source of information taken alone. A somewhat moretechnical examination of some of these materials can be found in Holland (2003).

We begin by describing gure 5 in some detail to show how the basic behaviourpatterns can be identied from the traces. Elsie (with the smooth one-piece shell) isat the top left at the beginning of the exposure, and Elmer (with the segmented shell,the original tortoise) is at the top right. After a rather messy interaction with Elmer,Elsie crosses his track. Immediately afterwards, we can see Elsie executing behaviourpattern E: the faint cycloidal trace (about ve cycles) is made by the headlamp,and the heavy zigzag by the candle. Elsie then switches into behaviour pattern Pfor about a body length, presumably as a result of catching a glimpse of the hutchlight, and then reverts to E for a couple of cycles. She then makes a long straightexcursion towards the hutch (P again) followed by another ve cycles of what may




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2104 O. Holland

Figure 6. Elsie demonstrates `pertinacity.

be E, or a mixture of E and N. Elmers behaviour is less clear because his headlampis too dim to be seen, but the candle trace implies a similar alternation of E with P.

`Accomplishments of an artefact contains what appears to be a rather misleadingdescription of this photograph:

Social organisation

The formation of a cooperative and a competitive society. When the twocreatures are released at the same time in the dark, each is attracted bythe others headlight but each in being attracted extinguishes the source

of attraction to the other. The result is a stately circulating movement of minuet-like character; whenever the creatures touch they become obsta-cles and withdraw but are attracted again in rhythmic fashion. Whilethis evolution was in progress the light in the feeding hutch was turnedon; the common goal disrupted the cooperative organization and trans-formed it into a ruthless competition, in which both creatures jostled forentrance to the source of nourishment.

Walter (1953 b)

Our dissatisfaction with this is triggered by the description in the same documentof the behaviour of Elsie in what is almost certainly gure 6:

Pertinacity

Catching sight of a faraway candle the creature loses itself behind anopaque and polished re-screen, behind which it sidles. On the way itcatches sight of the reection of its candle in the re-screen and spendssome time chasing its tail, but later catches another glimpse of the distantcandle and homes into an orbit round its original goal.

Walter (1953 b)

This passage, reasonably satisfactory in itself, shows that the candles used toproduce the trajectory traces are bright enough to trigger behaviour pattern P, andso it is probable that the interaction between the two tortoises in gure 5 is mediatedwholly or partly by the candles, rather than by the headlamps.




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Figure 7. Elsie performs in front of a mirror, but is probablyresponding to the candlelight rather than to her pilot light.

The same criticism can be applied to gure 7, which shows Elsie in front of amirror. This may be the photograph described in Àccomplishments of an artefactas follows:

Recognition of self

A pilot light is included in the scanning circuit in such a way that theheadlamp is extinguished whenever another source of light is encoun-tered. If, however, this other source happens to be a reection of theheadlamp itself in a mirror, the light is extinguished as soon as it is per-ceived and being no longer perceived, the light is again illuminated, andso forth. This situation sets up a feedback circuit of which the environ-ment is a part, and in consequence the creature performs a characteristicdance which, since it appears always and only in this situation, may beregarded formally as being diagnostic of self-recognition. This suggeststhe hypothesis that recognition of self may depend upon perception of ones eect upon the environment.

Walter (1953 b)

The drawing of the famous `mirror dance in Àn imitation of life is nothing likethe regular alternation between approach and avoidance shown in the photograph,being an altogether more irregular and complex trajectory. There may well havebeen a mirror dance that could have been argued to be a form of self-recognition,but unfortunately this photograph cannot be said to be a record of it. The brightestlight visible to the camera, and presumably to the photocell, is the candle on thetortoises back and its reection in the mirror. The trace is far more likely to reectthe alternation of behaviour pattern P (approach to the reected candlelight) withbehaviour pattern O (obstacle avoidance on contact with the mirror). We can be sure

that Walter used this image as an example of the mirror dance because it appearsin the form of a diagram in the transcript of a talk he gave in 1954 (Walter 1956 b);the text matches closely the account given in Àccomplishments of an artefact.

