# Abstracts of HCRC Research papers, 1991

Keith Stenning:
Distinguishing Conceptual and Empirical Issues about Mental Models
The mental models' concept has been variously employed in several related fields. This paper concentrates on Johnson-Laird's use of the term in his theory of syllogistic reasoning which has made strong claims about the relation of logic to human reasoning. The aim of the paper is to distinguish conceptual issues such as the distinction between syntactic and semantic formulations of logic, from empirical issues about the representations and strategies of human reasoning. It is claimed that mental models' should be regarded as an unorthodox implementation of a theorem prover working over a classical logical calculus. Further, that a distributed theory of binding in human memory can explain why people reason in this way.
(February 1991, 18 pages)
Ref. No: HCRC/RP-15 Price: UKL 1.00

Alex Lascarides and Nicholas Asher:
Discourse Relations and Common Sense Entailment
This paper presents a formal account of the temporal interpretation of text. The distinct natural interpretations of texts with similar syntax is explained in terms of defeasible rules characterising causal laws and Gricean-style pragmatic maxims. Intuitively compelling patterns of defeasible entailment that are supported by the logic in which the theory is expressed are shown to underly temporal interpretation.
(February 1991, 65 pages)
Ref. No: HCRC/RP-16 Price: UKL 2.30

Jerry Seligman:
Physical Situations and Information Flow
In this paper we take Rosenschein's physicalist ontology used in his work on Situated Automata and use it to construct a number of Situation Theoretic categories: situations, types and perspectives. In so doing we replace Rosenschein's notion of information content by a conception of information based on the idea of an information channel. This provides a perspectival account of information flow which does not depend on modal alternatives, like possible worlds. We hope to sharpen intuitions about situations and information flow by focussing on physical'' situations and thereby illuminate the place of information in the physical world.
(March 1991; 37 pages)
Ref. No: HCRC/RP-17 Price: UKL 1.40

Chris Brew:
Systemic Classification and its Efficiency
This paper examines the problem of classifying linguistic objects on the basis of information encoded in the system network formalism developed by Halliday. We show that this problem is NP-hard, and suggest a restriction to the formalism which renders the classification problem soluble in polynomial time. We then develop an algorithm for the unrestricted classification problem, separating a potentially expensive second stage from a cheaper first stage which is known to be tractable.
(March 1991; 38 pages)
Ref. No: HCRC/RP-18 Price: UKL 1.40

Keith Stenning and Jon Oberlander:
Reasoning with Words, Pictures and Calculi: computation versus justification
Hyperproof is a system due to Barwise and Etchemendy for teaching heterogeneous reasoning which allows both graphical and linguistically defined steps of inference. In this paper we draw a distinction between the performance as opposed to the justification of inference. The processes relate to cognitive as opposed to foundational theories of inference respectively. We argue graphical reasoning does not necessarily require a novel foundational account but that a cognitive theory of graphics is required to understand heterogeneous reasoning. We sketch such an account centered on the property of graphical representations that they force the specification of much information which may go beyond the intended message.
(April 1991; 15 pages)
Ref. No: HCRC/RP-19 Price: UKL 1.00

Keith Stenning and Jon Oberlander:
A Cognitive Theory of Graphical and Linguistic Reasoning: Logic and Implementation
Our main subject is the processing characteristics of external graphical representations. Our main aim is to argue for the thesis that some of these characteristics can be explained by the property of specificity. We take the presence or absence of this property to be independent of the modality in which information is encoded; it can be present in linguistic systems, just as in graphical systems. To indicate the practical ramifications of the thesis, we discuss in detail the use of a version of Euler's Circles, an external graphical system, in syllogistic reasoning tasks. In particular, we show that mental models, an apparently non-graphical system, is equivalent---at one level---to our graphical system. This vindicates our appraoch to cognitive representation, which permits the characterisation of the equivalences and differences between graphical and non-graphical representations. The equivalences can be captured at a logical level; the differences are a matter of implementation. The cognitive properties of graphical representations are best understood in terms of this relationship between logic and implementation.
(March 1992; 43 pages)
Ref. No: HCRC/RP-20 Price: UKL 1.60

Rosemary J. Stevenson, Rosalind A. Crawley, David Kleinman:
Semantic Constraints on the Comprehension of Definite References
Two experiments are described which investigate the effect of context on the comprehension of definite references. A distinction is made between contexts that require the use of bridging inferences and those that are infelicitous. It is argued that infelicitous contexts affect the interpretation of noun phrases and pronouns equally while contexts that require bridging inferences impair the comprehension of pronouns but not of names.
Ref. No: HCRC/RP-21 Price: UKL 1.00

