Karl Newell | The University of Georgia (original) (raw)

Papers by Karl Newell

Acta psychologica, 2018

The practice of a motor task has been conceptualized as a process of search through a perceptual-... more The practice of a motor task has been conceptualized as a process of search through a perceptual-motor workspace. The present study investigated the influence of information and task constraints on the search strategy as reflected in the sequential relations of the outcome in a discrete movement virtual projectile task. The results showed that the relation between the changes of trial-to-trial movement outcome to performance level was dependent on the landscape of the task dynamics and the influence of inherent variability. Furthermore, the search was in a constrained parameter region of the perceptual-motor workspace that depended on the task constraints. These findings show that there is not a single function of trial-to-trial change over practice but rather that local search strategies (proportional, discontinuous, constant) adapt to the level of performance and the confluence of constraints to action.

Ecological Psychology, 2018

We investigated whether perceptual learning via dynamic touch can facilitate the discovery of too... more We investigated whether perceptual learning via dynamic touch can facilitate the discovery of tooling affordances. Twelve blindfolded participants manipulated two structurally identical aluminum objects consisting of a blade and a shaft; one object was seven and a half times heavier than and twice as large as the other object. Flexions/extensions at two joints in the shaft changed the configuration and functionality of each object. A rigid shaft (one of four possible configurations) rendered each object a functional hoe. The number of changes in the configuration produced prior to determining that the grasped object had been rendered a functional hoe greatly exceeded the number of possible configurations and declined with experience, whereas the rate of change in configuration increased with experience. Inertial properties specifically support perception via dynamic touch and explained the observed differences in actions with the two objects. These findings demonstrate that perceptual learning via dynamic touch can facilitate the discovery of tooling affordances.

Entropy

The preservation of static balance in both upright- and hand-stance is maintained by the projecti... more The preservation of static balance in both upright- and hand-stance is maintained by the projection of center of mass (CM) motion within the region of stability at the respective base of support. This study investigated, from a degrees of freedom (DF) perspective, whether the stability of the CM in both upright- and hand-stances was predicted by the respective dispersion and time-dependent regularity of joint (upright stance—ankle, knee, hip, shoulder, neck; hand stance—wrist, elbow, shoulder, neck) angle and position. Full body three-dimensional (3D) kinematic data were collected on 10 advanced level junior female gymnasts during 30 s floor upright- and hand-stands. For both stances the amount of the dispersion of joint angle and sway motion was higher than that of the CM and center of pressure (CP) with an inverse relation to time-dependent irregularity (SampEn). In upright-standing the variability of neck motion in the anterior–posterior direction was significantly greater than t...

ISBS Proceedings Archive, 2021

The goal of a handstand, a fundamental skill in gymnastics, is to maintain a balanced stance by c... more The goal of a handstand, a fundamental skill in gymnastics, is to maintain a balanced stance by controlling center of mass (COM) position. Successful handstands predominantly use wrist torque to control the COM in the anterior-posterior (AP) plane. The aim of this study was to determine the underlying motor control mechanisms necessary to maintain a strong handstand stance through analysis of joint angle and COM position variability. Full body 3D kinematic data were collected on three competitive level gymnasts during 30 s floor handstands. Variability of joint angles were consistently higher than the center of mass, demonstrating that joints self-organize in a motor control strategy to produce torques in order to control the COM. Using multiple linear regression analysis, it was found that shoulder flexion/extension variability was the largest contributor to controlling the COM in both the medio-lateral (ML) and AP planes.

The purpose of this study was to identify parameters that are associated with more successful mot... more The purpose of this study was to identify parameters that are associated with more successful motor control during handstand performance. For two groups of gymnasts, ‘less skilled’, who were able to hold handstands for 4 to 6s, and ‘more skilled’, who held handstands in excess of 10s, centre of mass (CoM) and centre of pressure (CoP) motion during the initial 3s of the handstand stability phase were analysed, as well as the 6 to 9s stabilised period for the more skilled gymnasts (balance phase). Time-space, timefrequency, CoM-CoP coherence, Hurst Exponent and CoM-CoP causality were investigated in anterior-posterior (AP) and medio-lateral (ML) directions. Characteristics of CoM and CoP for more and less skilled gymnasts were found to be directionally dependent (AP and ML). Nonlinear and frequency domain measures distinguished skill levels to a greater extent than time-space domain measures. The study findings shed light on the subtleties and complexities of the mechanics and dynamic...

