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Abstract

Motion based driving simulators have a limited physical workspace. One method to perceptually expand their workspace is to simulate sustained linear acceleration by a combination of translation and tilt below drivers' vestibular threshold (tilt coordination). The tuning of tilt
coordination filters is often done empirically, without considering the variability of perceptual thresholds. However, previous studies have shown that the perceptual threshold for tilt derived from vestibular self-motion information alone varies when visual cues are also provided.
There is also evidence that the mental load induced by complex tasks such as driving influences threshold values. Active driving simulation provides a variety of visual and vestibular cues as well as demands on attention which vary with task difficulty. It is thus important to measure perceptual thresholds for tilt in conditions that closely resemble typical driving simulation to determine how different sensory and cognitive factors contribute to drivers' motion sensitivity. Knowing the relative contribution of these components will lead to more
optimized simulated driving. To assess these factors, we measure roll rate perception thresholds under 4 different conditions which include an active motor task, visual information and combined translational and rotational motion. In each condition, motion stimuli are adjusted according to a single-interval adaptive procedure (yes-no task) specifically designed to induce a neutral response criterion. This procedure allows for an unbiased estimate while at the same time minimizes the number of presentations. The first condition provides drivers with full visual and vestibular motion cues. They actively drive through a curve while the tilt coordination filter systematically varies the roll rate saturation level. This allows the identification of the roll rate threshold during active control of self-motion. The second condition is the same as condition 1 but drivers sit as passive observers in the simulator cabin and report tilt perception while the simulator drives them through the curve. Here, the roll rate saturation is adjusted to determine the absolute threshold in passive conditions, with multisensory (visual and vestibular) stimulation still presented. In the third condition drivers are deprived of the visual stimulus as well, to assess the effect of lateral acceleration on drivers' roll rate detection threshold. In the fourth condition, the absolute roll rate threshold is measured removing every additional sensory cue to self-motion. Drivers report here the perception of tilt while being passively tilted in darkness. Questionnaires about motion sickness, simulation realism and cognitive workload are also collected for all drivers before, during and after each condition. Overall, perceptual thresholds are expected to increase with task difficulty and attentional
load. If so, this will allow for higher roll rates to be employed for tilt coordination without losing simulation fidelity. Results from the planned experiment will be discussed with regards to previous literature, motion simulator workspace and motion drive algorithms.