Labs

Question 1

Which balance conditions had the largest difference between them?
- normal surface eyes open
- normal surface eyes closed
- foam surface eyes open
- foam surface eyes closed

Answer 1

• biggest difference was between eyes open and eyes closed on a foam surface. because of the difference in proprioception.
• Not the best measure of balance was used as only incorporated 1 trial and 1 participant.

Question 2

Examine the pros and cons of measuring static balance using:
- SD
- range
- sway velocity
- ApEn
- Lyapunov Exponent
What trends can be seen?

Answer 2

• SD: increases throughout the conditions
• range: also increases throughout the conditions
• sway vel: increases throughout conditions
  these are the trend we would expect to see
• ApEn: fluctuates, increasing then decreasing
• Lyapunov Ex: also fluctuates throughout
  these measures are more sufficient for measuring a dynamic eq

Although using these comparison measures makes balance able to be compared with all members of the population

Question 3

Balance is often referred to as COM, but static balance is measured in COP. Can these be used interchangeably based on your lab results?

Answer 3

• NO, as results show similar trends but not the same results.
• cannot be used interchangeably but e.g.: sway vel can be applied to other measures

Question 4

Using a PID controller (Peterka, 2000) how does changing the proportional, integral and derivative affect the COM and COP motion?

Answer 4

Increased Proportional:
* increased COP amp & freq
* increased COM, freq & amp stays same
* Increased sway vel
Increased derivative:
* Damped COP
* Damped COM
* Reduced sway vel
Increased Integral:
* COP towards the zero-line reducing drift
* COM towards the zero-line reducing drift
* higher sway vel to start with then decreases

Question 5

What are some issues with the way the lab implemented the field and lab based hop and stick test?
What could be improved?

Answer 5

• Normalise hop distance by taking max rep and have it as a percentage of max hop distance
• Normalise jump height and get participant to jump over something

Question 6

Define:
- COM
- COP
- Entropy
- ApEn

Answer 6

• the weighted sum of all the mass in the body
• a point on the ground where resultant forces act (sum of all forces exerted by ground)
• a measure of unpredictability of info and relates to the loss of info over time
• estimate of the entropy in a signal (complexity/regularity of data). 0 = periodic signal, increased value = less predictability.
  –> measures how small sections of a trajectory repeat over the whole trajectory

Question 7

Define:
- Lyapunov Exponent
- Time to stabilisation

Answer 7

• measures exponential divergence of nearby trajectories. Relating to the chaos theory. LyE = 0 (periodic signal, with 0 trajectory divergence), as value increases trajectory paths become more chaotic and random
• a measure of dynamic balance, the time it takes a person to return to a stable balanced position after landing (using 3 velocity vectors: Fx, Fy, Fz-BW) to get the magnitude of force.
  –> a 5% threshold of BW is used to determine when a person has regained balance

Question 8

What was the rationale behind the (Harbourne & Stergiou, 2003) study?

Answer 8

• assumes that posture is controlled by 2 CPGs, selection of an appropriate pattern and the modulation of that pattern.
• a genetically determined behavior, revealed as the NS matures.
• independent sitting requires dynamic stabilization of all linked body segments (complex learning & adaptation to environmental forces) = visible from 5 months (tested at 3 points) -> As infants begin to walk, they begin to decouple the whole leg synergies seen in kicking to allow crawling and walking

Question 9

How does age impact ability to maintain posture stability (Harbourne & Stergiou, 2003)?

Answer 9

• at 3-year-old children restrict the degrees of freedom by decreasing dimensionality and complexity.
• at age 5, the child is able to have more control over the body’s degrees of freedom, and shows increased dimensionality and complexity as reflected in the COP time series (an adultlike behavior).
• dynamic stability was measured using LyE

Question 10

What is meant by
Surrogation?
The correlation dimension?

Answer 10

• a technique that can accurately determine if the source of a given time series is actually deterministic in nature
• a method to evaluate the number of degrees of freedom during posture or, in other words, to determine the dimensionality of the COP time series

Question 11

What were the findings from the infant study (Harbourne & Stergiou, 2003)?

Answer 11

• The LyE values reduced (toward zero) with sitting emerging (a more periodic path of the COP - not random/noise).
• infants increasingly occupied trajectories close together within the state space. = more locally stable with experience
• correlation dimensionality decreased through the stages(freezing DoF), increasing adaptability/flexibility in maintaining postural control over the base of support in sitting
• ApEn decreased complexity of sitting, but increased complexity in exploring getting in & out of sitting, but only 5 study participants

Question 12

What are the key finding of Peterka, 2002?

Answer 12

Postural Control Mechanisms (adaptive):
- achieved through dynamic feedback of visual, vestibular, and somatosensory system.
- study used pseudorandom rotations of the visual environment to induce (AP) body sway in participants = analysis of sensorimotor system’s response to control perturbations.
- sensorimotor system dynamically reweights sensory inputs depending on their reliability and context. e.g.: when visual becomes unreliable, system relies more on vestibular/ somatosensory inputs.

Question 13

What are the clinical applications for Peterka, 2002 study?

Answer 13

• Understanding the principles of sensorimotor integration can help in developing better rehabilitation strategies for individuals with balance disorders.
• The findings can inform the design of assistive devices and interventions aimed at improving balance in populations such as the elderly or those with neurological impairments.

