The Concept of Inference in Discourse Comprehension

INFERENCES IN TEXT PROCESSING G . Rickheit and H. Strohner (Editors) 0Elsevier Science Publishers B.V. (North-Holland), 1985

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THE CONCEPT OF INFERENCE IN DISCOURSE COMPREHENSION Gert Rickheit Universitat Bielefeld

Wolfgang Schnotz Deutsches Institut fur Fernstudien an der Universitat Tubingen Hans Strohner Universitat Bielefeld

Abstract In this chapter a short introduction to the subject of inference in discourse comprehension is given. It is a common view in linguistics and philosophy that forming inferences is a n important part of communication. The special role of inferences in the various communicative processes, however, can be understood only in the light of experimental and simulation studies. This chapter, therefore, gives an review of inference research from the experimental viewpoint. In the first part of the chapter some conceptual problems of inference are discussed. The central problem discussed here is the distinction of the concepts of inference and of comprehension. Since comprehension is not possible without inferences both notions are sometimes used as interchangeable terms. In order to avoid this we delimit inferences to the semantic part of the comprehension process: An inference is the generation of new semantic information from old semantic information. In contrast, the concept of decoding refers to the generation of semantic information from non - semantic information. Furthermore, the concept of encoding entails the generation of non - semantic information from semantic information. For all three cases examples and borderline cases are presented.

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The second part of the chaptex considers some theoretical aspects of inference in discourse comprehension, First, the representational aspect describes which types of semantic information are relevant for inference making. Several representational levels are distinguished and some interactions of inferences with these levels are discussed. Secondly, the functions of working memory for the processes of drawing inferences are analysed with respect to the procedural aspect. The central question here is the point of time at wfhich the inference process starts, i.e. the question of forward vs. backward inferences. Whereas backward inferences seem to be the usual type of inference, forward inferences may be restricted to special comprehension strategies. Other special processes in discourse comprehension are the strategies for solving comprehension problems. Thirdly, inferences have a contextual component which includes cultural, situational, and personal factors. Inferences will, therefore, depend on all of these factors. The third part of the chapter discusses some classifications of inferences. According to our definition of inference, three aspects are crucial for the classification. The first aspect is the input of the inference process, i.e. the knowledge which exists already before the inference is drawn. The second aspect is the output of the inference process: The resulting mental representation of the text may be categorized according to the levels of semantic representation. The third aspect is the direction of the process between input and output: This may be vertical between different levels of the representation or horizontal at the same level. In the fourth part of the chapter methodological problems of experimental inference research are discussed. Here we argue for a multi - perspective approach in order to get converging evidence about the hypothetical constructs which are necessary for a theory of inference. In the fifth and final part of the chapter some perspectives for future research into inferences in discourse comprehension are presented. O n the one hand, it seems necessary in the coming years to take a more functionally oriented view in order to explain the flexibility of the processes of inferring. On the other hand, the interdisciplinary framework of the developing Cognitive Science promises to provide a good theoretical and methodological support for psycholinguistic inference research.

INTRODUCTION T h e aim of this introductory chapter is to discuss some of the basic aspects of inferences in discourse comprehension. T h e notion of discourse comprehension is in one respect more specific and in another more general than the notion of text processing. T h e notion of discourse comprises not only a text, but also the speaker or writer on the one hand and the listener or reader on the other as well as the communicative situation itself. If we define a text as the subject matter of a discourse, the notion of comprehension will refer to the initial phase of processing the text, retrieval and reconstruction to another phase. In the present chapter we

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focus on those aspects which are related to the comprehension phase of discourse processing. T h e concept of inference is one of the central concepts in every integrated theory of discourse comprehension. In fact, the first studies which were related to discourse comprehension in the early seventies ( e .g. Bransford, Barclay, & Franks, 1972; Bransford & Johnson, 1972) made it clear that without some theory of inference process it would be hard to understand what happens during discourse comprehension. The notion of inference is important because language itself is ambiguous, vague, and fragmentary. It would even be destructive for communication if the discourse provided all information as being in an unambiguous, specific, and complete manner (Grice, 1975; Clark, 1978). T h e participants in a communicative event have a distinct ability to infer the information which is lacking in the discourse. Thus comprehension can be regarded as an inferential activity. This insight at the philosophical level, however, does not say very much about the empirical role of inferences in discourse comprehension. With regard to the empirical role of inferences many questions have to be asked which are not easily answered philosophically, e. g. :

(1)

(2) (3)

(4) (5) (6)

Do psycholinguistic inferences have anything in common with conscious reasoning or even with logical drawing of inferences? How are inferences mentally represented? What is actually going on during the process of inferring? T o what degree are inferences dependent on the context? Are there different types of inferences? Which methods can be used to investigate inferences?

Each of these questions aims at a central aspect of psycholinguistic inference research: Question (1): Questions (2) Question (5): Question (6):

conceptual aspects,

-

(4): theoretical aspects of representation (2), procedures (3), and context (4), classificational aspects, methodological aspects.

In the present chapter we will discuss these central aspects of inference research in the above - mentioned order.

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CONCEPTUAL ASPECTS Due to complementary developments in psycholinguistics, cognitive psychology, and Artificial Intelligence there has been a tremendous increase in research on discourse processing since the beginning of the seventies. But since it is still a very new scientific field, research on inference as part of these efforts is also marked by a variety of open issues. O u r inexperience far exceeds the known facts. As van Dijk and Kintsch (1983) put it: ”In every way our knowledge about inferences in comprehension is as yet inadequate” (van Dijk & Kintsch, 1983, p . 52). If we enter into a discussion of some conceptual problems of research on inference in the following, we must point out that it can be done only in a very incomplete way. In a first attempt we define the concept of inference in discourse processing as a cognitive process by which the reader or hearer acquires new information starting out from the explicitly conveyed textual i n f o r mation and taking into account the context of the discourse. A central point of this definition is the interactive influence of text and context on the process of inferring. This interaction is the most prominent difference between psycholinguistic and logical inferences. Whereas logical i n f e r ences are the same in all contexts, psycholinguistic inferences are highly context - dependent (Harris, 1981). O n closer examination of this definition, however, we see that certain problems do arise. First of all, according to the preliminary definition, the completion of sub - semantic information would also come under the concept of i n f e r ence. If, for example, the misprint ’infe ences’ were to be found somewhere in this chapter, every reader could decipher this as ’ i n f e r ences’ without any difficulty. This is done by a bottom - up activation of letter clusters and of the lexical unit as well as the succeeding top - down activation of the missing letter (e.g. Adams, 1979). T h e first part of the deciphering can be called decoding, i.e. the generation of semantic information from sub - semantic information, and the second encoding, i.e. the generation of sub - semantic information from semantic information. Whereas decoding is a necessary part of every comprehension process, encoding is a special strategy for solving perception problems. It occurs particularly often in auditory comprehension if a word in a context cannot be heard precisely. In this case the listener often introduces a word which complies with the available semantic and phonetic information of the poorly understood word. Should we therefore include decoding and encoding into the concept of inference?

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Secondly, the definition given above implies that certain pieces of information are given explicitly in the text and that inferences are something going beyond what is explicitly given. T h e distinction explicitly vs. implicitly given textual contents is not, however, clear-cut. Let us assume for a moment that the reader processes the following passage: John met Mary. H e was glad to see her T h e reader certainly knows that ”he” stands for ”John” and ”her” for ”Mary”. Several authors call this realization ’pronominal inference’ ( e .g. Warren, Nicholas, & Trabasso, 1979). We are dealing here with rather automatic processes which usually happen unconsciously. The reader does not have the feeling to go beyond what is given in the actual text. Should we include such automatic reference processes into the concept of inference? In this context Garrod (this volume) only talks about ’pseudo - inferences’ and differentiates these from ’true inferences’. The distinction between explicit and implicit text information becomes problematic even if we would agree with a constructivist point of view concerning discourse comprehension as is described, for example, by Bransford (1979). According to this view, the meaning of a text is not something to be found in the actual text, but something to be constructed in the reader’s or listener’s head by using the text. A proposition, for example, is never taken straight from the text but is generated with the aid of the text and therefore inferred by the reader or listener. Seen this way, discourse comprehension as a whole would consist of inferring an internal mental model from the text information (Collins, Brown, & Larkin, 1980). An assumption of semantic information stated explicitly in the text becomes obsolete when applying such an opinion. T h e notion of inference would cover the whole field of discourse comprehension and thus would become too vague to serve a special function in theory construction.

