Under the microgravity of the International Space Station, many of the normal processes that determine the perceptual upright on Earth are disrupted. For example, somatosensory cues are absent and an applied physical linear acceleration can provide an artificial "gravity" reference. Here, we hypothesized that visual linear acceleration could also be interpreted as an orientation cue in microgravity. Using virtual reality, we subjected twelve astronauts experiencing long-duration exposure to microgravity to visually simulated accelerating linear self-motion along a virtual corridor at 0.8 m•s