4. Theoretical foundations
In this part I give a short overview of the psychological theories of emotion which form the basis of the computer models described in the following chapters. I do not aim to describe and evaluate each theoretical approach in its entirety; these are rather some core elements of the respective theoretical approaches insofar as they are taken up in the computer models.
It is interesting to note that the majority of the computer models of emotions, if they refer expressly to psychological theories, are based on the so-called appraisal theories.
The fascination with these approaches probably stems from the fact that they can be converted (relatively) simply into program code.
Ortony, Clore and Collins (1988) developed their theoretical approach expressly with the aim to implement it in a computer:
The theory of Ortony, Clore and Collins assumes that emotions develop as a consequence of certain cognitions and interpretations. Therefore it exclusively concentrates on the cognitive elicitors of emotions.
The authors postulate that three aspects determine these cognitions: events, agents, and objects.
Emotions, so their central assumption, represent valenced reactions to these perceptions of the world. One can be pleased about the consequences of an event or not (pleased/displeased); one can endorse or reject the actions of an agent (approve/disapprove) or one can like or not like aspects of an object (like/dislike).
A further differentiation consists of the fact that events can have consequences for others or for oneself and that an acting agent can be another or oneself. The consequences of an event for another can be divided into desirable and undesirable; the consequences for oneself as relevant or irrelevant expectations. Relevant expectations for oneself finally can be differentiated again according to whether they actually occur or not (confirmed/disconfirmed).
This differentiation leads to the following structure of emotion types:
Fig.2: Structure of emotion types in the theory of Ortony, Clore and Collins (after Ortony, Clore, Collins, 1988, p.19)
The intensity of an emotional feeling is determinded predominantly by three central intensity variables: Desirability is linked with the reaction to events and is evaluated with regard to goals. Praiseworthiness is linked with the reaction to actions of agents and is evaluated with regard to standards. Appealingness is linked with the reaction to objects and is evaluated with regard to attitudes.
The authors further define a set of global and local intensity variables. Sense of reality , proximity , unexpectedness and arousal are the four global variables which operate over all three emotion categories. The local variables, to which the central intensity variables mentioned above also belong, are:
Table 1: Local variables in the theory of Ortony, Clore and Collins (after Ortony, Clore and Collins, 1988, p. 68ff.)
In a concrete case, each of these variables is assigned a value and a weight. Furthermore, there is a threshold value for each emotion, below which an emotion is not subjectively felt.
On the basis of this model the emergence of an emotion can be decribed in formal language: Let D (p, e, t) be the desirability (D) of an event (e) for a person (p) at a certain time (t). This function possesses a positive value for a desirable event, a negative value for a not desirable event. Furthermore let I g (p, e, t) be a combination of global intensity variables and P j (p, e, t) the potential for a state of joy. Then the following rule for "joy" can be provided:
IF D(p,e,t) > 0
THEN set Pj(p,e,t) = fj(D(p,e,t), Ig(p,e,t))
The resulting function f j releases a further rule which determines the intensity for joy ( I j) and thereby makes possible the experience of the joy emotion. Let T j be a threshold value, then:
IF Pj(p,e,t) > Tj(p,t)
THEN set Ij(p,e,t) = Pj(p,e,t) - Tj(p,t)
ELSE set Ij(p,e,t) = 0
If the threshold value is exceeded, this rule produces the emotion of joy; otherwise it supplies the value "zero", i.e., no emotional feeling. Depending upon the intensity of the emotion, different tokens are used for its description. Such tokens are words which describe this emotion.
Ortony, Clore and Collins supply no formalization for all of their defined emotions but give only a few examples. They postulate, however, that every emotion can be described using a formal notation, although with many emotions this is by far more complex than with the presented example.
With the help of such a formal system a computer should be able to draw conclusions about emotional episodes which are presented to it. The authors limit their goal quite explicitly:
The theory of Roseman, which he presented for the first time in 1979 (Roseman, 1979), was modified by him several times in the following years. It changed in (partially substantial) details; what remained the same was only the basic approach of an appraisal theory of the emotions.
Roseman developed his first theory based upon 200 written reports of emotional experiences. From the analysis of these documents, he derived his model, in which five cognitive dimensions determine whether an emotion arises and which one it is.
The first dimension describes whether a person possesses a motivation to a desired situational state or a motivation away of an unwanted situational state. The dimension thus knows thus the states "positive" and "negative".
The second dimension describes whether the situation agrees with the motivational state of the person or not. The dimension thus knows thus the states "situation present" or "situation absent".
