Biometrics

·  Reasons for studying human movement

Movement is a way in which we interact with our world  

· The three “lenses” of studying movement

Mechanical- how to quantify movement

Coordination and control-measurements to understand how the brain controls movement

Learning-how do we enhance

Units and Vectors

·  Fundamental units in mechanics

Mass (kg)

Length (m)

Time (s)

·  Unit conversions

1ft=0.3048m       1mile=1610m.    1hr=3600s

·  Vectors and scalars

Vectors: magnitude and direction              ex: mass, distance, speed 

Scalars: magnitude only               ex: position, velocity, acceleration

·  Vector addition rules

Two vectors in same direction add     two vectors opposite subtract

Two vectors coming at angle require Pythagorean theorem

·  Resolving a vector into components

·  Average and instantaneous rates of change – interpreting the slope of a graph

Average rate: rate of change over time

Instantaneous rate: rate of change in specific given interval

Kinematics

·  Projectiles – path taken by projectiles

Under the influence of gravity          ex: long jump

· 3 Parameters determining projectile motion – speed, angle and height

Projection speed

Projection angle

Projection height

·  Influence of each parameter on horizontal distance traveled by projectile

Speed increase: increase in distance most impact

Increased height: increase in distance

Angle: depends on all

·  Why projection angle is not 45° in sporting contexts

Air resistance

·  Angular kinematics – planes and axes of motion

Absolute: angle is fixed to plane or line, does not move relative to earth

Relative: able to move on plane or line, changes based on angles in body  

·  Motions in frontal, sagittal and transverse planes (major motions of arm and leg are important)

Sagittal: side view, flexion or extension               ex: lifting leg and bending, bending knee

Frontal: abduction/adduction, moves front of body.     Ex: lift arm sideways so elbow touches ear

Transverse: internal/external rotation, birds eye.          Ex: “no” head nodding

·  Relation between linear and angular velocity

Linear: change in position/change in time (v)

Angular: spins, change in angle/change in time (w)

·  Steps in kinematic analysis

1: describe movement

2: analyzing movement

3: measuring movement

·  Applications of projectile motion in the long jump

Athlete takes off from board, projectile in the air- body’s movement is governed by the horizontal velocity (constant) and vertical acceleration due to gravity. Allows maximization of horizontal distance traveled before landing. 

Kinetics - Forces

·  Newton’s 3 laws of motion and applications

1. Law of Inertia,  “object in motion stays in motion, until acted upon by a force”

2. Law of acceleration, “amount of acceleration an object has when you apply force is proportionally to the force and inversely proportional to mass”

3. Law of action-reaction,  “ to every action there is an opposite and equal reaction”

·  Impulse momentum relationship

Impulse applied to object is equal to the change in its momentum

·  Applications when increasing or decreasing momentum

Increasing: increase final speed, increase magnitude of force, increase time force is applied

Decrease: decrease final speed, increase time

·  Application of Newton’s laws in the long jump

Weight and air resistance

·  Applications of impulse-momentum in designing safety equipment

Max time of impact thereby reducing peak force experienced by body, Impulse=(Force)(time)

Ex: airbags, seatbelts, helmets, crash pads

Kinetics - Torques

·  Concept of torque and moment arm

How much force applied, where said force is applied is the moment arm

·  Moment of inertia and factors that affect Moment of inertia

Objects likelihood of spinning, low inertia= very likely to rotate, high inertia=less likely to rotate

Mass and mass distribution effect inertia

·  Center of gravity and factors affecting center of gravity

Balance point, all mass is evenly distributed, belly button is normally CoG

Changes with body posture, potentially be outside of body

·  Center of gravity and relation to stability

CoG has to be within Base of support,

·  Application of moment of inertia in gymnastics

Changes in body position can control rotational speed during maneuvers like flips and rotations

·  Center of gravity in jumping activities and why certain techniques are better

The lower and controlled CoG is during initial phase of jump allows for greater force generated and optimal launch trajectory

Measuring skill

·       Characteristics of skilled performance

Ability to bring results with max certainty and min outlay of energy of time and energy

-max goal achievement

-min physical and mental energy cost of performance and time used

Ex: training, practice, fitness label, self-advocacy

·       Types of skills – Open v Closed, Discrete v Serial v Continuous

Open: variable and unpredictable skills

Closed: stable and predictable skills

Discrete: Easily defined beginning and end

Serial: discrete stills strung together to make up new complicated skill

Continuous: arbitrary beginning and end pt, behavior is flowing for min or hours

·       Types of Errors used to measure skill – CE, AE, VE and RMSE

CE: average of all scores, overall tendency to under throw or overthrow

AE: absolute value of the error and take average of those error scores

VE: measure of subject’s inconsistency

RMSE: 2 types of behavior to bias tendency

Reaction Time

·       Information processing model for human performance

Input-processing-output.                  Input-human-output

Sensory info-black box nervous system-movement/behavior

·       Stages of processing between input and output

Stim identification- decide if stim has been presented and if so what it is,   Primary a sensory stage, Components of stimuli are thought to be assembled in this stage, Patterns of movement are detected

Response selection-stim stage, what response to make based on nature of situation and environment

Movement- organizing motor system to make desired movement, ready lower-level mechanisms in the brain stem and spinal cord for action and retrieve

·       Definition of reaction time, movement time and response time

RT: performance measure for speed and effectiveness of decision making

MT: initiate release        ex: from accelerator, depressed brake pedal starts when you do the action

Response time: both RT and MT,    ex: see break lights from car Infront and you stopping your own car

·       Understand impact of each of the three processing stages on reaction time

As possible S-R alternatives increase, there is an increase in the time required to respond to any one of them.

