Download - 1 Unit1.1 Skills Merged (1)

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KNES 385

Motor Control & Learning

Prof John Jeka

What is this class??? Course Description: Physiological and cognitive bases for motor control and their applications to the acquisition of movement skills and understanding of movement disorders.

Basic Question

•  HOW are motor skills learned and controlled??

This includes: •  Execution of ‘simple’ movements

•  Expert performance

•  Infant motor ‘learning’ (i.e., learning to walk)

•  Rehabilitation (i.e., stroke patient re-learning to walk)

Course Outline

Unit 1: Motor Learning Unit 2: Neurophysiology of Motor Control Unit 3: Theories of Motor Control Unit 4: Role of Memory / Attention

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UNIT 1.1: Introduction to motor control, learning, skill and performance

Objectives

1.  Define / compare and contrast: motor learning, control,

coordination, skill and ability •  Name and describe the factors that influence the above terms?

2.  Classify motor skills based on established criteria

3.  Identify characteristics of skillful behavior

Some Early Definitions

As an area of study….

• Motor control – understanding how the neuromuscular system functions to activate and coordinate the muscles and limbs involved in the performance of a motor skill (Magill, 2007)

•  Coordination – the patterning of body and limb motions relative to each other and to the environmental objects and events

•  Three aspects / dimensions of control???

Some Early Definitions

As an area of study…..

• Motor learning – study of the processes involved in acquiring and refining motor skills that promote or inhibit that acquisition

Sample Questions… •  What is the role of feedback in motor learning?

•  What type of feedback enhances learning?

•  How do practice schedules impact motor learning?

•  What is the role of memory in motor learning? Coker, 2004

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You have to go faster….

Skills, Movements and Abilities

What is Skill?

Write down a skill you think you possess

Do the answers vary?

Consider the many activities we perform on an everyday basis. We perform actions that we have acquired over time. From walking down steps to playing video games, these are skills.

A skill is an action or task that has a specific goal to achieve (Magill, 2001).

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Are all activities skills?

An activity is a skill if it: 1)  Is directed toward the attainment of a goal 2) Is performed voluntarily 3) Has been acquired by experience/

practice

What makes a skill a motor skill?

A motor skill requires voluntary body/limb movement (Magill, 2001).

Is the skill you wrote down a motor skill under these criteria?

Unless you thought of a cognitive skill, or one of the primary behaviors we are born with (i.e. suckling), it should be!

What about activities like…

sitting standing walking

Another conceptualization of skill is something which distinguishes competence between, for example, experts and novices.

vs.

Levels of Skillfulness

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•  In addition to the criteria for a movement to be considered a skill, there are additional characteristics of skilled performance

1.  Adaptable

2.  Consistent

3.  Efficient

Levels of Skillfulness

What are Movements?

Movements are behavioral characteristics of specific limb(s) that are components of a skill (Magill, 2001)

i.e., movements are the building blocks of a skill

Why differentiate between skill, movement, etc?

There is a taxonomy or hierarchy (e.g., Biology: phylum – class – order – family etc…)

Goal

Skill

Movement

Put the ball in the basket

Jump shot, dunk, lay-up

Characteristics that vary within and between people Process

measures

outcome measures

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Classifying skills

Why classify skills?

•  Simplifies discussion

•  Allows comparison across research

•  Provides context for coaches/therapists

Hot Cold

A one-dimensional continuum is a range between two ‘ends’ on a given variable

Unlike biological classifications, we use a continuum so that a skill does not have to exactly match a condition or fit into a box on some chart… skills have high variation across many variables.

Stuff

Animal Vegetable Mineral

Classifying skills

Consider the 8 skills below

What characteristics do they have in common?

Which characteristics differentiate them?

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Commonalities All require concentration.

All must focus attention on a specific point/thing.

???

Differences Some have a stable, predictable environment in which the skill is

performed, some do not. Some use the whole body, some

just use the hands/arms. Some are continuous, some are

sporadic. Some involve fast movements,

some slow. Some involve standing posture,

some seated.

… Basis for continua.

Classifying skills

Classification 1: Size of musculature used

The prime movers used in surgery and long jumping are clearly not the same.