Journal of Functional Morphology and Kinesiology, 2021

The present study examined how prevalent methods for determining maximal voluntary contraction (M... more The present study examined how prevalent methods for determining maximal voluntary contraction (MVC) impact the experimentally derived functions of graded force-force variability. Thirty-two young healthy subjects performed continuous isometric force tracking (20 s trials) at 10 target percentages (5–95% MVC) normalized to a conventional discrete-point (n = 16), or sustained (n = 16) MVC calculation. Distinct rates and magnitudes of change were observed for absolute variability (standard deviation (SD), root mean squared error (RMSE)), tracking error (RMSE, constant error (CE)), and complexity (detrended fluctuation analysis (DFA)) (all p < 0.05) of graded force fluctuations between the MVC groups. Differential performance strategies were observed beyond ~65% MVC, with the discrete-point group minimizing their SD at force values below that of the criterion target (higher CE/RMSE). Moreover, the sustained group’s capacity to minimize SD/RMSE/CE corresponded to a more complex struc...

Neuroscience Letters, 2020

Journal of Motor Learning and Development, 2020

A review and synthesis of the literature on the learning and development of motor skills supports... more A review and synthesis of the literature on the learning and development of motor skills supports the postulation that whether a motor skill can be deemed fundamental is dependent on the collective presence of three conditions: (i) uniqueness to the movement pattern and/or outcome; (ii) near universality of the functional outcome in the healthy population; (iii) capacity to act as an antecedent influence supporting generalization to a large and broad set of perceptual-motor skills. Within this framework, it is proposed that the infant motor development sequence underpinning upright posture (e.g., sitting, bipedal standing), locomotion (e.g., walking, running), and object-interaction (e.g., grasping) represents the minimum set of fundamental motor skills from which all other skills evolve with over the lifespan. This position is in contrast to the views of many students of motor development and learning who describe numerous skills that typically emerge in the ∼2- to 18-year-old rang...

PloS one, 2017

There is preliminary evidence that there are several types of submovements in movement aiming tha... more There is preliminary evidence that there are several types of submovements in movement aiming that reflect different processes of control and can result from particular task constraints. The purpose of the study was to investigate the effect of movement space and time task criteria on the prevalence of different submovement control characteristics in discrete aiming. Twelve participants completed 3 distance x 5 time conditions each with 100 trials in a target-aiming movement task. The kinematic structure of the trajectory determined the prevalence of 5 submovement types (none; pre-peak, post-peak movement velocity; undershoot, overshoot). The findings showed that the overall number of submovements increased in the slower space-time conditions and was predominantly characterized by post-peak trajectory submovements rather than discrete overshoot submovements. Overshoot submovements were more frequent in the high average movement velocity and short time duration conditions. We conclud...

Human movement science, 2018

The purpose of the study was to examine the macroscopic dynamics of the longswing through a limit... more The purpose of the study was to examine the macroscopic dynamics of the longswing through a limit cycle analysis of the motion of the center of mass (CM) as a function of skill level. One elite international, five gymnasts able to perform release and regrasp skills, five gymnasts unable to perform release and regrasp skills, and five novice gymnasts each performed four consecutive longswings on a high bar. Kinematic data were collected to facilitate the calculation of the center of mass position of the performer during swinging. Poincare plots were used to explore the limit cycle dynamics of the center of mass movement. The attractor dynamic was very close to a one-dimensional limit cycle for the elite (D = 1.18) but higher for the release and regrasp group (D = 1.35 ± 0.06) and non-release and regrasp group (D = 1.37 ± 0.07). The novice dynamic was characterized by a two-dimensional limit cycle (D = 2.49 ± 0.28) that also had more variability and lower determinism. In the frequency...

