Representation of causation in the relational element theory

they are members of the canine category). Accordingly, the concepts are associated because they are highly similar.

Semantic and causal relations in feature models

Feature comparison models can represent different kinds of semantic relation, especially part-whole (a bird has a beak) and class inclusion (a car is a vehicle)

relationships, but other types of semantic relations, such as ownership relations, drive these models to their limits. In ownership relations such as “people own cars” there is no overall similarity to be computed between the concept “people” and “car”. People have different features than cars (e.g., head and legs vs. motor and wheels) and therefore a feature comparison model would yield a “no” as an answer to the verification of this sentence.

The same is true for causal relations: most causal relations consist of concepts that do not have a high featural overlap or other similarities. Consequently an overall similarity between the cause and the effect cannot be computed. Therefore, it seems unlikely that feature comparison model can represent causal relations.

How could causal asymmetry be represented in feature models?

Feature overlap models face problems when it comes to representing relations that do not require overlapping features of concepts. Causal relations belong to these kinds of relations. Given that these models cannot explain the representation of causal relations in general, there is only little doubt that they can also not explain causal asymmetries.

So far, the three different semantic memory models have difficulties in representing causal asymmetry explicitly instead of explaining it post-hoc.

3.2.2 Representation of causation in the relational element theory

A completely different perspective on the representation of different types of

relation in semantic memory is given by the relational element theory (Hermann & Chaffin, 1986), in which a processing theory of semantic relations comprehension is proposed. The authors made various assumptions, based on linguistic and psychological research, about

Theory Semantic memory

the representation of relations in semantic memory, but not about the structure of semantic memory itself, which stands in contrast to the semantic memory models introduced before.

They make the following assumptions:

· Relations can be decomposed into simpler elements, derived from the meaning of the concepts (Figure 9).

· Relations can share one or more elements with other relations. These common elements can be achieved by a rating procedure of these relations.

· Relations have a hierarchical structure: They contain a basic element and qualifying elements that function in such a manner that the primary qualifying element modifies the basic element, the secondary qualifying element modifies the primary qualifying element and so on. Independent elements are not hierarchically related.

Language tasks require the processing of relation perception, which means the determination of the relation type between two concepts.

Figure 9: A relation between two concepts containing three relational elements indicated by the three thin lines.

To perceive a relation, specific relational elements have to be present or absent. A specific criterion for each type of relation needs to be established and then the relational elements of this relation are retrieved from long-term memory. After that each relational element has to be evaluated starting from the basic element to the qualifying element. If the process fails to find a relational element in a pair of concepts, the evaluation is terminated.

The processing of independent elements can be accomplished without the order constraints.

When there are no relational elements left to be evaluated, the decision can be made. The evaluation process is carried out depending on the strictness of the response requirements: if the requirements are very strict, then the pair has to possess each single relational element of the relation, if the requirements are less strict, only some of the relational elements are evaluated to provide a positive response.

concept concept

relational elements of a specific relation

Theory Semantic memory

Hermann and Chaffin (1986) validated their relational element theory on several studies investigating class inclusion, synonymity, and antonym verification. They found that, with an increasing number of elements to evaluate, the latencies of a “no” response increased (e.g., “slow-late” was rejected slower than “stubborn-angry” in the synonymity verification), the verification time decreased with an increasing number of elements (e.g.,

“insane-crazy” was verified faster than “abnormal-crazy” in the synonymity verification), and response latencies were longer for non-related word pairs that possessed characteristics similar to, but not the same as, the elements of the verification relation (e.g., “bird-moth”

was rejected slower than “bird-soap” in a class inclusion verification).

Causal relations within the relational element theory

The approach Herrmann and Chaffin (1986) take has an interesting implication. Its foundation stems from network models, but it opens up a whole new dimension of relational processing. The links between the concepts are not just meaningless connections, they are concepts themselves, relational concepts. These relational concepts in turn can be

decomposed into more elements to get the fine-grained structure of a relation. The relational elements can share similar properties with other relations. Thus, it is the overlap of

relational not of conceptual features, that can be compared. A causal relation could be made of a spatial, temporal, and causal relational element. Temporal and causal relations share similar features such as directionality and order. Two events appear along a time line and the event A (the rooster crows) appears always before event B (the morning dawns).