Use large musculature; involve less movement precision Fundamental motor skills (jumping, locomotion, etc…)

Require control of small muscles; hand-eye coordination Writing, typing, sewing, etc…

GROSS FINE

≠

Classification 2: Type of Movement

Discrete Serial Continuous

Have a clearly specified beginning and end (e.g., hitting a switch) – one movement skills.

Involve a series of discrete movements (e.g., playing piano, hammering a nail)

Have arbitrary start and end (e.g., swimming)

Implications for analysis

??

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Classification 3: Motor-cognitive dimension

Low cognitive Moderate cognitive High cognitive demand demand demand

Actions are automatic, with little thinking about task required

The motor component is less significant than the cognitive element

Classification 4: Stability of the environment

Environment refers to the characteristics of objects/people the skill is performed with

Closed Open Environment does not change while performing the skill. These tend to be self-paced; the object ‘waits for your action’.

Environment is changing during performance of the skill. These are usually not self-paced, require constant adjustment.

Gross or Fine motor skill? Order the following skills in terms of the size of musculature used in the action.

Punching a speed bag Typing your name Getting out of your car

Open or Closed motor skill? Order the following skills in terms of the environment the skill is performed in.

Snapping a football Basketball jump shot Bowling

Classifying skills

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So how does Skill relate to Ability?

An ability is a stable trait or capacity of the individual that is a determinant of a person’s potential for the performance of specific skills (Magill, 2001).

Abilities are generally thought to be hereditary/genetically determined, and by large unmodified by experience (Schmidt & Wrisberg, 2000).

The hardware people bring to a task.

Ability

INDIVIDUAL DIFFERENCES

Stable, enduring differences among people that contribute to differences in task performance (Schmidt & Wrisberg, 2000)

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Body type Abilities

Cultural background Emotional

make-up

Developmental Stage


Body type Abilities

Cultural background Emotional

make-up

Developmental Stage

ABILITIES SKILLS

Stable Modified by practice

Inherited traits Developed

Few in number Many in number

(Schmidt & Wrisberg, 2000)

Underlie performance Depend on different of many skills subsets of abilities

Abilities vs. Skills

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Abilities are highly related and can be characterized by a single, global ability (Brace, 1927; McCloy, 1934)

- Minimal empirical evidence

=

Generalized Motor Ability???

Abilities are relatively independent. The ‘all-around’ athlete has a high number of abilities (Henry, 1958)

Research evidence for specificity of motor abilities

Correlation ≠

Specificity of Motor Ability???

Rehabilitation

Identifying abilities allows the practitioner to get to the source of a problem. This can be achieved via a task analysis.

May identify areas for compensation.

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Skill or Ability?

Skill or Ability?

Skill or Ability?

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Skill or Ability?

Hall of Shame???

Preparing for a career in professional sports is risky business because it requires focusing on getting a job that statistically, does not exist.

Skill or Ability?

UNIT 1.1 : Introduction to motor control, learning, skill and performance

Objectives

1.  Define / compare and contrast: motor learning, control,

coordination, skill and ability •  Name and describe the factors that influence the above terms?

2.  Classify motor skills based on established criteria

3.  Identify characteristics of skillful behavior

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Measurement and Evaluation Of Performance

Unit 1.2

Prof. John Jeka

Unit 1.1 Outline 1.1 Introduction to Motor Control and Learning

a)  Motor coordination vs. motor control vs. motor learning

b)  Motor skills and abilities

c)  Classification of motor skills

d)  Characteristics of skillful performance

1.2 Assessment of Motor Skill Performance

a)  Outcome Measures (i.e., error scores, timing, etc.)

b)   Process Measures (i.e., kinematics, kinetics, brain imaging, etc.)

1.3 Motor Learning

a)  Characteristics of the learning process

b)  Assessment of motor learning

c)  Learning stages

1.4 Effects of practice on motor learning

1.5 Assisting the Learning Process

a)  Observational learning

b)  Augmented feedback

In order to:

•  understand skilled performance….

•  infer learning ….

