Effects of horizontal acceleration on human visual acuity and stereopsis

The effect of whole-body vibration on public transportation passenger performance while typing on smartphones

This study verified typing performance on smartphones of public transportation passengers using subjective assessments of comfort and difficulty and objective assessments of the number of errors and typing speed. Three frequency values (5, 10, and 15 Hz), two magnitudes (0.6 and 1.2 m/s²) and two types of operating systems (Android and IOS) were adopted. Tests without vibration were applied to analyse the residual effect of vibration. The results showed that vibration significantly influences comfort. The higher the frequency, the less errors and the faster the typing speed. In the magnitude analysis, the increase caused a greater number of errors and greater difficulty. In both assessments, the discomfort was proportional to the increase in frequency or magnitude and the number of errors was inversely proportional to the typing speed. Finally, the IOS operating system showed worse comfort when compared to Android, although no significant differences were observed for the objective assessment. Practitioner summary: Public transportation passengers are exposed to WBV while typing on smartphones. The results showed that vibration influences comfort, the number of errors and the typing speed. Therefore, manufacturers should be aware of the level of vibration that vehicles are exposed to in order to provide more performance to the user. Abbreviations: WBV: whole-body vibration; PID: proportional-integral-derivative; RMS: root mean square; HLM: hierarchical linear modeling; OLS: ordinary least squares; STH: seat-to-head.

The effects of different seat suspension types on occupants' physiologic responses and task performance: implications for autonomous and conventional vehicles

This study evaluated whole body vibration (WBV), non-driving task performance, muscle activity, and self-reported discomfort and motion sickness between different seat suspension systems in a simulated vehicle environment. In a repeated-measures laboratory experiment where field-measured 6-degree-of-freedom (6-DOF) passenger vehicle vibration was replicated on a 6-DOF motion platform, we measured WBV, non-driving task (pointing, typing, web-browsing, and reading) performance, low back (erector spinae), shoulders (trapezius) and neck (splenius capitis and sternocleido-mastoid) muscle activity, and self-reported discomfort and motion sickness from three different seats: a vertical (z-axis) active suspension, multi-axial active suspension [vertical (z-axis) + lateral (y-axis)], and a static suspension-less seat (current seat type in all passenger cars). Both the vertical and multi-axial active suspension seats significantly reduced the vertical WBV exposure (p < 0.0001). However, no significant differences were found in non-driving task performance (p > 0.30), muscle activity (p > 0.22), self-reported discomfort (p > 0.07), and motion sickness (p = 0.53) across three different seats. These findings indicate that the active suspension seats may have potential to future reduce the vertical and total WBV exposures, respectively. However, none of the suspension seats demonstrate any significant benefits on the non-driving task performance, muscle activity, self-reported discomfort and motion sickness measures in a simulated vehicle environment.

Dynamic Visual Measurement of Driver Eye Movements

Vibrations often cause visual fatigue for drivers, and measuring the relative motion between the driver and the display is important for evaluating this visual fatigue. This paper proposes a non-contact videometric measurement method for studying the three-dimensional trajectories of the driver's eyes based on stereo vision. The feasibility of this method is demonstrated by dynamic calibration. A high-speed dual-camera image acquisition system is used to obtain high-definition images of the face, and the relative trajectories between the eyes and the display are obtained by a set of robust algorithms. The trajectories of the eyes in three-dimensional space are then reconstructed during the vehicle driving process. This new approach provides three-dimensional information and is effective for assessing how vibration affects human visual performance.

Evaluation of commercially available seat suspensions to reduce whole body vibration exposures in mining heavy equipment vehicle operators

As mining vehicle operators are exposed to high level of Whole body vibration (WBV) for prolonged periods of time, approaches to reduce this exposure are needed for the specific types of exposures in mining. Although various engineering controls (i.e. seat suspension systems) have been developed to address WBV, there has been lack of research to systematically evaluate these systems in reducing WBV exposures in mining heavy equipment vehicle settings. Therefore, this laboratory-based study evaluated the efficacy of different combinations of fore-aft (x-axis), lateral (y-axis), and vertical (z-axis) suspensions in reducing WBV exposures. The results showed that the active vertical suspension more effectively reduced the vertical vibration (∼50%; p's < 0.0001) as compared to the passive vertical suspension (10%; p's < 0.11). The passive fore-aft (x-axis) and lateral (y-axis) suspension systems did not attenuate the corresponding axis vibration (p's > 0.06) and sometimes amplified the floor vibration, especially when the non-vertical vibration was predominant (p's < 0.02). These results indicate that there is a critical need to develop more effective engineering controls including better seat suspensions to address non-vertical WBV exposures, especially because these non-vertical WBV exposures can increase risks for adverse health effects including musculoskeletal loading, discomfort, and impaired visual acuity.

The effect of a multi-axis suspension on whole body vibration exposures and physical stress in the neck and low back in agricultural tractor applications

Whole body vibration (WBV) exposures are often predominant in the fore-aft (x) or lateral (y) axis among off-road agricultural vehicles. However, as the current industry standard seats are designed to reduce mainly vertical (z) axis WBV exposures, they may be less effective in reducing drivers' exposure to multi-axial WBV. Therefore, this laboratory-based study aimed to determine the differences between a single-axial (vertical) and multi-axial (vertical + lateral) suspension seat in reducing WBV exposures, head acceleration, self-reported discomfort, and muscle activity (electromyography) of the major muscle of the low back, neck and shoulders. The results showed that the multi-axial suspension seat had significantly lower WBV exposures compared to the single-axial suspension seats (p' < 0.04). Similarly, the multi-axial suspension seat had lower head acceleration and muscle activity of the neck, shoulder, and low back compared to the single-axial suspension seat; some but not all of the differences were statistically significant. These results indicate that the multi-axial suspension seat may reduce the lateral WBV exposures and associated muscular loading in the neck and low back in agricultural vehicle operators.