Categorisation and cognitive semantics

In fact, ‘Prototype Theory’ was less a theory of knowledge representation than a series of findings that provided startling new insights into human categorisation. In so far as the findings led to a theory, Rosch proposed in her early work that humans categorise not by means of the necessary and sufficient conditionsassumed by the classical theory (to which we return below), but with reference to a prototype: a relatively abstract mental representation that assembles the key attributes or features that best represent instances of a given category. The prototype was therefore conceived as a schematic representation of the most salient or central characteristics associated with members of the category in question.

A problem that later emerged was that the view of prototypes as mental representations failed to model the relational knowledgethat humans appear to have access to (recall from the last chapter that relational knowledge is one of the properties of encyclopaedic knowledge addressed by Frame Semantics). These criticisms led to further developments in prototype theory.

Some scholars argued for a revised view of the prototype, suggesting that the mental representation might correspond to an exemplar: a specific category member or ‘best example’ of a category, rather than a schematic group of attributes that characterise the category as a whole. However, these exemplar-based modelsof knowledge representation were also problematic because they failed to represent the generic informationthat humans have access to when they use concepts in order to perform a host of conceptual operations, including categorisation.

Despite this, there are a number of reasons why a chapter on categorisation in general, and prototype theory in particular, is essential for a thorough understanding of cognitive semantics.

Firstly, an investigation of prototype theory provides a picture of the historical context against which cognitive linguistics emerged as a discipline.

Secondly, and perhaps more importantly, although it now seems that prototype theory cannot be straightforwardly interpreted as a theory of knowledge representation, the empirical findings that emerged from this research demand to be accounted for by any theory of categorisation.

Thirdly, as we mentioned above, Lakoff’s (1987) book set the scene for the development of three important strands of research within cognitive linguistics:

(1) Conceptual Metaphor Theory; (2) cognitive lexicalsemantics; and (3) a cognitive approach to grammar.

Prototype theory

Prototype theory is most closely associated with the experimental research of cognitive psychologist Eleanor Rosch and her colleagues.

Principles of categorisation

Prototype theory posits that there are two basic principles that guide the formation

of categories in the human mind: (1) the principle of cognitive economy, and (2) the principle of perceived world structure. These principles together give rise to the human categorisation system.

Principle of cognitive economy

This principle states that an organism, like a human being, attempts to gain as much information as possible about its environment while minimising cognitive effort and resources. This cost-benefit balance drives category formation.

In other words, rather than storing separate information about every individual stimulus experienced, humans can group similar stimuli into categories, which maintains economyin cognitive representation.

Principle of perceived world structure

The world around us has correlational structure. For instance, it is a fact about the world that wings most frequently co-occur with feathers and the ability to fly (as in birds), rather than with fur or the ability to breathe underwater.

This principle states that humans rely upon correlational structure of this kind in order to form and organise categories.

The categorisation system

These two principles give rise to the human categorisation system. While the principle of cognitive economy has implications for the level of detail or level of inclusivenesswith which categories are formed, the principle of correlational structure has implications for the representativenessor prototype structureof the categories formed (Rosch 1977, 1978). Rosch (1978) suggests that this gives rise to a categorisation system that has two dimensions: a horizontal and a vertical dimension. This idea is represented in Figure 2.

The vertical dimension relates to the level of inclusiveness of a particular category: the higher up the vertical axis a particular category is, the more inclusive it is. Consider the category DOG in Figure 2. Relative to this category, the category MAMMAL is higher up the vertical axis and includes more members than the category DOG. The category MAMMAL is therefore more inclusive than the category DOG. The category COLLIE, however, is lower on the vertical axis and has fewer members; this category is less inclusive than the category DOG.

In contrast, the horizontal dimension relates to the category distinctions at the same level of inclusiveness. Hence, while DOG and CAR are distinct categories, they operate at the same level of detail. In the next two subsections, we look in more detail at the evidence for these two dimensions of categorisation.

