  The consideration of such scenarios was initiated by Wigner (1961).  Wigner considered a hypothetical scenario in which a friend conducts an observation, and he himself treats the joint system, consisting of the friend and the system experimented upon, as a quantum system. For this reason, scenarios of this sort have come to be known as “Wigner’s friend” scenarios.  Wigner was led by consideration of such scenarious to hypothesize that conscious observers cannot be in a superposition of states corresponding to distinct perceptions; the introduction of conscious observers initiates a physical collapse of the quantum state; this involves, according to Wigner, “a violation of physical laws where consciousness plays a role” (Wigner 1961, 294 ;167, 181).  