Sensitivity to scene motion for phases of head yaws

In order to better understand how scene motion is perceived in immersive virtual environments and to provide guidelines for designing more useable systems, we measured sensitivity to scene motion for different phases of quasi-sinusoidal head yaw motions. We measured and compared scene-velocity thresholds for nine subjects across three conditions: visible <u>W</u>ith head rotation (W) where the scene is presented during the center part of sinusoidal head yaws and the scene moves in the same direction the head is rotating, visible <u>A</u>gainst head rotation (A) where the scene is presented during the center part of sinusoidal head yaws and the scene moves in the opposite direction the head is rotating, and visible at the <u>E</u>dge of head rotation (E) where the scene is presented at the extreme of sinusoidal head yaws and the scene moves during the time that head direction changes.

The W condition had a significantly higher threshold (decreased sensitivity) than both the E and A conditions. The median threshold for the W condition was 2.1 times the A condition and 1.5 times the E condition. We did not find a significant difference between the E and A conditions, although there was a trend for the A thresholds to be less than the E thresholds. An Equivalence Test showed the A and E thresholds to be statistically equivalent.

Our results suggest the phase of user's head yaw should be taken into account when inserting additional scene motion into immersive virtual environments if one does not want users to perceive that motion. In particular, there is much more latitude for artificially and imperceptibly rotating a scene, as in Razzaque's redirecting walking technique, in the same direction of head yaw than against the direction of yaw.

The implications for maximum end-to-end latency in a head-mounted display is that users are less likely to notice latency when beginning a head yaw (when the scene moves with the head) than when slowing down a head yaw (when the scene moves against the head) or when changing head direction (when the head is near still and scene motion due to latency is maximized).