Journal of motor behavior, Jan 29, 2018

Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We inv... more Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We investigated the space-time account of Hancock and Newell (1985) and the hypothesis of complementarity between the four moments of the error distribution in space and time. Twelve participants performed 15 conditions in a line drawing task composed of different spatial (10, 20, and 30 cm) and temporal (250 to 2,500 ms) criteria. The results showed that all moments of distributions changed systematically between conditions but there were some departures from the Hancock and Newell predictions. In contrast, individual analysis revealed the complementarity of the spatial and temporal error including a trade-off between the four moments of error. These findings support a complementary space-time account of movement speed and accuracy.

Journal of motor behavior, Jan 14, 2018

This study was designed to examine the effect of increasing age and type 2 diabetes on the averag... more This study was designed to examine the effect of increasing age and type 2 diabetes on the average responses and inter- and intraindividual variability of falls risk, reaction time, strength, and walking speed for healthy older adults and older persons with type 2 diabetes (T2DM). Seventy-five older individuals (controls) and 75 persons with T2DM aged between 50 and 79 years participated in the study. Assessments of falls risk, reaction time (RT), knee extension strength, and walking speed were conducted. The results revealed that advancing age for both control and T2DM groups was reflected by a progressive increase in falls risk, decreased leg strength and a decline (i.e., slowing) of reactions and gait speed. Conversely, the level of intraindividual variability for the RT, strength and gait measures increased with increasing age for both groups, with T2DM persons tending to be more variable compared to the healthy controls of similar age. In contrast to the intraindividual changes...

Human movement science, 2018

It is generally held that transfer of practice is a function of the similarity between the origin... more It is generally held that transfer of practice is a function of the similarity between the originally learned task and the subsequent transfer task. In the present paper, we examine the proposition that individuals learn a coordination function that is specific to the task, individual and yet generalizable, depending on the characteristics of the learned coordination function. Seventeen individuals performed for 5 days the task of learning to throw for accuracy to a target and then performed two transfer tests that differed in terms of the axis of variation that individuals could vary in task outcome. The results showed individual differences in terms of the acquired movement pattern even when a similar performance was achieved. Additionally, the coordination function characterized by principal component analysis and its projection into the landing plane predicted performance in the transfer tests. These results support the proposition that individuals learn a coordination function ...

Sports biomechanics, Jan 18, 2018

A case study visualisation approach to examining the coordination and variability of multiple int... more A case study visualisation approach to examining the coordination and variability of multiple interacting segments is presented using a whole-body gymnastic skill as the task example. One elite male gymnast performed 10 trials of 10 longswings whilst three-dimensional locations of joint centres were tracked using a motion analysis system. Segment angles were used to define coupling between the arms and trunk, trunk and thighs and thighs and shanks. Rectified continuous relative phase profiles for each interacting couple for 80 longswings were produced. Graphical representations of coordination couplings are presented that include the traditional single coupling, followed by the relational dynamics of two couplings and finally three couplings simultaneously plotted. This method highlights the power of visualisation of movement dynamics and identifies properties of the global interacting segmental couplings that a more formal analysis may not reveal. Visualisation precedes and informs...

Journal of athletic training, 2018

Subclinical postural-control changes may persist beyond the point when athletes are considered ... more Subclinical postural-control changes may persist beyond the point when athletes are considered clinically recovered postconcussion. To compare postural-control performance between former high school football players with or without a history of concussion using linear and nonlinear metrics. Case-control study. Clinical research laboratory. A total of 11 former high school football players (age range, 45-60 years) with 2 or more concussions and 11 age- and height-matched former high school football players without a history of concussion. No participant had college or professional football experience. Participants completed the Sensory Organization Test. We compared postural control (linear: equilibrium scores; nonlinear: sample and multiscale entropy) between groups using a 2 × 3 analysis of variance across conditions 4 to 6 (4: eyes open, sway-referenced platform; 5: eyes closed, sway-referenced platform; 6: eyes open, sway-referenced surround and platform). We observ...

