Mental beliefs about blood, and not its smell, affect presence in a violent computer game

Presence in virtual reality - the feeling that one is inside mediated reality - has fascinated academics in the field of virtual reality from its onset. While conceptual analyses and empirical research unequivocally stressed the importance of immersion through sensory input, agent-related aspects such as mental beliefs received less attention. We are the first to examine the separate and combined effects of being exposed to the smell of a particular stimulus and/or having a representation of this stimulus in mind. Blood was considered to be interesting to work with, because of widespread folk ideas about its capacity to induce aggression in violent contexts. Using a violent computer game in a between-subjects design, male subjects were tested for the immersive impact of blood, first as an olfactory cue, and second as a mental belief, i.e. the true or false belief that one is smelling 'blood'. Lower skin conductance and game scores showed that 'blood' served as a distractor hindering the subject's spontaneous engagement. Subjects higher in dispositional aggressiveness, however, got more immersed during the 'blood' game rounds, by displaying more combativeness. We discuss our results in light of the undervalued importance of subjective realism in research on presence, and explain the relevance of this work for applications in virtual training in the military and for clinical intervention in combat-related PTSD.