The vertical dimension

The vertical dimension derives from the discovery by Rosch and her colleagues (Rosch et al. 1976) that categories can be distinguished according to level of inclusiveness. Inclusiveness relates to what is subsumed within a particular category. As we have seen, the category FURNITURE is more inclusive than the category CHAIR because it includes entities like DESK and TABLE in addition to CHAIR. In turn, CHAIR is more inclusive than ROCKING CHAIR because it include so ther types of chairs in addition to rocking chairs. The category ROCKING CHAIR only includes rocking chairs, and therefore represents the least inclusive level of this category.

Rosch and her colleagues found that there is a level of inclusiveness that is optimalfor human beings in terms of providing optimum cognitive economy. This level of inclusiveness was found to be at the mid-level of detail, between the most inclusive and least inclusive levels: the level associated with categories like CAR, DOG and CHAIR. This level of inclusiveness is called the basic level, and categories at this level are called basic-level categories.

Categories higher up the vertical axis, which provide less detail, are called superordinatecategories. Those lower down the vertical axis, which provide more detail, are called subordinatecategories. This is illustrated in Table 1.

The horizontal dimension

The horizontal dimension of the categorisation system relates in particular to the principle of perceived world structure which we introduced earlier. This principle states that the world is not unstructured, but possesses correlational structure.

In other words, the world does not consist of sets of attributes with an equally probable chance of co-occurring. Instead, the world itself has structure, which provides constraints on the kinds of categories that humans represent within the cognitive system.

One consequence of the existence of correlational structure in the world is that cognitive categories themselves reflect this structure: the category prototypereflects the greater number of correlational features. Recall that categories often exhibit typicality effects, where certain members of the category are judged as ‘better’ or more representative examples of that category than other members. Members of a category that are judged as highly prototypical(most representative of that category) can be described as category prototypes. Not only do categories exhibit typicality effects (having more or less prototypical members), category members also exhibit family resemblancerelations. While for many categories there are no attributes common to all members (not all members of a family are identical in appearance), there is sufficient similarity between members that they can be said to resemble one another to varying degrees (each having some, but not all, features in common).

Lakoff argues that it is mistaken to equate prototype or typicality effects with cognitive representations. Rather, typicality effects are ‘surface phenomena’. This means that they are a consequence of complex mental models that combine to give rise to typicality effects in a number of ways. Typicality effects might therefore be described in intuitive terms as a superficial ‘symptom’ of the way our minds work, rather than a direct reflection of cognitive organisation. Lakoff (1987) therefore attempts to develop a theory of cognitive models that might plausibly explain the typicality effects uncovered by Rosch and her colleagues.

The theory of idealised cognitive models

In his book, Women, Fire And Dangerous Things (1987), George Lakoff set out to develop a theory of category structure at the cognitive level that could account for the empirical findings presented by Rosch and her colleagues. This theory was called the theory of idealised cognitive models, and represented one of the early frameworks that helped define cognitive semantics as a research programme.

Lakoff argued that categories relate to idealised cognitive models (ICMs).These are relatively stable mental representations that represent theoriesabout the world. In this respect, ICMs are similar to Fillmore’s notion of frames, since both relate to relatively complex knowledge structures. While ICMs are rich in detail, they are ‘idealised’ because they abstract across a range of experiences rather than representing specific instances of a given experience.

In Lakoff’s theory, ICMs guide cognitive processes like categorization and reasoning. For example, Barsalou (1983) argues that ‘ad hoc’ categories like WHAT TO TAKE FROM ONE’S HOME DURING A FIRE also exhibit typicality effects. Lakoff argues that categories of this kind, which are constructed ‘online’ for local reasoning, are constructed on the basis of pre-existing ICMs. In other words, faced with a house fire, our ability to construct a category of items to be saved relies on pre-existing knowledge relating to the monetary and sentimental

value attached to various entities, together with knowledge of the whereabouts in the house they are, the amount of time likely to be available and so on.

Date: 2016-01-14; view: 1956