How prism adaptation reveals the distinct use of size and positions in grasping.

The size of an object equals the distance between the positions of its opposite edges. However, human sensory processing for perceiving positions differs from that for perceiving size. Which of these two information sources is used to control grip aperture? In this paper, we answer this question by prism adaptation of single-digit movements of the index finger and thumb. We previously showed that it is possible to adapt the index finger and thumb in opposite directions and that this adaptation induces an aftereffect in grip aperture in grasping. This finding suggests that grasping is based on the perceived positions of the contact points. However, it might be compatible with grasping being controlled based on size provided that the opposing prism adaptation leads to changes in visually perceived size or proprioception of hand opening. In that case, one would predict a similar aftereffect in manually indicating the perceived size. In contrast, if grasping is controlled based on information about the positions of the edges, the aftereffect in grasping is due to altered position information, so one would predict no aftereffect in manually indicating the perceived size. Our present experiment shows that there was no aftereffect in manually indicating perceived size. We conclude that grip aperture during grasping is based on perceived positions rather than on perceived size.

Number line estimation strategies in children with mathematical learning difficulties measured by eye tracking.

INTRODUCTION: Number line estimation is one of the skills related to mathematical performance. Previous research has shown that eye tracking can be used to identify differences in the estimation strategies children with dyscalculia and children with typical mathematical development use on number line estimation tasks. The current study extends these findings to a larger group of children with mathematical learning disabilities (MLD). METHOD: A group of 9-11-year-old children with MLD (N = 14) was compared to a control group of children without math difficulties (N = 14). Number line estimation was measured using a 0-100 and a 0-1000 number-to-position task. A Tobii T60 eye tracker was used to measure the children's eye movements during task performance. RESULTS: The behavioral data showed that the children with MLD had higher error scores on both number lines than the children in the control group. The eye tracking data showed that the groups also differed in their estimation strategies. The children with MLD showed less adaptation of their estimation strategies to the number to be estimated. CONCLUSION: This study shows that children with MLD attend to different features of the number line than children without math difficulties. Children with math difficulties are less capable of adapting their estimation strategies to the numbers to be estimated and of effectively using reference points on the number line.

Simultaneous adaptation of the thumb and index finger of the same hand to opposite prism displacements.

It only takes a few goal-directed hand movements to adapt one's movements to a prism-induced displacement of the visual scene. Adaptation to the displacement leads to errors in the opposite direction from the initial displacement when the prisms are removed. Such aftereffects are thought to arise from some form of spatial realignment of the senses or from motor learning. Here, we show that humans can simultaneously adapt the movements of the thumb and index finger of the same hand to opposing visual displacements. Neither the felt position of the hand nor the visually perceived direction can change in two opposite directions at the same time, ruling out an explanation based on realignment of the senses. It is conceivable that one could learn to adjust the movements differently for the two digits despite the fact that both adjustments would involve the same hand, but such motor learning should not transfer to matching the position of the unseen digit. As transfer was observed when visually matching the position of the unseen digit, motor learning cannot explain all of the results. An explanation involving supplementing proprioception with a memory-based visual estimate of the position of each unseen digit could explain all of the results. Irrespective of the mechanism, we can conclude that it is possible to adapt the perceived locations of the unseen digits without influencing proprioception.

A challenge-based interdisciplinary undergraduate concept fostering translational medicine.

