Vidal, Amorim, McIntyre, and Berthoz (2006) demonstrated a difference in perception of pitch turns in an upright position and in pitch and yaw turns in a reclining position, i.e. the relative angular error of the estimated turn angle was higher in downward turns in an upright and in downward and rightward turns (downward in egocentric frame reference) in a reclining position. Thus, the results are in line with other studies (Matsuo et al., 1979), proposing an asymmetry of OKN. When subjects were instructed to stay on a fixation point, turns were underestimated for pitch and yaw in the upright position and asymmetry occurred similar to the experiment with normal pursuit. When only static pictures of the turn were presented, asymmetry of perception was far less for pitch turns in the upright position compared to visual cues rather corresponding to OKN. Thus, it was concluded that asymmetry in OKN is responsible for pitch asymmetry. Geometry-based perception is asymmetric to some extent and cognitive effects (i.e. fear of falling) increased the estimated turn angle in the direction of gravity.