We therefore propose that the constructive process of discourse comprehension may be divided into the following subprocesses of information generation: (1) decoding, i.e. the generation of semantic information from non semantic information,

(2) encoding, i.e. the generation of non semantic information, and

- semantic information from

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(3) inference, i.e. the generation of semantic information from semantic information. T h e semantic information can be word concepts o r higher semantic units like propositions, mental models, o r categories of super - structure. T h e non - semantic information can be the phonetic o r graphemic information. T h e rationale behind this differentiation of semantic and sub semantic processes is that they play a diffcrent role in communicarion in terms of acquisition, attention, and memory (e.g. Brewer & H a y , 1984). Accordingly the underlying constructivist position must be complemcnted by a functionalist approach (Schnotz, Ballstaedt, & Mandl, 1981; Rickheit & Strohner, 1985; Strohner & Rickheit, 1985). When viewcd from this perspective, discourse comprehension will be a complex system of processes which may be differentiated according to its functions for the entire system. T h u s , decoding, encoding, and inference are constructive generations of new information in language processing with clearly different functions. If one accepts this differentiation and relates it to the examples listed above, then the completion of sub - semantic information (as for example the completion of the word pattern 'infe ences') on the one hand, would no longer come under the concept of inference, and, discourse comprehension on the other hand, would no longer be equated with inferring an internal mental model, even if one generally accepts the hypothesis of constructivity. As to the above - mentioned pronouns, these would have to be regarded as a borderline case of inference, because they contain a component of decoding as well as a component of inference. T h e component of decoding would be the generating of a word concept from the phonetic or grahemic information of the pronoun (e.g. "he" is something which is male and individual), and the component of inference would be the linking of this general word concept to the concept of the specific antecedent (see Sanford, this volume). T h e definition of concepts are neither correct nor incorrect, but only more or less productive for the inquiry into a certain subject. This is true not only for the concept of inference in general but also for the distinction between various aspects of inferences. T h u s , our full definition of inferences in discourse Comprehension can be stated as follows: An inference is the generation of new semantic information from old semantic information in a given context.

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If we denote the old information with A, the new information with B, the context with C , and the process of generation with an arrow, then an inference can be illustrated in the following way: I N F E R E N C E

=

A - - - - - >

C

B

This formula consists of four parts A, B, C , and the symbol for the inference process. If we take information A and B together, then we have to deal the following parts of an inference:

(1) the psychological representation of information A and B,

(2) the process of inferring B from A, and

(3) the notion of context C and its effect on inferring. W e would now like to discuss some theoretical aspects of inferences in discourse processing in the following order. We will first focus our attention on the representational aspects of inferences by asking what kind of representations are produced on drawing inferences. Secondly, we will discuss the central question connected with the procedural aspects, i.e. : At which point in time is a specific inference made? Thirdly, we will refer to contextual aspects of inference. One of the questions to be asked about the contextual aspect here is: What are the contextual influences on the process of inferring?

THEORETICAL ASPECTS T h e formation of inferences in discourse comprehension can be analysed according to various points of view, each representing a different complex of questions. Looking at it from the representational point of view, one has to ask what kinds of relations exist between the formation of inferences and the mental representation built up by the hearer or reader when comprehending a text. From the procedural point of view it is of major interest to know what kind of processes take place and when these processes occur. From the contextual point of view, the question arises in what way inferences and the contextual conditions of discourse comprehension are interrelated. In the following we would now like to give a brief outline of recent developments in research from these points of view.

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Representation

T h e representational aspect refers to the relations between the infer ences on the one hand and the mental representation on the other hand. W e will start with a short survey of a few approaches to a theory of mental representation. T h e n we will deal with the interactions of i n f e r ences and mental representation.

Theoretical concepts o f the mental representation of texts Theories of the mental representation in discourse comprehension try to answer the questions how the meaning of the text which is generated by the reader or listener is structured internally, what the units of this internal structure are, and how these units are combined into a coherent whole. In recent years several theoretical concepts have been put forward concerning these issues (Clark, this volume; Graesser Pr Clark, this volume; Wagener & Wender, this volume; Zimmer & Engelkamp, this volume). Craik and Lockhart (1972) in their research on memory proposed the

so - called levels - of - processing approach as a n alternative to the con-

ventional storage models. According to this approach several levels of processing can be differentiated. At each of these processing levels, processing leaves memory traces which become part of the mental representation. This general concept of various processing levels was adopted for discourse comprehension, among others, by Dooling and Christiansen (1977). Following this approach, Kintsch (1977) also differentiated between several levels of processing in text comprehension with their c o r responding memory traces. Within this framework mental representation can be regarded as a n ensemble of traces consisting of several levels, (e.g. Thibadeau, Just, & Carpenter, 1982; Johnson - Laird, 1983; van Dijk & Kintsch, 1983). Furthermore, these levels will include conceptual units, propositional units, mental models, and a super - structure level. (1) Conceptual units T h e basic level of semantic structure is the conceptual level. Various authors believe that concepts function as cognitive schemata (e. g. Rumelhart, 1975, 1980; Anderson, 1978; Bower, 1978; Graesser & Clark, this volume), which are seen as organizational units of knowledge. Textual information is selected by activated cognitive schemata, i n t e r preted and integrated into already existing knowledge (Spiro, 1980;

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Thorndyke & Yekovich, 1980). T h e goal - directedness of text processing, appropriate to a certain perspective in reading, can also be explained by the activation of corresponding schemata (e.g. Pichert & Anderson, 1977; Anderson & Pichert, 1978). In its general form, however, the theory of cognitive schemata is not detailed enough to facilitate exact predictions about text processing (Thorndyke & Yekovich, 1980; Herrmann, 1982; Alba & Hasher, 1983). A viable alternative to the schema theory may be the theory of reality monitoring of Johnson and Raye (1981) which focuses more on the functional embedding of cognitive processing than the schema theory does.

(2) Propositional units Influenced by models of semantic memory, some researchers have put forward propositional theories of mental representation (e. g. Kintsch, 1974; Meyer, 1975, 1981; Frederiksen, 1975, 1977; de Beaugrande, 1980; Graesser, 1981). In their view, the meaning of a text at the different semantic representational levels consists of propositions which are integrated into a coherent whole. T h e proposition is a relational structure consisting of one predicate and one or more arguments. T h e meaning of a text can then be represented as a list or network of propositions (e.g. Simons & Bruce, 1971). At the lowest, most detailed representation level the meaning of the text is formed by the propositional micro - structure. This micro - structure consists of propositions which capture the meaning of the text in all its details. At the higher, more general levels the meaning of the text is representated by the propositional macro - structure. These macro - propositions are units which represent the meaning of the text in a reduced or summarized form (van Dijk, 1977, 1980; Guindon & Kintsch, 1984). Propositions have also been shown to be important units of discourse processing (cf. van Dijk & Kintsch, 1983). (3) Mental models While propositional theories try to reconstruct a mental representation which is relatively close to the text, a new generation of theories of mental representation is based on much more comprehensive structures. Johnson - Laird (1980, 1983), for example, assumes that there exists in addition to the propositional representation of a text a representation by mental models. These mental models include much accumulated world knowledge which is independent of the text and can thereby reach far beyond the text. Likewise, van Dijk and Kintsch (1983) distinguish between the representation of the actual text, i.e. the so-called text basis, and the representation of the facts dealt with in the text, i.e. the so - called situation model. Collins, Brown, and Larkin (1980) see dis-

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course comprehension as the construction of a mental model founded on a successively extending data basis of the read or heard text. T h e scenario theory of Sanford and Garrod (1981) is also based on extensive units of world knowledge about social situations. Mental models seem to have a great influence on inferences in discourse comprehension (Garrod, this volume; Sanford, this volume). (4) Super - structures In addition to conveying its special contents, a text has a more or less conventionalized form. This conventionalized form may be called super - structure (e.g. van Dijk, 1980) because it is the most fundamental characteristic and relates the semantic level to the pragmatic level. T h e conventional units may be categories such as introduction, problem, example, conclusion, etc. Several studies have proved that these units have an influence on text processing (e.g. Thorndyke, 1977; Haberlandt, 1980; Yekovich & Thorndyke, 1981; Mandler & Goodman, 1982; Schnotz, this volume). Super - structures were mainly described for stories under the notion of 'story grammars' (e.g. Rumelhart, 1975; Mandler & Johnson, 1977; Thorndyke, 1977; Stein & Nezworski, 1978). T h e approaches were, however, criticized as being too formal and not only specific for stories, but also for other narrative discourses (Black & Wilensky, 1979; Garnham, 1983; Wilensky, 1983; see also Rumelhart, 1980; Mandler, 1982; Stein, 1982).

