Eye-Hand Coordination: Dexterous Object Manipulation in New Gravity Fields

The stabilisation of an object manipulated with the hand depends on applying a sufficiently strong force with each finger such that sufficient friction is generated to resist the load force acting tangentially to the contact surfaces. Gravity normally provides a constant force acting on the object (depending on its weight) which is adequately taken into account by an appropriate level of grip force.Variations in inertial forces caused by the subject's own arm movements over a range of accelerations also produce synchronous changes in grip forces that rise and fall with the changes in the tangential load forces on the fingers.That is, grip force reflects an anticipatory adjustment to the fluctuations in inertial forces.The modulation of grip force in anticipation of load force implies that the nervous system has access to information concerning the object's weight, mass and the kinematics of the forthcoming movement, since changes in any of these require a different grip force.This suggests that the internal models used to predict load forces and generate appropriate grip forces are pretty good. It remains to be proved, however, whether the entire control process of grip-force compensation is based on feedforward, model-based control, or if some components of the required grip responses are generated through reflex actions. Microgravity presents a significant challenge to dexterous object manipulation for a number of reasons. Owing to all the potential deviations from the expected characteristics of the load forces, planning movement under microgravity conditions might involve a greater reliance on visual, tactile and/or memory cues to an object's mass. In addition, there might be over- gripping to reduce the consequence of an erroneous estimate of mass. Alternatively, the hand might initially be moved more slowly than normal to allow more time for feedback-based adjustments to grip force. In this regard, a series of experiments has been designed in order to study the effects of a change in gravity on the dynamics of prehension, on the kinematics of upper limb movements and on eye-hand coordination. This report describes the results of some experiments already performed and the scientific objectives of the experiments that will be carried out in the coming years

The effect of parabolic flight on perceived physical, motivational and psychological state in men and women: Correlation with neuroendocrine stress parameters and electrocortical activity

Previous findings of decreased mental and perceptual motor performance during parabolic flights have been attributed mainly to the primary effects of weightlessness rather than the accompanying effects of stress and altered mood. Although recent studies have alluded to the possible negative effects of stress on performance, there has been no attempt to investigate this during parabolic flights. Over a period of 3 years, 27 human participants (male n = 18, mean age ± SD 34.67 ± 7.59 years; female n = 9, 36.22 ± 9.92 years) were recruited with the aim to evaluate if, and to what extent, parabolic flights are accompanied by changes in mood. Furthermore, the relationships between mood and physiological markers of stress and arousal, namely circulating stress hormones (ACTH, cortisol, epinephrine, norepinephrine, prolactin and brain activity (EEG)) were investigated. A strong and significant correlation was found between circulating stress hormone concentrations and perceived physical state, motivational state (MOT) and psychological strain (PSYCHO), whereas no interaction between mood and EEG or EEG and stress hormone concentrations was observed. Therefore, two different stress responses appear to be present during parabolic flight. The first seems to be characterised by general cortical arousal, whereas the second seems to evolve from the adrenomedullary system. It is likely that both these mechanisms have different effects on mental and perceptual motor performance, which require further investigation and should to be taken into account when interpreting previous weightlessness research