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7. Encounters on Taros

One of the most substantial impulses for the computer modelling of emotions comes from the Japanese psychologist Masanao Toda. It is the description of an autonomous robot system, the so-called Fungus Eater.

Masanao Toda was born 1924 in Okagi in Japan. After graduation, he studied physics at the Imperial University of Tokyo. After the war he worked as mathematics and physics teacher at a secondary school and, in 1949, took up the study of psychology at the University of Tokyo. Some years after finishing his studies he  took a chair for psychology at the University of Hokkaido.

Toda brought into the experimentally oriented psychology  a  sharp mind, accustomed to the deductive thinking of  theoretical physics. Even if he worked a lot experimentally, his basic philosophy read nevertheless:

"...what finally counts are theories and ideas, no matter where they were originally hatched, either in an armchair or in an experiment. If an idea is good, it will eventually find a way to be experimentally tested, while a blind experiment produces only a trickle of possible facts out of the whole ocean of possibly obversable facts."


(quoted by Hans F.M. Crombag in Toda, 1982, p. XIV)

Already in the 1950s, the high time of behaviourism, Toda could not make friends with this direction of thinking. For him, behaviour was always the result of a personal choice between several possible action alternatives. He saw the mind as an intermediate between requirements of the environment and actions. To that extent, Masanao Toda was a kind of cognitivist. Only his basic assumption that human psyche and human behaviour are answers to the requests of the environment can be called behaviouristic.

Between 1961 and 1980 Masanao Toda developed his theory of the Fungus Eater; the appropriate essays appeared collected in his book "Man, Robot, and Society" in the year 1982.


7.1. What is a Fungus Eater?

The model of the Fungus Eater resulted from Todas discontent with experimental psychology.

"Psychology...will tell you a lot about human beings in experimental laboratories. Experimental laboratories are, however, not our natural habitat. The major difference between these two types of environment can be stated this way: In experimental laboratories, information is usually coded in a single - or at most, a couple of - sensory dimensions in a fairly abstract way, and the kind of task given to human subjects usually requires persistent, single-track thinking......


But...human beings handle multiple-channel information input efficiently and engage in multiple-track thinking in their natural habitat. ...


...Experimental psychology tells us facts, but to obtain these facts we have been sacrificing important information coming from the multiplicity of our input channels and the multiplicity of our thinking and other activities....."


(Toda, 1982, p. 94)

From this criticism Toda developed the Fungus Eater first as the main actor of an experimental situation in which participants played a kind of science fiction game. Perception, learning, thinking, behaviour, and the effective organization of these activities were demanded at the same time and should result in a better experimental situation.

The Fungus Eater was described to the test subjects as follows:

"You are a remote control operator of the robot miner nicknamed "Fungus-Eater", sent to a planet called Taros to collect uranium ore, which uses wild fungi growing on the surface of the planet as the main energy source for its biochemical engine. The uranium ore and fungi are distributed over the land of Taros, which is covered mainly with black and white pebbles, and little is known about the mode of their distribution. As the operator you can control every activity of the Fungus-Eater, including the sensitivity of the fungus- and uranium-detection devices. All the sensory information the robot obtains will be transmitted here and displayed on this console so that you will feel as if you are the Fungus-Eater itself.


Note that your mission is to collect as much uranium ore as possible, and your reward will be determined in proportion to the amount of uranium you collect. Note also that the amount of fungi you collect and consume during your mission is irrelevant to the reward. Remember, however, that every activity of the Fungus-Eater, including the brain-computer operations, consumes some specified amount of fungus-storage. Never forget that the Fungus-Eater cannot move to collect further uranium ore or fungi once it runs out of its fungus-storage, and your mission would be over then and there. Good luck!"


(Toda, 1982, p. 95)

What at first sight looks like a simple role playing game, is in reality a situation from which a most complex behaviour results. One is reminded of the "vehicles" of Braitenberg (1993) whose behaviour, regarded by the observer as"complex", is in reality the result of some few simple rules.

On the one hand, the Fungus Eater possesses a rudimentary system of attention control. If it has taken up enough nutrients, it can concentrate completely on the collecting of ore and vice versa.

On the other hand it has a system of different goals. Its mission is to collect as much ore as possible; for this purpose it must repeatedly fill up its supply of nutrients. This construction can lead to conflicting goals, and the Fungus Eater must decide, after different criteria, whether it should collect ore or fungi.

Such a decision situation is still relatively trivial, if the Fungus Eater has to decide at a given time only between two alternatives (ore or fungi), if it finds itself, for example, on a certain point on Taros from which it can locate an ore occurrence to the right and a fungus occurrence to the left. As soon as further factors are added, for example obstacles, changing lighting (day/night) etc., the Fungus Eater must make long-term plans. This complicates the model, because "thinking" likewise costs energy, which is thus lost for the collecting of ore.

A further factor which has serious consequences is the assumption that there are not one, but several Fungus Eater on Taros. Thus the system is confronted with completely new challenges which let the decision problems of the solitary Fungus Eaters appear as almost trivial.

These few remarks should make clear that already a few simple basic assumptions can produce complex planning and decision-making processes which are not explicitly formulated in the basic model.


7.2. Emotional Fungus Eaters

In a further thought experiment, Toda speculated upon which consequences it would have for his model if the Fungus Eater would have emotions. For him, emotions are a necessary condition for the survival of a humanoid robot:

"My intention is to demonstrate that a group of experimental humanoid robots, sent to some biologically wild environment, would have to be programmed to be more emotional than intellectual in order to survive there."


(Toda, 1982, p. 130 f.)

Toda calls the emotions in his model urges. Pfeifer (1988) sees a connection between Toda's urges and Frijda's concerns to that respect,

"...that urges are the programs which are activated once a situation has been identified as being relevant to some concern."