Motor Control, 2007

This experiment examined the magnitude and structure of force variability in isometric index fing... more This experiment examined the magnitude and structure of force variability in isometric index finger force production tasks at 5, 15, 25, 35, 45, 55, 65, 75, 85, and 95% of maximal force in two different finger orientations. In the finger flexion task, the participants generated a downward isometric force through index finger flexion. In the finger abduction task, isometric force was generated by adducting the index finger (mediolateral motion of the middle finger and forearm were restricted). The task-related, normal force (Fz) and tangential forces (Fx and Fy) were collected with a three-dimensional force transducer. The standard deviation (SD) of the task-related force output (Fz) increased exponentially with force level. With increasing force level, approximate entropy (ApEn, a measure of irregularity) of Fz followed an inverted-U function for finger flexion, but decreased linearly in finger abduction. However, changes in the ApEn of the tangential forces were generally opposite ...

Attention, Perception, & Psychophysics, 2017

Rotational inertia-a mechanical quantity that describes the differential resistance of an object ... more Rotational inertia-a mechanical quantity that describes the differential resistance of an object to angular acceleration in different directions-has been shown to support perception of the properties of that object through dynamic touch (wielding). The goal of the present study was to examine if perception of the length of an object through dynamic touch depends on its rotational inertia, independent of the medium in which it is wielded. The participants (n = 14) wielded 12 different objects held in air or completely immersed in water and reported perceived lengths of those objects. Each object consisted of a rod of a particular density with a particular number of stacked steel rings attached at a particular location along its length. Perceived length was invariant across medium. In addition, a singlevalued function of the major eigenvalue, I 1 , and the minor eigenvalue, I 3 , of the rotational inertia, I, of the 12 objects predicted the perceived lengths of those objects in both air and water, and the perceived lengths were invariant across the two media. These results support the hypothesis that the informational support for perception of the length of an object through dynamic touch is invariant across changes in the medium.

Frontiers in Integrative Neuroscience, 2017

PloS one, 2017

Traditionally, gait analysis has been centered on the idea of average behavior and normality. On ... more Traditionally, gait analysis has been centered on the idea of average behavior and normality. On one hand, clinical diagnoses and therapeutic interventions typically assume that average gait patterns remain constant over time. On the other hand, it is well known that all our movements are accompanied by a certain amount of variability, which does not allow us to make two identical steps. The purpose of this study was to examine changes in the intra-individual gait patterns across different time-scales (i.e., tens-of-mins, tens-of-hours). Nine healthy subjects performed 15 gait trials at a self-selected speed on 6 sessions within one day (duration between two subsequent sessions from 10 to 90 mins). For each trial, time-continuous ground reaction forces and lower body joint angles were measured. A supervised learning model using a kernel-based discriminant regression was applied for classifying sessions within individual gait patterns. Discernable characteristics of intra-individual ...

PloS one, 2016

This investigation examined the effects of slope of the surface of support (35°, 30°, 20°, 10° Fa... more This investigation examined the effects of slope of the surface of support (35°, 30°, 20°, 10° Facing(Toe) Down, 0° Flat and 10°, 20°, 25° Facing (Toe) Up) and postural orientation on the margins of postural stability in quiet standing of young adults. The findings showed that the center of pressure-CoP (displacement, area and length) had least motion at the baseline (0° Flat) platform condition that progressively increased as a function of platform angle in both facing up and down directions. The virtual time to collision (VTC) dynamics revealed that the spatio-temporal margins to the functional stability boundary were progressively smaller and the VTC time series also more regular (SampEn-Sample Entropy) as slope angle increased. Surface slope induces a restricted stability region with lower dimension VTC dynamics that is more constrained when postural orientation is facing down the slope. These findings provide further evidence that VTC acts as a control variable in standing post...