•  compare individuals/groups …

We must measure performance

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Objectives

1. Compute, utilize, and interpret outcome and process

measures used to assess motor control, coordination, and learning

2. Design a research experiment to examine specific research questions in motor control and learning.

UNIT 1.2: Measurement and Evaluation of Performance

Motor Performance

Motor performance is what we actually measure when a person performs a skill. It is divided into 2 types of measure:

Performance outcome measures (outcome scores)

Performance production measures (process measures)

What is Motor Performance???

Indicate the outcome of performing a skill, such as:

How accurate was a shot/throw etc? …ACCURACY

How fast did a person move? …TIME/SPEED

How far did an object travel? …MAGNITUDE

Outcome Measures

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Measures of Accuracy: Error Scores

Why measure error? Accuracy is a major component of human skill from everyday tasks to sports performance. The way in which we understand the accuracy of performance is simply to measure the extent to which performance differed from a criterion.

How do we measure error? The criterion can be a specific target in space, such as an archery target or a time, such as matching a rhythm.

1 Dimension 3 Dimensions

X axis

Y ax

is

Z axis X axis

Y ax

is

X axis

2 Dimensions

Dimensionality of Error Scores

A dichotomy (hit/miss): This performance has 6 hits/4 misses (60%).

So does this!

Is there a difference in the quality of performance?

Information Obtained from Error Scores

4

10

8

6

4

28 points

Only 40% hit

28 points

60% hit

Information Obtained from Error Scores

The absolute difference in relevant units between the criterion and the performance outcome

abs (xi – T) Absolute Error (AE) describes the error along a single dimension

We take multiple trials to gain a representative measure of performance…the average.

AE = ∑ abs (xi – T) n

Where:

• ∑ = the sum of

• T = target

• n = number of trials

Absolute Error (AE)

0 10

Target

x1 x2

x3

11 9 AE = ∑ abs (Xi – T)

n

Σ 2.5

AE = 0.833

Trial Xi Abs Xi-T = 1 11 11-10 1 2 9 9-10 1 3 9.5 9.5-10 0.5

Absolute Error (AE)

Then divide by “n”

the number of trials

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What skill might this be appropriate for?

•  Absolute error for two dimensional tasks

Radial Error (RE)

RE = Errorx2 + Errory

2

X axis

Y axis

Target

c

a

b

Radial Error (RE)


2

c2 = a2 + b2

c = a2 + b2

Pythagorean Theorem


2

X axis

Y axis

a

b

c d

Point X-axis

Y-axis

a 3 3 b -3 1 c -1 -3 d 2 -2

Radial Error (RE)

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RE = (x-axis error)2 + (y-axis error)2

Point X-axis

Y-axis

a 3 3 b -3 1 c -1 -3 d 2 -2

X2 Y2

9 9 9 1 1 9 4 4

X2+Y2 sqrt

18 4.24 10 3.16 10 3.16 8 2.83 ∑ 13.39

/ n 3.35 Average RE

•  Absolute measures of accuracy may hold insufficient information. For example, they fail describe tendencies to over or under shoot.

•  Constant error (CE): represents magnitude of error in a specific direction (i.e., it is no longer absolute).

CE = ∑ (xi – T)

0 10 ft

Target

Error

AE = ∑ abs (xi – T) … “you missed by that much” Vs.

CE = ∑ (xi – T) … “you overshot by that much”

Bias in Performance Outcomes

0 10

Target

x1 x2

x3

11 9 CE = ∑ (Xi – T)

n

Trial Xi Xi-T = 1 11 11-10 1 2 9 9-10 -1 3 9.5 9.5-10 -0.5

Constant Error (CE)

Σ -0.5

Then divide by “n”

the number of trials

CE = -0.167

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•  Variability is a measure of consistency in performance. The typical measure is the standard deviation (Std Dev).

•  Variable error (VE) is an index of how much variability there is in the accuracy of performance.