Mental representation and inference According to the levels - of - processing approach, every comprehension process leads to memory traces at the respective processing levels. T h e resulting ensemble of traces makes up the mental representation of the contents processed. T h e information a t the various levels of representation is only in part given explicitly in the text. A large portion of the textual information is referred to only by implication. This implicit part of the representation is the inferrnce. Inferences in discourse comprehension are cognitive processes in which the hearer o r reader, starting out from the explicitly conveyed textual information and taking into account the respective context, constructs new semantic representations. For the result of the processing i t does not make much difference whether rhe processed i n f o r mation is given explicitly in the text o r is inferred. In both cases the processing leaves traces in the memory. T h e explicitly conveyed i n f o r

The concept

(if

inference

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mation as well as the information inferred thereby become part of the mental representation of the test. Inferences are thus a n important part of what is actually conveyed by a text. In general, the interaction of mental representation with inferences has two important aspects. O n the one hand, the formation of inferences is influenced by the mental representation already built up. O n the other hand, the emerging mental representation is partly the result of the inferences which have already been drawn. Because of this close linking of inference formation and mental representation, it is not only the research on mental representations which can contribute to a theory of inference, but also vice versa. From this theory of inference great impetus can be expected for research into mental representation. O n the basis of tion and inferences, constructing mental different theories of

this general relationship between mental representahowever, different specific functions of inferences for representations are conceived of in the framework of discourse comprehension.

Researchers who support propositional theories often claim that inferences mainly serve to close coherence gaps in the text (e.g. Kintsch & van Dijk, 1978; Crothers, 1979). At the text basis level as well as at the macro - structure level it can be the case that the propositions directly conveyed in the text are not actually interrelated and therefore do not constitute a coherent whole. In that case inferences must be drawn to fill the corresponding gaps. Researchers closer to the theory of mental models, however, regard the formation of inferences as a process less dependent on the text. Warren, Nicholas, and Trabasso (1979), for example, assume that the reader o r hearer, starting out from the proposition being focused, puts questions to the text already processed. In the case of a stor): the questions would be who, what, when, where, why, o r how to relate the focused event to preceding events. Here, inferences are nothing but the reader’s or hearer’s answers to the questions asked by himself. Collins, Brown, and Larkin (1980) start from the assumption that the developing mental representation contains blanks. These blanks are then filled by inferences during discourse comprehension. Inferences, in this case, are not only means to fill in gaps of coherence in the test, but also processes for the extension and completion of already existing knowledge structures (Graesser & Clark, this volume; Schnotz, this volume).

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Procedure Inferring is a process which takes a certain amount of time. During this time an initial state of mental representation is changed into another. T h e inferential process is furthermore heavily influenced by contextual factors. In the present section we will focus on the procedural aspects (Garrod, this volume; Sanford, this volume; Vonk, this volume). Text processing is only partially an automatic process. Several studies show that there are differences between automatic processes and processes controlled by attention during text comprehension. Subsequent to the theory of perception of Posner and Snyder (1975) perception was seen as a dichotomy of automatic processes which are passing very quickly and processes which are controlled by attention and which are passing more slowly (e.g. Stanovich, 1981; Stanovich & West, 1981, 1983). But Fischler and Bloom (1979, 1980) suggested these processes to be a continuum instead of a dichotomy. Garrod (this volume) proposes an inference theory which is based on the distinction between automatic and controlled processes. Van Dijk and Kintsch (1983) argue that discourse processing consists of several kinds of processing strategies. T h e concept of strategy was introduced into psycholinguistics by Bever (1970) in the sense of a goal - directed cognitive process. Van Dijk and Kintsch expand the concept of strategy into the level of discourse processing and other complex cognitive processes. They link this concept up with the concept of action by interpreting strategy as a ”global instruction for each necessary choice to be made along the path of the course of action: whatever happens, always choose the cheapest, fastest, surest, etc., alternative” (van Dijk & Kintsch, 1983, p. 65). Van Dijk and Kintsch base their theory on a multi -level model of text processing. T h e processing occurs simultaneously on all levels. The procedures on one level are independent of those on other levels, but report the result of their analysis to the other levels so that a high degree of interactivity is achieved. T h e model contains the following levels: atomic propositions, complex propositions, local coherence, macro - structure, and super-structure. Apart from these main levels of processing there are strategies on the stylistic, rhetorical, and non - verbal level, which van Dijk and Kintsch, however, deal with only in passing.

The coricept of inference

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At each point in time discourse processing works on only a very small portion of the entire information available. This active information is the working memory. T h e function of working memory for inferential processes are described in the first part of this section. Some examples of the inferential processes going on in working memory are then presented with respect to the main direction of processing. Finally, those inferential processes which are related to solving comprehension problems are discussed.

Working memory T h e time span over which the actual inference processes takes place is usually called the working memory (Baddeley, 1979, 1981). Since this span of time is limited to a few seconds the capacity of the working memory is also very limited. Thus, the issues of efficiency and economy become highly important for the functioning of the working memory. For instance, only the most important inferences can be drawn during the short time available. But which information is important? How is the importance of inferences computed so quickly? Which are the mechanisms and strategies that integrate the new text information into textual and world knowledge? Those are the questions with which a theory of working memory and inferences have to be concerned. New textual information is received, ordered and connected with textual information, which has already been processed, and world knowledge. I n order to bring about the most effective integration only selected information from previous parts of the text is preserved. T h e other parts of the text are preserved in the long - term memory from which they can be reinstated if needed (Kintsch & van Dijk, 1978; Kintsch, 1982). There appears to be an optimal amount of information in the working memory in order to affect integration of new text information into the text which has already been processed. If the working memory is confronted with too much new information, only little old information can be held in working memory. Important old information, which may be necessary for the integration of the new information, must then be removed from the working memory and only after a time consuming search can it be recalled again. Should, however, too much of this old information be held in the working memory, then too little new information has room, so that the chances of its being integrated are considerably reduced. Thus, it is a principle of economy in text processing to fix the

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capacity of the working memory, so that an optimal amount of old and new information is available for integration (Monsell, 1984). There are several studies which point out which parts of the old text information have a high possibility of remaining in the working memory. Sanford and Garrod (1981) have considered in detail the question of what information of the text already processed has been preserved in the working memory. They found that the main characters of a scenario are constantly present in the working memory, whereas the secondary c h a r acters are removed from the working memory when they are no longer of significance. T h e theme of a text is also information which is held in the working memory even if at times another subject comes up (Lesgold, Roth, & Curtis, 1979). T h e duration of a scenario also appears to be always actual. Sanford and Garrod suppose that this also applies to the place of processing. So far, it is not clear which other parts of a scenario are available to working memory. It is likely, however, that only a very small selection of the entire scenario information is constantly activated. Research has only begun to clarify this question (see Garrod, this volume). Such studies would be relevant for the inference process at the level of global coherence as well as at the level of local coherence. Highly selected old information waits for the new portion of the text which enters into the working memory. Recent research has shown that there seems to be a fixed amount of new text information which can remain in the working memory. Glanzer, Dorfman and Kaplan (1981) performed experiments in order to find out the capacity of the working memory in respect to the new information. T h e subjects heard or read a series of different texts which were of various text types. T h e task of the subjects was to reproduce verbally specific signs which occured at any time in the text, either in the sentence just read or spoken, in the preceding sentence or in the sentence preceding that one. T h e results showed that for the immediate sentence the reproductions were practically complete, for the penultimate sentence still half, but for the antepenultimate sentence only about 20%, and for all other preceding sentences practically no more reproductions could be made. These results are in good agreement with the results using unconnected sentences (e.g. Glanzer & Razel, 1974; Jarvalla, 1971, 1979). Two sentences seem to be the optimal unit of the new incoming text in working memory. T h e size of this unit may be related to one important goal of working memory, namely, to establish local coherence. For establishing local coherence one must have available at least two sentences between which referential relations can be constructed.

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After having discussed the size of the newly entering text fragment, we must now turn to the question of processing. What happens with the new information when it enters the working memory? Is it just stored, or is it processed immediately and if SO, then to what extent? Glanzer, Fischer, and Dorfman (1984) questioned whether the content of the working memory is the w o r d - f o r - w o r d information of both of the last sentences or if this information has already been processed. Following interruption of the working memory by a twofold task, they gave the subjects either the sentence in the text immediately before the interruption or information about the theme of the text. These served as different reactivations of the working memory. A sentence which showed a immediate connection to the test sentence was shown to be easier to understand than a sentence having a connection to the theme. Glanzer et al. concluded from these results that the verbal information of the preceding sentence is retained in the working memory. It is, however, very likely that the actual information was also semantically processed at the same time. This is indicated, for instance, by the immediacy principle of Just and Carpenter (1980), by Fletcher (1981) and by recent experiments of Le Ny, Achour, Carfantan, and Verstiggel (1983). Le Ny et al. measured the time for recognizing single words of a complex sentence which had just been read. From these experiments it was concluded that the words remain more or less strongly activated depending on their importance for the meaning of the entire sentence. Le Ny et al. also supposed that this importance depends on the relative frequency of using separate words in building up the sentence proposition. In summarizing, it may be supposed that not only a very selective choice of already processed text information is available in working memory, but also that about two new sentences are available containing word - for - word information. This information seems to be processed semantically and in a selective manner. O n the basis of the old and new information available in the working memory, inferences at both the local and the global coherence level can take place very easily. W e will discuss some of these processes in the ensuing part of this chapter.