(Pfeifer, 1988, p. 305)

Toda defines an urge as a built-in motivational subroutine which links cognition with action.

"A separate set of cognitive contents is responsible for the activation of each urge, while each member of the set is characterized by a value corresponding to its estimated relevance to the issue of survival. Whenever one of the members of this set is brought into cognition, the urge subroutine is activated or "called", with the relevance value of the cognition transferred as the urge intensity, and the subroutine will be immediately executed if no competing urge with a higher intensity exists."


(Toda, 1982, p. 136)

The meaning of such a cognitive element for the current behaviour of the Fungus Eater is determined by two variables: On the one hand, through experiences made in the past, thus by learning; on the other hand by the context, in which the Fungus Eater finds itself in this moment. This context dependence is controlled by a mechanism which Toda calls mood control.

The mood control with its associated mood-operators determines the meaning which is attached to cognitions, thus functioning as a kind of threshold setting. The message of the death of another Fungus Eater by  the hands of an enemy, for example, will lead to the fact that the Startle Urge of the other Fungus Eaters is activated by even the smallest changes in their perception.

Toda classifies his urges in four large groups: "biological urges", "emergency urges", "social urges", and "cognitive urges".

7.2.1. The "biological urges"

Biological urges have primarily to do with the preservation of a good physical condition and are, according to Toda, relatively independent from each other. Their main characteristics are similar to those of the emergency urges, but usually with a far lower excitation level.

Among the biological urges rank elementary needs, for example the Hunger Urge. At this point one can already ask whether the equating of urges with emotions is justified.

7.2.2 The "emergency urges"

Among the emergency urges Toda ranks

Startle Urge

Fear Urge

Anxiety Urge

These threee are not independent of one another, but possess a close relationship.

The Startle Urge is activated with each discovery of an unexpected stimulus in the environment of the Fungus Eater and leads to the initiation of three parallel processes:

(1) stopping of all current actions;

(2) physical excitation;

(3) concentrated cognitive effort in order to identify the source of the disturbance.

In other words: The Startle Urge leads to cognitive information processing, attention control and physical excitation. If the third process actually detects a threat, the Fear Urge is initiated.

Here Toda brings two further parameters into play: intensity and importance .

"The cognition that has activated an urge will also determine the intensity of the urge, depending mainly on the appraisal of the importance of the urge activities in relation to the survival or welfare of the individual....Once so determined, the intensity of an urge will function as the urge-regulating parameter."


(Toda, 1982, p. 134)


This construction makes it possible for the Fungus Eater to have competing urges and to give priority to the most important one in each case, because the urge with the highest intensity controls the behaviour. 

If the Fungus Eater cannot detect a direct source of danger after the Startle Urge, this initiates the Anxiety Urge which is characterized by a constant shift of attention from one potential source of danger to the next. 

To each urge belongs a pre-defined group of procedural instructions.  The result of the three processes mentioned is the selection of a specific action from this repertoire. 

7.2.3. The "social urges"

Social urges are important for Fungus Eaters, because they help them to lead a cooperative social life.  It is important to know that Toda‘s Fungus Eater society represents a hierarchically arranged system.  Toda groups his social urges into three categories: 

a) Helping urges

Rescue Urge, Gratitude Urge, Love Urge

b) Social System urges

Protection Urge, Demonstration Urge, Joy Urge, Frustration Urge, Anger Urge, Grief Urge, Hiding Urge, Guilt Urge

c) Status-related urges

Confirmation Urge

I shall not discuss the definitions of the individual social urges here in greater detail.  It should only be noted that here, too, from relatively simple basic elements which are given to the Fungus Eater, a very complex social interaction results. 

7.2.4. The "cognitive urges"

Toda’s remarks about the cognitive urges are unfortunately only very sketchy, since for his model social urges possess a by far greater importance.  He defines expressly only one cognitive urge, the Curiosity Urge. 

The definition of what represents a cognitive urge we can infer from another essay (Toda, 1982, p. 151).  There Toda, however in a completely different connection, defines a Cognitive Urge as a learned a posteriori urge, which he also designates as a motivational process.


7.3. Evaluation of Toda's model

The importance of Toda‘s model lies primarily in the fact that his Fungus Eater is an autonomous being which must survive in an uncertain and unpredictable environment, which is not possible without emotions.


The Fungus Eater was never implemented by Toda in an actual computer model, but possesses all prerequisites for it.  Toda himself made first suggestions for an operationalisation in a work with the title "The Design of a Fungus Eater" (Toda, 1982).


Furthermore, the model demonstrates in an impressing way what complexity can develop in a system which only contains a set of simple basic functions.  This "emergent" behaviour is what generates new interest in Toda's model.


Pfeifer sees the meaning of the Fungus Eaters also in its epistemological dimension: 


"The Fungus-Eater clearly becomes emotional when the necessary mechanisms are introduced for functioning in a "wild" environment, for which the human emotional system was obviously originally designed."


(Pfeifer, 1988, p. 305)


It is noticeable that Toda deals with the term urges quite generously.  This is confirmed by his tentative suggestions for Rule Observance Urges or Ambition Urge.  These urges, which he equates with emotions, are mainly defined a priori by him.  A reason for this arbitrary proceeding may lie in the fact that he did not translate his theory into an actual computer model to observe which emotions would develop due to the interaction of the few basic parameters. 

To that extent, Toda‘s model, in all its detail, is certainly no useful model for the modelling of emotions;  his basic principles of an emotional autonomous agent, however, definitely are. 

In particular if one considers that artificial intelligence in the last decades neglected this aspect of the modelling almost completely, the heuristic value of Toda‘s model cannot be estimated highly enough.


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