Accuracy in the badminton short serve: A methodological and kinematic study

In sports, accuracy is an essential component of actions such passing, shooting, and aiming. Executing a movement or action that requires a high degree of accuracy is a critical determinant of success in many individual and team sports. Each sport has different methods for evaluating accuracy, however an overarching goal is to determine whether an object hits its target, or assess the distance by which it misses. However, in some sports accuracy is not readily measureable because an object might not reach a target, i.e. the object is intercepted, or it collides with another object or a person, or an endpoint might not be visible. One example of this is the badminton serve, where the shuttlecock is normally hit by a receiving player before it reaches the ground, its intended endpoint. The goal of one common serve type, the short serve, is to force the opponent into hitting the shuttlecock upward at a steep angle in order to clear the net, allowing a serving player to hit the shuttlecock from a point high above the net from which it is easier to score. The optimal trajectory of the short serve, therefore, is one in which the apex occurs before the shuttlecock crosses the net and results in a steep downward trajectory. To accomplish this, the swing trajectory of the racquet must be accurate itself, which is usually accomplished by use of a short period of swing (i.e. swing length). In practice the analysis of both swing technique and shuttlecock trajectory is usually done subjectively (by the coach), however objective quantification is necessary in order to determine the shuttlecock trajectories and racquet swing techniques that provide the best serve result to allow correct representation of serve accuracy. The main issue is that an objective measurement is needed, and since the shuttlecock doesn’t land on the ground, it makes it difficult to determine serve accuracy with the existing protocols. The broad aims of this Master’s thesis were to (i) develop a new method of measuring accuracy of the short serve;(ii) compare and contrast the technique/s of elite badminton players using principal component analysis; and, (iii) determine the magnitude of variability in the movement patterns of elite players performing the short serve. In the first study (Study I), a specific definition of accuracy was presented that allowed assessment when the endpoint is not reached (i.e. when the shuttlecock does not land on the court). The accuracy of an object’s trajectory is typically evaluated by determining whether it hits a target, or measuring the distance by which it misses. For the badminton short serve, the rules dictate that the shuttlecock must land on or beyond the service line (1.98 m from the net) after traversing the net. However these constraints are insufficient to distinguish poor from good serves; a serve where the shuttlecock clears the net by a small margin but continues and does not reach its apex until after it passes the net might be considered poorer in accuracy (easier for receiver to return) than one in which the shuttlecock reaches its apex before the net even if its height over the net is greater. In this study, short serve trajectories were recorded with and without a receiver present. Two separate data collection sessions and 13 players were tested across both sessions (Session A and B) (age: 23.4 ± 5.1 years, body mass: 73.2 ± 11.1 kg, height: 175 ± 8.6 cm). Data from trials with full trajectory (without an opponent) were used to create a model enabling the prediction of shuttlecock landing. This model was then used to predict the shuttlecock landing point in trials with a receiver, with an important finding being that 69% of serves would have landed on or short of the service line. Thus, receivers might benefit from leaving a majority of serves in competition in order to win the point; servers make the assumption that receivers will return most serves and therefore choose to serve short. Using the new accuracy method, serve accuracy was categorised as accurate, inaccurate, apex good, and clearance good. This provided individual and group accuracy ratings. In Study II a three-dimensional model was developed to examine the upper body kinematics during the badminton short serve. Textbook definitions hold that push-like movement patterns produce trajectories of the highest accuracy, however reducing complexity (i.e. degrees of freedom) is also stated as essential. Nonetheless, these patterns may be mutually exclusive, since push-like patterns may exhibit considerable complexity. The purpose of Study II was to describe the short serve movement patterns used by elite badminton players to determine whether push-like or low-complexity (or both) patterns predominate. Eight participants were recruited from the Senior Australian National Doubles Badminton squad (mean age: 23.4 ±5.1 years, body mass: 73.2 ±11.1 kg, height: 175 ±8.6 cm). Three-dimensional kinematics were measured with an opponent present and analysed using principal component analysis to determine what movement patterns were used in this accuracy-based skill. Results showed that all players adopted a push-like movement pattern, but the most accurate servers also constrained the number of degrees of freedom by allowing movements of the elbow and wrist joints only in a single plane. The main objective of Study III was to understand the role that movement variability plays in a precision-based movement. Little research has been published examining movement variability in sports, specifically in skills that require accuracy. The badminton short serve provided a unique opportunity to examine how elite athletes vary their movement patterns, since it requires precise multi-joint coordination to achieve an accurate serve. Recent research has shown that a rigid or inflexible system may not be good for performance and that it is more appropriate to understand the adaptability of a movement in an ever-changing environment. A three-dimensional motion analysis of eight elite badminton players performing30 short serves with an opponent present to replicate match condition s was conducted. The results identified that players incorporate variability in specific phases of their movements reduce variability at racquet-shuttlecock contact. Higher medio-lateral (transverse plane) variability was displayed in most joint angles across all players. This strategy incorporated variability in the task-redundant dimension (transverse) to reduce variability in the task-relevant dimension (sagittal), which directly impact accuracy of the serve. Variability was also present in the timing of the swing itself, varying the timing of the backswing to reduce the variability at the contact point was a common feature displayed across all subjects, irrespective of whether the serve was accurate or not. Findings suggest elite badminton players use joint and timing variability in a functional capacity. In conclusion, the methods developed to analyse the accuracy and kinematics of an accuracy-based task such as the badminton short serve revealed a greater insight into what defines an accurate serve, and how elite players coordinate and vary their movement to achieve accuracy. The results from Study I suggest that training either with an opponent present or serving on or slightly short of the service line may lead to better serve performance. The results from Study II provide the coach or player with information on the ideal movement patterns for short serve accuracy i.e. reducing the number of degrees of freedom involved (i.e. reduce movement complexity), using a push-like movement, and paying close attention to the movement from the elbow and wrist joints. The final study (Study III) revealed that elite badminton players vary their movement in a plane (transverse) that has less impact on the outcome of the task, thus reducing the variability in the plane (sagittal) that has the larger impact on the serve movement