Acta psychologica, 2018

The practice of a motor task has been conceptualized as a process of search through a perceptual-... more The practice of a motor task has been conceptualized as a process of search through a perceptual-motor workspace. The present study investigated the influence of information and task constraints on the search strategy as reflected in the sequential relations of the outcome in a discrete movement virtual projectile task. The results showed that the relation between the changes of trial-to-trial movement outcome to performance level was dependent on the landscape of the task dynamics and the influence of inherent variability. Furthermore, the search was in a constrained parameter region of the perceptual-motor workspace that depended on the task constraints. These findings show that there is not a single function of trial-to-trial change over practice but rather that local search strategies (proportional, discontinuous, constant) adapt to the level of performance and the confluence of constraints to action.

Ecological Psychology, 2018

We investigated whether perceptual learning via dynamic touch can facilitate the discovery of too... more We investigated whether perceptual learning via dynamic touch can facilitate the discovery of tooling affordances. Twelve blindfolded participants manipulated two structurally identical aluminum objects consisting of a blade and a shaft; one object was seven and a half times heavier than and twice as large as the other object. Flexions/extensions at two joints in the shaft changed the configuration and functionality of each object. A rigid shaft (one of four possible configurations) rendered each object a functional hoe. The number of changes in the configuration produced prior to determining that the grasped object had been rendered a functional hoe greatly exceeded the number of possible configurations and declined with experience, whereas the rate of change in configuration increased with experience. Inertial properties specifically support perception via dynamic touch and explained the observed differences in actions with the two objects. These findings demonstrate that perceptual learning via dynamic touch can facilitate the discovery of tooling affordances.

Entropy

The preservation of static balance in both upright- and hand-stance is maintained by the projecti... more The preservation of static balance in both upright- and hand-stance is maintained by the projection of center of mass (CM) motion within the region of stability at the respective base of support. This study investigated, from a degrees of freedom (DF) perspective, whether the stability of the CM in both upright- and hand-stances was predicted by the respective dispersion and time-dependent regularity of joint (upright stance—ankle, knee, hip, shoulder, neck; hand stance—wrist, elbow, shoulder, neck) angle and position. Full body three-dimensional (3D) kinematic data were collected on 10 advanced level junior female gymnasts during 30 s floor upright- and hand-stands. For both stances the amount of the dispersion of joint angle and sway motion was higher than that of the CM and center of pressure (CP) with an inverse relation to time-dependent irregularity (SampEn). In upright-standing the variability of neck motion in the anterior–posterior direction was significantly greater than t...

ISBS Proceedings Archive, 2021

The goal of a handstand, a fundamental skill in gymnastics, is to maintain a balanced stance by c... more The goal of a handstand, a fundamental skill in gymnastics, is to maintain a balanced stance by controlling center of mass (COM) position. Successful handstands predominantly use wrist torque to control the COM in the anterior-posterior (AP) plane. The aim of this study was to determine the underlying motor control mechanisms necessary to maintain a strong handstand stance through analysis of joint angle and COM position variability. Full body 3D kinematic data were collected on three competitive level gymnasts during 30 s floor handstands. Variability of joint angles were consistently higher than the center of mass, demonstrating that joints self-organize in a motor control strategy to produce torques in order to control the COM. Using multiple linear regression analysis, it was found that shoulder flexion/extension variability was the largest contributor to controlling the COM in both the medio-lateral (ML) and AP planes.

The purpose of this study was to identify parameters that are associated with more successful mot... more The purpose of this study was to identify parameters that are associated with more successful motor control during handstand performance. For two groups of gymnasts, ‘less skilled’, who were able to hold handstands for 4 to 6s, and ‘more skilled’, who held handstands in excess of 10s, centre of mass (CoM) and centre of pressure (CoP) motion during the initial 3s of the handstand stability phase were analysed, as well as the 6 to 9s stabilised period for the more skilled gymnasts (balance phase). Time-space, timefrequency, CoM-CoP coherence, Hurst Exponent and CoM-CoP causality were investigated in anterior-posterior (AP) and medio-lateral (ML) directions. Characteristics of CoM and CoP for more and less skilled gymnasts were found to be directionally dependent (AP and ML). Nonlinear and frequency domain measures distinguished skill levels to a greater extent than time-space domain measures. The study findings shed light on the subtleties and complexities of the mechanics and dynamic...

