I've not heard of this phenomenon, communicating with a person in a dream state: could you cite it?
People saying things could be like the images appearing in the visual cortex that I tried to address in brief. They can appear, be processed, provide external output and such without necessarily being part of a dream experience happening at that time.
Back to my analogy, the magic secretary plays back some sound files, which maybe someone in a different office hears and attributes to you being present, but which you aren't "there" to experience. When you start to wake to consciousness you see the files and infer you were working on them, your partner mentions utterances consistent with one file and your brain meshes that in to part of the "story" it is writing of the dream experience (a la deja-vu).
People saying things could be like the images appearing in the visual cortex that I tried to address in brief. They can appear, be processed, provide external output and such without necessarily being part of a dream experience happening at that time.
Back to my analogy, the magic secretary plays back some sound files, which maybe someone in a different office hears and attributes to you being present, but which you aren't "there" to experience. When you start to wake to consciousness you see the files and infer you were working on them, your partner mentions utterances consistent with one file and your brain meshes that in to part of the "story" it is writing of the dream experience (a la deja-vu).