However, only the causal relational element contains the meaning of causation: event A (spark) not only appears before event B (fire), it is the reason why event B appears. Every time A appears, B will follow, thus A is necessary for B to appear; they form a constant conjunction (Figure 10). If subjects are instructed to look for a causal relation as a target relation, they have to consider the strict constraints of a causal relation, especially the causal element of that relation. Otherwise they would base their assumption on co-variance and temporal order and not on causation. Therefore, causality is the basic element and temporal order and contiguity would be qualifying elements as proposed by the relational element theory.

Theory Semantic memory

Figure 10: Example for the relational element theory: left: causal relation; right: temporal relation. The solid lines indicate basic relational elements and the dotted lines indicate qualifying relational elements.

As described above the retrieval of a causal relation from long-term memory could be accomplished by retrieving its relational elements. Each single element needs to be evaluated and then a decision can be reached. The evaluation of a causal relation would depend on the degree to which the elements possible of two events resemble the criterial elements such as temporal order, spatial and temporal contiguity and causality (i.e., necessary connection). If two events are connected by a relation that possesses these elements, they will be regarded as causal. For example if the two concepts “spark” and

“fire”, and a causal relation has to be evaluated, then the evaluation could start with retrieving the features of a causal relation from long-term memory (Figure 11). The following criteria would have to be met: there is a temporal and spatial contiguity in that spark and fire occur in a certain time and location frame; there is a temporal order in that the spark present itself prior to the fire; and finally, it is possible that a spark can cause a fire. The basic relational element of causality would be the most important one to determine a causal relation. Because once a causal relationship is established between two concepts, the only element that differentiates it from other relationships is causality.

contiguity temporal causality

fire spark

causal relation

contiguity temporal

morning rooster

temporal relation

Theory Semantic memory

Figure 11: Retrieval process of a causal and a temporal relation in a causal relation task.

How could causal asymmetry be represented in the relational element theory?

The relational element theory has no problem representing causal relations. The representation of causal asymmetry, however, is more difficult within the theory. The causal relational elements represent the direction of the causal relation. An evaluation of a

predictive causal relation can be processed by the model and would yield a positive outcome and hence a verification of the causal relation. In a diagnostic causal relation the direction is reversed. Consequently, the evaluation of causal relational elements would yield a negative outcome for the relational elements temporal order and causality. The relation would be rejected and the evaluation would elicit a “no” answer. Therefore the model would make different predictions for the outcome of the evaluation process of a predictive and a diagnostic evaluation. That is, the evaluation of a predictive causal relation yields a positive answer, whereas the evaluation of a diagnostic relation yields a negative answer.

However, human beings are able to determine diagnostic causal relations between two Select elements from relational

criteria to be evaluated ( contiguity [c], temporal order

[t], causality [ ca])

Select elements from relational criteria to be evaluated (contiguity [c], temporal order

[t], causality [ ca ])

Evaluate pair for presence of elements

Record nature of elements found (c, t)

Compare type of relational elements found with response

rules

Response: No Is there a causal relation between the two words?

spark - fire elements found with response

rules

Response: No spark - fire

Is there a causal relation between the two concepts?

Evaluate pair of concepts for

presence of relational elements Evaluate pair of concepts for presence of relational elements

found (ca, t, c) Record nature of elements found (t, c)

Theory Semantic memory

concepts as a causal relation, thus, relational element theory is not in accord with empirical data.

To summarize, the relational element theory can represent causal relations and causal asymmetries, but the predictions of the theory for diagnostic causal relations cannot account for empirical findings.

However, the relational element model could answer the question whether or not the relation between concepts in semantic memory might have different features and, moreover, if the relation can be accessed and evaluated according to its specific features. According to the theory the processing of a causal relation is task dependent.