Interestingly, the description of the mirror dance in de Latils book also matchesthis photograph rather than Grey Walters original description and Bernarda BrysonShahns sketch:




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2106 O. Holland

Figure 8. `Discernment. Elsie at rst approaches the lamp, but on encounteringthe obstacle she `ignores the lamp until she has escaped from the obstacle.

Yet another trap, a mirror, was placed in front of Elsie. What would shedo? As if attracted by her own image, she approached the mirror, wherethe light from her breast was reected. But she hit herself against the

glass. She then waltzed around the mirror in zigzag movements, to andfro, as if admiring her own reection.

de Latil (1956)

In The living brain , Grey Walter characterizes discernment as `Distinction betweeneective and ineective behaviour and describes the tortoises manifestation of it asfollows:

When the machine is moving towards an attractive light and meets an

obstacle, or nds the way too steep, the induction of internal oscillationdoes not merely provide a means of escape|it also eliminates the attrac-tiveness of the light, which has no interest for the machine until after theobstacle has been dealt with. There is a brief `memory of the obstacle,so that the search for lights, and the attraction to them when found, isnot resumed for a second or so after a material conict.

Walter (1953 a , p. 128)

This `memory is simply the persistence of the oscillation for a few cycles after the

switch is opened.Figure 8 appears to correspond to the description of `discernment in `Accomplish-ments of an artefact:

Presented with a remote goal (seen at the top of the slide) the creatureencounters a solid obstacle which it cannot move, and although it can still




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Figure 9. Elsie appears to achieve an optimum.

see the candle it devotes itself to circumventing the obstacle (of which itretains a short memory) before it circles round in an orbit and reachesthe objective.

Walter (1953 b)

It is clearly not possible to deduce all of this from the trace of this trajectory.Dealing with the obstacle involves four or ve forward and backward movements of the candle; it is impossible to be sure that the forward movements did not contain anyepisodes of behaviour pattern P. Similarly, the trajectory contains no unequivocalevidence for the claimed memory of the obstacle. However, it is at least consistentwith the description.

Figure 9 is probably the photograph described in `Accomplishments of an artefactas `search for an optimum:

Attracted at rst by a distant bright light the creature reaches the zoneof brilliant illumination where it is repelled by the excessive brilliance of the light and circles round it at a respectful distance, exhibiting a searchfor optima rather than maxima|the idea of moderation of the classicalphilosophers.

Walter (1953 b)

The implication here is that the tortoise approaches the light using behaviourpattern P, but when the light becomes too intense, it is repelled by behaviour pattern

N. The problem is that, although P is easily recognized by its long straight or curvingruns, it is impossible to tell whether a run of P is terminated by E or N. E willoccur quite frequently, when the motion due to P causes the photocell to lose itsalignment with the light; N will occur only if the light becomes too bright while stillin alignment|but the immediate eect of N will be to rotate the photocell, which willsoon cause the light to become misaligned and lead immediately to E. It is therefore




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2108 O. Holland

Figure 10. Elsie demonstrates `free will: the solution of the dilemma of Buridans ass.

impossible to conclude from the photographic evidence that N is denitely involvedto any degree in this particular trajectory; it could easily have been produced by Pand E acting alone, and would then merely constitute a failure to achieve a maximum,rather than a success in achieving an optimum.

For Grey Walter, one of the major achievements of the tortoise was the demonstra-tion of `free will, in the sense of unpredictability; in fact, the 1950 Scientic American article was subtitled `Concerning the authors instructive genus of mechanical tor-toises. Although they possess only two sensory organs and two electronic nerve cells,they exhibit `free will. Figure 10 shows the experimental set-up he used to demon-strate this: two light sources, with the tortoise started equidistantly from them. In`Accomplishments of an artefact, the commentary on what is probably gure 10runs as follows:

Free-will

The solution of the dilemma of Buridans ass. The photoelectric cell whichfunctions as the creatures eye scans the horizon continuously until a

light signal is picked up; the scanning stops, and the creature is directedtowards the goal. This mechanism converts a spatial situation into a tem-poral one and in this process the dilemma of two symmetrical attractionsis automatically solved, so that by the scholastic denition the creatureappears endowed with `free-will. It approaches and investigates rst onegoal and then abandons this to investigate the other one, circling betweenthe two until some other stimulus appears or it perishes for want of nour-ishment.

