Abstract: Text comprehension is viewed as the construction of a mental representation of the situation described by the text. Based on the evidence from narrative comprehension, Zwaan et. al., (1995) have proposed an event-indexing model of text comprehension. According to the model, during comprehension, readers construct their representations from five indexes: time, space, causality, intentionality, and agent. Actually, these five indexes are corresponding to the framework of an event, and the model fits the comprehension of narrative that usually involves creating a mental representation of the states of affairs described by the text. In view of both theoretical consensus and the evidence from narrative text experiments, it is somewhat surprising that evidence for the construction and the structure of representation is not clear when comprehension of expository text is considered.
There has been much less research using expository than there has been using narrative texts, and a major issue concerning these studies has been the effect of knowledge map on the processing of expository. During expository comprehension, knowledge map was more helpful for the participants who without interrelated domain knowledge than the participants who with some interrelated domain knowledge in the construction of the representation. Based on the systematic analysis of previous theories and evidences from text reprehension in the reading of narrative and expository text, it raised a question that whether the construction of text representation can be realized in expository comprehension like that in the narrative reading. This research was designed to throw some light on the question. We examine the status of construction and the structure of mental representation of expository text about familiar topics.
Three experiments were conducted. Experiment 1 was to explore whether participants construct the representation of causal sequence presented in the expository. Experiment 2 varied the order of the description to make it differ from the inherent order of the causal sequence. In Experiment 3, two causal sequences were provided. Participants read the short expository on familiar topic and finished a probe task after reading each passage. All materials were presented on a monitor controlled by computer. Participants read the passages in a self-paced manner, advancing the text one line at a time by pressing the space bar. Participants were instructed to read carefully so that they would be able to judge whether the probe word appeared in the text. The reaction times for the probe followed by the prime sentence were recorded and analyzed.
The results showed that in the reading of expository on familiar topics, mental representation was constructed based on the causal relation, rather than the surface relation, the representation of the expository about a causal chain was organized with the causal order, but not affected by the descriptive order, the corresponding causal relations were grasped if the content illuminated more than one causal chain.
The present findings indicate that the construction of representation of causal sequence can be realized in comprehending expository on familiar topics. Also, the evidence implied the pattern of causal representation of expository text.

Key words: expository, causal sequence, text representation