Models of Video Feedback for Youth Athletes Performing an American Football Tackle.

CONTEXT: Video feedback is an expeditious method for improving athlete safety when performing activities with an inherent risk of injury. Providing appropriate and validated feedback during tackling training in American football may be a mechanism for athletes to learn safe tackling performance. OBJECTIVE: To determine the effect of video feedback in the instruction of tackling form. DESIGN: Controlled laboratory study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 32 youth football athletes (28 boys, 4 girls; age = 11.8 ± 0.8 years) participated in 1 day of training. Of those, 14 participants completed 2 additional days of training and a 48-hour retention and transfer test. INTERVENTION(S): Video feedback using self as model, expert as model, combined self and expert model, and oral feedback to promote safe tackling performance in a laboratory environment. MAIN OUTCOME MEASURE(S): Shoulder extension, cervical extension, trunk angle, pelvis height, and step length by training block and over time. RESULTS: For the 1-day training group, main effects for time were observed for shoulder extension (P < .01), cervical extension (P = .01), pelvis height (P < .01), and step length (P < .01), with better performance for pelvis height and step length after combined feedback. For the 3-day training group, main effects of time were identified in pelvis height (P < .01) and step length (P < .01), with combined feedback showing better performance than other methods in shoulder extension and pelvis height. Combined feedback resulted in better performance compared with its component parts and oral feedback alone. In the combined model, participants viewed both their performance and the expert model, enabling them to see the difference between current and required performance. CONCLUSIONS: Combined feedback may be superior to other forms of feedback in improving movement performance. This effect can be generalized across disciplines that provide instruction and feedback in movement.

Spatio-Temporal Flexibility of Attention Inferred from Drivers' Steering Movements.

Participants attempted to center a cursor on a video display of a winding roadway with a rate control system. Fourier analysis of their steering movements in response to sinusoidal perturbations of the roadway revealed how much attention they allocated to different roadway preview locations. We compared a full 1.0 s of preview with preview restricted to a narrow slit around 0.3 s or 0.6 s. Participants were able to flexibly shift their attention to either slit. However, they performed better in terms of root-mean-squared error, velocity error, and acceleration error with the fuller view. They concentrated their attention over a range from 0.1 s to 0.3 s of preview in a manner qualitatively consistent with Miller's optimal control model.

Drivers' Spatio-Temporal Attentional Distributions Are Influenced by Vehicle Dynamics and Displayed Point of View.

OBJECTIVE: The aim of this study is to measure drivers' attention to preview and their velocity and acceleration tracking error to evaluate two- and three-dimensional displays for following a winding roadway. BACKGROUND: Display perturbation techniques and Fourier analysis of steering movements can be used to infer drivers' spatio-temporal distribution of attention to preview. Fourier analysis of tracking error time histories provides measures of position, velocity, and acceleration error. METHOD: Participants tracked a winding roadway with 1 s of preview in low-fidelity driving simulations. Position and rate-aided vehicle dynamics were paired with top-down and windshield displays of the roadway. RESULTS: For both vehicle dynamics, tracking was smoother with the windshield display. This display emphasizes nearer preview positions and has a closer correspondence to the control-theoretic optimal attentional distributions for these tasks than the top-down display. This correspondence is interpreted as a form of stimulus-response compatibility. The position error and attentional signal-to-noise ratios did not differ between the two displays with position control, but with more complex rate-aided control much higher position error and much lower attentional signal-to-noise ratios occurred with the top-down display. CONCLUSION: Display-driven influences on the distribution of attention may facilitate tracking with preview when they are similar to optimal attentional distributions derived from control theory. APPLICATION: Display perturbation techniques can be used to assess spatially distributed attention to evaluate displays and secondary tasks in the context of driving. This methodology can supplement eye movement measurements to determine what information is guiding drivers' actions.

The bottleneck of the psychological refractory period effect involves timing of response initiation rather than response selection.