Walter (1953 b)

In his writings about the tortoises, Grey Walter gave much weight to an attributehe called `internal stability|the claimed ability of the tortoises to maintain theirbattery charge within limits by recharging themselves when necessary. (In fact,the names Elmer and Elsie were derived from ELectroMEchanical Robots, Light-Sensitive with Internal and External stability (Walter 1950 a , p. 43).) A feature of




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Figure 11. Elsie enters the hutch from a starting position on the left. The reection on the oorshows that the hutch light is on, and so behaviour pattern N must have been disabled, eitherby running down the battery or by adjusting the relay settings.

the tortoises circuitry was that, as the batteries became exhausted, the amplier gaindecreased, making it increasingly dicult to produce behaviour pattern N (negativephototropism). Walter installed an automatic recharging system inside the tortoiseshutch, along with a 20 W lamp. (Part of the charging system can be seen at the backof the hutch in gure 1; the light from the lamp is also visible.) Initially, a tortoisewould be repelled by the bright light from the lamp (behaviour pattern N), but oncethe battery had run down suciently, behaviour pattern P would be produced, andthe tortoise would approach the lamp, enter the hutch, and be engaged by the charg-ing system. Any further movement would be prevented until the battery was fullycharged. When the tortoise was automatically released from the charger, it wouldonce again be repelled by the lamp (behaviour pattern N) and would leave the hutch.

Although the scheme is obviously satisfactory in theory, there are no records show-ing that this cycle of events was ever demonstrated with complete success, thoughthe reduction in gain denitely occurs. Perhaps signicantly, Walter remarks:

This arrangement is very far from perfect; there is no doubt that, if left tothemselves, a majority of the creatures would perish by the wayside, theirsupplies of energy exhausted in the search for signicant illumination orin conict with immovable obstacles or insatiable fellow creatures.

Walter (1953 b, p. 130)

Interestingly, when the original hutch was set on re by the lamp and destroyed, thereplacement hutch was tted with a lamp, but no charging system.

Whatever doubt may exist concerning the success of the implementation of internalstability, there is no doubt that the tortoises could make their way into the hutchunder the inuence of the lamp; gures 11 and 12 show the trajectories of two such




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2110 O. Holland

Figure 12. Elsie enters the hutch from a starting position on the right.

movements. In `Accomplishments of an artefact, these two photographs are describedas follows:

Simple goal-seeking

Started in the dark the creature nds its way into a beam of light andhomes on the beam into its feeding hutch.

Walter (1953 b)

The reference to the feeding hutch is now the only relic of the idea of internalstability.

Although the analyses of the surviving photographs and of the BBC newsreel havegiven us some clues to the tortoises abilities, there is still considerable doubt aboutthe exact nature of some of the claimed behaviours. One possible method of resolvingthe situation would be to construct replicas of the original tortoises, and to studytheir behaviour in the same way as did Walter. The problem with this approachis that there is simply not enough detailed information available about Elmer and

Elsie; the best source, Appendix B of The living brain , is too general to serve as aspecication, and every roboticist knows that, in robotics more than in most otherareas of engineering, the devil is in the details. However, things are dierent when itcomes to the 1951 batch of tortoises: we have excellent documentation, as well as twosurviving examples. In 1995, two replica tortoises were constructed at the Universityof the West of England. They used two 1951 shells obtained from the BNI, and wereclose to the originals in all important aspects, though modern motors and batterieswere used. (For a description of this project, and for the rst publication of some of the archival materials from the BNI, see Holland (1996).)