Translational medicine (TM) is an interdisciplinary branch of biomedicine that bridges the gap from bench-to-bedside to improve global health. Fundamental TM skills include interdisciplinary collaboration, communication, critical thinking, and creative problem-solving (4Cs). TM is currently limited in undergraduate biomedical education programs, with little patient contact and opportunities for collaboration between different disciplines. In this study, we developed and evaluated a novel interdisciplinary challenge-based educational concept, grounded in the theoretical framework of experimental research-based education, to implement TM in undergraduate biomedicine and medicine programs. Students were introduced to an authentic clinical problem through an interdisciplinary session with patients, medical doctors, and scientists. Next, students collaborated in groups to design unique laboratory-based research proposals addressing this problem. Stakeholders subsequently rewarded the best proposal with funding to be executed in a consecutive interdisciplinary laboratory course, in which mixed teams of biomedicine and medicine students performed the research in a fully equipped wet laboratory. Written questionnaires and focus groups revealed that students developed 4C skills and acquired a 4C mindset. Working on an authentic patient case and the interdisciplinary setting positively contributed to communication, collaboration, critical thinking, and creative problem-solving skills. Furthermore, students were intrinsically motivated by (i) the relevance of their work that made them feel taken seriously and competent, (ii) the patient involvement that highlighted the societal relevance of their work, and (iii) the acquisition of a realistic view of what doing science in a biomedical research laboratory is. In conclusion, we showcase a widely applicable interdisciplinary challenge-based undergraduate concept fostering TM.

Grasping and hitting moving objects.

Some experimental evidence suggests that grasping should be regarded as independent control of the thumb and the index finger (digit control hypothesis). To investigate this further, we compared how the tips of the thumb and the index finger moved in space when grasping spheres to how they moved when they were hitting the sphere using only one digit. In order to make the tasks comparable, we designed the experiment in such a way that subjects contacted the spheres in about the same way in the hitting task as when grasping it. According to the digit control hypothesis, the two tasks should yield similar digit trajectories in space. People hit and grasped stationary and moving spheres. We compared the similarity of the digits' trajectories across the two tasks by evaluating the time courses of the paths of the average of the thumb and the index finger. These paths were more similar across tasks than across sphere motion, supporting the notion that grasping is not controlled fundamentally differently than hitting.

A novel undergraduate biomedical laboratory course concept in synergy with ongoing faculty research.

Optimal integration of education and ongoing faculty research in many undergraduate science programs is limited to the capstone project. Here, we aimed to develop a novel course-based undergraduate research experience (CURE) in synergy with ongoing faculty research. This 10-week course called Biomedical Research Lab is embedded in the curriculum of the undergraduate program Biomedical Sciences and grounded in the theoretical framework of research-based learning. Four groups of four students work together in a dedicated laboratory on an actual ongoing research problem of faculty. All groups work on the same research problem, albeit from different (methodological) perspectives, thereby stimulating interdependence between all participants. Students propose new research, execute the experiments, and collectively report in a single research article. According to students, the course enhanced scientific, laboratory, and academic skills. Students appreciated ownership and responsibilities of the research, laboratory teachers as role models, and they were inspired and motivated by doing authentic actual research. The course resulted in a better understanding of what doing research entails. Faculty valued the didactical experience, research output and scouting opportunities. Since topics can change per course edition, we have showcased a widely applicable pedagogy creating synergy between ongoing research and undergraduate education.

Posture of the arm when grasping spheres to place them elsewhere.

Despite the infinitely many ways to grasp a spherical object, regularities have been observed in the posture of the arm and the grasp orientation. In the present study, we set out to determine the factors that predict the grasp orientation and the final joint angles of reach-to-grasp movements. Subjects made reach-to-grasp movements toward a sphere to pick it up and place it at an indicated location. We varied the position of the sphere and the starting and placing positions. Multiple regression analysis showed that the sphere's azimuth from the subject was the best predictor of grasp orientation, although there were also smaller but reliable contributions of distance, starting position, and perhaps even placing position. The sphere's initial distance from the subject was the best predictor of the final elbow angle and shoulder elevation. A combination of the sphere's azimuth and distance from the subject was required to predict shoulder angle, trunk-head rotation, and lateral head position. The starting position best predicted the final wrist angle and sagittal head position. We conclude that the final posture of the arm when grasping a sphere to place it elsewhere is determined to a larger extend by the initial position of the object than by effects of starting and placing position.

Does planning a different trajectory influence the choice of grasping points?