Forward and backward inferences O n e of the greatest problems with discourse inferences is to determine when they are made. Are inferences nidde at every point in time during comprehension process or are they made only if they are needed in order to bridge a gap in the text? Carpenter and Just (1977) called the first

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type of inference forward inference because the inference is directed to parts of the text which probably follow the inference - generating part of the text. The second type of inference is called backward inference because the inference is directed to parts of the text preceding the inference - generating part. It is clear that a general answer to the question concerning forward and backward inferences can not be given unless we differentiate between the various levels of inference production (van Dijk & Kintsch, 1983). W e will now try to give a short and selecrivc review of some of the main areas of research dealing with forward and backward inference processes.

(1) Lexical decomposition Many theorists view language comprehension as a decomposition from the text information into semantic primitives and their interrelations (e. g. Schank, 1972). Sanford and Garrod (1981) suggested that the inference between sentence (1) and sentence (2) is made before the reader encounters sentence (2) since the inference is already built into the conceptualization underlying (1). (1) Mary dressed the baby. (2) T h e clothes were made of pink wool. T h e critical test of conceptually driven inferencing arises with a comparison of the reading times for sentences like ( 2 ) , either in the context of an implied antecedent like in sentence (1) o r in the context of a explicitly stated antecedent like in sentence (1’).

(1’) Mary put the baby’s clothes on.

If, as Sanford and Garrod suggested, the antecedent entity ”clothes” is already represented as part of the decomposition in the implied antecedent condition, there should be no difference in the reading time for the critical sentences in both conditions, since no extra backward i n f e r ence would be necessary. However, if there is no lexical decomposition the time to make a backward inference should result in longer reading times for the critical sentence in the implied antecedent condition. As Sanford and Garrod found no significant difference of reading times between both conditions they concluded that the readers inferred ”clothes” when reading ”dressed”. A study by Gentner (1981) also confirmed the decomposition theory. In three experiments subjects recalled subject - verb - object sentences

The concept o f inferetice

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with general o r specific verbs:

(3) Ida gave her tenants a clock. (4) Ida sold her tenants a clock. T h e level of recall of the object noun, given the subject noun as a cue, was correctly predicted by the relative number of connecting subpredicates in the verb. Van Dijk and Kintsch (1983) seem to believe that there is no lexical decomposition in the process of discourse comprehension. They refer to a study of Fodor, Garrett, Walker, and Parkes (1980). Fodor et al. devised a rating procedure in which subjects were asked to rate the degree of relatedness between words. They first showed that this procedure was sensitive enough to reflect the difference of the relation between "John" and "Mary" in the propositional structure of the two sentences:

(5) John expected Mary to leave. (6) John persuaded Mary to leave. I n sentence (6) "John" and "Mary" are more closely connected in the propositional structure than in sentence (5). Subjects rated "John" and "Mary" to be more strongly related in the persuade sentence where "John" and "Mary" are part of the same proposition than in the expected sentence where they are not part of the same proposition. This rating procedure was applied to other sentences like:

(7) John killed Mary. (8) John bit Mary. If "John killed Mary" is decomposed into "John caused Mary to die", the rating procedure should result in a difference between sentence (7) and (8). Fodor et al. report that the degree of relationship of the two sentence types did not differ, contradicting obligatory lexical decomposition. In our opinion, however, it is doubtful whether the rating procedure of Fodor et al. is a valid procedure to detect lexical decomposition. After a more direct effort to resolve the decomposition issue Wender (1984) proposed a discrimination between a semantic and a cognitive level of decomposition. Decomposition would be more relevant for the semantic than for the cognitive level of language processing.

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G. Rickheit, W. Schnotz, H Strohner

(2) Instantiation o f gcneral terms A particular instance of a general term may be a better recall cue for a sentence containing the general term than is the general term itself. For example, subjects are better able to recall the sentence (9) The fish attacked the swimmer when given "shark" as a cue than when given "fish" as a cue (Anderson, Pichert, Goetz, Schallert, Stevens, & Trollip, 1976). Garnham (1979) regarded this instantiation of a general term not as a context - sensitive aspect of word meaning but as a type of inference on the word level. This would be then, besides lexical decomposition, a second type of forward inference on the word level (Garnham, 1981). Recent evidence by Whitney and Kellas (1984), however, confirmed the proposal of Gumenik (1979) that the results of Anderson et al. are due not to the encoding process of the sentence, but instead reflect processes occurring at the time of retrieval. The pattern of semantic i n t e r ference obtained in a modified Stroop paradigm clearly contradicted the position that readers routinely encode general terms as inferred instantiations. An effect of instantiation processes was found only when typical exemplars served as targets. T h e pattern of semantic activation of the category terms was not dependent on the type of semantic context as it should be according to the instantiation hypothesis.

(3) Case - filling inferences

In two studies Singer (1979, 1980) asked whether people draw inferences about implied case - filling elements like agents, patients, and instruments, during reading. Singer asked, for example, whether one infers the participation of a dentist when the sentence (10) T h e tooth was drilled. is read. It was shown that people need more time to verify, recognize, and understand sentences expressing the implications of antecedent material than sentences expressing ideas that are stated directly. In the study of 1980, Singer added to the forward inference condition a backward inference condition in order to make clear the difference between the two conditions:

The concept o f inference

21

(11) Direct condition:

T h e tourist took the picture with the camera. T h e scene was more beautiful than he remembered.

(12) Backward inference condition: T h e tourist took the picture of the church. T h e camera was the best he had ever owned. (1 3) Forward inference condition: T h e tourist took the picture of the church. T h e scene was more beautifui than he remembered. For all three versions of the tourist passage the test sentence was: (14) T h e tourist took the picture with the camera. T h e subject needed about 200 msec. more to verify the test sentences in the forward inference condition than in the other two conditions. Singer concluded that missing case - filling elements, like agents, and instruments are inferred only in backward inferences but not in forward inferences. Singer proposed that there are too may possible forward inferences which can be derived from a message to permit many of them to be included in the representation of the discourse. Backward inferences, on the other hand, are drawn during reading because, without them, a message would become disjointed. This conclusion is consistent with results of studies by Corbett and Dosher (1978) and Carpenter and Just (1978). (4) Causal inferences Causal relationship are among the most important relationships between events in a discourse. Singer and Ferreira (1983) asked whether readers infer the consequences of events described in stories. They presented their subjects with short stories in which some sentences occasioned backward inferences to be drawn and other sentences forward inferences. In the following an example is given of these two inference conditions.

(15 ) Target inference: T h e report burned up.

(16) Forward inference condition:

T h e spy threw the report into the fire.

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G. Rickheit,

W.Schnotz, H. Strohiier

(1 7) Backward inference condition: T h e spy threw the report into the fire. T h e ashes floated up the chimney. After the presentation of this spy story the subjects had to answer the question:

(18) Did the spy burn the report? T h e response latencies to these inference questions on four stories showed that answer latencies were about 200 msec. faster for backward inference questions than for forward inference questions. These results clearly indicate that the consequences of action are only then inferred if the i n f e r ence contributes to the coherence of the story.

(5) Model - based inferences T h e inferences which we have discussed so far are all based on relations between concepts or propositions. We have seen that forward i n f e r ences occur only seldom at these two levels of drawing inferences. Subjects seem to make inferences only in order to decompose words into conceptual units or to connect a proposition to other propositions in the text. But what about inferences which are based on more complex knowledge structures, like scripts, mental models, or scenarios? It seems plausible to hypothesize that forward inferences should be the easier to make the larger the domain of reference is. T o the best of our knowledge, however, there is no clear - cut answer to this question. An example might clarify our argument. Let us take a study on inferences based on scenarios which is reported in Sanford and Garrod (1981). They argue that an article about a court case might evoke a wide variety of entities such as lawyers, a judge, a jury, and so on, which need not be explicitly mentioned. Sanford and Garrod think of all these as part of our knowledge constituting the scenario behind a court case. If the title of the article is, for example, "in court" then the court scenario is evoked with all the entities relevant to a court. This evoked scenario would be reinforced by the following sentences if these sentences also refer somehow to the court situation. T o test this prediction texts of the following kind were presented: (19) In court Fred was being questioned (by a lawyer). He had been accused of murder.