·       Hick’s law

As number of alternatives increase, reaction time increases

·       Stimulus-Response compatibility and its effect on RT

Extent to which the stim and the response evokes are connected in natural way

S-R alternatives, increase S-R comp to decreases choice RT

·       Anticipation as a means of decreasing RT

Cope with long RT delays

Event, spatial, and temporal

Incorrect anticipation can prove more costly than not anticipating at all

Speed-Accuracy

·       Speed-accuracy tradeoff and Fitts’ law

As speed of a movement increases, accuracy diminishes

Accuracy increases the movement time also increases

Quantified using Fitt’s Law (how long it takes to move to a target based on size and distance)

·       Reasons for speed-accuracy tradeoff

Signal-dependent noise-faster movements require more force

Online corrections- high accuracy is required movement cannot be accomplished in one shot  

·       Exceptions to speed-accuracy tradeoff – temporal accuracy

Movement time is goal, reduce the MT increases temporal accuracy

Faster you move the more temporally accurate you are

·       Exceptions to speed-accuracy tradeoff – bimanual movements

Congruent: same target on each hand, MT increase as ID increases

Incongruent: different target on each hand, MT decrease and ID target was much slower than anticipated

·       Using Fitts’ law in computer interface design

Optimize experience by making it easier for users to interact w/ elements on the screen

Decrease amplitude (distance between starting pt of movement and center of target)

Increase width (dimension of target)

·       Fitts’ law as a measure of motor performance – importance of the slope and intercept parameters

Provide a good index of motor function

Intercept (a)-how fast the person can move in general

Slope (b)- time it takes to complete when the ID is increased by 1

·       The challenge of coincident timing in tasks like baseball

Adjust-swing initiation faster the pitch—swing duration decreasing

Closed-loop control

·       Characteristics of closed-loop control

A-control system which relies on feedback to achieve desire goal

Error is feedback to the system

·       Components in closed-loop control

Executive-you

Effector-your friends

Error signal where your friend is relative to object

·       Types of sensory feedback in humans

Visual, audition, touch, taste, smell, exteroception, proprioception

·       Role of Vision – Two streams, Optic flow

Optic: information specific to control of movement

Two: control of movement also called dorsal stream

·       Role of proprioception - reflexes

Provide info about the state of body itself

·       Advantages and disadvantages of closed loop control

Ad: flexibility in movement control (adapt to changes in environment)

Dis: slow when its high in demand for processing time

Open-loop control

·       Characteristics of open-loop control

No feedback is open loop control

Actions are organized ahead of time in open loop control, sequence and timing

·       Advantages and disadvantages of open loop control

Ad: simplicity and stability-simpler in layout and hence are economical and stable, construction-simple layout so are easier to construct

Dis: accuracy and reliability-don’t have feedback mechanism-very inaccurate, removal of disturbance-absence of feedback mechanism, unable to remove disturbance

·       Motor programs and evidence for motor programs

Structed set of motor commands that defines and shapes movement

Evidence: reaction time-complexity of response increase reaction time

Startle reaction-prepared movement is initiated about 100ms earlier than usual

Deafferentation-movements disrupted but still possible

·       Learning in open-loop control

Feedback is still required to make corrections

Make errors and fix them on next trial

·       Need and evidence for Generalized Motor Programs

·       Predictions as fast “feedback”

Feedback is required for flexibility but is slow

·       Combining open- and closed-loop

By itself is not satisfactory to explain full range of motor behavior

Combine of both types of control is required

Coordination

·       Degrees of freedom definition

Influence the number of unique ways something can move

·       The degrees of freedom “problem” in movement control

WE have to control-movements and body parts, body parts have several joints, each joint has 3 dimensions

·       Context conditioned variability – anatomical, mechanical and physiological

Bernstein argued that motor program couldn’t be a feasible solution for the DoF problem

Anatomical: movement depends on the body anatomy, depends on context

Mechanical: brain alone does not control input in muscles, spinal cord, reflexes, interneurons

Physiological: brain alone does not control input in muscles, spinal cord, reflexes

·       Solving degrees of freedom problem – freezing/freeing

Motor system must reduce amount of degree of freedom to control

Can be modified during learning

Freezing DOF in one way to reduce the number of DOF controlled

·       Solving degrees of freedom problem – synergies

Expert shooters coordinate motion of shoulder and wrist so that aim is not affected

