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4.1 Reading Model

The theory of semiotics or the study of symbols shows that the understanding of knowledge takes place at four levels : lexical, syntactic, semantic and pragmatic [Rettig, 1992], [Rada, 1991]. At the lexical level, the user determines the definition for each word encountered. At the syntactic level, the subject, action and object of a sentence are determined. The meaning of a sentence is determined at the semantic level. The pragmatic interpretation of text depends on the integration of semantic meaning of text with the reader’s knowledge of self and of the world.

While reading text, people proceed from a lexical level to the syntactic level, to the semantic and to the pragmatic levels in that order. All these levels interact continuously and they cannot be truly separated. The reader might have to have knowledge of the world in order to understand the meaning of a word. The correct syntactic and semantic interpretation of text may depend on the reader’s knowledge of the world. Hence, though readers may proceed from words to sentences, to paragraphs and to the overall document, the progress is more forward and backward.

A mental representation of the meaning of text is then constructed which is in the form of propositions or relationships. While reading text, readers establish local coherence in short-term memory – small scale inferences from few small units of information (relationships between words, sentences and so on) [Thuring et al., 1991]. The reader makes preliminary hypotheses based on titles, words, propositions, and knowledge about the real world. A reading control system retrieves knowledge from the real world, present in long-term memory, in order to filter out information present in short-term memory. These hypotheses are refined as the reading of the text proceeds with the reading control system being invoked continuously. These propositions are combined into larger structures, also called global coherence [Thuring et al., 1991]. This hypothesized macroproposition or superstructure is used to understand the overall content of the text. The construction of a coherent mental representation has important consequences for navigation. In addition to generating forward references, we accumulate cues for backward navigation.

The reading control system uses the spreading activation model to access propositions or concepts. In semantic memory, each concept is connected to a number of other concepts. Activating one concept activates its adjacent concepts which in turn activate their adjacent concepts. Thus, activation spreads through the memory structure, determining what is to be added and what is to be removed from the interpretation of text. This process continues until further activation of adjacent propositions does not change the propositions used to interpret the text. That is, spreading activation decreases over time and semantic distance.