The concept of inference

23

Target sentence: T h e lawyer was trying to prove his innocence T h e reading time of the target sentences in the explicit condition and in the implicit condition were about the same. Sanford and Garrod i n t e r preted this result as a confirmation of their scenario hypothesis. According to this view the scenario enables references to individuals because these individuals are already given in the representation. This would be one way in which the scenario representation provides more information than is present in the propositional structure of the discourse. We feel, however, that the result can also be explained in terms of backward inferences. It need not be the case that the concept "lawyer" is already activated when reading "In court" and then reinforced by the following two sentences. It may be that only by reading the sentence "Fred was being questioned", readers make a backward inference in order to connect the sentence with the title. T h e content of this backward inference may well be the concept "lawyer". In conclusion, we would like to say that in order to solve the question of forward and backward inferences at the text level the matter of methodology becomes extremely important. Most studies work with global on-line measurements, e.g. reading time (Sanford & Garrod, 1981) or off-line recognition tests (Walker & Yekovich, 1984). What is needed to answer the question relating to forward and backward inferences at the schema - level are more on - line measurements, e.g. the cross modal - priming task of Swinney (1979), or Stroop - tasks (e.g. Whitney & Kellas, 1984). Only with on-line measurements which show us the state of activation at a certain moment of discourse processing will it be possible to see more clearly what happens in terms of forward and backward inferences when subjects read or listen to a discourse.

Solving comprehension problems Discourse comprehension is often a difficult task since in many cases it is not immediately clear what was meant by the speaker o r writer. T h e listener or reader has to use several specific strategies in order to cope with the communicative demands of a discourse. Therefore, language comprehension may be conceived of as a kind of problem solving (Clark, 1977, 1978).

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G. Rickheit, W. Schnotz, H. Strohner

In most cases the problem solving processes in discourse comprehension do not reach a conscious level. Readers or listeners do not notice that they are solving complex problems very quickly. Text researchers are only now beginning to realize the complexity of these processes. Two basic types of comprehension problems may now be distinguished. First of all, a comprehension problem may occur if the listener or reader does not draw certain inferences which the speaker or writer intended, Secondly, a comprehension problem may occur if the listener or reader draws certain inferences although the inferences are not intended by the speaker or writer. I n both cases, however, it is possible that the listener or reader recognizes that he or she is on the wrong path. Then the listener or reader has to reanalyse that part of the text which he or she probably has misunderstood. This reanalysis is performed by means of special processes (e.g. Frazier & Rayner, 1982). T h e goal of the reanalysis is to attain a representation of coherent text. This goal is identical to that of the inferences in discourse comprehension. It is probable, therefore, that the reanalysis consists to a certain degree of inferential processes. Thus, we have to take into consideration that inferences occur not only in the first pass of the comprehension process, but also in the second pass which aims at solving comprehension problems. Are the inferential processes in the first pass the same as the inferences in the second pass? Garrod (this volume) calls the inferences of the first pass 'pseudo-inferences' in contrast to the 'true inferences' of the second pass. Garrod shows that the two inference types also include different processes. For example, true inferences take more time and are often more conscious than pseudo - inferences. It is, however, not clear whether besides these differences there are other systematic differences between the two inference types. In order to have two clearly separable classes of inferences, systematic differences should also be existent with respect to other representational, procedural, and functional aspects. An important goal of further research should be to offer more data concerning these possible differences.

Context

There is no doubt that the context is very important for the u n d e r standing of language and for making inferences, but the concept of context is generally left undefined in most of the current studies of language use. Although Miller pointed out already in 1951 that the context plays

The concept of inference

25

an important role in communication it was not taken into account for many years. One of the first psycholinguists who investigated the influence of context on language processing was H. Clark. H e subdivided the context into the following three s’ections:

”1. T h e explicit content of the sentence. 2. T h e circumstances surrounding the utterance. 3. A tacit contract the speaker and listener have agreed upon as to how sentences are to be used” (Clark, 1977, p. 244). T h e first point corresponds to the verbal context; i.e. the parts of a speech or text that precede and follow a word or passage and contribute to its full meaning. T h e second point we may call nonverbal context; i.e. the conditions and circumstances that are relevant to an event. Considering the third section of context: T h e tacit contract or the tacit agreement (Clark, 1978) between speaker and hearer is, according to Grice (1975), a central precondition for successful communication. Speaker and listener tacitly agree to cooperate with each other in order to communicate successfully. Grice called this basic assumption the ’cooperative principle’. According to this principle the speaker has to follow four ’maxims’: be informative, be truthful, be relevant, and be clear. T h e listener will, on the other hand, assume that the speaker conforms to these maxims. The cooperative principle and its maxims are fundamental ingredients for this type of context because they are critical to the inferential strategies in language comprehension. T h e influence of context on language processing has been investigated in many psycholinguistic studies, but there is no consistent use of the term ’context’. There are however, as Clark and Carlson (1981) showed in their review of relevant experimental attempts, some features of context common to most of the uses they reviewed (Le. information, person relativity, process relativity, occasion relativity, availability, interactibility). ”TOsum up, context is information that is available to a particular person for interaction with a particular process on a particular occasion” (Clark & Carlson, 1981, p. 318). This definition implies however, that all information which is available to the listener or hearer at a certain moment belongs to the context of language processing. This extended notion of context has lost some of its explanatory force due to such a vague and general definition.

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G. Rickheit, W. Schnotz, H Strohrier

T o avoid such an unspecific term of context Clark and Carlson (1981) suggested differentiating between two types of contexts: the intrinsic and the incidental context. ”The intrinsic context [...I is that part of the context that, a priori, has the potential of being necessary on some occasion for carrying out the process in question [...I. T h e incidental context is what remains, the parts of the context that never need to be consulted” (Clark & Carlson, 1981, p. 319). They emphasize that an adequate theory of language processing has to distinguish between the intrinsic and the incidental context. T h e intrinsic context refers to information not given by a speaker, but assumed to be inferred by the listener. T h e listener is able to recognize the speaker’s intention, i.e. to make the authorized inferences (Clark, 1977) on the common ground of both: T h e speaker’s and addresbee’s mutual knowledge, beliefs, and suppositions are relevant for the process of language comprehension. In order to find out what is part of their common ground, speakers and addressees have three main sources of information:

(1) community membership, (2) physical co - presence, (3) linguistic co - presence (cf. Clark & Marshall, 1981). These three sources for a common ground constitute the intrinsic context for comprehension. Physical and linguistic co - presence are time -bound and tied to a particular place, whereas community membership refers to an ever continuing knowledge of social groups or cultures (Kintsch & Greene, 1978; Markova, 1978; Reynolds, Taylor, Steffensen, Shirey, & Anderson, 1982). According to these statements we distinguish between the following types of context:

(1) cultural context, (2) situational context, (3) medium context, (4) verbal context, and (5) personal context.

T1ic coticept of inferrricr

21

T h e investigation of the relationship between these types of context and language processing is very important because the context influences the process of understanding and the drawing of inferences.

Cultural con text T h e cultural context with its conventions of communication constitutes an important framework for discourse processing (e.g. Clark & Carlson, 1981; Freedle & Fine, 1981). Cultural conventions and conventions of communication influence both knowledge within the particular representational units and inferences which are drawn with the assistence of these units and according to these conventions. If these conventions are not taken into consideration, misconceptions will arise (Dore & McDermott, 1982). There is also some empirical information concerning the influence of culture on the processing of text structure. Kintsch and Greene (1978) suggested that a culture - specific schema of super - structure aids in comprehending and reconstructing stories. Kintsch and Greene showed that readers wrote better summaries of stories for which they had an appropriate super - structure (i.e. stories of the Decameron) than for stories for which they lack such a schema (i.e. stories of Alaskan Indian myths). This effect is not restricted to the level of propositions or local coherence, but is related to the overall organization of the story. In a second experiment the subjects had to recall either a fairy tale from the Brothers Grimm or an Apache Indian tale. T h e first text had a well known structure, whereas the second text was lacking a conventional super - structure because the episodes were not related according to the Fausal sequence of actions. T h e Grimm fairy tale was recalled almost completely, but the Indian tale was recalled very poorly. Reynolds, Taylor, Steffensen, Shirey, and Anderson (1982) investigated the relationship between cultural schemata and reading comprehension. Black and white students read a letter about a school incident that could be interpreted as a fight or as an instance of ’sounding’ which is a special form of ritual insult predominantly found in the bIack community. There was evidence that the subjects’ perceptions of the incident as either ritual insulting or a fight was related to culturally - based knowledge and belief. Black students tended to interpret the passage as a verbal play, while white students tended to interpret it as physical ag-

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G. Rickheit.