·       Motor plan, motor command and feedback for postural, locomotion and hand-eye coordination

Motor plan: goal directed movements, object manipulation

Motor command: upper limbs, endpoint, trajectory control

Feedback: vision and receptors within muscles  

Bimanual Coordination

·       Dynamical systems view of coordination (contrast with motor program view)

Motor coordination is due to self-organization of several levels of behavior, some are stable while others are not

·       Kelso’s “finger wiggling” experiment to demonstrate self-organization

Wiggle 2 fingers independently at slightly different speeds, people’s movement naturally synchronize into a coordinated pattern without conscious effort, even if they try to resist it

·       Temporal coordination rules

Move two limbs in a particular time, move to a particular beat

-need to coordinate interdependent activities in time

·       Spatial coordination rules

Movement with different amp or directions are harder to coordinate, same direction of movement easier to coordinate

·       Bimanual Fitts

Motor control where a person is required to simultaneously move both hands to target locations

·       Overcoming temporal and spatial constraints through task conceptualization

Difficulty in coordination arises due to difficulty in planning

Ex: draw a circle with 2 hands

·       Learning “part” vs. “whole” in bimanual coordination

Part learning is practicing individual components of a movement with each hand separately

Whole learning means practicing the entire coordinated movement with both hands simultaneously

Introduction to Motor Learning

·       Definition of motor learning – three important criteria

Practice or experience leading to permanent gains in the capability for skilled performance  

·       3 stages of motor learning

Cognitive (beginner or novice), understand movement, frequent errors

Associative (Intermediate or practice), technique, understands errors

Autonomous (Advanced or fine-tuned), movement is automatic, don’t think

·       Performance curves – the law of practice

Plots of individual or average performance against practice trials

-improvements show steep curve first, followed by more gradual curve later

·       Limitations of performance curves

-they are not learning curves

-between subject effects are masked

-within-subject variability is masked

·       Use of transfer designs (transfer/retention tests) to distinguish learning from performance

To identify type of performance change

Transfer test: change of test conditions

Retention test: test done after an empty period without practice

·       Transfer of learning – Positive and negative transfer

Facilitate performance capability of task under different situations

Positive: learning in one context facilitates performance or learning in another

Negative: pervious learning inhibits learning or performance in new context

Augmented Feedback

·       Intrinsic and augmented feedback

Intrinsic: natural consequence of making an action

Augmented: external agent that is not naturally or easily available

·       Types of augmented feedback – KR, KP and concurrent feedback

Knowledge of result (KR): info about outcome or success of an action with respect to goal

Knowledge of performance (KP): info about the movement pattern

·       Functions of feedback

Provide motivation, info to modify future, direct learner’s attention, creates dependence

·       The “Guidance hypothesis” – avoiding dependence on feedback

Learning cannot always be determined by performance

·       Influence of amount of feedback

More is not better-too much info can overload

·       Influence of precision of feedback

Can vary in precision, depends on learners’ skill level

·       Influence of Frequency of feedback

Absolute: total number of feedback presentation given to a learner across a set of trials in practice

Relative: percentage of trials receiving feedback

·       Strategies to reduce dependence on feedback – faded, bandwidth, summary feedback

Faded: relative frequency is high in early practice and reduced in later practice    -lots of feedback at the start but slowly removed

Bandwidth: feedback only when errors fall outside a certain zone or bandwidth

Summary: effectiveness of performance on a series of trial is presented only AFTER the series is finished

·       Learner-determined feedback schedules

Feedback is a schedule in which learner request feedback, they request less frequently

·       Reducing negative effects of frequent feedback through subjective estimations

Concurrent feedback: during movement (physical guidance)

Terminal feedback: after movement

Applications of Augmented Feedback

·       Distinguishing Performance and learning (review with graphs)

Learning: relatively permanent change for responding, from practice or experience

Performance: momentary/ temporary ability to execute a skill

·       Frequent feedback in children

This kind of feedback for kids is beneficial and helps with their understanding

·       Effectively using robots to facilitate learning

Used for physical guidance for motor learning (concurrent feedback), assist with certain and restricts other movements

Practice Schedules

·       Effects of Massed and Distributed Practice on performance and learning o Why is distributed practice more effective

Massed: Rest period is less than trial time

Distributed: rest period is longer than trial time

·       Variable vs. Constant Practice
Why is variable practice better at generalization

Variable: same skill is repeated in different situations

Constant: same skill repeated in same situation over again

Variable is better because it exposes learners to wider range of conditions and identify patterns

·       Blocked vs. Random Practice (Low vs. High Contextual Interference)
 Why is random practice more effective

Blocked: repeat same skills in same order until certain level of competence

Random: practice by switching between different skills at random

Random is better because it makes the learn actively retrieve between different skills or concepts

·       Concept of “Desirable Difficulties”

Learn task that are challenging but beneficial and can improve long term performance

Ex: testing effect (space out study sessions, vary practice conditions)