a state that describes when an experiencer responds to a virtual reality as if it were real

If you are there (PI) and what appears to be happening is really happening (Psi) then this is happening to you! Hence you are likely to respond as if it were real. We call this ‘response-as-if-real’ RAIR.1

1. Slater, M. “Place Illusion and Plausibility Can Lead to Realistic Behaviour in Immersive Virtual Environments”Philos Trans R Soc Lond B Biol Sci. 2009 Dec 12; 364(1535): 3549–3557 Pg 11.