BACKGROUND: This study examined the effects of display lag and gain on visual self-motion perception (i.e., vection) in active observers. METHODS: Our subjects viewed displays simulating self-motion in depth while physically oscillating their heads from side to side at approximately 1 Hz. Their horizontal head movements were recorded and incorporated into self-motion displays with four levels of added lag (0, 50, 100,and 200 ms; baseline system lag was 113 ms) and three levels of gain (i.e., subjects' head movements were either not incorporated into the display or were incorporated at either the same or twice the amplitude). At the end of each trial, subjects rated the strength of their perceived self-motion in depth. RESULTS: While increasing display lag above baseline by an additional 50 ms impaired vection strength ratings, increasing display lag beyond this level eventually improved vection. For example, 200 ms added display lag produced vection strength ratings that were similar to those found with the baseline lag. As expected, larger simulated display gains were shown to improve vection strength ratings regardless of the level of added display lag. CONCLUSIONS: We conclude that increasing display lag during active head oscillation only impairs vection until the resulting sensory conflict becomes too great to tolerate. Beyond this critical level of lag, the visual system appears to override or downplay such sensory conflicts.
BACKGROUND: This study examined the effects of display lag and gain on visual self-motion perception (i.e., vection) in active observers. METHODS: Our subjects viewed displays simulating self-motion in depth while physically oscillating their heads from side to side at approximately 1 Hz. Their horizontal head movements were recorded and incorporated into self-motion displays with four levels of added lag (0, 50, 100,and 200 ms; baseline system lag was 113 ms) and three levels of gain (i.e., subjects' head movements were either not incorporated into the display or were incorporated at either the same or twice the amplitude). At the end of each trial, subjects rated the strength of their perceived self-motion in depth. RESULTS: While increasing display lag above baseline by an additional 50 ms impaired vection strength ratings, increasing display lag beyond this level eventually improved vection. For example, 200 ms added display lag produced vection strength ratings that were similar to those found with the baseline lag. As expected, larger simulated display gains were shown to improve vection strength ratings regardless of the level of added display lag. CONCLUSIONS: We conclude that increasing display lag during active head oscillation only impairs vection until the resulting sensory conflict becomes too great to tolerate. Beyond this critical level of lag, the visual system appears to override or downplay such sensory conflicts.