While consciousness is unitary it can produce differentiated subminds. Differentiated Identity Disorder shows this dispite the large current controversy on the causes of this in clinical situations. These alternate identities may also be concurrent. All of this is rare but is increasingly being shown empirically. The first reference is general the second is specific experimental validation.
Here are some references:
Kelly, EF et al. (2009). Irreducible Mind: Toward a Psychology for the 21st Century. Lanham, MD: Rowman & Littlefield.
Strasburger, H. and Waldvogel, B. (2015). Sight and blindness in the same person: Gating in the visual system. PsyCh Journal, 4 (4): 178–185.
Most of what I am citing is from “The Idea of the World: A Multi-Disciplinary Argument for the Mental Nature of Reality” by Bernard Kostrup.