Congress Paper 856103 Visual Contrast Thresholds during Single-axis and Dual-axis Whole-body Vibrations

The hypothesis was proved that whole body vibrations transmitted through the seat impair spatial retinal resolution and oculomotor alignment parallel to the vibration axis. More specifically, it was assumed that the decrement increases gradually from single-axis lateral via single-axis vertical and dual-axis linear to dual-axis circular motions. 20 subjects (19-26 yrs, 14 men, 6 women) with good vision participated in the study where in separate experimental sessions either fixation disparity or contrast threshold for vertically and horizontally oriented test patterns were determined during 5 conditions. The latter comprized a control (az = ay = 0) and 4 conditions where 5 Hz sinusoidal vibrations of 1.2 ms -2 r.m.s. were applied separately, either in the vertical or in the lateral direction or simultaneously in both directions, once without and once with a phase shift of 90° thus causing dualaxis linear or circular motions. The variability of vertical fixation disparity and contrast thresholds for horizontal gratings increased significantly whenever the subjects were exposed to vertical motions (alone or combined with lateral motions). These results indicate an increased difficulty to recognize properly characters and graphic patterns that contain horizontal lines. This may lead to the development of asthenopic complaints.