Motor learning and sensory plasticity in healthy adults and Parkinson's disease

We use multiple sources of sensory information to guide goal-directed movements, such as reaching. When information from multiple modalities (i.e. vision, proprioception) is incongruent, one learns to adapt his or her movements and recalibrate one sense to more closely match the other; simply put, one begins to perceive his/her hand where one sees it. This thesis attempts to better characterize this sensory recalibration (termed 'proprioceptive recalibration') following adaptation to a visuomotor distortion under a variety of contexts, and contributes to the existing literature that describes sensory plasticity associated with motor learning. Specifically, chapter two describes the effect of initial exposure to a visuomotor distortion and the dominance of the hand trained on proprioceptive recalibration. In. this study, participants used their dominant right or non-dominant left hand to reach to targets with visual feedback of hand position that was abruptly rotated clockwise relative to their unseen hand. Proprioceptive recalibration was then assessed and found to be comparable in the two hands and consistent with previous studies employing a gradual perturbation; these findings suggest that neither the initial error signal nor dominance of the hand trained influence recalibration. Chapter three describes how the magnitude of the visuomotor distortion affects the magnitude of recalibration, and how this is related to changes in reach aftereffects. Changes in reach aftereffects and proprioception were measured following adaptation to increasingly misaligned visual hand feedback; these changes were found to increase systematically as a function of the distortion magnitude. However, while these changes were directly correlated with the distortion magnitude, they were not correlated with each other, which suggests that these two processes may be mediated by simultaneous yet separate underlying mechanisms. Chapter four similarly describes how the magnitude of a cross-sensory error signal (generated in the absence of a visuomotor signal derived from goal-directed movement) affects the magnitude of recalibration, and how this is related to changes in reach aftereffects. Participants moved their unseen hand along a grooved path while viewing a cursor that moved towards a target; the position of the path was gradually rotated counter-clockwise with respect to the cursor. Following this cross-sensory adaptation, changes in reach aftereffects and proprioception were both found to saturate at a small distortion as no further changes were observed with training with increasing misalignment. Furthermore, these changes were not correlated with the magnitude of the misalignment. However, in contrast to the findings in chapter three, these changes were correlated with each other, suggesting that the cross-sensory discrepancy drives changes in both reach aftereffects (partially) and proprioception. This study helps to characterize the contribution of different error signals to changes in motor and sensory systems. Lastly, chapter five describes how damage to central nervous system structures integral to sensorimotor integration (i.e. the basal ganglia) affects proprioceptive recalibration. Patients with Parkinson's disease were able to learn to reach to targets with gradually rotated and translated visual feedback of hand positions comparably to healthy older adults. Patients also recalibrated proprioception comparably to healthy older adults, although the trend for greater recalibration in patients suggests that they may depend more on salient visual information of hand position than proprioceptive feedback to guide movement