Journal of Functional Morphology and Kinesiology, 2021

The present study examined how prevalent methods for determining maximal voluntary contraction (M... more The present study examined how prevalent methods for determining maximal voluntary contraction (MVC) impact the experimentally derived functions of graded force-force variability. Thirty-two young healthy subjects performed continuous isometric force tracking (20 s trials) at 10 target percentages (5–95% MVC) normalized to a conventional discrete-point (n = 16), or sustained (n = 16) MVC calculation. Distinct rates and magnitudes of change were observed for absolute variability (standard deviation (SD), root mean squared error (RMSE)), tracking error (RMSE, constant error (CE)), and complexity (detrended fluctuation analysis (DFA)) (all p < 0.05) of graded force fluctuations between the MVC groups. Differential performance strategies were observed beyond ~65% MVC, with the discrete-point group minimizing their SD at force values below that of the criterion target (higher CE/RMSE). Moreover, the sustained group’s capacity to minimize SD/RMSE/CE corresponded to a more complex struc...

Neuroscience Letters, 2020

Journal of Motor Learning and Development, 2020

A review and synthesis of the literature on the learning and development of motor skills supports... more A review and synthesis of the literature on the learning and development of motor skills supports the postulation that whether a motor skill can be deemed fundamental is dependent on the collective presence of three conditions: (i) uniqueness to the movement pattern and/or outcome; (ii) near universality of the functional outcome in the healthy population; (iii) capacity to act as an antecedent influence supporting generalization to a large and broad set of perceptual-motor skills. Within this framework, it is proposed that the infant motor development sequence underpinning upright posture (e.g., sitting, bipedal standing), locomotion (e.g., walking, running), and object-interaction (e.g., grasping) represents the minimum set of fundamental motor skills from which all other skills evolve with over the lifespan. This position is in contrast to the views of many students of motor development and learning who describe numerous skills that typically emerge in the ∼2- to 18-year-old rang...

PloS one, 2017

There is preliminary evidence that there are several types of submovements in movement aiming tha... more There is preliminary evidence that there are several types of submovements in movement aiming that reflect different processes of control and can result from particular task constraints. The purpose of the study was to investigate the effect of movement space and time task criteria on the prevalence of different submovement control characteristics in discrete aiming. Twelve participants completed 3 distance x 5 time conditions each with 100 trials in a target-aiming movement task. The kinematic structure of the trajectory determined the prevalence of 5 submovement types (none; pre-peak, post-peak movement velocity; undershoot, overshoot). The findings showed that the overall number of submovements increased in the slower space-time conditions and was predominantly characterized by post-peak trajectory submovements rather than discrete overshoot submovements. Overshoot submovements were more frequent in the high average movement velocity and short time duration conditions. We conclud...

Human movement science, 2018

The purpose of the study was to examine the macroscopic dynamics of the longswing through a limit... more The purpose of the study was to examine the macroscopic dynamics of the longswing through a limit cycle analysis of the motion of the center of mass (CM) as a function of skill level. One elite international, five gymnasts able to perform release and regrasp skills, five gymnasts unable to perform release and regrasp skills, and five novice gymnasts each performed four consecutive longswings on a high bar. Kinematic data were collected to facilitate the calculation of the center of mass position of the performer during swinging. Poincare plots were used to explore the limit cycle dynamics of the center of mass movement. The attractor dynamic was very close to a one-dimensional limit cycle for the elite (D = 1.18) but higher for the release and regrasp group (D = 1.35 ± 0.06) and non-release and regrasp group (D = 1.37 ± 0.07). The novice dynamic was characterized by a two-dimensional limit cycle (D = 2.49 ± 0.28) that also had more variability and lower determinism. In the frequency...