At that time, the newly discovered tortoise now in the Science Museum had beenmade functional again with the assistance of `Bunny Warren; although testing waslimited in extent by the poor condition of the original tortoise, the replicas appearedto behave in very much the same way. This was unfortunate, because the productionof behaviour pattern N in a normal environment turned out to be a very dicultand uncertain matter, even for the original tortoise. There is probably no single




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reason for this. The magnetic properties of the relays of the replicas were inferior tothose of the original, and so the switching threshold characteristics were dierent; thephotoelectric cells used were the original type, but were of necessity several decadesold, and known to become less sensitive both with use and with time; and there isdocumentary evidence that the tortoises of the 1951 batch were much less sensitive

to light than Elmer and Elsie, and so the production of N may have been a problemanyway (Holland 1996). The replicas were able to reproduce behaviour sequencesinvolving only behaviour patterns E, P and O, but failed when the involvement of Nwas required. It would of course be possible to modify the circuitry of the replicas toamplify the output of the photocell, but this has not yet been undertaken. In fact,there are no records of any of the 1951 tortoises having been used to demonstrate allthe functions claimed by Walter, so any tests (especially unsuccessful ones) carriedout on the replicas would not necessarily enable conclusions to be drawn about thebehaviour of Elmer and Elsie.

6. Later work: CORA and IRMA

Walter did not conne himself to reproducing the behaviours identied in the originalpaper on the tortoises, but extended his observations intermittently over the years.Some of his ideas have a very modern ring to them. For example, he noticed howthe tortoises behaviour in a modiable environment could produce apparently usefulchanges in the environment:

If there are a number of light low obstacles that can be moved easily over

the oor and over which the model can see an attractive light, it will ndits way between them, and in doing so will butt them aside. As it ndsits way toward the light and then veers away from it and wanders aboutit will gradually clear the obstacles away and sometimes seems to arrangethem neatly against the wall. This tidy behaviour looks very sensible butis an example of how apparently rened attitudes can develop from theinteraction of elementary reex functions.

Walter (1960)

Figure 13 shows what is clearly the set-up for such an experiment. Unfortunately,no further accounts or images of this work have yet been found, but it is withoutany doubt a signicant anticipation of the section of modern robotics dealing withthe use of stigmergy (Bonabeau et al . 1999).

In his obituary of Walter, Shipton noted:

The successful design of Machina speculatrix , the famous tortoise, gaveGrey enormous satisfaction and led him to consider whole families of cybernetic models of biological systems, only a few of which saw the lightof day.

Shipton (1977)

We have no means of knowing just how many were physically realized, but at leasttwo have survived: CORA and IRMA (innate releasing mechanism analogue). Bothare now in the Science Museum.




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2112 O. Holland

Figure 13. Walter watches as one of the 1951 tortoises clears some movable blocksout of its path|perhaps the rst observations of stigmergy in robots.

(a ) CORA

In the list of life-like characteristics presented in The living brain , Walter included`foresight, memory, learning, forgetting, association of ideas, form recognition. Noneof these was present in the tortoises; in fact, they are the claimed attributes of anotherelectromechanical model (CORA; see gure 14) originally developed to illustratesome of his ideas about Pavlovian conditioning. In many ways, CORA was closerto his heart than were the tortoises, as becomes clear on reading The living brain ,which contains a whole chapter on the theory underpinning the model, along withdiagrams of its outputs, and an appendix giving detailed circuit information. Hehad worked on conditioning for many years, and had met Pavlov, and worked withPavlovs students. More importantly, he had studied the eects of the process of conditioning on the EEG, his primary sphere of interest.

In Walters view of Pavlovian conditioning, an initially neutral stimulus acquiresthe ability to produce the specic reex response normally triggered by some spe-cic stimulus; the learning procedure consists of the repeated presentation of theneutral stimulus before the specic stimulus. His analysis had convinced him that inorder to reproduce this type of learning in a model `. . . no fewer than seven distinctoperations must be performed (Walter 1951). CORA was a straightforward elec-tronic implementation of these operations. As a neutral stimulus, he chose a whistle,coupled to CORA with a microphone. The specic stimulus could be any stimulusinput producing one of the tortoises behaviour patterns|he mentions a moderate

light (producing P), and contact with an obstacle (producing O). Although he givesdetailed treatments of the signal processing within CORA during and after learning,his descriptions of actual experiments with tortoises are very sketchy:

In one arrangement. . . the specic stimulus is a moderate light and theneutral one is the sound of a whistle. The whistle is blown just before




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Figure 14. CORA.

the light is seen; after this has been repeated 10 or 20 times the modelhas `learned that the sound means light and will come to the whistle asthough it were a light. . . . In another arrangement the specic stimulus is

touch, that is, an encounter with an obstacle. In that case the whistle isblown just as the model comes into contact with the obstacle, so that aftera while the warning whistle triggers a withdrawal and avoidance reaction.This process may of course be accelerated by formal education: insteadof waiting for the creature to hit a natural obstacle the experimenter canblow the whistle and kick the model. After a dozen kicks the model willknow that a whistle means trouble, and it can thus be guided away fromdanger by its master.

