Mental rotation of a letter, hand and complex scene in microgravity.

Previous studies showed egocentric but not allocentric mental rotation tasks to be impaired in microgravity when feedback cues about vertical surroundings were restricted. Those studies are difficult to reconcile, however, since they were limited not only to small subject groups, but also differed dramatically in design. According to this lack, the present study was conducted in order to compare three typical egocentric and allocentric mental rotation stimuli in microgravity within a single experiment and using the same subjects and setup conditions. In order to simulate astronauts' working conditions in space, visual and tactile vertical references were provided. Six subjects mentally rotated letters, body parts, and complex scenes in parabolic flight during near-weightlessness and level flight conditions. Subjects viewed letters and judged whether they were mirror-reversed or not (task LETTER), viewed pictures of a hand and assessed whether it was a right or a left hand (task HAND), and viewed drawings of a person at a table that contained both a weapon and a rose and had to decide whether the weapon was on the right or left side of the table (task SCENE). Material could be in canonical orientation or rotated from 0° up to 180° in ±60° steps. We calculated reaction times and error scores for each task, orientation in each condition, and performed additionally intra-subject correlations between reaction times of both conditions for each task. We found typical reaction times and error scores for each stimulus category with increasing rotation level. More importantly, response time and error score were not impaired in microgravity, independent of stimulus type and orientation. This finding is further confirmed by correlation analysis. We conclude that the mental rotation of letters, hand shapes, and complex scenes is not affected by short periods in microgravity when visual and tactile vertical references are provided. This finding is relevant for astronauts who are normally aware of their surroundings, and it is in accordance with previous findings, where only egocentric stimuli were impaired in microgravity when sensory cues about the vertical reference were restricted.