The author proposes to review the criteria indicated (by Gregory Bateson) - in order to define a process as mental. To approach this kind of revision, a preliminary work on Information Theory is required, and the author infers that to reach this goal a revision of the Batesonian view of the same Information Theory should be implied. Therefore a proposal of revision is examined. The proposed revision is based not only on the concept of difference, but as well on the concept of similarity that was already outlined some years ago. Key words: criteria of mental process, Information Theory, difference, similarity