Walter (1951, p. 62)

In spite of his eorts, which included the publication of an article in Scientic American (Walter 1951), CORA had only a small fraction of the impact of thetortoises, and made little lasting impression. This is perhaps unfortunate and unfair,because his ideas on the relationship between learning and statistical prediction werefar ahead of their time. Nevertheless, he was undoubtedly the rst person to integratea meaningful physical model of learning into a robot worthy of the name, althoughthe closeness of that integration is not at all clear. Some of his writings give theimpression that the rst version of CORA had been built into a tortoise, but noneof Grey Walters colleagues at the time have any clear recollection that this was ever

done. Once more, de Latil provides some interesting information:At rst, the learning circuits were incorporated in a `Tortoise. . . but thiswas too complicated for class demonstrations, so they were put in a dis-play box.

de Latil (1956, caption facing p. 51)




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2114 O. Holland

Figure 15. Grey Walter posing with a tortoise and CORA on a visit to New York.

The main purpose of the nal version of CORA was undoubtedly pedagogic|thesuperstructure can be unplugged and replaced to face away from the controlling dials,so that the operator does not block the classs view of the progress of `learning.De Latil also sheds some light on Elsies fate:

At the end of 1950, Elsie and Elmer had a little sister, unless it was adaughter as it may well have been. In truth it appears to have been a caseof parthenogenesis. CORA, the newcomer, was constructed with organsbelonging to Elsie, who thus succumbed, poor thing!

de Latil (1956, p. 247)

(However, an inspection of CORAs internals reveals that the components are moresimilar to those used in the later batch of tortoises than to those visible in pho-tographs of Elsie.)

In Walters 1954 talk, he states. . . the situation gets incredibly complicated when you have a model. . . of learning by association actually moving round the room. . . . So I detachedthe learning apparatus from the moving model, and what I am going toshow you now are preparations rather than complete working models.

Walter (1956 b, pp. 40, 41)

He then goes on to demonstrate CORA, later remarking, `I have done some workwith a moving model equipped with one of these learning devices (Walter 1956 b,p. 53). The photograph accompanying the published talk is the one used in thesecond Scientic American article; from the shell, the tortoise appears to be fromthe 1951 batch, so it is unlikely that it is tted with an internal version of CORA.However, Walter certainly performed experiments with CORA externally connectedto a tortoise; gure 15 shows such an arrangement, clearly posed for the camera




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2116 O. Holland

give way to a recency eect, in which the system responds to the latest buttonpress regardless of any made previously: `. . . instead of being an imprinting model itbecomes a model of fashion (Walter 1956 b, p. 43). He does not mention having madeany attempt to connect it to a tortoise, and apart from a note of its appearance ina display at the Royal Institution in 1956 it does not seem to be mentioned in print

again.

7. Grey Walter and biologically inspired robotics

We can approach the assessment of the signicance of Grey Walters work for bio-logically inspired robotics by asking three distinct questions. What was he the rstto do? To what extent did his work inuence the subsequent course of biologicallyinspired robotics? To what extent has biologically inspired robotics developed in thedirections he foresaw?

It will be convenient to examine each of these in turn, but we should rst attemptto decide what we mean by biologically inspired robotics. There are two main moti-vations for linking biology and robotics. The rst is to attempt to make good robotsby copying or adapting ideas from biology; the second is to use robots as toolsfor biological investigation. These proceedings furnish examples of each. Straddlingboth approaches is the area of what has become known as adaptive behaviour, inwhich both natural and articial systems, including biologically inspired robots, arestudied in a context emphasizing such notions as embodiment, autonomous agents,emergence, morphology and agent{environment coupling. A technique, even a phi-losophy, common to much of this work is that of behaviour-based robotics, associated

with R. A. Brooks and MIT. However, the scope of behaviour-based robotics is muchbroader than that of biologically inspired robotics; it was developed as a reaction tothe dominant paradigm of knowledge-based robotics, and is now established as oneof the main strands within robotics research.