The Psychological Refractory Period (PRP) effect is a delay in responding that is assumed to be caused by a bottleneck that prevents preparation of a second action until preparation of the previous action has been completed. The bottleneck is usually attributed to a limitation that prevents concurrent selection of two responses. However, evidence reviewed here challenges this selection interpretation. We propose instead that the bottleneck is due to a process that programs the timing of response initiation, and which must be completed immediately prior to responding. This hypothesis is based on two conclusions from recent developments in research, which includes findings from paradigms that do not involve the PRP. The first conclusion is from studies involving the startle response and single-task simple (precued) reaction time; these studies indicate that programming the timing of response onsets is needed to enable response initiation. This programing takes longer for more complicated timing, and must be delayed until just prior to responding. The second conclusion is from studies of concurrent rhythmic movements demonstrating that the representation of timing is restricted to one temporal frame unless very rapid performance enables parallel timing. These findings reveal limitations that can combine to produce the PRP bottleneck. This interpretation clarifies otherwise puzzling aspects of the PRP effect and indicates that a fundamental restriction concerning response timing may underlie both limitations and the PRP effect that they produce. This restriction might arise because timing is controlled by subcortical neural structures with limited working memory.

THE EFFECT OF TACKLING TRAINING ON HEAD ACCELERATIONS IN YOUTH AMERICAN FOOTBALL.

BACKGROUND: Many organizations have introduced frameworks to reduce the incidence of football related concussions through proper equipment fitting, coach education, and alteration of tackling technique. PURPOSE: The purpose of this study was to examine the effects of training in a vertical, head up tackling style on the number of head accelerations experienced while tackling in a controlled laboratory situation. The authors hypothesized that training in a head up tackling technique would reduce the severity of head acceleration experienced by participants. DESIGN: Controlled Laboratory Study. METHODS: Twenty-four participants (11.5 ± 0.6 years old, 60.5 ± 2.2 in, 110 ± 18.4 lbs.) with previous playing experience completed a one-day training session on tackling technique utilizing a tackling dummy. A subgroup of these participants completed an additional two days of training with a 48 hour retention test. Head accelerations were analyzed at baseline and end of training. Feedback consisted of verbal feedback utilizing the Qualitative Youth Tackling Scale (QYTS) and video tackling playback. RESULTS: A significant reduction in the number of peak linear head accelerations over 10 g and peak rotational head accelerations over 1885 deg/s2 were found in dummy tackling after training in both the one day and three day training regimens. A significant change in QYTS tackling form score was found between pretest and post-test (p = 0.004). Participants with larger steps had a 2.28, 4.42 and 4.14 increased odds ratio of sustaining head accelerations over 10, 15 and 20 g respectively. CONCLUSIONS: Training in a vertical, head up tackling style decreased the number of head accelerations over threshold values sustained while tackling; decreased step length may be the driving factor in the effectiveness of this tackling form. LEVEL OF EVIDENCE: Level 3b.

INTER-RATER AGREEMENT AND VALIDITY OF A TACKLING PERFORMANCE ASSESSMENT SCALE IN YOUTH AMERICAN FOOTBALL.

BACKGROUND: Long term neurologic injury and concussion have been identified as risks from participation in American football. Altering tackling form has been recommended to reduce the risk of neurologic injury caused by head accelerations when tackling. The purpose of this research is to determine the inter-rater agreement and validity of the Qualitative Youth Tackling System (QYTS), a six-item feedback scale to correct tackling form, when utilized by novice and expert raters. HYPOTHESIS: Experienced raters will have higher levels of agreement with each other and with motion capture when compared to novice raters. METHODS: Both novice and experienced raters viewed video of youth athletes (ages 9-13) tackling a dummy in a laboratory setting along. The raters identified successful performance according to a binary rating scale for each component. Analysis of both the raters' agreement with each other and with an objective motion capture measure were completed. RESULTS: Fliess' Kappa measures between all raters were found to be moderate for head placement (k=.48), fair for cervical extension (k=.38), trunk inclination (k=.37), shoulder extension (k=.27) and step length (k=.29), and there was no agreement for pelvic height (k=.-16). When compared to the dichotomized validation measures of each of the five components provided by the motion capture system the average Cohen's Kappa agreement was substantial for pelvic height (k=.63), fair for step length (k=.34), cervical extension (k=.40), trunk inclination (k=.35), and slight for shoulder extension (k=.16). The experienced raters outperformed the novice raters in all categories. CONCLUSION: The results of this study indicate that skilled raters are better able to identify the movement patterns included in the QYTS when compared to a validation measure as well have higher rates of inter-rater agreement than novice raters. LEVEL OF EVIDENCE: 3b.

