When humans can fly: Imprecise vertical encoding in human 3D spatial navigation.

ABSTRACT

Previous research indicates that while animals who locomote on surfaces have a more variable and less precise spatial coding vertically than horizontally, animals who fly do not demonstrate a horizontal advantage (Hayman et al., 2011; Yartsev and Ulanovsky, 2013). The current study investigated whether humans' localization is more variable vertically than horizontally in different locomotion modes. In an immersive virtual room, participants learned the locations of objects presented on one wall. By locomoting from a location on the floor to each object, they replaced objects using memories. One group of participants (the flying group) flew three-dimensionally along their viewing direction by pushing a joystick. The second group (floor-wall group) locomoted only on the floor and the wall along the projection of the viewing direction onto the current travelling surface. The third group pressed a button to be teleported from the floor to the wall and then locomoted on the wall (wall-only group). The results showed that the variance of localization error was larger vertically than horizontally in the flying and floor-wall groups but that the pattern reversed in the wall-only group. In addition, while both the flying and wall-only groups locomoted straight towards the target location, the floor-wall group locomoted straight towards the projection of the target location onto the ground rather than straight towards the wall, indicating that the floor-wall group tried to avoid horizontal movement on the wall. These results suggest that for humans a horizontal advantage occurs in encoding the objects' locations presented on the wall whereas a vertical advantage occurs in locomotion on the wall.