Human perception of self-motion is the result of combining information from many sensory systems such as visual, vestibular, and proprioceptive systems. Research on vestibular thresholds has mainly focused on estimating absolute thresholds for translational and rotational motions and estimating difference thresholds for rotational velocities. In this study, psychophysical methods are used to determine the ability of normal subjects to discriminate among sinusoidal accelerations in the horizontal plane. Difference thresholds were estimated using four different acceleration amplitudes ranging from peak amplitude of 0.5-2.0 m/s2 and three different frequencies ranging from 0.25 to 0.6 Hz. Difference thresholds ranged from 0.05 m/s2 for a sinusoidal acceleration with peak amplitude of 0.5 to 0.13 m/s2 for a sinusoidal acceleration with peak amplitude of 2.0 m/s2. The relationship between difference threshold estimates and peak accelerations is found to compare favorably to Weber's law, which is often used to represent changes in threshold values in other sensory systems. Moreover, the threshold estimates tend to decrease as frequency increases. The effect of visual condition on thresholds was also investigated. It was shown that when the visual scene is stationary with respect to the subject, there are no significant differences between threshold estimates based on closed-eye and open-eye scenarios.

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NLR is a leading international research centre for aerospace. Bolstered by its multidisciplinary expertise and unrivalled research facilities, NLR provides innovative and integral solutions for the complex challenges in the aerospace sector. For more information visit: www.nlr.nl NLR's activities span the full spectrum of Research Development Test & Evaluation (RDT & E). Given NLR's specialist knowledge and facilities, companies turn to NLR for validation, verification, qualification, simulation and evaluation. NLR thereby bridges the gap between research and practical applications, while working for both government and industry at home and abroad. NLR stands for practical and innovative solutions, technical expertise and a long-term design vision. This allows NLR's cutting edge technology to find its way into successful aerospace programs of OEMs, including Airbus, Embraer and Pilatus. NLR contributes to (military) programs, such as ESA's IXV re-entry vehicle, the F-35, the Apache helicopter, and European programs, including SESAR and Clean Sky 2. Founded in 1919, and employing some 650 people, NLR achieved a turnover of 71 million euros in 2016, of which three-quarters derived from contract research, and the remaining from government funds. UNCLASSIFIED EXECUTIVE SUMMARY Problem areaThe tuning of a motion system for a flight simulator is still a highly subjective, and therefore costly, process. There simply is a lack of objective evaluation criteria specifying the motion requirements for the simulation of different aircraft (transport, fighter, or rotary wing) or manoeuvres. In practice, the determination of motion cues is based on a subjective process that relies mainly on the perception of the pilot or simulator instructor. Consequently, the simulation is sub-optimal for specific motion-critical manoeuvres (such as engine failure), which negatively affects the control behaviour of the simulator pilot, and may also give rise to simulator sickness. The efforts to optimise motion cueing should be in accordance with the relevance of a manoeuvre for training purposes.Considerable progress has been achieved in the modeling of human control behaviour and motion perception to address the problem of objectively evaluating and optimising simulator motion cues. The effect and optimization of simulator lateral and yaw motion, occurring during flight critical maneuvers, is of particular interest.

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