The third dimension describes whether an event is noticed as certain or only as a possibility. This dimension knows the conditions "certain" and "uncertain".
The fourth dimension describes whether a person perceives the event as deserved or undeserved, with the two states"deserved" and "undeserved".
The fifth dimension finally describes, from whom the event originates. This dimension knows the states "the circumstances", "others" or "oneself".
From the combination of these five dimensions and their values a table can be arranged (Roseman, 1984), from which, according to Roseman, emotions can be predicted.
Altogether 48 combinations can be formed of Roseman's dimensions (positive/negative x present/absent x certain/uncertain x deserved/undeserved x circumstances/others/oneself). With these 48 cognitive appraisals correspond, according to Roseman, 13 emotions.
After experimental examinations of this approach did not furnish the results postulated by Roseman, he modified his model (Roseman, 1984). The second dimension of his original model (situation present or absent) now contained the states "motive consistent" and "motive inconsistent", whereby "motive consistent" always corresponds to the value "positive" of the first dimension and "motive inconsistent" to the value "negative" of the first dimension. In place of the alternatives "present" and "absent" now the terms "appetitive" and "aversive" were used.
A further correction concerned the fourth dimension of the original model (deserved/undeserved). Roseman replaced it by the dimension of strength, i.e. whether a person in a given situation perceives himself or herself as strong or weak. States of this dimension thus are "strong" and "weak".
Roseman also supplemented the third dimension of his original model (certain/uncertain) by a further state: "unknown". That was necessary in order to incorporate the emotion of surprise in his model.
Roseman concedes (Roseman et al., 1996) that this model, too, could not be empirically validated. As a consequence he developed a third version of his theory (Roseman et al., 1996). It differs from his second approach in several points: The fourth dimension (strong/weak) is replaced by a relational appraisal of the own control potential, with the states "low" and "high". The value "unknown" of the third dimension is replaced by the state "unexpected", since this is, according to Roseman, the condition for the emotion of surprise. And finally Roseman adds still another dimension for the negative emotions which he calls "type of problem". It describes whether an event is noticed as negative because it blocks a goal (with the result "frustration") or because it is negative in its nature (with the result" abhorrence"). This dimension has the states "non-characteristic" and "characteristic".
How far this (as of now) last model by Roseman can be proven empirically cannot be said. One weakness of the model, however, is evident: It has problems dealing with a situation in which one person makes two different appraisals. If, for example, a student is of the opinion that his teacher gives him a test that ist not fair but knows at the same time that he has not sufficiently prepared for the test, then Roseman's model cannot clearly predict what the student's emotions are - because two states of the fifth dimension are present at the same time.
Because of their simple structure which can be translated quickly into rules which exactly define which appraisals elicit which emotions, Roseman's models were received very positively in AI circles. Dyer's model BORIS is based on Roseman's first model, and Picard writes: "Overall, it shows promise for implementation in a computer, for both reasoning about emotion generation, and for generating emotions based on cognitive appraisals." (Picard, 1997, S. 209)
For Scherer five functionally defined subsystems are involved with emotional processes. An information-processing subsystem evaluates the stimulus through perception, memory, forecast and evaluation of available information. A supporting subsystem adjusts the internal condition through control of neuroendocrine, somatic and autonomous states. A leading subsystem plans, prepares actions and selects between competitive motives. An acting subsystem controls motor expression and visible behaviour. A monitor subsystem finally controls the attention which is assigned to the present states and passes the resulting feedback on to the other subsystems.
Scherer is especially interested in the information-processing subsystem. According to his theory this subsystem is based on appraisals which Scherer calls stimulus evaluation checks (SEC). The result of these SECs causes again changes in the other subsystems.
Scherer sees five substantial SECs, four of which possess further subchecks. The novelty check decides whether external or internal stimuli have changed; its subchecks are suddenness, confidence and predictability. The intrinsic pleasantness check specifies whether the attraction is pleasant or unpleasant and causes appropriate approximation or avoidance tendencies. The goal significance check decides whether the event supports or prevents the goals of the person; its subchecks are goal relevance, probability of result, expectation, support character and urgency. The coping potential check determines to what extent the person believes to have events under control; its subchecks are agent, motive, control, power and adaptability. The compatibility check finally compares the event with internal and external standards and standards; its subchecks are externality and internality.
