Static and dynamic visual information about the size and passability of an aperture.

The role of static eyeheight-scaled information in perceiving the passability of and guiding locomotion through apertures is well established. However, eyeheight-scaled information is not the only source of visual information about size and passability. In this study we tested the sufficiency of two other sources of information, both of which are available only to moving observers (ie are dynamic) and specify aperture size in intrinsic body-scaled units. The experiment was conducted in an immersive virtual environment that was monocularly viewed through a head-mounted display. Subjects walked through narrow openings between obstacles, rotating their shoulders as necessary, while head and shoulder position were tracked. The task was performed in three virtual environments that differed in terms of the availability of eyeheight-scaled information and the two dynamic sources of information. Analyses focused on the timing and amplitude of shoulder rotation as subjects walked through apertures, as well as walking speed and the number of collisions. Subjects successfully timed and appropriately scaled the amplitude of shoulder rotation to fit through apertures in all three conditions. These findings suggest that visual information other than eyeheight-scaled information can be used to guide locomotion through apertures.