Jerry Seligman:
A Cut-free Sequent Calculus for Elementary Situated Reasoning
A first-order language is interpreted in the following way: terms are regarded as referring to situations and the truth of formulae is relativized to a situation. The language is then extended to include formulae of the form $t:\phi$ (where $t$ is a term and $\phi$ is a formula) meaning that $\phi$ is true in the situation referred to by $t$. Gentzen's sequent calculus for classical first-order logic is extended with rules which capture this interpretation. Variants of the calculus and extensions of the language are discussed and the Cut rule is shown to be eliminable from some of the proposed calculi.
(September 1991; 23 pages)
Ref. No: HCRC/RP-22 Price: UKL 1.10

A J Sanford \& L M Moxey:
Notes on Plural Reference and the Scenario-Mapping Principle in Comprehension
This paper concerns the way in which plural reference might be handled within the framework of text comprehension offered by Sanford and Garrod (1981), and other related accounts. It is motivated by the fact that there has been relatively little work on the conditions which control plural reference patterns, and we suggeset an approach to this problem, based on considerations of focus and mapping of discourse to general knowledge. We also address a number of critical comments recently made in which a basic inability of the Sanford-Garrod framework to encompass plurals is suggested. We suggest that the framework is quite capable of handling at least some of the problems of plural reference. The basic argument is that plural reference is licensed if and only if two or more individuals map into the same role-slot of the memory-representation of the situation depicted. Complications introduced by questions of cohesion and focus are discussed. In particular, coherence problems force a distinction between correct reference resolution in the face of unsatisfactory discourse, and its acceptability from the standpoint of felicity. It is concluded that this approach does not require arbitrary rules for when plural anaphors can be used, and that it provides a natural solution for mechanisms of grouping.
(October 1991; 19 pages)
Ref. No: HCRC/RP-23 Price: UKL 1.10

Robin Cooper:
A Working Person's Guide to Situation Theory
This is meant to provide an informal introduction to naive situation theory which will be useful to a working linguist or a cognitive scientist who wishes to apply the theory. It may also be of interest to some situation theorists. We use Extended Kamp Notation ({\sc ekn) as developed in Barwise and Cooper (forthcoming) as well as introducing the basic elements of the standard linear notation which is to be found in the literature on situation theory and situation semantics. {\sc ekn is so called because it takes its inspiration from the notation that is used by Kamp in developing Discourse Representation Theory ({\sc drt).
(October 1991; 27 pages)
Ref. No: HCRC/RP-24 Price: UKL 1.20

Anne H. Anderson and Elizabeth H. Boyle:
Forms of Introduction in Dialogues: Their Discourse Contexts and Communicative Goals
For effective communication to occur, speakers must share enough knowledge to understand one another's contributions: they must achieve `mutual knowledge'. A criticial point in a dialogue is therefore when one speaker wishes to introduce a new item. We explore the forms of introduction used by adult speakers in task-oriented dialogues. In previous studies researchers have concentrated on how indefinite and defintie articles are used to signal the speaker's assumptions about her hearer's knowledge state, and hence ability to understand a reference to a newly introduced topic. From studying a corpus of comparable dialogues we identify a range of forms of introduction---questions and statements containing definite or indefinite articles which are used by speakers. By studying the discourse contexts in which these various forms occur, and the success of the communication in which they are embedded, we identify a number of different factors which predict which forms of introduction will be chosen and the probably communicative consequences of the selections made. The choice of question forms of introduction was found to be a more salient aspect of the communicative process than the choice of article.
(December 1991; 38 pages)
Ref. No: HCRC/RP-25 Price: UKL 1.40

Keith Stenning, Alexander W.R. Nelson, Mukesh J. Patel, Joe Levy, Martin Gemell:
Three Experiments Investigating Reference Change in Simple Descriptions

Stenning, Shepherd and Levy (1988) showed that when simple texts switch reference predictably between individuals, changes of reference neither cost reading time nor degrade memory performance. The present experiments examine the effects of unpredictable referential change. Experiment 1 demonstrates that unpredictable reference change does cost processing time, as a function of the amount known about the referent to which attention shifts. Analysis reveals a distinction between {\em primary and secondary individuals related to referential change. It also reveals word length effects, both decelerations and accelerations proportional to description length, which are interpreted in terms of use of the articulatory loop (Baddeley, 1986). Experiment 2 replicates and extends Experiment 1. It extends observations of the involvement of primary/secondary status in the process of switching reference, and shows that the word length effects cannot be interpreted in terms of frequency. Experiment 3 strengthens support for the primary/secondary distinction and confirms the use of the articulatory loop. The present results suggest a central role for distributed information about sequence in representing complex semantic structures both in immediate and in long term memory. Predictable switching costs no time because the transparency of the relation between surface sequence and underlying semantic structure is preserved. The distinction between primary and secondary individuals emerges with unpredictable reference because it restores this transparency.
(December 1991; 38 pages)
Ref. No: HCRC/RP-26 Price: UKL 1.40