EEG theta dynamics within frontal and parietal cortices for error processing during reaching movements in a prism adaptation study altering visuo-motor predictive planning

Modulation of frontal midline theta (fmθ) is observed during error commission, but little is known about the role of theta oscillations in correcting motor behaviours. We investigate EEG activity of healthy partipants executing a reaching task under variable degrees of prism-induced visuo-motor distortion and visual occlusion of the initial arm trajectory. This task introduces directional errors of different magnitudes. The discrepancy between predicted and actual movement directions (i.e. the error), at the time when visual feedback (hand appearance) became available, elicits a signal that triggers on-line movement correction. Analysis were performed on 25 EEG channels. For each participant, the median value of the angular error of all reaching trials was used to partition the EEG epochs into high- and low-error conditions. We computed event-related spectral perturbations (ERSP) timelocked either to visual feedback or to the onset of movement correction. ERSP time-locked to the onset of visual feedback showed that fmθ increased in the high-but not in the lowerror condition with an approximate time lag of 200 ms. Moreover, when single epochs were sorted by the degree of motor error, fmθ started to increase when a certain level of error was exceeded and, then, scaled with error magnitude. When ERSP were time-locked to the onset of movement correction, the fmθ increase anticipated this event with an approximate time lead of 50 ms. During successive trials, an error reduction was observed which was associated with indices of adaptations (i.e., aftereffects) suggesting the need to explore if theta oscillations may facilitate learning. To our knowledge this is the first study where the EEG signal recorded during reaching movements was time-locked to the onset of the error visual feedback. This allowed us to conclude that theta oscillations putatively generated by anterior cingulate cortex activation are implicated in error processing in semi-naturalistic motor behaviours. © 2016 Arrighi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Visual perception for basketball shooting

Vision is one of the six sensory systems that we use to know and interact with our environment but has been singled out as the most important form of exteroception for motor control. The reason for this implicit upgrade is probably that many human actions are directed at objects or targets beyond our immediate physical contact. The only link between these objects and us is the pattern of light reflected from their surfaces, and yet we identify and act upon them with great ease. No doubt humans make significant strides in establishing appropriate relations between perceptions and actions at early stages of their development. When my nephew Rodrigo was three months old it took him considerable perseverance and a lot of jerky movements to finally grasp the toy my mother was patiently holding and rambling. But once the relations between perceptions and actions are better established, humans can be incredibly skilful at interacting with distant objects even when the constraints imposed on the interaction are severe and a high degree of precision is required. Like many other sportive tasks, basketball shooting is characterised by tight temporal constraints, limited spatial variation, and high accuracy demands. How basketball players manage to consistently throw a ball through the basket, even if severely challenged by their opponents, is a remarkable feat that has occupied scientists for years, and the present work is but another step in understanding the intricate relations between visual perception and action in such a context where few errors are allowed and few are made. The research reported in the present thesis was conducted to uncover the visual basis of basketball shooting. Basketball shooting consists of throwing a ball on a parabolic flight that passes through a metal rim twice the size of the ball at three metres height. Common shooting types are the free throw and the jump shot. Free throws are taken in less than 10 s from the 4.6 m line without opposition. Jump shots can be taken from anywhere in the field, usually in the presence of opponents, and imply that the ball is released while the player is airborne. Conventional knowledge stipulates that players must see the basket before they shoot. Straightforward as this statement may seem, it can be incorrect in two ways. First, it is not granted that vision is required before the shot, as opposed to during the shot. While vision gathered before the movement may be useful, it may also be insufficient or unnecessary for accurate shooting. This temporal aspect is relevant because it gives insight into the timely interaction between visual perception and action. Second, it is not certain that the player must actually see the basket, as opposed to merely looking at it. The location of the target may be perceived through various information sources, not necessarily retinal ones. This spatial aspect is relevant because it gives insight into the optical basis of goal-directed movement. In what follows we describe in more detail what these temporal and spatial aspects of visual perception andaction consist of, backed up with relevant literature. Next, we briefly review the available literature on the visual perception of basketball shooting and introduce six experiments in which the temporal and spatial aspects of basketball shooting are investigated

