In this thesis, within the framework provided by the Construction-Integration 
(CI) model of comprehension, we investigate the 
topicality of referents in discourse in terms of the activations of the memory 
elements corresponding to those referents. We discovered 
the inherent deficiencies of the CI model in displaying the linguistic 
observations about how different syntactic cues relate to sentence-level 
topic. This thesis proposes enhancements to the CI model so that it
incorporates and makes use of the two sources of grammatical information 
prevalent for topicality at the sentence-level: the grammatical role of the 
participants and the clausal organization 
of sentences. Computational tests are carried out to compare the original and
the modified CI models.  The comparisons have shown 
that the modified CI model is more successful at identifying the topic of 
single sentences. We have also implemented two aspects of discourse-level 
topic, i.e.~topic shifts and referential continuity, in the modified CI model.

Keywords: Cognitive modeling, Construction-Integration model, sentence-level
topic, topic continuity, centering theory.