(a ) What was Grey Walter the rst to do?

Walters list of rsts in biologically inspired robotics and the related areas isimpressive. The tortoises were designed to test a biological hypothesis about howcombinations of relatively few elements might give rise to complexity of behaviour;they were probably the rst biologically inspired robots of any real interest. y Therobots were intended to produce behaviour characteristic of animals, and Walter wasthe rst to emphasize the importance of behavioural completeness:

Not in looks, but in action, the model must resemble an animal. There-fore, it must have these or some measure of these attributes: explo-ration, curiosity, free-will in the sense of unpredictability, goal-seeking,self-regulation, avoidance of dilemmas, foresight, memory, learning, for-getting, association of ideas, form recognition, and the elements of socialaccommodation. Such is life.

Walter (1953 a , pp. 120, 121)

y Some earlier phototropic mobile robots had been given animal-like names (e.g. the `Electric Dog of Hammond and Miessner, dating from 1912 (Cordeschi 2002) and the 1929 `Philidog designed by Piraux(de Latil 1956)); however, as de Latil remarks, such automata `did nothing unexpected (de Latil 1956,p. 240).




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The tortoises had to exist in a normal everyday environment, rather than in somespecial environment created to take account of their limitations. He was the rst toimplement a self-recharging robot. He made the rst observations of emergence inrobotics, both in the sense of the designer being pleasantly surprised at the unan-ticipated appearance of some useful side eect of his design, and in the sense that

the interaction of two or more behavioural subsystems could produce a distinct anduseful additional behaviour. The second sense is clearly demonstrated by several of his remarks in Walter (1960); in fact, they amount to the earliest formulation of thebasic idea of behaviour-based robotics (Holland 1996). As noted above, he was therst to show how a robots actions on an environment could change it in such a waythat the robots future behaviour was changed in a useful way, and he was also therst to carry out experiments in learning on a behaving robot.

Because he built more than one robot, he was also the rst in the eld of multiplerobotics, showing how the behavioural interactions between two robots of the same

type would produce emergent characteristics of interest if not utility. He also madethe earliest observations in the eld of what is now known as collective robotics:

Simple models of behaviour can act as if they could recognize themselvesand one another; furthermore, when there are several together they beginto aggregate in pairs and ocks, particularly if they are crowded into acorral. . . . The process of herding is nonlinear. In a free space they areindividuals; as the barriers are brought in and the enclosure diminishes,suddenly|there is a ock. But if the crowding is increased, suddenlyagain there is a change to an explosive society of scuing strangers.And at any time the aggregation may be turned into a congregation byattraction of all individuals to a common goal. Further studies have shownthat in certain conditions one machine will tend to be a `leader. Oftenthis one is the least sensitive of the crowd, sometimes even it is `blind.

Walter (1957)

(b) To what extent did Grey Walters work inuence the subsequent course of biologically inspired robotics?

This question is somewhat embarrassing for the robotics community, because theanswer is that it had very little direct inuence. Perhaps the technology of the tor-toises was too inaccessible; without a grounding in the electronics of the post-warworld, it can be dicult to understand how their circuits operate. Perhaps the papersand the book are too removed in time, tone and style from modernity; The living brain , in particular, is very old fashioned, but this is perhaps not surprising whenone discovers that it was written by his father, who was of course educated in thenineteenth century. Many of what are regarded as the key achievements within bio-logically inspired and behaviour-based robotics have involved techniques and obser-vations with which he was familiar, but which have had to be painstakingly rediscov-ered in modern times. His technical priority does not of course diminish the creditdue to the modern investigators, especially since one of his most important texts(Walter 1960) was rst published less than a decade ago. However, one wonderswhether robotics in general, and biologically inspired robotics in particular, might




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2118 O. Holland

have advanced further and faster if his work had not been allowed to fade away quiteso fast.

