The skin is the largest organ of the human body. It is a barrier between our body and the environment protecting us from dehydration, infection and injuries. The skin thus provides us with a sense of touch which has several functions such as 1) providing tactile information about our environment and 2) providing input to enable motor interactions with our direct environment e.g. grasping and manipulating objects. Due to the bimodal functionality of the tactile sense, the skin is particularly interesting for communicating motion related instructions through haptic cues directly engaging our motor learning systems. Opportunities for applications have been identified in sports and training, surgery, music, navigation, prosthesis, to develop assistive devices e.g. navigation aid for the visually impaired and for balance correction in vestibular disorders, to attain correct posture, gait, and for the purpose of rehabilitation e.g. after stroke. However, research is mainly confined to in-lab applications. In order to unlock the realm of opportunities for off-site applications, wearable haptic communication systems for posture and movement management should be developed and evaluated. Thereby vibrotactile signals directly deployed onto the skin are identified most promising for wearable systems. Frequency, intensity/amplitude, burst, and rhythm characteristics for optimal perception at various body locations are known in literature.
We will investigate the accuracy of a basic system that steers actual posture and movement towards a reference condition through feedforward, that is, the subject receiving instructions on the actual or future desired reference condition. The independent variable in our study design is the feedforward time. The depended variable is a measure accuracy obtained by integrating the total immediate joint angle differences of desired and reference position over the time domain. An optimal feedforward time is explored and validated for movement instructions and for obstacle avoidance with vision and in blindfolded subjects.