We report three experiments using a new form of direct subjective presence evaluation that was developed from the method of continuous assessment used to assess television picture quality. Observers were required to provide a continuous rating of their sense of presence using a handheld slider. The first experiment investigated the effects of manipulating stereoscopic and motion parallax cues within video sequences presented on a 20 in. stereoscopic CRT display. The results showed that the presentation of both stereoscopic and motion parallax cues was associated with higher presence ratings. One possible interpretation of Experiment 1 is that CRT displays that contain the spatial cues of stereoscopic disparity and motion parallax are more interesting or engaging. To test this, observers in Experiment 2 rated the same stimuli first for interest and then for presence. The results showed that variations in interest did not predict the presence ratings obtained in Experiment 1. However, the subsequent ratings of presence differed significantly from those obtained in Experiment 1, suggesting that prior experience with interest ratings affected subsequent judgments of presence. To test this, Experiment 3 investigated the effects of prior experience on presence ratings. Three groups of observers rated a training sequence for interest, presence, and 3-Dness before rating the same stimuli as used for Experiments 1 and 2 for presence. The results demonstrated that prior ratings sensitize observers to different features of a display resulting in different presence ratings. The implications of these results for presence evaluation are discussed, and a combination of more-refined subjective measures and a battery of objective measures is recommended.

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