Where:

∑ = the sum of x = the individual score m = the mean n = the sample size

∑ (x-m)2

Std Dev =

n - 1

Variability in Performance Outcomes

Std Dev = ∑ (x-m)2

n - 1

1

4

5 2

3

Trial 1 1.5 Trial 2 0.25 Trial 3 0.25 Trial 4 3 Trial 5 0.5

Variable Error (Std Dev)



n - 1

Trials Error (x – m) (x – m)2

1 1.5 0.16 2 0.25 -0.85 0.7225 3 0.25 -0.85 0.7225 4 3 1.9 3.61 5 0.5 -0.6 0.36

Mean 1.1 Sum 5.5 5.5775

5.5

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n - 1


1 1.5 0.4 0.16 2 0.25 -0.85 0.7225 3 0.25 -0.85 0.7225 4 3 1.9 3.61 5 0.5 -0.6 0.36

Mean 1.1 Sum 5.5 5.5775

5.5



n - 1


1 1.5 0.4 0.16 2 0.25 -0.85 0.7225 3 0.25 -0.85 0.7225 4 3 1.9 3.61 5 0.5 -0.6 0.36

Mean 1.1 Sum 5.5

Std Dev 1.181

5.5775

5.5

(A) (B) Which would be regarded as most skilled?

(A) has a lower AE & lower CE, but a higher VE than (B).

(B) has a higher AE & higher CE, but a lower VE than (A)

Skilled Performance??

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Root mean square error (RMSE)

•  Error between a participant’s displacement (position) curve and a criterion (ideal) curve

•  Computes one error score for the total duration of the task

Continuous Skills

Dichotomy hit/miss Zones of accuracy Absolute error (AE)

Radial Error (RE) Constant error (CE) Variable error (VE)

RMSE

Magnitude Accuracy Time/speed

Performance Outcome Measures

•  Reaction time (RT): interval between the onset of a signal or stimulus, to the initiation of a response

Stimulus or

‘Go’ signal

Light/Color

Word/Sound

Shock/Vibration

Vision

Hearing

Touch

Speed: Reaction and Movement Time

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Stimulus

Simple RT

Response key

Index Index Middle Ring Index

Used in information processing studies

Reaction Time

Choice RT Discrimination RT

Simple RT

Choice RT

Discrimination RT

Match the following

Reaction Time

Simple RT:

Choice RT: # of choices 1 2 3 4 5 6 7 8 9 10

~RT (ms) 200 350 400 450 500 550 600 600 650 650

Damon et al. (1966)

Light 240 ms Siren 220 ms

Electrical shock 210 ms All together 180 ms

Swink (1966)

What are typical RT values?

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• Reaction time (RT): the interval of time from the onset of a ‘go’ signal or stimulus to the initiation of a response

• Movement time (MT): the interval from the initiation of the response to the completion of the movement.

• Response time: the sum of RT + MT. From the onset of a ‘go’ stimulus to the completion of the movement.

These are all defined by observable events

Performance Measures: Time

•  EMG, which indicates electrical activity of muscle, has been used to separate RT into central and peripheral components.

Electromyography (EMG) in RT measures

•  Research shows that following presentation of a stimulus, for a portion of RT, there is no electrical activity. This 40-80 ms period is known as pre-motor RT represents CENTRAL PROCESSES (decision making/perceptual processes etc). Weiss, 1965

EMG

Response time

Foreperiod RT MT

Pre-motor Motor

Electromyography (EMG) in RT measures

Warning Stimulus Presentation

Movement Onset

Movement Offset

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Indicate the ‘size’ of an outcome, and have particular relevance in sports settings.

Distance

How far you throw

Weight

How much you lift

Height

How high you jump

Measures of Magnitude

Dichotomy hit/miss Zones of accuracy

Absolute error Constant error Variable error

RMSE

Magnitude Accuracy Time/speed

Reaction Time Movement Time Response Time

Distance Height Weight

Performance Outcome Measures

• Outcome measures do not tell us how a result was achieved. To understand what underlies performance, we need process measures

Kinematics

Kinetics EMG

Brain activity/imaging

Performance Process Measures

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•  Measures which describe motion, without regard to the cause of that motion.

•  Muybridge (1878) in California, was the first to capture serial images of fast animal motion.

Kinematics

•  Modern systems such as Optotrak use infra-red technology to relay the spatio-temporal positions of markers. 3-D Data can be captured at 1000 Hz.