Question 14

What was the key finding from the (Ross et al., 2005) paper?

Answer 14

• Subjects with functional ankle instability (FAI) exhibited significantly longer stabilization times compared to the control group.
• This indicates a compromised ability to quickly stabilize after landing, which is critical for preventing further ankle injuries.
• The study discusses several factors that may contribute to prolonged stabilization times in individuals with FAI, including deficits in neuromuscular control, proprioception, and muscle strength.

Question 15

What are the clinical implications from the (Ross et al., 2005) study?

Answer 15

• The primary goal was to evaluate the differences in jump-landing stabilization times between subjects with functional ankle instability (FAI) and those without.
• These findings highlight the need for targeted rehabilitation programs focused on improving neuromuscular control and proprioceptive training to reduce stabilization times and prevent recurrent ankle injuries in individuals with FAI.

Question 16

What are the key findings of the Abernethy & Russell, 1987?

Answer 16

• Experiment 1: manipulated the duration of visible stroke sequences, Experiment 2: masked specific display features.
• Results = experts extract more relevant information from earlier cues (167 ms & 83ms pre-impact), from playing side arm and racquet, so are better at predicting stroke outcomes than novices(only extracted info 83ms pre-impact).
• experts had better lateral and depth error but the extent of their superiority depends on the severity of the temporal occlusion.

Question 17

What are the main conclusions from experiment 1: manipulating duration of visible stroke sequences (Abernethy & Russell, 1987)

Answer 17

• the critical time for extracting directional information = between 83 ms before & 83 ms after racquet-shuttle contact
• the critical time for extracting depth information = last 83 ms before racquet contact
• advance cues resolve depth uncertainty (forcefulness), early flight cues resolve uncertainty of the shuttle direction
• There are consistent differences in prediction accuracy between expert & novice players for all occlusion conditions (t2-t5), difference that experts better extract early lateral & depth information (167-83 ms prior to contact)

Question 18

What are the conclusions from experiment 2: masked specific delay features (Abernethy & Russell, 1987)?

Answer 18

• Novices relied on the opponent’s racquet for anticipatory information = ignores cues from opponent’s playing-side arm,head, or lower body
• Experts extracting no information from opponent’s head and lower body, but get anticipatory information from raquet arm & raquet = stroke force & direction prediction
• distal racquet cues(raquet action) = more reliable than proximal arm segment cues(arm action, available earlier than the racquet), so is a better preparatory cue.

Question 19

What were the main findings from the (Savelsbergh et al., 2002) study?

Answer 19

• used gaze-tracking technology to analyze the visual search patterns of goalkeepers during penalty kicks.
• Expert = more efficient visual search pattern, focusing on specific kicker’s body movement and ball positioning + better anticipation skills compared to novices, accurately predicting the direction of the penalty kick more often.
• Because they picked up early visual cues from the kicker’s approach and movement, processing relevant visual information more quickly and ignore irrelevant cues = faster and more accurate decision-making.

Question 20

What are the implications for training from the (Savelsbergh et al.,2002) study?

Answer 20

• The findings suggest that training programs for goalkeepers should emphasize the development of visual search strategies and anticipation skills.
• Specific drills that mimic game scenarios and require quick decision-making based on visual cues could be beneficial.
  A methodological approach:
• The novel methodological approach of using gaze tracking provided insights into the cognitive processes underlying expertise in sports.
• This approach can be applied to other sports to understand the visual and cognitive skills required for high-level performance.

Question 21

Define:
- Temporal occlusion
- Spatial occlusion
- Reaction time paradigm

Answer 21

• where a movement sequence is cut short, the viewing time of an activity is controlled to see how participants use advance cues
• where physical movement aspects are removed to determine what advance cues are being used
• where subject makes a decision on what action to take, in sufficient time in order to respond to a stimulus. e.g.: penalties

Question 22

How does success in determining shot direction change with length of occlusion?

Is there a point where visual info is redundant?

Answer 22

• after impact & after +80ms
• as length of occlusion decreases before impact success rate increases
• after impact there is no change so info becomes redundant

Question 23

is there any evidence that badminton players are better able to use info earlier in the sequence of actions?

Answer 23

• higher at all occlusion aspects than class avg, as they are able to use info at all parts shown by their higher success%

Question 24

When spatial occlusion was added, was there any change in the badminton players or class performance?

Why might this have happened?

Answer 24

• yes for badminton player
• on avg class gets better when spatial occlusion is introduced, as we are getting rid of useless info.
• there is some learning effect from multiple trials before spatial occlusions

Question 25

were you better at predicting height or direction of the penalty?

does this match Savelsbergh et al., 2002?

Answer 25

• class avg better at direction of the ball (71%)
• similar to the study

Question 25

How does the class success rate compare to that of the Savelsberg et al., 2002 study on penalties?

is your performance closer to a novices/experts?

Answer 25

• closer to novices performance
• postural cues are harder to pick up for the height of the ball, only occurring 30ms before contact with the ball.
• non-kicking foot direction points towards the ball direction

Question 26

When a spatial occlusion was added, did your performance change?

if it did, what does this tell you about the advance cues you rely on?

Answer 26

• means potentially looking/fixating at wrong thing before.
• suffer less with deception as info provided is more true to actual actions of the shooter
• experts fixated on the kicking/non-kicking leg and ball areas (early eye location)
• novices had more fixations on the trunk, arm and hip