Cognitive Effects of a Structural Overview in a Hypertext

Disorientation and navigation inefficiency are the consequences of the fragmented and incoherent structure of most hypertexts. To avoid these negative effects, researchers recommend—among other things—an interface with a structural overview of the relations between sections. Some authors have found that with such an overview, information is looked up faster and remembered better. This study examined whether a structural overview also leads to a deeper understanding. Forty students read a hypertext about the effects of ultraviolet radiation in one of two presentation conditions (structural overview and list). In the list condition, the same topics were mentioned as in the overview condition, but just in the format of a list. After reading, they answered textbase questions which measured their recognition and also inference questions supposed to measure their situation model constructed from the information read. The last type of questions indicated the readers’ understanding of the text. On textbase questions, subjects with low as well as high prior knowledge scored equally well in both conditions. In contrast to our expectation, the overview did not improve the recognition of main points. However, on situation model questions low prior knowledge subjects scored significantly lower in the overview condition than in the list condition. These results supported our hypothesis that a structural overview may hinder the understanding of less knowledgeable readers, because it draws their attention to the textual macrostructure at the expense of attention to the microstructure of the text. Introduction Hypertext is emerging as an increasingly prevalent form of information presentation. The links in this medium make it possible to flexibly combine linear and hierarchical structures of information. Links are connections between sections on different levels (pages) in the hierarchy of the text. However, as the number of links goes up, the structure of a hypertext becomes more fragmentary. The consequences of a fragmented structure are: cognitive overload, navigation inefficiency and disorientation (Conklin, 1987; Gärling and Golledge, 1989; Oliver and Oliver, 1996; Van Nimwegen et al., in press). To avoid these negative effects, researchers recommend—among other things— an interface with a structural overview of the links between sections (Jonassen, 1986; Halasz and Conklin, 1989; Heller, 1990; Thüring et al., 1996). With the help of overviews that make clear which sections on which pages are present, users have less problems with looking up task-relevant information (Nielsen, 1995). In view of the educational possibilities of hypertext, Dee-Lucas (1996) investigated the effects of a structural overview. She found that with such an overview as browser, information is looked up faster. Besides this, she reported that subjects who used the overview recalled more main points of the text. However, it remains the question of whether a structural overview also leads to better comprehension. This question formed the focus of our study. Theoretical background According to Van Dijk and Kintsch (1983) there exist three levels whereby readers mentally represent textual information (see also Van Oostendorp and Goldman, 1998). The first level concerns the surface structure of sentences. On this level, readers remember, for instance, the sequence of words in a sentence. A text is remembered at the textbase level. The representation at this level can be seen as a network of related propositions. However, what readers really understand of a text and integrate with prior knowledge is called the situation model (Van Dijk and Kintsch, 1983; Van Oostendorp, 1996). Because of the importance of comprehension and application of knowledge in education, the construction of situation models is the most important objective of instructional texts (Perrig and Kintsch, 1985). For this reason, the question of effect of the structure of a text has on the construction of situation models is highly relevant. McNamara et al. (1996) examined the role of structure in the comprehension of science texts and based their research on the Construction-Integration (CI) model developed by W Kintsch (1988). Structure is defined by the extent of connectiveness between propositions in the textbase. In constructing a textbase, the reader must infer the semantic relations between propositions underlying sentences. The process of drawing these inferences is relatively simple when the surface level of the text has a well developed or explicit structure. In this situation, the semantic relations between propositions are almost explicitly present. A text has a locally coherent structure if propositions refer clearly to each other, for example, by the presence of referents. A text has a globally coherent structure if the semantic relations across parts, such as paragraphs and larger sections, are fully expressed. A writer may explicitly link each section to other sections and to the overall topic with topic headers and sentences which explain these links providing the text with a globally coherent structure. The crux of the CI-model is that readers can only integrate the textbase and prior knowledge successfully into a situation model if the textbase is sufficiently interrelated. Thus, a well developed structure is a necessary condition for the integration and situation model construction. If the text makes this integration process too difficult by 130 British Journal of Educational Technology Vol 30 No 2 1999 © British Educational Communications and Technology Agency, 1999. lack of structure, the reader must try to (re)construct the relevant semantic relations on the basis of prior knowledge. Results reported by McNamara et al. (1996) are in line with this notion. They measured the textbase by free recall and recognition questions and the situation model by inference and problem solving questions (see also Van Oostendorp and Bonebakker (1998) for the plausibility of this distinction). McNamara et al. found interactions between level of prior knowledge and the structure of a text on comprehension, that is on the construction of the situation model. In their experiment, a well developed structure improved the comprehension of readers with low prior knowledge, but impaired comprehension of high prior knowledge readers. This result fits the CI-model of Kintsch (1988); for answering inference and problem solving questions, readers must have developed a coherent textbase representation during the reading. The coherence of the textbase depends on the structure of the text: a well developed structure leads to a coherent textbase, a weak structure to an incoherent textbase. If the text has a weak structure, then the textbase is not coherent and, consequently, a reader must derive the required semantic relations between propositions from background knowledge. Low knowledgeable readers encounter here more problems than high knowledgeable readers. Thus, low knowledgeable readers can only develop an adequate situation model if the textbase is coherent. In contrast, subjects with high prior knowledge scored better on situational questions if they had read the incoherent version of the experimental text. McNamara et al. explain this result by supposing that a strong textual structure hinders the understanding of knowledgeable readers, because it reduces the amount of active processing during reading. Easing the reader’s burden of figuring out the meaning of the text could result in less effective learning (see also Kintsch, 1990). McNamara et al. further established that a strong textual structure improved textbase recall. This result was found earlier by Beyer (1990) and Britton and Gulgoz (1991). McNamara et al. (1996) distinguished in correspondence with the theory of Van Dijk and Kintsch (1983) macropropositions and micropropositions. Macropropositions concern the central, summarizing idea units of a text, micropropositions concern details. They reported that both a strong local and a strong global structure significantly supported the recall of macropropositions, but structure manipulation did not have a significant effect on the recall of micropropositions. They also found that a strong global structure improved the recall of macropropositions better than a strong local structure. The effect that a strong textual structure particularly supported the recall of macropropositions corresponds to the result found by Dee-Lucas (1996) in her study of hypertext. Hypotheses In our study we presume that the effect of a structural overview on the situation model that learners construct of a hypertext deviates in one respect from the study of McNamara et al. (1996). We agree that the local structure of a text is highly relevant in constructing a situation model in the case of low prior knowledge. Indeed, particularly less knowledgeable readers must attentively keep track of the local semantic Cognitive effects of a structural overview in a hypertext 131 © British Educational Communications and Technology Agency, 1999. relations to attain comprehension, because they lack the prior knowledge to infer these relations themselves. The CI-model of Kintsch (1988) and the study of McNamara et al. (1996) provide evidence of this assumption. However, in the case of a structural overview adjoined to a (hyper)text that has a strong local structure, we suppose that during reading learners do not use the in principle available local structure because of the negative attentional effect of the global structure added by the overview. This effect particularly hinders the comprehension of readers with low prior knowledge: their construction of a situation model depends more on the local structure of the text than the model construction of readers with sufficient prior knowledge does. Thus, in contrast to McNamara et al., we expect that a well developed global structure provided by the structural overview hinders