Independence of bilateral symmetry detection from a gravitational reference frame

Data were collected during three orbital flights aboard the Russian MIR space station from eight cosmonauts tested on a bilateral symmetry detection task. It is known that on earth subjects' performance is significantly superior for a vertical or horizontal than for an obliquely oriented axis of symmetry, giving a so-called oblique effect. The present results show that this oblique effect did not disappear in microgravity. They confirm that the detection of visual symmetry is not tied to a gravitational reference frame. An unexpected result of the experiments was that practice reduced the reaction time for detection of asymmetrical patterns below that for symmetrical patterns. This result suggests the presence of two separate detection processes. The detection of symmetry, being useful for the efficient encoding of visual information, is well developed in naive subjects. Extensive practice on a symmetry-detection task, however, increases the efficacy of the asymmetry-detection process.