PubMed · 14198662
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E A JAEGER, R J SEVERS, S D WEEKS, T D DUANE. 1964. VISUAL FIELD CHANGES DURING POSITIVE ACCELERATION.. https://pubmed.ncbi.nlm.nih.gov/14198662/
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On Earth, eye velocity of horizontal optokinetic nystagmus (OKN) orients to gravito-inertial acceleration (GIA), the sum of linear accelerations acting on the head and body. We determined whether adaptation to micro-gravity altered this orientation and whether ocular pursuit exhibited similar properties. Eye movements of four astronauts were recorded with three-dimensional video-oculography. Optokinetic stimuli were stripes moving horizontally, vertically, and obliquely at 30 degrees/s. Ocular pursuit was produced by a spot moving horizontally or vertically at 20 degrees/s. Subjects were either stationary or were centrifuged during OKN with 1 or 0.5 g of interaural or dorsoventral centripetal linear acceleration. Average eye position during OKN (the beating field) moved into the quick-phase direction by 10 degrees during lateral and upward field movement in all conditions. The beating field did not shift up during downward OKN on Earth, but there was a strong upward movement of the beating field (9 degrees) during downward OKN in the absence of gravity; this likely represents an adaptation to the lack of a vertical 1-g bias in-flight. The horizontal OKN velocity axis tilted 9 degrees in the roll plane toward the GIA during interaural centrifugation, both on Earth and in space. During oblique OKN, the velocity vector tilted towards the GIA in the roll plane when there was a disparity between the direction of stripe motion and the GIA, but not when the two were aligned. In contrast, dorsoventral acceleration tilted the horizontal OKN velocity vector 6 degrees in pitch away from the GIA. Roll tilts of the horizontal OKN velocity vector toward the GIA during interaural centrifugation are consistent with the orientation properties of velocity storage, but pitch tilts away from the GIA when centrifuged while supine are not. We speculate that visual suppression during OKN may have caused the velocity vector to tilt away from the GIA during dorsoventral centrifugation. Vertical OKN and ocular pursuit did not exhibit orientation toward the GIA in any condition. Static full-body roll tilts and centrifugation generating an equivalent interaural acceleration produced the same tilts in the horizontal OKN velocity before and after flight. Thus, the magnitude of tilt in OKN velocity was dependent on the magnitude of interaural linear acceleration, rather than the tilt of the GIA with regard to the head. These results favor a 'filter' model of spatial orientation in which orienting eye movements are proportional to the magnitude of low frequency interaural linear acceleration, rather than models that postulate an internal representation of gravity as the basis for spatial orientation.
In the present study, using the mental chronometry paradigm, we examined the hypothesis that during motor imagery the brain uses a forward internal model of arm inertial properties to predict the motion of the arm in different dynamic states. Seven subjects performed overt and covert arm movements with one (motion around the shoulder joint) and two (motion around both the shoulder and elbow joints) degrees of freedom in the horizontal plane. Arm movements were executed under two loading conditions: without and with an added mass (4kg) attached to the subject's right wrist. Additionally, movements were performed in two different directions, condition which implies changes in the arm inertia due to the inertial anisotropy of the arm. Our analysis was focused on the timing features of overt and covert movements measured by means of an electronic stopwatch. Durations of right-direction arm movements (low inertial resistance) were smaller compared to durations of left-direction arm movements (high inertial resistance). Additionally, loading the arm with an added mass of 4kg significantly changed the dynamics of motion: movements were indeed more prolonged under loaded conditions. In both cases, the duration of simulated movements mirrored that of overtly executed movements. Therefore, neither the inertial anisotropy of the arm nor the addition of an external mass affected the timing correspondence between overt and covert movement execution. These findings suggest that the brain internally represents the inertial properties of the arm and makes use of it both for sensorimotor control and for the generation of motor images.
Since 1970, traumatomechanics has been a focal point in research at the Institute for Legal Medicine and Traffic Medicine in Heidelberg. Here, the main topics are the understanding of the interrelation between mechanical strain and the resulting degree of injury; at the forefront of all interest is the determination of the mechanical resilience in humans, their organs and tissues. Important are not only the means, but likewise the individual strain tolerance and the causes for its variability. Their understanding leads to scientifically justifiable expert's reports. In safety research, these data are of major importance for the validation of crash-dummies and for the improvement of safety protection systems. Before this background, national and international institutions have supported numerous projects. With the help of 2 examples, the Thorax-Trauma-Index (TTI) and the synergy between safety belt and airbag, the relevance of these data for international regulatory provisions and the progress in safety practice are illustrated. Some traumatomechanical insights can only be gathered from human corpses. Legal prerequisites and ethical problems of experiments with corpses are discussed.