Using behavioral realism to estimate presence: A study of the utility of postural responses to motion stimuli

We recently reported that direct subjective ratings of the sense of presenc e are potentially unstable and can be biased by previous judgments of the s ame stimuli (Freeman et al., 1999). Objective measures of the behavioral re alism elicited by a display offer an alternative to subjective ratings. Beh avioral measures and presence are linked by the premise that, when observer s experience a mediated environment (VE or broadcast) that makes them feel present, they will respond to stimuli within the environment as they would to stimuli in the real world. The experiment presented here measured postur al responses to a video sequence filmed from the hood of a car traversing a rally track, using stereoscopic and monoscopic presentation. Results demon strated a positive effect of stereoscopic presentation on the magnitude of postural responses elicited. Posttest subjective ratings of presence, vecti on, and involvement were also higher for stereoscopically presented stimuli . The postural and subjective measures were not significantly correlated, i ndicating that nonproprioceptive postural responses are unlikely to provide accurate estimates of presence. Such postural responses may prove useful f or the evaluation of displays for specific applications and in the corrobor ation of group subjective ratings of presence, but cannot be taken in place of subjective ratings.