Oculomotor Alignment and Visual Contrast Thresholds during Separate and Simultaneous Lateral and Vertical Whole-Body Vibrations (5 Hz,1.2 ms −2 )

This paper concerns the hypothesis that whole-body vibrations transmitted through the seat impair oculomotor alignment and degrade spatial retinal resolution. The decrement was assumed to increase gradually from single-axis lateral via single-axis vertical and dual-axis linear to dual-axis circular motions.

14 men and 6 women (19–26 yrs,) with good binocular vision took part in two experimental sessions where either fixation disparity or contrast threshold for vertically and horizontally oriented test patterns were determined during 5 conditions. The latter comprised a control (a_z = a_y = 0) and 4 conditions where 5 Hz sinusoidal vibrations of 1.2 ms⁻² r.m.s. were applied separately, either vertically or laterally or simultaneously in both directions, once without and once with a phase shift of 90° thus causing dual-axis linear or circular motions.

The variability of vertical fixation disparity and the contrast thresholds for horizontal gratings increased whenever the subjects were exposed to vertical motions (alone or combined with lateral motions). The results indicate an increased difficulty to recognize properly characters and graphic patterns that contain horizontal lines. The greater difficulty for binocular alignment may eventually cause asthenopic complaints.