Each emotion can, according to Scherer, thus be clearly determined by a combination of the SECs and subchecks. An appropriate table with such allocations can be found in [ Scherer, 1988 ]. A number of empirical studies has supported Scherer's model so far.
Frijda points out that the word "emotion" does not refer to a "natural class" and that it is not able to refer to a well-defined class of phenomena which are clearly distinguishable from other mental and behaviour events. For him, therefore, the process of emotion emergence is of larger interest.
The center of Frijda's theory is the term concern. A concern is the disposition of a system to prefer certain states of the environment and of the own organism over the absence of such conditions. Concerns produce goals and preferences for a system. If the system has problems to realize these concerns, emotions develop.
The strength of such an emotion is determined essentially by the strength of the relevant concern(s).
Frijda defines six substantial characteristics of the emotion system which describe its function:
For Frijda, emotions are absolutely necessary for systems which realize multiple concerns in an uncertain environment. If a situation occurs, in which the realization of these concerns appears endangered, so-called action tendencies develop. These action tendencies are linked closely with emotional states and serve as a safety device for what Frijda calls concern realization (CR).
As substantial action tendencies Frijda (1986) defines the following (associated emotions in parentheses):
According to Frijda, a functioning emotional system must have the following components:
Concerns: Internal representations against which the existing conditions are tested.
Action Repertoire: Consisting of fast emergency reactions, social signals and mechanisms to develop new plans.
Appraisal Mechanisms: Mechanisms which establish the fit between events and concerns as well as connections to the action control system and the action repertoire.
Analyser: Observation of the incoming information and subsequent coding regarding their implications and consequences.
Comparator: Test of all information on concern relevance. The result are relevance signals, which activate the action system and the Diagnoser and cause attentional arousal.
Diagnoser: Responsible for context evaluation, scanning the information for action-relevant references. Performs a number of tests (e.g. whether consequences of an event are safe or uncertain, who is responsible for it etc.) and results in an appraisal profile.
Evaluator: Agreement or discrepancy signals of the Comparator and the profile of the Diagnoser are combined into the final relevance signal and its intensity parameter. The intensity signals the urgency of an action to the action system. The relevance signal constitutes the so-called control precedence signal.
Action Proposer: Prepares the action by selecting a suitable alternative course of action and by making available the resources necessary for it.
Actor: Generates actions.
This general description of an emotional system can be formalized in such a way that it can form the basis for a computer model:
Fig. 3: Frijda's emotion system(Frijda and Moffat, 1994)
To theory outlined so far was presented by Frijda in 1986. On it is based the computer model ACRES (Frijda and Swagerman, 1987) which is described further below. The evaluation of ACRES led Frijda to make a number of modifications of his theoretical approach. These are described likewise further below in connection with the computer model WILL (Moffat and Frijda, 1995).
Oatley and Johnson-Laird developed their theory expressly in a form which can be implemented as a computer model, even if they did not carry out this step. They see the necessity for their model in the fact that almost all computer models of the human mind did not consider emotions, while they regard this as a central component for the organization of cognitive processes.
Oatley and Johnson-Laird assume in their theory, called by them "communicative theory of emotions" (Oatley & Jenkins, 1996, p. 254), a hierarchy of parallelly working processing instances, which work on asynchronously different tasks. These instances are coordinated by a central control system (or operating system). The control system contains a model of the entire system.
The individual modules of the system communicate with one another, so that the system can function at all. According to Oatley and Johnson-Laird there are two kinds of communication. They call the first kind propositional or symbolical; through it actual information about the environment is conveyed. The second kind of communication is nonpropositional or of emotional nature. Its task is not to convey information but to shift the entire system of modules into a state of increased attention, the so-called emotion mode. This function is comparable to global interrupt programs on computers:
According to Oatley, the central postulate of the theory is:
Emotions coordinate quasi-autonomous processes in the nervous system by communicating significant way marks of current plans (plan junctures). Oatley and Johnson-Laird bring such plan junctures in connection with elementary emotions:
Table 2: Plan junctures (after Oatley, 1992, p. 55)
Since they arise at plan junctures, emotions are a design solution for problems of plan changes in systems with a multiplicity of goals.
The name "communicative theory of emotions" was chosen because it is the task of emotions to convey certain informations to all modules of the overall system.
After a suggestion by Sloman ,Oatley specified again that there are two kinds of signals in the model: Semantic signals and control signals. The two can occur together, but do not have to. Thus Oatley (1992) states that his model is the only one which can explain a vague emotional condition: in this case only the control signals are active, not the semantic ones.