W.Schnotz, H Strohner

gression. These results show how cultural schemata can influence reading comprehension. Cultural context constitutes the common ground for understanding. Culture - specific schemata thus aid in comprehending texts of this culture. These schemata provide the listener and reader with special knowledge from which he o r she may draw the inferences which are necessary for text comprehension (Smith, 1984; Clark, this volume). Information that does not fit into this cultural frame is processed worse.

Situational con text Text processing is always part of a more comprehensive context of action, by which the listener’s or reader’s aims and perspectives are affected. Attempts have been made in several studies at generating certain perspectives in test subjects with the aid of preliminary texts or i n s t r u c tions (e.g. Anderson, 1978; Bower, 1978; Thuring, Groflmann, & Wender, this volume). In a famous study, Pichert and Anderson (1977) asked their subjects to read a description of a house from the point of view of a housebuyer or a burglar. T h e reproductions showed a strong dependence on the chosen perspective immediately after the presentation of the text and an even stronger one after a week. Goetz, Schallert, Reynolds, and Radin (1983) were able to replicate the results of Pichert and Anderson. In addition, they found that the reading times of sentences which contained information relevant to the chosen point of view were longer. This finding confirms that the perspective given by instruction affects not only the recall performance but also the comprehension process during input. A further result of Goetz et al. was that the findings were clearer with experimentally induced perspectives than those obtained using estate agents and genuine policemen as subjects. In another study Anderson and Pichert (1978) investigated the effect of shift in perspective. College students read a story from the perspective of either a burglar or a person interested in buying a home. After recalling the story once, subjects were directed to shift perspectives and then recall the story again. In two experiments, subjects produced on the second recall significantly more information important to the second perspective than had been the case in the first perspective. They also recalled less information which was unimportant to the second perspective

The concept of inference

29

but which had been important to the first. These data clearly show the operation of retrieval processes to be independent of encoding processes (Anderson, Pichert, & Shirey, 1983). Frederiksen (1975) found that reader’s inferential processing, as measured by later false memories, was altered by instructions varying the reading purpose. Subjects read a text describing the characteristics of an imaginary island. One group of subjects read the passage for a later memory test; another group read the passage with a view to proposing a solution of a political problem posed in the text. Frederiksen varied the reading purpose by instructions and then he examined free recall of the text for the reproduction of statements and the intrusion of inferences. Black (1981) also investigated the effects of the purpose of reading the text on the memory. H e found that reading a text for different p u r poses influenced the drawing of inferences during reading. One group read a text to evaluate how understandable it was; another group read this text in preparation for a memory test; and a third group read the text in order to write an essay that would apply each text’s main point to an issue related to it. Black used a recognition test in order to check the false memories for inferences. When subjects read a text only to rate its comprehensibility, they falsely recognized fewer inferences than subjects who read the text for either a memory test or an essay test. Another type of situational context can be seen in pictures illustrating texts. I n some studies pictures served as the context. Bransford and Johnson (1972) studying effects of a picture context on text processing, found that the picture had a great influence on text comprehension. Subjects who saw the picture before the text presentation were able to understand and reproduce the text. Subjects who did not see the picture or who saw the picture only after the text presentation, were not able to understand the text. T h e picture context provided information concerning the coherence of different parts of the text which otherwise remained unintelligible. If the text is comprehensible per se, a picture may have no further explanatory function and may not lead to better comprehension (Bock, 1983). Medium context Text researchers have been trying for several years to answer the question whether reading or listening tcr a text facilitates better achieve-

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ment in comprehension and reproducrion. Several studies show a tendency towards better reproductions after reading difficult texts (e.g. Rickheit & Strohner, 1983; Hron, Kurbjuhn, Mandl, & Schnotz, this volume). This advantage on reading seems to be counteracted by an advantage of inference forming on listening to easy texts (e.g. Hildyard & Olson, 1978, 1982; Musseler, Rickheit, & Strohner, this volume). T h a t modality effects were found in text processing may be put down to the fact, on the one hand, that reading and listening are different processes, on the other hand that the studies have certain methodical shortcomings. These shortcomings which possibly lead to artefacts mainly refer to the comparability of reading and listening, the selection of subjects, and the texts chosen. T h e medium effects may be caused by the following factors: First, modality specific differences of memory; it may be that the store of one modality is more persistent than the corresponding store of the other modality. Secondly, differences in controlling language processing; it is very likely that the reader is freer in his or her search for information than the hearer in terms of comprehension time, regressions, and reanalysis. Thirdly, differences in attention; since reading is a very complex activity the reader must take care to avoid external distractions. Thus, irrelevant acoustic and visual context information must be ignored (Margolin, Griebel, & Wolford, 1982). Listening operates on other strategies of processing than reading. T h e temporal sequence of text presentation cannot be controlled by the listener. It is important to note that the listener is not visually and motorically inactive during text processing. Usually the attention of the listener is not only entirely focused on the text because he or she visually explores the environment whilst listening to a text. All these differences may influence the processes of drawing inferences in text comprehension. But even today the modality effect on making inferences remains for the most part unexplored. Future research should investigate which types of inferences are preferably drawn on reading or on listening to a text.

Verbal context Text comprehension must be seen as complex mental process which extracts informarion from a text and combines this information with rhose

The concept of inf’ererice

31

parts of the text which have been presented previously. These processes are influenced by particular linguistic properties of the text, such as pronominal reference, lexical entailments, and the topic markers (van Dijk, 1980). T h e parts of a text have a definite relationship to each other. T h e antecedent phrases establish the context of the following phrases. T h e serial position of each phrase of a text proved to be important. A sequential disorganization of sentences caused difficulties in a subject’s text recall. This difficulty increased according to the degree in which the order of sentences was disturbed (Meyers & Boldrick, 1975; Thorndyke, 1977). T h e empirical results of these studies indicate that the processing of each sentence of a text is dependent on the verbal context of the sentence. T h e specific sequence and connection of phrases are elementary factors which effect text cohesion (Schnotz, this volume). T h e title plays a special role for the verbal context. Several studies have confirmed the influence of title upon text comprehension (Dooling & Lachman, 1971; Bransford & Johnson, 1972; Dooling & Mullet, 1973; Schallert, 1976; Bock, 1980; Niegemann, 1982).

Personal con text T h e personal context includes knowledge, attitudes, and emotional factors of the recipient. In recent years several investigations have shown that the knowledge of the recipient influences the comprehension processes. Listeners or readers acquire meaning from a text by analysing words, sentences, and paragraphs against the background of their p e r sonal knowledge. This includes knowledge of the world and of linguistic rules and conventions in general. This knowledge is furthermore conditioned by sex, age, education, occupation, etc. Thus, the inferences which are drawn during text comprehension are not only data-driven (bottom - up) information but also knowledge - driven (top - down) inferences. Some experiments show that texts on a particular topic are processed in another way by experts in this field than by laymen (e.g. Chiesi, Spilich, & Voss, 1979; Spilich, Vesonder, Chiesi, & Voss, 1979; Voss, Vesonder, & Spilich, 1980; Johnson & Kieras, 1983). These studies showed that the greater knowledge of the experts stimulate more i n f e r ences, which are drawn automatically. Thus, listeners and readers with high domain knowledge can pay more attention to the details of a text of this domain than those people with low domain knowledge.

