The current criteria and recommendations for assessing the acceptability of wind-induced building motion were largely established based on human perception thresholds and/or tolerance to wind-induced building motion. Therefore, they may not be able to ensure the performance of manual tasks is unaffected by wind-induced building motion. Few studies have investigated the effects of wind-induced building motion on manual task performance, and the findings of these studies are inconclusive. Hence the relationships between manual task performance and the wind-induced building motion and the mechanisms causing manual task performance degradation are yet to be explored and fully understood. Sopite syndrome describes a set of symptom centering around drowsiness due to exposure of healthy individuals to real or apparent motion. Recent studies have shown that symptoms of sopite syndrome are the most frequent manifestations of the effects of wind-induced building motion and decrease subjective work performance and objective cognitive task performance of building occupants. However, no study has investigated the effects of sopite syndrome on manual task performance.
This thesis investigates the effects of low-frequency, low-acceleration motion and sopite syndrome on manual task performance based on a series of motion simulator experiments. Twelve low-frequency, low-acceleration motion conditions were generated using four frequencies (0.125, 0.25, 0.5, and 1 Hz) and three acceleration magnitudes (8, 16, and 30 milli-g) for both fore-aft and lateral directions. A continuous tracking task (CTT) was used as a paradigm to investigate the effects of the motion on manual task performance. Aiming accuracy of the CTT is the dependent measure. Twenty (10 males and 10 females) participants completed the experiment under fore-aft motion conditions and another 20 participants (10 males and 10 females) under lateral motion conditions. A Motion Sickness Assessment Questionnaire (MSAQ) was used to measure motion sickness severity, in particular sopite syndrome severity, of the participants before and after the exposure to the motion conditions. Activation levels of soleus (SOL) and tibialis anterior (TA), the lower leg muscles involved in maintaining balance in the fore-aft direction, were measured using electromyography (EMG) to provide supporting evidences for the effects of motion and sopite syndrome on manual task performance from a physiological perspective. Both acceleration and frequency were found to contribute to the degradations of manual task performance. Acceleration shows a strong inverse relationship with manual task performance; manual task performance decreases as the acceleration increases from 8 milli-g to 30 milli-g. The acceleration effect is attributable to an increase in inertial force. The activation levels of the SOL and TA also increase as acceleration increases from 8 milli-g to 30 milli-g. Evidently, the increase in inertial force can, in turn, induce visual impairment, disrupt balance, increase vibration breakthrough, and/or trigger motion sickness or sopite syndrome.
In contrast, frequency has a complex nonlinear relationship with manual task performance. The worst manual task performance was measured at 0.5 Hz among the test frequencies ranging from 0.125 Hz to 1 Hz. This frequency effect is associated with the frequency response characteristic of the human body. Body sway increases as frequency approaches the resonant frequency of a standing human, which occurs at near 0.5 Hz. The activation levels of SOL and TA increase as frequency increases from 0.125 Hz to approximately 0.5 Hz, then drop as frequency increases from 0.5 Hz to 1 Hz. This affirms that the body sways the most at 0.5 Hz. The increases in body sway can cause discomfort, divert attention resources from performing a manual task, and trigger anxiety that increases difficulty to response to manual tasks