Journal of motor behavior, Jan 29, 2018

Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We inv... more Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We investigated the space-time account of Hancock and Newell (1985) and the hypothesis of complementarity between the four moments of the error distribution in space and time. Twelve participants performed 15 conditions in a line drawing task composed of different spatial (10, 20, and 30 cm) and temporal (250 to 2,500 ms) criteria. The results showed that all moments of distributions changed systematically between conditions but there were some departures from the Hancock and Newell predictions. In contrast, individual analysis revealed the complementarity of the spatial and temporal error including a trade-off between the four moments of error. These findings support a complementary space-time account of movement speed and accuracy.

Journal of motor behavior, Jan 14, 2018

This study was designed to examine the effect of increasing age and type 2 diabetes on the averag... more This study was designed to examine the effect of increasing age and type 2 diabetes on the average responses and inter- and intraindividual variability of falls risk, reaction time, strength, and walking speed for healthy older adults and older persons with type 2 diabetes (T2DM). Seventy-five older individuals (controls) and 75 persons with T2DM aged between 50 and 79 years participated in the study. Assessments of falls risk, reaction time (RT), knee extension strength, and walking speed were conducted. The results revealed that advancing age for both control and T2DM groups was reflected by a progressive increase in falls risk, decreased leg strength and a decline (i.e., slowing) of reactions and gait speed. Conversely, the level of intraindividual variability for the RT, strength and gait measures increased with increasing age for both groups, with T2DM persons tending to be more variable compared to the healthy controls of similar age. In contrast to the intraindividual changes...

Human movement science, 2018

It is generally held that transfer of practice is a function of the similarity between the origin... more It is generally held that transfer of practice is a function of the similarity between the originally learned task and the subsequent transfer task. In the present paper, we examine the proposition that individuals learn a coordination function that is specific to the task, individual and yet generalizable, depending on the characteristics of the learned coordination function. Seventeen individuals performed for 5 days the task of learning to throw for accuracy to a target and then performed two transfer tests that differed in terms of the axis of variation that individuals could vary in task outcome. The results showed individual differences in terms of the acquired movement pattern even when a similar performance was achieved. Additionally, the coordination function characterized by principal component analysis and its projection into the landing plane predicted performance in the transfer tests. These results support the proposition that individuals learn a coordination function ...

Sports biomechanics, Jan 18, 2018

A case study visualisation approach to examining the coordination and variability of multiple int... more A case study visualisation approach to examining the coordination and variability of multiple interacting segments is presented using a whole-body gymnastic skill as the task example. One elite male gymnast performed 10 trials of 10 longswings whilst three-dimensional locations of joint centres were tracked using a motion analysis system. Segment angles were used to define coupling between the arms and trunk, trunk and thighs and thighs and shanks. Rectified continuous relative phase profiles for each interacting couple for 80 longswings were produced. Graphical representations of coordination couplings are presented that include the traditional single coupling, followed by the relational dynamics of two couplings and finally three couplings simultaneously plotted. This method highlights the power of visualisation of movement dynamics and identifies properties of the global interacting segmental couplings that a more formal analysis may not reveal. Visualisation precedes and informs...

Journal of athletic training, 2018

Subclinical postural-control changes may persist beyond the point when athletes are considered ... more Subclinical postural-control changes may persist beyond the point when athletes are considered clinically recovered postconcussion. To compare postural-control performance between former high school football players with or without a history of concussion using linear and nonlinear metrics. Case-control study. Clinical research laboratory. A total of 11 former high school football players (age range, 45-60 years) with 2 or more concussions and 11 age- and height-matched former high school football players without a history of concussion. No participant had college or professional football experience. Participants completed the Sensory Organization Test. We compared postural control (linear: equilibrium scores; nonlinear: sample and multiscale entropy) between groups using a 2 × 3 analysis of variance across conditions 4 to 6 (4: eyes open, sway-referenced platform; 5: eyes closed, sway-referenced platform; 6: eyes open, sway-referenced surround and platform). We observ...