We examined whether the movement path is considered when selecting the positions at which the digits will contact the object's surface (grasping points). Subjects grasped objects of different heights but with the same radius at various locations on a table. At some locations, one digit crossed to the side of the object opposite of where it started. In doing so, it moved over a short object whereas it curved around a tall object. This resulted in very different paths for different objects. Importantly, the selection of grasping points was unaffected. That subjects do not appear to consider the path when selecting grasping points suggests that the grasping points are selected before planning the movements towards those points.

Changes in corticospinal excitability and the direction of evoked movements during motor preparation: a TMS study.

BACKGROUND: Preparation of the direction of a forthcoming movement has a particularly strong influence on both reaction times and neuronal activity in the primate motor cortex. Here, we aimed to find direct neurophysiologic evidence for the preparation of movement direction in humans. We used single-pulse transcranial magnetic stimulation (TMS) to evoke isolated thumb-movements, of which the direction can be modulated experimentally, for example by training or by motor tasks. Sixteen healthy subjects performed brisk concentric voluntary thumb movements during a reaction time task in which the required movement direction was precued. We assessed whether preparation for the thumb movement lead to changes in the direction of TMS-evoked movements and to changes in amplitudes of motor-evoked potentials (MEPs) from the hand muscles. RESULTS: When the required movement direction was precued early in the preparatory interval, reaction times were 50 ms faster than when precued at the end of the preparatory interval. Over time, the direction of the TMS-evoked thumb movements became increasingly variable, but it did not turn towards the precued direction. MEPs from the thumb muscle (agonist) were differentially modulated by the direction of the precue, but only in the late phase of the preparatory interval and thereafter. MEPs from the index finger muscle did not depend on the precued direction and progressively decreased during the preparatory interval. CONCLUSION: Our data show that the human corticospinal movement representation undergoes progressive changes during motor preparation. These changes are accompanied by inhibitory changes in corticospinal excitability, which are muscle specific and depend on the prepared movement direction. This inhibition might indicate a corticospinal braking mechanism that counteracts any preparatory motor activation.

Unusual prism adaptation reveals how grasping is controlled.

There are three main theories on how human grasping movements are controlled. Two of them state that grip aperture and the movement of the hand are controlled. They differ in whether the wrist or the thumb of the hand is controlled. We have proposed a third theory, which states that grasping is a combination of two goal-directed single-digit movements, each directed at a specific position on the object. In this study, we test predictions based on each of the theories by examining the transfer of prism adaptation during single-digit pointing movements to grasping movements. We show that adaptation acquired during single-digit movements transfers to the hand opening when subsequently grasping objects, leaving the movement of the hand unaffected. Our results provide strong evidence for our theory that grasping with the thumb and index finger is based on a combination of two goal-directed single-digit movements.

Are people adapted to their own glasses?

Negative lenses, either in the form of glasses or contact lenses, can correct nearsightedness. Unlike contact lenses, glasses do not only correct, but also induce optic distortions. In the scientific literature, it has often been assumed that people who wear corrective glasses instantaneously account for these distortions when they put their glasses on. We tested this assumption and found that, when people switched between their contact lenses and their glasses, they made the errors that one would predict based on the optics. This shows that people are not immediately adapted to their own glasses when they put them on.

Robust movement segmentation by combining multiple sources of information.

One of the first steps in analyzing kinematic data is determining the beginning and end of movement segments. This is often done automatically on the basis of one parameter (such as a speed minimum) and subsequently corrections are made if visual inspection of other kinematic parameters suggests that the obtained value was incorrect. We argue that in many cases it is impossible to find a satisfactory endpoint for all possible movement segments within an experiment using a single parameter because the intuition about the end of a segment is based on multiple criteria. Therefore by taking the maximum of an objective function based on multiple sources of information one can find the best possible time point to call the endpoint. We will demonstrate that this Multiple Sources of Information method (MSI-method) for finding endpoints performs better than conventional methods and that it is robust against arbitrary choices made by the researcher. Using it reduces the chance of introducing biases and eliminates the need for subjective corrections. Although we will take goal directed upper limb motion as an example throughout this paper, it should be stressed that the method could be applied to a wide variety of movements.