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Abstract:
Spatial representations rely on a reference frame comprising of at least one reference direction. As humans do not only interact with horizontal, but also with vertical space (e.g., recalling where something is in a shelf) the nature of the used reference system for vertically distributed locations is an important research topic. We aimed to infer the reference direction used in memory of vertical locations experimentally and proposed three potential axes: the body
vertical, the environmental vertical, or the direction of gravity. In three experiments, participants judged spatial
relations in vertical layouts in a virtual environment. We systematically varied the orientation of the body (sitting vs. laying) and the visually presented environment (e.g., shifted by 90°) during learning and testing. Participants
consistently were quicker or more accurate when the relationship between the body vertical and the visual room
matched the learning situation. This suggests that the body vertical is used as reference direction in representations of vertical spatial relations. Additionally, we tested whether and how an alignment of multiple reference axes affects the outcome of the used task. We tested for effects of consistency between learning and testing (e.g., identical body orientation relative to gravity) and parallelism of reference axes during learning or testing (e.g., visual room vertical was parallel to gravity). Results showed an effect of parallel body vertical and gravitational axis during testing: participants recalled spatial relations more accurately when tested upright. This upright body advantage might stem from a reference frame selection conflict in misaligned situations. Overall, the study suggests that in vertical memory alignment of body and gravity provides processing advantages and for longterm memory preferably relies on an egocentric reference frame despite salient allocentric alternatives.