On the other hand, the indirect eects of Grey Walters work may have inuencedmodern robotics in a number of ways. The publicity the tortoises received encouragedmany technically inclined individuals to try and build similar machines; the electronic

hobbyist magazines of the period record many such projects. In particular, RodneyBrooks recalls attempting to build his own version of the tortoise after reading The living brain (Brooks 2002). Later, while Brooks was working with Hans Moravec onthe Stanford Cart, the tortoises again came to mind:

Despite the serious intent of the project, I could not but help feelingdisappointed. Grey Walter had been able to get his tortoises to operateautonomously for hours on end, moving about and interacting with adynamically changing world and with each other. His robots were con-structed from parts costing a few tens of dollars. Here at the centre of hightechnology, a robot relying on millions of dollars of equipment did notappear to operate nearly as well. Internally it was doing much more thanGrey Walters tortoises had ever done|it was building accurate three-dimensional models of the world and formulating detailed plans withinthose models. But to an external observer all that internal cogitation washardly worth it.

Brooks (2002, p. 30)

Less than a decade later, Brookss own design principles were producing simplereactive robots within the new behaviour-based philosophy.

(c ) To what extent has biologically inspired robotics developed in the directions Walter foresaw?

Answering this question is made easier because in 1968, in his last writings on thetortoises, Walter speculated about how they might be developed in the future:

It would only be a matter of patience and ingenuity to endow M. specula-trix with other `senses besides sight and touch, to enable it to respond toaudible signals audibly, and so forth; also to provide it with hands. Thereis no serious diculty about the elaboration of function, once the prin-ciples of mechanical `life have been demonstrated in a working model.If the principles are preserved, no matter how elaborate the functions of the machine, its mimicry of life will be valid and illuminating.

Our experiments and observations with Machina speculatrix and itscousins and ospring (of which there are now quite a number) shows usthat, as we had suspected, the complexity of the brain and its behaviourcan be imitated to an extraordinary degree by relatively simple machin-ery. And a new era has opened out in our experiments. Instead of usingthe old-fashioned valves with their extravagant heaters and their enor-mous bulk, we can make the same device with transistors. And withmicromodular construction in which whole ampliers are built into thespace of what only yesterday was one transistor we can include all the




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ampliers needed for quite an elaborate synthetic animal. We are nowenvisaging the construction of a creature which instead of looking asthe original did, like a rather large and clumsy tortoise, resembles moreclosely a small eager, active and rather intelligent beetle.

There seems no limit to which this miniaturisation could go. Alreadydesigners are thinking in terms of circuits in which the actual scale of theactive elements will not be much larger, perhaps even smaller, than thenerve cells of the living brain itself. This opens a truly fantastic vista of exploration and high adventure. . .

Walter (1968)

We do not have to look far to see that things have progressed in the directions heforesaw. The behaviour-based principles with which he would surely be in sympathyhave been applied to more complex entities such as the humanoid robots COG andKismet (Brooks 2002); their mimicry of life is certainly `valid and illuminating. Theconcept of the `small, eager, active and rather intelligent beetle matches several of theproducts of Brookss Articial Insect Lab at MIT; no doubt we should also include thewidely used commercial research robots such as the Khepera y in this category. As forthe scale of `the active elements, modern semiconductor manufacturing techniquesroutinely produce transistors three orders of magnitude smaller than typical neurons,and so we are well placed to undertake the `exploration and high adventure heanticipated, even if there are as yet few signs of it in the present state of robotics.

In modern usage, the word `legacy has acquired a new meaning: a legacy system

is something left over from a previous technological generation, something obsoletethat we would rid ourselves of if only we could. Some might be tempted to dismissWalters tortoise project as a mere historical quirk|a legacy system with no realcontemporary relevance. This is certainly a mistaken attitude. His work constitutesa real legacy in the traditional sense: something built up by a previous generation,and preserved and passed on so that it can benet a new generation. Twenty-veyears after his death, his uniquely personal approach still repays the eort madeto understand it, a

grey walter's robots

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