EVects of head-down bed rest and artiWcial gravity on spatial orientation

We studied spatial orientation before and after 21 days of 6° head-down bed rest in 15 subjects. During bed rest, 8 subjects were treated daily with 1 h Gz centrifugation (artiWcial gravity) (2.5 g at the feet; 1.0 g at the heart), with 7 subjects serving as controls. Ocular counterrolling and subjective visual vertical were assessed during 90° whole body roll tilt to the left and right. Ocular counterrolling was unaVected by bed rest and bed rest + artiWcial gravity. Performance on the subjective visual vertical task was unchanged in the control group, but exhibited a signiWcant increase in error for 48 h after bed rest in the treatment (artiWcial gravity) group. Intermittent application of linear acceleration along the long body axis may have increased the weighting of the idiotropic vector, resulting in an increased bias of the subjective visual vertical toward the long body axis during 90° roll tilt.