Role of reward and punishment in motor learning in health and after stroke

Is the carrot more effective than the stick? Through a combination of behavioural experiments, pharmacological manipulations and computational modelling, this thesis investigates the effects of reward and punishment feedback on adaptive motor learning, in both healthy subjects and stroke survivors. The role of error-based motor learning in neurorehabilitation is still unclear partly because, although it leads to fast and large changes in behaviour, these changes are often short-lived once the perturbation is removed. Nevertheless, recent evidence shows that motivational feedback can increase adaptation to a perturbation and retention of the motor memory in healthy subjects. In the first study presented in this thesis I show that these effects partially apply also to stroke survivors. In particular, reward or punishment-based feedback enhance error-correction during adaptation, and reward increases the retention of the new motor memory in stroke survivors. I then moved to investigate the role of dopamine in error-based motor learning under reward or punishment in healthy young subjects. Consistently with results in stroke patients, reward increased motor memory retention. In addition, I show here that this effect of reward on retention is mediated by dopaminergic pathways. Finally, I investigated if pharmacologic dopaminergic stimulation can potentiate the positive effect of reward on retention in dopamine-deficient subjects, such as older adults. Unfortunately, likely due to the dopaminergic deficit, reward had no effect on elderly participants, and this study failed to show a benefit of dopaminergic stimulation in the elderly. However, this evidence is not sufficient to rule out possible positive effects of pharmacologic dopaminergic stimulation on motor learning in brain injured patients, such as stroke survivors. Taken together, these results represent a step further toward the combined use of reward feedback, pharmacological stimulation and motor learning paradigms in clinical rehabilitation. Indeed, as shown by the qualitative survey presented at the beginning of this thesis, an evidence-based guide to the use of reward and punishment feedback during rehabilitation would be welcome by stroke professionals

The Anchor: Fall 2021, Issue III

The Anchor began in 1887 and was first issued weekly in 1914. Covering national and campus news alike, Hope College’s student-run newspaper has grown over the years to encompass over two-dozen editors, reporters, and staff. For much of The Anchor\u27s history, the latest issue was distributed across campus each Wednesday throughout the academic school year (with few exceptions). As of Fall 2019 The Anchor has moved to monthly print issues and a more frequently updated website. Occasionally, the volume and/or issue numbering is irregular

L’influence de l'anticipation sur les modulations de puissance dans la bande de fréquence bêta durant la préparation du mouvement et L'effet de la variance dans les rétroactions sensorielles sur la rétention à court terme

