Virtual Reality (VR) systems have increasingly leveraged multisensory feedback to enrich user experience and mitigate cybersickness. With a similar goal in focus, this paper presents an in-depth exploration of integrating airflow with visual and kinesthetic cues in a VR surfing simulation. Utilizing a custom-designed airflow system and a physical surfboard mounted on a 6-Degree of Freedom (DoF) motion platform, we present two studies that evaluate the effect of the different feedback modalities. The first study assesses the impact of variable airflow, which dynamically adjusts to the user's speed (wind speed) in VR, compared to constant airflow conditions, under both active and passive user engagement scenarios. Results demonstrate that variable airflow significantly enhances immersion and reduces cybersickness, particularly when users are actively engaged in the simulation. The second study evaluates the individual and combined effects of vision, motion, and airflow on acceleration perception, user immersion, and cybersickness, revealing that the integration of all feedback modalities yields the most immersive and comfortable VR experience. This study underscores the importance of synchronized multisensory feedback in dynamic VR environments and provides valuable insights for the design of more immersive and realistic virtual simulations, particularly in aquatic, interactive, and motion-intensive scenarios.

Muscle coordination studies repeatedly show low-dimensionality of muscle activations for a wide variety of motor tasks. The basis vectors of this low-dimensional subspace, termed muscle synergies, are hypothesized to reflect neurally-established functional muscle groupings that simplify body control. However, the muscle synergy hypothesis has been notoriously difficult to prove or falsify. We use cadaveric experiments and computational models to perform a crucial thought experiment and develop an alternative explanation of how muscle synergies could be observed without the nervous system having controlled muscles in groups. We first show that the biomechanics of the limb constrains musculotendon length changes to a low-dimensional subspace across all possible movement directions. We then show that a modest assumption--that each muscle is independently instructed to resist length change--leads to the result that electromyographic (EMG) synergies will arise without the need to conclude that they are a product of neural coupling among muscles. Finally, we show that there are dimensionality-reducing constraints in the isometric production of force in a variety of directions, but that these constraints are more easily controlled for, suggesting new experimental directions. These counter-examples to current thinking clearly show how experimenters could adequately control for the constraints described here when designing experiments to test for muscle synergies--but, to the best of our knowledge, this has not yet been done.

We propose a complete methodology to find the full set of feasible grasp wrenches and the corresponding wrench-direction-independent grasp quality for a tendon-driven hand with arbitrary design parameters. Monte Carlo simulations on two representative designs combined with multiple linear regression identified the parameters with the greatest potential to increase this grasp metric. This synthesis of computational approaches now enables the systematic design, evaluation, and optimization of tendon-driven hands.