DEVELOPMENT OF A CLASSIFICATION SYSTEM ON ANKLE-JOINT STIFFNESS

AIM OF THE PROJECT Aim of the project is to develop a classification system for the ankle stiffness in sideward rotations of the fool. MOTIVATION In a previous study (1) a classification system for (running) shoes has been developed on the aspects stability and shock absorption based on a mechanical test protocol. If corresponding features can be quantified for the (lower) legs of the runner, running shoes can be more carefully selected. For example, a runner with less stiff ankles may need shoes which have high stabilizing properties, whereas runners with stable ankles may ask for (more) shock absorbency of their shoes. Consequently, classification systems may contribute to the reduction and /or prevention of running-related injuries. In the present project we have focused ourselves on the stiffness of the ankle. Method: An apparatus has been constructed to quantify the resistance of the foot against sideward rotations. The foot of a person to be tested in a sitting position is placed on a platform and fixed by a special technique. The lower leg is kept in vertical position by straps. The leg is allowed to rotate and translate to some extent around and along the vertical axis of the lower leg. By rotating the platform, the foot can be moved through plantar/dorsal flexion, abduction/adduction and inward/outward rotation. In the first two planes of motion discrete positions of the foot are prescribed while the inward/outward motion is imposed in a motor-driven way. The axes of rotation can be adjusted to individual differences. The axial load on the lower leg can be varied in discrete steps. In this project, the moment of force (M) as a function of rotation (Φ) is measured during inversion/aversion cycle in two positions of the foot, viz. neutral position (0 degrees flexion, 0 degrees adduction) and flexed position (20 degrees plantar flexion, 10 degrees adduction) without axial loading of the tibia. At present, the left ankles of a group of 14 volunteers without ankle complaints and 6 with ankle complaints are measured. Results and Discussion:Based on the specific and reproducible non-linear M- Φ relationship several parameters are deduced such as primary stiffness, mobility, and secondary stiffness for aversion and inversion. One of the results is that in both foot positions the primary stiffness shows to be linear related to the mobility ( a higher stiffness results in a lower mobility.) In the flexed position the primary stiffness is less than in neutral foot position. Using the primary stiffness results of the “sound” group in the flexed foot position a starting classification is made in terms of “stiff”, “neutral”, and “lax”. Depiction of the results of the “injured” ankles in this classification shows that most of these ankles belong to the “lax” category. Biomechanical and epidemiological studies are necessary to evaluate the ultimate effects of combinated foot/shoe classifications

The time course of exogenous and endogenous control of covert attention

Studies of eye-movements and manual response have established that rapid overt selection is largely exogenously driven toward salient stimuli, whereas slower selection is largely endogenously driven to relevant objects. We use the N2pc, an event-related potential index of covert attention, to demonstrate that this time course reflects an underlying pattern in the deployment of covert attention. We find that shifts of attention that occur soon after the onset of a visual search array are directed toward salient, task-irrelevant visual stimuli and are associated with slow responses to the target. In contrast, slower shifts are target-directed and are associated with fast responses. The time course of exogenous and endogenous control provides a framework in which some inconsistent results in the capture literature might be reconciled; capture may occur when attention is rapidly deployed

Salience-based selection: attentional capture by distractors less salient than the target

Current accounts of attentional capture predict the most salient stimulus to be invariably selected first. However, existing salience and visual search models assume noise in the map computation or selection process. Consequently, they predict the first selection to be stochastically dependent on salience, implying that attention could even be captured first by the second most salient (instead of the most salient) stimulus in the field. Yet, capture by less salient distractors has not been reported and salience-based selection accounts claim that the distractor has to be more salient in order to capture attention. We tested this prediction using an empirical and modeling approach of the visual search distractor paradigm. For the empirical part, we manipulated salience of target and distractor parametrically and measured reaction time interference when a distractor was present compared to absent. Reaction time interference was strongly correlated with distractor salience relative to the target. Moreover, even distractors less salient than the target captured attention, as measured by reaction time interference and oculomotor capture. In the modeling part, we simulated first selection in the distractor paradigm using behavioral measures of salience and considering the time course of selection including noise. We were able to replicate the result pattern we obtained in the empirical part. We conclude that each salience value follows a specific selection time distribution and attentional capture occurs when the selection time distributions of target and distractor overlap. Hence, selection is stochastic in nature and attentional capture occurs with a certain probability depending on relative salience

Dual-wavelength laser source for onboard atom interferometry

We present a compact and stable dual-wavelength laser source for onboard atom interferometry with two different atomic species. It is based on frequency-doubled telecom lasers locked on a femtosecond optical frequency comb. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components which are intrinsically less stable, and to make the setup immune to vibrations and thermal fluctuations. The source provides the frequency agility and phase stability required for atom interferometry and can easily be adapted to other cold atom experiments. We have shown its robustness by achieving the first dual-species K-Rb magneto optical trap in microgravity during parabolic flights

Interferometry with Bose-Einstein Condensates in Microgravity

Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Due to their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this paper we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far-field of a double-slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.Comment: 8 pages, 3 figures; 8 pages of supporting materia

Evidence for a dissociation between the control of oculomotor capture and disengagement

The current study investigated whether capture of the eyes by a salient onset distractor and the disengagement of the eyes from that distractor are driven by the same or by different underlying control modes. A variant of the classic oculomotor capture task was used. Observers had to make a saccade to the only gray circle among red background circles. On some trials, a green (novel color), red (placeholder color) or gray (target color) distractor square was presented with sudden onset. Results showed that when participants reacted fast, oculomotor capture was primarily driven by bottom-up pop-out: both types of distractors (green and gray) that popped out among the red background elements showed more capture than a red distractor that did not pop-out. In contrast to initial capture, disengagement of the eyes from the distractor was driven by top-down target–distractor similarity effects. We also examined the time-course of this effect. The distractor could change from green to either the target or placeholder color. When the color change was early in time (30–40 ms after its onset), dwell times were strongly affected by the change, whereas the effect on oculomotor capture was weak. Importantly, a change occurring as early as 60–80 ms after distractor onset did neither affect capture nor dwell times, corroborating the assumption of parallel programming of saccades

Setting things straight: a comparison of measures of saccade trajectory deviation

In eye movements, saccade trajectory deviation has often been used as a physiological operationalization of visual attention, distraction, or the visual system’s prioritization of different sources of information. However, there are many ways to measure saccade trajectories and to quantify their deviation. This may lead to noncomparable results and poses the problem of choosing a method that will maximize statistical power. Using data from existing studies and from our own experiments, we used principal components analysis to carry out a systematic quantification of the relationships among eight different measures of saccade trajectory deviation and their power to detect the effects of experimental manipulations, as measured by standardized effect size. We concluded that (1) the saccade deviation measure is a good default measure of saccade trajectory deviation, because it is somewhat correlated with all other measures and shows relatively high effect sizes for two well-known experimental effects; (2) more generally, measures made relative to the position of the saccade target are more powerful; and (3) measures of deviation based on the early part of the saccade are made more stable when they are based on data from an eyetracker with a high sampling rate. Our recommendations may be of use to future eye movement researchers seeking to optimize the designs of their studies