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T h e influence of knowledge on text processing was shown by Anderson, Reynolds, Schallert, and Goetz (1977) in an experiment that involved female music majors and male physical education majors. T h e subjects read one passage that could be interpreted either as a prison break out or as a wrestling match and another passage that could be interpreted either as an evening of card playing or as a musical given by a woodwind quartet. Anderson et al. found a relationship between the disambiguations and the subjects’ background. Physical education majors mainly gave a wrestling interpretation to the wrestling/prison break passage and a card playing interpretation to the m u s d c a r d passage. T h e music students gave the reverse interpretation. Sjogren and Timpson (1979) replicated the findings of Anderson et al. (1977) using the same ambiguious passages. But they modified the experiments because in the study of Anderson et al. the background variable led to confusion due to sex: All of the music students were female and all of the physical education students were male. Therefore Sjogren and Timpson tested male and female students in both groups. T h e results of their study were consistent with the results reported by Anderson et al. There was also an interaction between the two versions of the texts and sex. T h e sex interaction supported their assumption that part of the relationship observed by Anderson et al. was due to sex being confused with background. In spite of some differences in their results Sjogren and Timpson agreed with the interpretation of the results given by Anderson et al.; both studies indicate that high - level schemata provide the framework for text understanding. Clifton and Slowiaczek (1981) were of the opinion that new i n f o r mation can only be processed meaningfully if it is integrated with the available knowledge. T h e degree of this integration may vary consider ably, as is shown in some studies (e.g. Schustack & Anderson, 1979). Not only cognitive factors have an influence upon text understanding, but also emotional factors. Texts comprise not only information but also opinions, attitudes, and feelings which are also brought to bear on the texts by the readers and listeners. Tyler and Voss (1982) showed that the attitude towards facts presented in the text greatly affects its processing. If the text which is heard o r read corresponds to the attitude of the hearer or reader towards the facts presented in it, the hearer or reader seems to be less inclined to activate his or her knowledge than in a case where he or she detects discrepancies between text and attitude. T h e knowledge of topics dealt with

The concept of inference

33

in the text seems to be made full use of only if conflicts of attitude with the text require the reader’s rapt attention. Thus the above - mentioned studies show that personal context can influence text processing. Knowledge, attitudes, and emotional factors are important subjective conditions for drawing inferences during text comprehension.

CLASSIFICATIONAL ASPECTS T h e classification of inferences poses difficulties of great magnitude because one has hitherto not succeeded in laying down generally accepted criteria for such a classification. Accordingly we have tried, as a preliminary step, to discuss in this section the epistemological function of the classification of inferences within a theoretical framework. In addition we attempt - on the basis of the reflections in the section on theoretical aspects - to give a few criteria for a systematic classification of i n f e r ences from a functional perspective.

Epistemological functions of the classification of inferences In every scientific discipline suitable concepts are prerequisites for finding regularities. Phenomena have to be categorized in such a way that they enable us to see overall relationships existing within this area of reality. This is also true for the classification of inferences. From this point of view we want to examine here some classification systems of inferences more closely. Crothers (1979) distinguished between a posteriori inferences and a priori inferences. T h e former are deduced from the preceding text, the latter come from the reader’s or hearer’s background knowledge. A systematic interrelation is presupposed between the two types of i n f e r ences and text coherence. A posteriori inferences contribute to coherence, while a priori inferences do not. Reder (1980) differentiates between obligatory inferences intendend by the author of a text, and facultative inferences not intended by the author. In this case, too, a systematic relation to coherence is presupposed. It is assumed that the obligatory inferences fill in existing blanks and so contribute to the coherence of the mental representation, whereas

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facultative inferences are additional elaborations which enrich the contents of the text but do not contribute to text coherence. T h e relationships taken for granted here seem doubtful for various reasons. First, every inference is due (according to the schema - theory) to the activating of cognitive schemata so that not only a priori inferences and facultative inferences, but also a posteriori inferences and obligatory inferences link the textual information with items of the reader’s or hearer’s previous knowledge. Secondly, there is no clear - cut division between previous knowledge and textual information during discourse comprehension. T h e text, which at a certain point in time during comprehension is already processed or its mental representation, is already part of the total previous knowledge in relation to the succeeding text. Thirdly - mainly in expository texts - the exact amount of inference activity expected from the reader or hearer is not known, and it is highly likely that the author, for one and the same text, expects a varying number of inferences from different groups of addressees. T h e boundary between intended and not intended inferences is therefore, from the start, hard to find. But even if an author was to specify exactly which i n f e r ences he expects, the fact that a reader or hearer infers something which has not been intended need not automatically prove that this inference no longer contributes to establishing coherence. It is not necessarily the case that facultative inferences, or elaborations, or even a posteriori inferences do not help to establish coherence.

If the relationships assumed so far do not exist, the question arises as to which function can be attributed to the categorization of inferences. This means then that we should also investigate conceptual differentiations or categorizations of inferences regarding the kind of theoretical context to be presupposed for the relevant sub - categories (Garrod, this volume). Some criteria for a classification T h e aspects which we have differentiated can also be the basis for distinguishing between different kinds of inferences. According to the model of levels - of - mental representation outlined above one can, for example, differentiate (above the sub - semantic processing level) between a lexical or word - concept level, a semantic - syntactic level, a text basis or micro - proposition level, a macro - proposition level and a super structure level. If inferences set out from the mental representation of a

The concept of’inference

35

text already formed and add new information to this representation, it will then be possible to classify the different inferences with regard to their specific contribution to such a mental representation. This classification can be drawn up focusing on: (a) the kind of semantic unit within the mental representation which is generated by the corresponding inference procedure, (b) the kind of knowledge -stores of inference, o r

consulted

for the formation

(c) the kind of extension of the mental representation as brought about by inference - formation, or the ’direction’ in which this extension is carried out.

The kind of semantic unit inferred

If one investigates the hierarchic level on which the inferred i n f o r

mation is established, a classification of inferences can be drawn up by focusing on the semantic unit generated. Such a classification is used e.g. by Frederiksen, Frederiksen, Humphrey, and Ottesen (1978). They distinguish between four main kinds of inferences: first stage inferences, connective inferences, structural inferences, and extensive inferences. T h e first stage inferences serve to ensure that an interpretation of the sentence just read is as clear as possible. They result in a certain text proposition which, according to Kintsch (1974), would have to be included in the implicit text basis. T h e connective inferences serve to link incoming text propositions to the preceding text propositions by constructing additional propositions which fill in or bridge the respective gaps in c o h e r ence. T h e structural inferences serve to bring out the thematic organization of a text. They split the text into thematically homogeneous passages, and ’analyse’ the structure of the representation, i.e. the corresponding super-structure. In the case of extensive inference we are dealing not only with linking what has already been read to the reader’s previous knowledge but also with spontaneous ideas and associations, i.e. those inferences which are very often called elaborations. Furthermore, Crothers (1979) implicitly divides up propositions according to their hierarchical position within the mental representation when he uses the complexity of the semantic units inferred as a criterion for classification. H e differentiates between the inferring of propositional

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arguments (case role inferences), the inferring of simple propositions, and the inferring of connective propositions, i.e. bigher, more complex propositions whose arguments are propositions in their own right. Specific inferences as analysed by some scientists, e.g. the inferring of r e f e r ence - connections between nouns, pronominal inferences or the instantiation of general terms, can all be included at the lexical or word concept level (cf. Anderson, Pichert, Goetz, Schallert, Stevens, & Trollip, 1976; Garrod & Sanford, 1977; Garnham, 1979; Warren, Nicholas, & Trabasso, 1979). T h e segmentation into so - called semantic primitives could be called the lowest level of semantic processing (Norman & Rumelhart, 1975). T h e question of how f a r these inferences are part of the ordinary text processing at all is a highly controversial matter (cf. Gentner, 1981; van Dijk & Kintsch, 1983).

The kind o f previous knowledge activated Inferences can also be classified from the point of view of representation according to the kind of previous knowledge consulted for the formation of inferences; i.e. which cognitive schemata are activated, o r which semantic relations filter through into the mental representation by this activation. Clark (1975) and Warren, Nicholas, and Trabasso (1979), for example, distinguish inferences, among others, according to the kind of semantic relation inferred (e. g. causal relations, motivational relations, etc.).

In addition, the connective inferences have been differentiared according to the kind of connective relation or according to the kind of corresponding proposition - predicate. Crothers (1979), for example, distinguishes between a priori inferences, which are drawn from the reader’s o r hearer’s background knowledge, and a posteriori inferences, which are drawn from the text already processed. This differentiation is a n implicit distinction according to the kind of knowledge activated in forming inferences.

T h e direction o f inference - formation Finally, one can further differentiate inferences from the representational point of view according to the direction in which the inference procedure ’moves’ within the mental representation. W e can, therefore, distinguish between vertical and horizontal inferences (cf. Ballstaedt,

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Mandl, Schnotz, & Tergan, 1981). Vertical inferences can start out from a lower level and produce a result which is part of a higher representational level. These are bottom - up - inferences as, for example, the macro - operations of van Dijk (1980), or the above outlined structural inferences of Frederiksen et al. (1978). Vertical inferences can also start out from a higher level and produce a result which is part of a lower level. These are top - down - inferences, such as, for example, the inverse macro - operations of van Dijk (1980), the above outlined inferring of propositional arguments according to Crothers (1979), or the instantiation of general terms in as much as the so-called default values of the activated superordinate cognitive schemata are taken over into the mental representation. T h e horizontal inferences, however, start out from a certain level and produce a result which is part of the same level. Examples of this kind of inferences are the bridging inferences as described by Clark (1975), or the above outlined connective inferences of Frederiksen et al. (1978), which serve to fill in the coherence gaps existing at a certain micro - or macro - level. T h e so - called elaborations could for the most part also be classed with the horizontal inferences.