Kinematics

Video/film Optoelectric

Slow sampling rate Fast sampling rate

Wide workspace of data collection Narrower workspace (less as Hz increases)

Variation in precision of measurement Very precise

Forgiving (extrapolation) Less forgiving

Inexpensive Expensive

Schmidt & Lee (1999)

Kinematics

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Both methods provide raw data in the form of x, y, and z coordinates. From this we can calculate the following:

Displacement (linear/angular)

Velocity (linear/angular)

Acceleration (linear/angular)

Coordination (relative motion)

3 Dimensions

X axis

Y ax

is

Z axis

Kinematics

Motion Analysis

Motion Analysis

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•  Change in spatial position

Displacement

Time (s) Disp (m) Velocity (m/s)

Accel (m/s^2)

0 0

4.1 20

7.9 40

11.9 60

15.7 80

19.8 100

24.1 120

28.1 140

32.1 160

35.8 180

40.0 200

Displacement

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40 45

Time (s)

Dis

plac

emen

t (m

)

•  the rate of change in position (displacement)

Velocity

v = Δdisplacement

Δtime


Accel (m/s^2)

0 0

4.1 20

7.9 40

11.9 60

15.7 80

19.8 100

24.1 120

28.1 140

32.1 160

35.8 180

40.0 200

v = 4.1 – 0s

20 – 0 m

v = 4.88 m/s

•  the rate of change in position (displacement)

Velocity

v = Δdisplacement

Δtime

v = 4.1 – 0s

20 – 0 m

v = 4.88 m/s


Accel (m/s^2)

0 0 4.88

4.1 20 5.29

7.9 40 5.02

11.9 60 5.22

15.7 80 4.91

19.8 100 4.61

24.1 120 5.06

28.1 140 4.88

32.1 160 5.43

35.8 180 4.76

40.0 200 N/A

Velocity

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30 35 40

Time (s)

Velo

city

(m/s

)

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•  the rate of change in velocity

Acceleration

a = Δvelocity

Δtime

a = 4.1 – 0s

5.29 - 4.88 m/s

a = 0.1 m/s^2


Accel (m/s^2)

0 0 4.88

4.1 20 5.29

7.9 40 5.02

11.9 60 5.22

15.7 80 4.91

19.8 100 4.61

24.1 120 5.06

28.1 140 4.88

32.1 160 5.43

35.8 180 4.76

40.0 200 N/A

•  the rate of change in velocity

Acceleration

a = Δvelocity

Δtime


Accel (m/s^2)

0 0 4.88 0.10

4.1 20 5.29 -0.07

7.9 40 5.02 0.05

11.9 60 5.22 -0.08

15.7 80 4.91 -0.07

19.8 100 4.61 0.10

24.1 120 5.06 -0.05

28.1 140 4.88 0.13

32.1 160 5.43 -0.18

35.8 180 4.76 N/A

40.0 200 N/A N/A

a = 4.1 – 0s

5.29 - 4.88 m/s

a = 0.1 m/s^2

Acceleration

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15 20 25 30 35

Time (s)

Acc

eler

atio

n (m

/s^2

)

Upright Stance Hip Pattern Ankle Pattern

Coordination •  Relative motion is the motion of one segment or point in a

configuration relative to another •  Postural coordination patterns

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ITO = ipsilateral take-off IFS = ipsilateral foot-strike CTO = contralateral take-off CFS = contralateral foot strike

Enoka et al. (1978)

Intra-limb Coordination: Running

•  Measurements of the forces which cause motion. •  Predominantly apply Newton’s laws of motion.

•  Examples: •  Force: push or pull on an object; product of an object’s mass

and acceleration (e.g., ground reaction force)

•  Torque: angular force directed around an axis of rotation; product of force and perpendicular distance to the axis

•  Momentum: product of an object’s mass and velocity

•  Equipment includes force platforms, strain gauges, etc.

Kinetics

Kinetics: Force Platform

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Electrodes detect electrical activity which result in muscular contraction. Electrical signals are amplified and recorded.

Data describes temporal patterning, and amplitude.

•  Measures the electrical activity in muscle. Electrodes are attached to the skin superficial to the muscle belly

Electromyography (EMG)

Brain activity and

Imaging

STUDYING THE LIVING BRAIN

•  Electrodes placed on skull detect and record ‘brainwaves’, or the electrical patterns created by the rhythmic oscillations of neurons.