Measuring Memory and Attention to Preview in Motion.

Objective Use perceptual-motor responses to perturbations to reveal the spatio-temporal detail of memory for the recent past and attention to preview when participants track a winding roadway. Background Memory of the recently passed roadway can be inferred from feedback control models of the participants' manual movement patterns. Similarly, attention to preview of the upcoming roadway can be inferred from feedforward control models of manual movement patterns. Method Perturbation techniques were used to measure these memory and attention functions. Results In a laboratory tracking task, the bandwidth of lateral roadway deviations was found to primarily influence memory for the past roadway rather than attention to preview. A secondary auditory/verbal/vocal memory task resulted in higher velocity error and acceleration error in the tracking task but did not affect attention to preview. Attention to preview was affected by the frequency pattern of sinusoidal perturbations of the roadway. Conclusion Perturbation techniques permit measurement of the spatio-temporal span of memory and attention to preview that affect tracking a winding roadway. They also provide new ways to explore goal-directed forgetting and spatially distributed attention in the context of movement. More generally, these techniques provide sensitive measures of individual differences in cognitive aspects of action. Application Models of driving behavior and assessment of driving skill may benefit from more detailed spatio-temporal measurement of attention to preview.

Parallel streams versus integrated timing in multilimb pattern generation: A test of Korte's Third Law.

Skilled drummers performed a 4:3:2 polyrhythm with 2 hands and 1 foot. For each pair of limbs patterns of temporal covariation were used to infer relatively independent parallel streams versus integrated timing relationships. Parallel timing was more prevalent between hand and foot than between the 2 hands, and parallel timing generally increased with tapping rate. Different combinations of integrated and parallel timing were found among the 3 limbs. A second experiment used a wider range of tapping rates and explored 3:2 tapping with 2 hands, 2 feet, or hand and foot. The latter 2 limb pairs resulted in greater prevalence of parallel timing. These results can be interpreted in terms of a Gestalt principle of grouping known as Korte's Third Law, which can be extended from the perceptual domain to the perceptual-motor domain. This principle indicates that perceived velocity is a key factor in determining whether a sequence of events is represented as a single integrated pattern or as multiple parallel patterns. The present results put disparate previous findings on bimanual polyrhythmic tapping and rhythmic aspects of the golf swing under a common theoretical perspective. (PsycINFO Database Record

Effects of task precision demands on behavioral and physiological changes during a repetitive asymmetric lifting activity.

OBJECTIVE: This study investigated the effects of task precision demands on behavioral and physiological changes during repetitive asymmetric lifting. BACKGROUND: Repetitive lifting encountered in manual material handling leads to muscle fatigue and is a documented risk factor for low back disorder. METHOD: A total of 17 healthy volunteers performed repetitive asymmetric lifting for 60 min (10 lifts/min). Task precision demands were imposed by varying the entry width onto the destination conveyor. Physiological changes were assessed using near-infrared spectroscopy obtained from the erector spinae muscles. Three-dimensional spine kinematics and moment responses were quantified to understand behavioral changes during the lifting activity. RESULTS: Task precision demands showed no effect on erector spinae muscle oxygenation levels. Behavioral changes associated with repetitive lifting included increases in the overall lift duration, peak forward bending motion, and three-dimensional movement velocities of the spine, along with a decrease in the lateral bending moment. Relative to low precision demands, high precision demands resulted in 20% longer placement periods, which, in turn, resulted in a 12% increase in the time-integrated twisting postures and a 10% increase in the time-integrated lateral bending moments during load placement. CONCLUSION: The elevated risk of low back injury when lifting under greater precision demands is likely due to the sustained spine twisting and the sustained lateral bending moment on the spine in the final phase of these lifts. APPLICATION: Understanding behavioral changes to repetitive asymmetric lifting, especially for tasks requiring greater precision can be used to support injury prevention efforts.

Exploring the effects of seated whole body vibration exposure on repetitive asymmetric lifting tasks.

This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifter's capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/min for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting movement, and three-dimensional movement velocities of the spine. The lateral bending movement of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted farther (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure.

Control of response timing occurs during the simple reaction time interval but on-line for choice reaction time.