METHODOLOGICAL ASPECTS Part of the controversy in research on inferences during discourse comprehension is due to the fact that the methods applied often do not enable us to draw unambiguous conclusions. T h e interpretations in many studies of inferences leave open alternative possibilities of interpretation. This is especially true for many studies in the first years of experimental inference research (cf. Rickheit & Strohner, 1985). A decisive question therefore would be which methods are most productive for serving the purpose of investigation (Kieras & Just, 1984). O n - line measurements (as, for example, the recording comprehension time, the analysis of eye movements, thinking aloud during text comprehension, and the registration of physiological reactions) and off - line measurements (as, for example, free or cued recall, recognition, verification, and answering questions about the text) have to be chosen with regard to the specific aim of the study.

As inference-forming is a very subtle and strategic process, the aspect of ecological validity has to be taken into account much more seriously now than it was at the beginning of inference research. We have shown in the contextual section of this chapter that many contextual variables can greatly influence the process of inferring.

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T h e various methods represent only various ways and means of approaching one and the same issue; a combined application of different methods in one study, o r in different studies with the same aim, would be advantageous. By doing this, one gets more qualitatively different information about the object of research and perhaps comes a bit closer to reality. It becomes possible by such a multi - perspective analysis to reach a more differentiated point of view of one problem.

PERSPECTIVES IN INFERENCE RESEARCH We have tried to describe several aspects and problems of the concept of inference in discourse comprehension. Research in this area is progressing very fast. We hope that the present volume contributes to this progress. Today we are only just beginning to see the complexity of discourse processing. It is today clearer than a few years ago that the transfer from research to it’s practical application is a difficult matter compare, for an illustration, Winograd (1972) and Winograd (1983). It also becomes evident that in theory many aspects of inference have to be considered (e.g. van Dijk & Kintsch, 1983). And last but not least, the naivity of the first years of experimental inference research has totally gone (Kieras & Just, 1984). We think that this critical insight into the problems of practical application, theory, and experimental research provides a good opportunity for creative efforts to cope with these problems. For the next years, two research perspectives may become particularly important. First, the concept of inference will be seen to be more closely related to the goal - directed action of discourse comprehension and to the communicational framework, than was the case in the first years of psycholinguistic inference research. Secondly, research into inference construction is not only a part of psycholinguistics, but also of cognitive psychology and Artificial Intelligence. In short, inference is a central research subject of the newly formed discipline of Cognitive Science. These two research perspectives are described in the following section.

The communicative framework One aim of language comprehension is the communicative agreement with the speaker or writer on some incident in the world, e.g. a fact, an action, or an opinion. Orientation toward the communicative function can

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have great effects on the processes and the results of language comprehension. This would, above all, be the case if it turned out that comprehension is not a process which attains its goals by firmly established procedures, but a creative action for which there exists no definite solution. T h e functional dependence of comprehension on the superordinate communicative system would also be the more plausible. Furthermore, one cannot only prove an interaction of the listener or reader with the text, but also with the speaker or writer. Having come to the conclusion that language is functional, Hormann

(1976) proposed an analysis of language behaviour which takes into ac-

count its functional dependencies. According to Hormann, the smallest grain of linguistic analysis is the action unit. If, nevertheless, linguistic units which are smaller than the action unit are made the objects of investigation, the smaller unit must be related to the action unit. Inferences in discourse comprehension belong to such smaller units. Schnotz, Ballstaedt, and Mandl (1981) have recently submitted a detailed analysis of discourse processing on the basis of reflections on the theory of goal -directed actions. Although linguistic activity is tied to the immediate situation to a much smaller extent than other activities, it is nonetheless always embedded in superordinate activities. This embedding in other activities determines the intentionality. T h e theory of action stresses the fact that linguistic activity, in spite of its becoming partially independent, originates in other social and physical activities. Schnotz et al. see the advantage of conceptualizing text processing within the framework of the action theory in the possbility that different aspects of the issue can be analysed as interrelated. The interaction of structural and functional factors of text processing becomes apparent. Text coherence, according to this view, is the result of the interaction of various activities, part of which is the processing of discourse. One such activity is the cooperation between the speaker or writer on the one hand and the listener or reader on the other. T h e relationship between the communicants has, provided it is meant to contribute to reciprocal understanding, all the features of close cooperation. Both sides agree on a communicative goal which they can attain together by mutual support. Because of their joint participation in the interaction, they have at their disposal a joint motivation to reach this goal. They also agree on certain practical strategies, which in all probability will lead them to that goal.

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Clark and his colleagues thoroughly discuss the cooperative characteristics of verbal communication (e.g. Clark, 1977, 1978; Clark & Murphy, 1982; Clark, Schreuder, & Buttrick, 1983). T h e structuring of linguistic utterances resulting from cooperation is called ’audience design’. By taking into account the present state of the listener’s processing system, the speaker can assume that he or she makes an optimum contribution to the communicative agreement with the listener. Clark et al. (1983) call this assumption the principle of ’optimal design’. T h e principles of audience design and optimal design can easily be applied to the issue of text processing. According to these principles the text is structured by the speaker or writer in such a way that the listener or reader can build up a coherent mental model of the message. T h e communicative framework of inference is furthermore a traditional theme in ethnolinguistic research (e.g. Gumperz, 1977; Enninger & Haynes, 1984). In o u r opinion, it is important for future research on inference processes that psycholinguistics takes into closer consideration the investigations carried out by reseachers in the field of ethnolinguistics (Frederiksen, 1981; Freedle & Fine, 1982).

The Cognitive Science framework Another interdisciplinary research perspective is the closer cooperation of psycholinguists with researchers of other subdisciplines in Cognitive Science. Inference is one of the major topics in cognitive psychology and Artificial Intelligence. Linguistic inferences may only be a special type of general inference processes in information processing (see Clark, this volume). It is an important task for future research workers to describe the general strategic of inference as well as the special characteristics of inferences in text processing. An important issue of Cognitive Science which is also relevant for inference research is the issue of autonomy and interactivity. T h e modules of the processing system can be seen either as interactive or as autonomous (e.g. Swinney, 1984). T h e problem of making inferences and controlling those inferences has been one of the central issues not only in the domain of psycholinguistics, but also in the domain of Artificial Intelligence (e.g. Lockman & Klappholz, 1980; Hobbs, 1982). First steps towards the problem of inference were taken by Schank and Rieger (1974), by Rieger (1976),

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and by Schank (1979). In order to avoid a cornbinatorial explosion of inferences as it was possible in the inference mechanism suggested by Rieger (1976), Schank (1979) introduced the concept of interestingness which is related to the 'significance principle' ("More processing should be given to knowledge sources whose result frames are more significant") and the 'goal satisfaction principle' ("More processing should be given to those knowledge sources whose responses are most likely to satisfy processing goals") (Schank, 1979, p.296). Thus, interestingness can be considered a guide for a text understanding system. In a later study Schank proposed a much more comprehensive mechanism than interestingness for controlling the inferencing process (Schank, Collins, Davis, Johnson, Lytinen, & Reiser, 1982). This mechanism is the search for the point which the writer or speaker tries to make. According to the point processing theory the listener or reader restricts his or her inferences to those which are related to the particular point of the discourse (Vipond & Hunt, 1984). This restriction protects the inference process from combinatorial explosion. Schank et al. differentiate several kinds of points, e.g. affective points, argument points, need points, explanatory points, prescriptive points, and interest points. Wilensky (1983) also developed a differentiated point theory of story processing. In comparison to Schank et al. he focuses on text - internal points of some intrinsic interest. T h e work in Cognitive Science on control mechanisms which direct the inference process is an important theoretical contribution to i n f e r ence research. In addition, Artificial Intelligence offers a new methodology for inference research. With the ever growing complexity of modern theories of discourse processing, the methodology of computer simulation becomes more and more important for theory proving (Kieras & Just, 1984). T h e years to come may show that comprehensive theory construction in the field of inferences in discourse comprehension must rely heavily on the close cooperation with theory and methodology provided by all disciplines of Cognitive Science.

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Acknowledgement We are indebted to Hans - Jurgen Eikmeyer, Reinhard Fiehler, Michael Giesecke, Joachim Huttemann, Walther Kindt, Jochen Miisseler, Hannes Rieser, and Rudiger Weingarten for many helpful discussions about the philosophical, logical, and linguistic aspects of inference.

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