Almost all polis citizens, except for those who specifically elect otherwise, experience the world through two sensory modalities: "Linear" and "Gestalt", which Egan describes as distant descendants of hearing and seeing, respectively. Linear conveys information quantitatively, as a string or strings of information formulated with a "language" hardwired into the mind of almost all Citizens. Citizens may "speak" to one another in Linear by sending streams of data back and forth, from mind to mind — either private conversations carried on between a specific subset of intended participants, or public announcements accessible to all involved in a conversation or otherwise "listening in".