Motor Control, 2007

This experiment examined the magnitude and structure of force variability in isometric index fing... more This experiment examined the magnitude and structure of force variability in isometric index finger force production tasks at 5, 15, 25, 35, 45, 55, 65, 75, 85, and 95% of maximal force in two different finger orientations. In the finger flexion task, the participants generated a downward isometric force through index finger flexion. In the finger abduction task, isometric force was generated by adducting the index finger (mediolateral motion of the middle finger and forearm were restricted). The task-related, normal force (Fz) and tangential forces (Fx and Fy) were collected with a three-dimensional force transducer. The standard deviation (SD) of the task-related force output (Fz) increased exponentially with force level. With increasing force level, approximate entropy (ApEn, a measure of irregularity) of Fz followed an inverted-U function for finger flexion, but decreased linearly in finger abduction. However, changes in the ApEn of the tangential forces were generally opposite ...

Attention, Perception, & Psychophysics, 2017

Rotational inertia-a mechanical quantity that describes the differential resistance of an object ... more Rotational inertia-a mechanical quantity that describes the differential resistance of an object to angular acceleration in different directions-has been shown to support perception of the properties of that object through dynamic touch (wielding). The goal of the present study was to examine if perception of the length of an object through dynamic touch depends on its rotational inertia, independent of the medium in which it is wielded. The participants (n = 14) wielded 12 different objects held in air or completely immersed in water and reported perceived lengths of those objects. Each object consisted of a rod of a particular density with a particular number of stacked steel rings attached at a particular location along its length. Perceived length was invariant across medium. In addition, a singlevalued function of the major eigenvalue, I 1 , and the minor eigenvalue, I 3 , of the rotational inertia, I, of the 12 objects predicted the perceived lengths of those objects in both air and water, and the perceived lengths were invariant across the two media. These results support the hypothesis that the informational support for perception of the length of an object through dynamic touch is invariant across changes in the medium.

Frontiers in Integrative Neuroscience, 2017

PloS one, 2017

Traditionally, gait analysis has been centered on the idea of average behavior and normality. On ... more Traditionally, gait analysis has been centered on the idea of average behavior and normality. On one hand, clinical diagnoses and therapeutic interventions typically assume that average gait patterns remain constant over time. On the other hand, it is well known that all our movements are accompanied by a certain amount of variability, which does not allow us to make two identical steps. The purpose of this study was to examine changes in the intra-individual gait patterns across different time-scales (i.e., tens-of-mins, tens-of-hours). Nine healthy subjects performed 15 gait trials at a self-selected speed on 6 sessions within one day (duration between two subsequent sessions from 10 to 90 mins). For each trial, time-continuous ground reaction forces and lower body joint angles were measured. A supervised learning model using a kernel-based discriminant regression was applied for classifying sessions within individual gait patterns. Discernable characteristics of intra-individual ...

PloS one, 2016

This investigation examined the effects of slope of the surface of support (35°, 30°, 20°, 10° Fa... more This investigation examined the effects of slope of the surface of support (35°, 30°, 20°, 10° Facing(Toe) Down, 0° Flat and 10°, 20°, 25° Facing (Toe) Up) and postural orientation on the margins of postural stability in quiet standing of young adults. The findings showed that the center of pressure-CoP (displacement, area and length) had least motion at the baseline (0° Flat) platform condition that progressively increased as a function of platform angle in both facing up and down directions. The virtual time to collision (VTC) dynamics revealed that the spatio-temporal margins to the functional stability boundary were progressively smaller and the VTC time series also more regular (SampEn-Sample Entropy) as slope angle increased. Surface slope induces a restricted stability region with lower dimension VTC dynamics that is more constrained when postural orientation is facing down the slope. These findings provide further evidence that VTC acts as a control variable in standing post...