Effects of Vibration on Approach Trajectory of In-Vehicle Reaching Tasks Kevin A. Rider, Jing Wang, Don B. Chaffin 28th Annual Meeting of the American Society of Biomechanics, Portland, Oregon, 2004. Target-directed reaching tasks have been analyzed using numerous qualitative and quantitative methods, ranging from simple observations to extensive laboratory experiments and analysis. The former suggests that human movements are stochastic at best, random at worst, but it is the latter that has provided the significant contributions to our current understanding of human movement. Plamondon (1998) presents an example of the derivation of human movement by his delta-lognormal law that describes the movement as the result of a planned and executed synergy of an agonist-antagonist system. This work also provides strong support for the argument that movements are planned through the kinematics and kinetics of the end effector trajectory, rather than joint-based theories or more abstract spatial representations. While general point-to-point trajectories can often be nicely described by Plamondon's theory, it does not take into consideration additional constraints of the task, such as movement time, accuracy, target characteristics, or even the volatility of the environment. It is this last consideration that our study is particularly concerned; how does a moving environment (i.e. vehicle motion) affect the occupant's ability to perform an in-vehicle reaching task? Breteler et al. (2001) identified ways that end-point constraints can affect the movement trajectory with respect to the approach angle into the target and the speed of the end effector. These metrics provide a solid foundation from which to proceed towards better characterization of the kinematic changes that result from various task demands. Another concern regarding the simplicity of Plamondon's theory is the reliance on openloop control theory. It does not incorporate the ever-present online modification of our movements to improve the performance of the output. Particularly in the dynamic environment of vehicles, substantial perturbations are introduced to everything in the system. This ride motion effect is the focus of this study, and we specifically analyzed the trajectory as the participant's fingertip approached the target and completed the reach. abs2004_05