Motion-Induced Interruptions and Postural Equilibrium in Linear Lateral Accelerations

The scope of this applied research was to conduct an experiment using a motion simulator in order to (a) revisit the relationship between sway parameters and Motion-Induced Interruptions (MIIs) in a controlled environment, and (b) focus on the effect of the frequency (period) of the acceleration stimulus on MII occurrence. This study assesses lateral tipping, as opposed to sliding, MIIs of standing persons in a simulated motion environment representing dry deck conditions. Results verify previous findings that MII occurrence increases with increasing peak sway acceleration. Although MII occurrence was associated with the frequency of the motion stimulus, the effect is not as clear as that of acceleration. Overall, results suggest that complex, multidirectional motions create more tipping MIIs than unidirectional motion. Beyond acceleration, MII research also should incorporate frequency characteristics and motion complexity as factors influencing MII occurrence. In this study, we introduce the probable MII, a novel term referring to a slight, temporary loss of balance without tipping. This term fills the gap between the theoretical definition of an MII and a human-centered perception of an MII, where loss of balance is not a binary phenomenon. From a human performance perspective, the investigation of the probable MIIs may be of a value because they are more common than the definite MIIs (depending on the motion profile, this difference ranged from 16% to 67%). As a result of these findings, we developed a mathematical model of MII occurrence based on the amplitude and period of motion stimulus acceleration. The model assumes an additive combination two functions: a generalized logistic associated with the amplitude of acceleration and a Gaussian for period. The developed model approximated the observed MIIs with good results ( +/ 9% difference). The original document contains color images.