La production du mouvement est un aspect primordial de la vie qui permet aux organismes vivants d'interagir avec l'environnement. En ce sens, pour être efficaces, tous les mouvements doivent être planifiés et mis à jour en fonction de la complexité et de la variabilité de l'environnement. Des chercheurs du domaine du contrôle moteur ont étudié de manière approfondie les processus de planification et d’adaptation motrice. Puisque les processus de planification et d'adaptation motrice sont influencés par la variabilité de l'environnement, le présent mémoire cherche à fournir une compréhension plus profonde de ces deux processus moteurs à cet égard. La première contribution scientifique présentée ici tire parti du fait que les temps de réaction (TR) sont réduits lorsqu'il est possible d'anticiper l’objectif moteur, afin de déterminer si les modulations de TR associées à l'anticipation spatiale et temporelle sont sous-tendues par une activité préparatoire similaire. Cela a été fait en utilisant l'électroencéphalographie (EEG) de surface pour analyser l'activité oscillatoire dans la bande de fréquence bêta (13 - 30 Hz) au cours de la période de planification du mouvement. Les résultats ont révélé que l'anticipation temporelle était associée à la désynchronisation de la bande bêta au-dessus des régions sensorimotrices controlatérales à la main effectrice, en particulier autour du moment prévu de l'apparition de la cible. L’ampleur de ces modulations était corrélée aux modulations de TR à travers les participants. En revanche, l'anticipation spatiale a augmenté de manière sélective la puissance de la bande bêta au-dessus des régions pariéto-occipitales bilatérales pendant toute la période de planification. Ces résultats suggèrent des états de préparation distinct en fonction de l’anticipation temporelle et spatiale. D’un autre côté, le deuxième projet traite de la façon dont la variabilité de la rétroaction sensorielle interfère avec la rétention à court terme dans l’étude de l’adaptation motrice. Plus précisément, une tâche d'adaptation visuomotrice a été utilisée au cours de laquelle la variance des rotations a été manipulée de manière paramétrique à travers trois groupes, et ce, tout au long de la période d’acquisition. Par la suite, la rétention de cette nouvelle relation visuomotrice a été évaluée. Les résultats ont révélé que, même si le processus d'adaptation était robuste à la manipulation de la variance, la rétention à court terme était altérée par des plus hauts niveaux de variance. Finalement, la discussion a d'abord cherché à intégrer ces deux contributions en revisitant l'interprétation des résultats sous un angle centré sur l'incertitude et en fournissant un aperçu des potentielles représentations internes de l'incertitude susceptibles de sous-tendre les résultats expérimentaux observés. Par la suite, une partie de la discussion a été réservée à la manière dont le champ du contrôle moteur migre de plus en plus vers l’utilisation de tâches et d’approches expérimentales plus complexes, mais écologiques aux dépends des tâches simples, mais quelque peu dénaturées que l’on retrouve dans les laboratoires du domaine. La discussion a été couronnée par une brève proposition allant dans ce sens.Abstract: Motor behavior is a paramount aspect of life that enables the living to interact with the environment through the production of movement. In order to be efficient, movements need to be planned and updated according to the complexity and the ever-changing nature of the environment. Motor control experts have extensively investigated the planning and adaptation processes. Since both motor planning and motor adaptation processes are influenced by variability in the environment, the present thesis seeks to provide a deeper understanding of both these motor processes in this regard. More specifically, the first scientific contribution presented herein leverages the fact that reaction times (RTs) are reduced when the anticipation of the motor goal is possible to elucidate whether the RT modulations associated with temporal and spatial anticipation are subtended by similar preparatory activity. This was done by using scalp electroencephalography (EEG) to analyze the oscillatory activity in the beta frequency band (13 – 30 Hz) during the planning period. Results revealed that temporal anticipation was associated with beta-band desynchronization over contralateral sensorimotor regions, specifically around the expected moment of target onset, the magnitude of which was correlated with RT modulations across participants. In contrast, spatial anticipation selectively increased beta-band power over bilateral parieto-occipital regions during the entire planning period, suggesting that distinct states of preparation are incurred by temporal and spatial anticipation. Additionally, the second project addressed how variance in the sensory feedback interferes with short-term retention of motor adaptation. Specifically, a visuomotor adaptation task was used during which the variance of exposed rotation was parametrically manipulated across three groups, and retention of the adapted visuomotor relationship was assessed. Results revealed that, although the adaptation process was robust to the manipulation of variance, the short-term retention was impaired. The discussion first sought to integrate these two projects by revisiting the interpretation of both projects under the scope of uncertainty and by providing an overview of the internal representation of uncertainty that might subtend the experimental results. Subsequently, a part of the discussion was reserved to allude how the motor control field is transitioning from laboratory-based tasks to more naturalistic paradigms by using approaches to move motor control research toward real-world conditions. The discussion culminates with a brief scientific proposal along those lines

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Investigating the neurobiological changes associated with cerebellar transcranial direct current stimulation (TDCS) using magnetic resonance imaging (MRI)

Anodal cerebellar transcranial direct current stimulation (tDCS) is known to enhance motor learning and it is suggested to hold promise as a therapeutic intervention. However, the neural mechanisms underpinning the effects of cerebellar tDCS are unknown. In addition, it is unclear whether this effect is robust across varying task parameters as if cerebellar tDCS is to be used clinically it must have a consistent effect across a relatively wide range of behaviours. Therefore, I performed four studies to address these questions. In the first three studies, I investigated the neural changes associated with cerebellar tDCS using magnetic resonance spectroscopy (MRS) and resting state functional magnetic resonance imaging (fMRI). My goal was to understand how cerebellar tDCS affected the metabolites within the cerebellum and functional connectivity between the cerebellum and distant brain areas. In addition, I wanted to understand if individual differences in how cerebellar tDCS influenced visuomotor adaptation could be explained by the effect tDCS had on neurobiology. Therefore, healthy participants underwent 3 sessions in which they received concurrent anodal cerebellar tDCS during visuomotor adaptation, MRS and resting state fMRI. I found that in 21% of participants cerebellar tDCS caused enhanced visuomotor adaptation, a decrease in GABA and increase in functional connectivity between the cerebellum and parietal cortex. This work suggests an ‘all-or-nothing’ type effect of cerebellar tDCS. In my final study, I examined the consistency of the cerebellar tDCS effect on visuomotor adaptation across a wide range of task parameters which were systematically varied. Each experiment examined whether cerebellar tDCS had a positive effect on adaptation when a unique feature of the task was altered. I found cerebellar tDCS to have an inconsistent effect on visuomotor adaptation. I conclude that such inconsistencies could be dependent on the amount of participants in each group that are receptive to cerebellar tDCS and suggest that at the very least it warrants substantially large sample size in cerebellar tDCS studies