This paper attempts to construct a dynamic model of dialogic discourse. We posit a cognitive interface between language and knowledge-base. This interface contains pointers or indices which control the access path to the knowledge-base and the temporary memorybase set up for each dialogue session. Utterances in a dialogue can be seen as instructions for operations on this interface:registering, searching, copying, and inferring, etc. We examine the nature of these operations by analyzing Japanese interjections such as "eeto" and "ano(o)". The mental processes which those interjections reflect can be well described using the data-base and the working buffer. "Eeto" reflects that the speaker is securing the working space in the buffer, whereas "ano(o)" reflects that the speaker is extracting linguistic information from the data-base.