The preparation of multiple element movements has been examined for decades, with no clear explanation offered for the disparate results observed. Results from 2 experiments are presented and, in conjunction with previous results, a theoretical interpretation is offered regarding the preparatory processes that occur before, during and after the reaction time (RT) interval for multiple element movements during both simple and choice RT paradigms. In Experiment 1, number of elements and timing complexity were manipulated in a simple RT key-press task, using a startling acoustic stimulus to probe advance preparation. Both startle and nonstartle RT increased with number of movement elements and for a movement with increased timing complexity, providing evidence that the control of response timing occurs during the RT interval. In Experiment 2, the production of key-press movements of varying number of elements was compared in a simple versus choice RT paradigm. Results indicated that simple RT was affected by the number of elements, yet choice RT was not. Additionally, choice RT trials showed significantly longer interresponse intervals compared with those observed in simple RT trials, providing evidence for online processing in choice RT. The results of both studies, together with previous findings, suggest that planning of the timing of the onsets of the elements is prepared during simple RT, whereas planning of other aspects of the sequence of elements seems to occur in the foreperiod prior to the "go" signal. Conversely, in the choice RT paradigm, timing seems to be controlled online. This explanation may bring closure on difficulties encountered in over 50 years of research examining response preparation for complex movements.

Physiological and biomechanical responses to a prolonged repetitive asymmetric lifting activity.

This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participant's maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder.

Age-related differences in the rhythmic structure of the golf swing.

Participants were 20 younger golfers (M age=19.8 years, SD=1.84 years) and 20 older golfers (M age=63.0 years, SD=2.55 years) who attempted 40- and 80-yard eight-iron shots requiring an adjustment of their force and timing. No age-related differences were found in the tempo or speed of the shot; however, there were differences in the rhythmic relationship between the clubhead force and the weight shift. Whereas younger golfers primarily exhibited a 3 versus 2 polyrhythmic pattern between the peak forces of the clubhead and weight shift, older golfers primarily exhibited a simpler 3 versus 3 rhythmic force pattern by adding a forward weight shift at the beginning of the shot. Additionally, older golfers exhibited less independence between the timing of the clubhead force and weight shift, which indicated greater use of a single integrated coordinative unit rather than 2 units. These findings are interpreted as compensations for age-related slowing and increased temporal variability that help to preserve tempo at a speed comparable to younger adults.

Gestalt principles in the control of motor action.

We argue that 4 fundamental gestalt phenomena in perception apply to the control of motor action. First, a motor gestalt, like a perceptual gestalt, is holistic in the sense that it is processed as a single unit. This notion is consistent with reaction time results indicating that all gestures for a brief unit of action must be programmed prior to initiation of any part of the movement. Additional reaction time results related to initiation of longer responses are consistent with processing in terms of a sequence of indivisible motor gestalts. Some actions (e.g., many involving coordination of the hands) can be carried out effectively only if represented as a unitary gestalt. Second, a perceptual gestalt is independent of specific sensory receptors, as evidenced by perceptual constancy. In a similar manner a motor gestalt can be represented independently of specific muscular effectors, thereby allowing motor constancy. Third, just as a perceptual pattern (e.g., a Necker cube) is exclusively structured into only 1 of its possible configurations at any moment in time, processing prior to action is limited to 1 motor gestalt. Fourth, grouping in apparent motion leads to stream segregation in visual and auditory perception; this segregation is present in motor action and is dependent on the temporal rate. We discuss congruence of gestalt phenomena across perception and motor action (a) in relation to a unitary perceptual-motor code, (b) with respect to differences in the role of awareness, and (c) in conjunction with separate neural pathways for conscious perception and motor control.

Managing the rhythmic complexity of hitting a golf ball.

The authors investigated how the force pattern exerted on a golf club is coordinated with the golfer's weight shift, which supplies power to the swing. Moderately skilled golfers (n = 10, 5-10 stroke handicap) hit short golf shots requiring different amounts of force. Across these different shots, the timing of the force pattern applied to the clubhead was approximately invariant even though the force magnitude varied. In contrast, the weight shift timing and magnitude both varied with the required force of the shot. Across repeated attempts at the same shot, temporal variations in the clubhead force pattern were either uncorrelated or only weakly correlated with temporal variations in the weight shift. Together, these data indicate that the weight shift is a relatively independent, adjustable rhythmic unit from the invariant clubhead timing pattern for moderately skilled golfers.