•  Technique often uses: –  Event related potentials (ERPs): electrical peaks that are related

to a specific stimulus.

–  Coherence- functional communication between brain areas of interest

Electroencephalography (EEG)

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•  Electrodes placed on skull detect and record ‘brainwaves’, or the electrical patterns created by the rhythmic oscillations of neurons.


Pros: Directly measure brain activation Good temporal Resolution Relatively cheap Easy to transport Silent! Easy to use for MANY behavioral paradigm

and with different populations

Cons: Spatial resolution Set-up time


•  Uses computed tomography (CT) and radioactive markers injected in the bloodstream.

•  Identifies areas of brain working most based on ‘fuel intake’ (i.e., glucose and O2 providing energy to firing neurons).

Positron Emission Tomography (PET)

•  Characteristics: Good spatial resolution; poor temporal resolution

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•  Records the magnetic fields produced by the electrical activity of the brain.

Magnetoencephalography (MEG)

•  Characteristics: Better spatial resolution; good temporal resolution

Pros: Magnetic fields are less

distorted Excellent temporal resolution Reference-Free Less set-up time Direct measure of brain

activation

Cons: Orientation of MEG Less readily available

Magnetoencephalography (MEG)

•  Aligns atomic particles in tissues by magnetism, then ‘bombards’ them with radiowaves. Different tissues return different radio signals. fMRI determines areas in brain where there is most oxygenated hemoglobin.

Functional Magnetic Resonance Imaging (fMRI)

•  Characteristics: Good spatial resolution; poor temporal resolution

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Pros: Excellent spatial resolution

Cons: Indirect measure of brain

activity Susceptible to movement

artifacts Use of templates and

atlases

Functional Magnetic Resonance Imaging (fMRI)

Brain Imaging

Spa

tial R

esol

utio

n H

igh

Res

olut

ion

Low

Res

olut

ion

Low Resolution Temporal Resolution

Human Connectome

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Summary of Performance Measures

Outcome Accuracy Error scores

- Absoluter error (1-D) - Radial error (2-D) - Constant error - Variable error

Movement Speed Reaction time

- simple - choice - discrimination

Movement time Response time Magnitude

Process

Description of movement Kinematics

- displacement - velocity - acceleration - relative motion - phase plane portraits

Forces underlying movement Kinetics

- force - torque - moment

Electrical activity of muscle EMG Brain activity/images EEG, PET, fMRI & MEG

But before you start measuring performance…..

Is it an objective measure?

A measure is objective if it can be employed consistently by different people. It is also objective if the measurement scale is appropriate.

Is it a valid measure?

This refers to whether a test measures what it is supposed to measure. Does your measure have construct validity? Magnitude measures almost always do. However, is accuracy, consistency, bias a construct of your skill?

Is it a reliable measure?

Is the measurement repeatable? Deviations in the way a test is performed can result in markedly different results. As a result, change may be incorrectly attributed to difference in performance.

Improving your tests’ objectivity, reliability, and validity

• Consider the purpose of the skill

• Keep the test environment consistent

• Document your methodology

• Standardize measures

• Don’t test yourself!

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Step 1

• Develop a testable research question

Step 2

•  Formulate hypotheses – what is the anticipated outcome and why?

Scientific Method

Step 3

• Operationally define independent and dependent variables

–  Independent : the ‘manipulated’ variables/factors

– Dependent: the measured variable (presumably influenced by the independent variable(s))

Scientific Method

Step 4

• Design study to test research question

M F

1 2 3 4

Subjects….? Who… How many? Independent groups or repeated measures? # of trials? How will you control for extraneous variables?

Scientific Method

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Step 5

• Observe behavior and gather data Male Female

SUB 1 12 11

SUB 2 16 14

SUB 3 21 12

SUB 4 22 17

SUB 5 16 12

SUB 6 16 16

SUB 7 14 11

SUB 8 25 21

SUB 9 22 17

SUB 10 34 26

SUB 11 12 11

Scientific Method

Step 6

• Analyze and interpret results of study

• Run descriptive statistics (and inferential statistics)

Male Female

SUB 1 12 11

SUB 2 16 14

SUB 3 21 12

SUB 4 22 17

SUB 5 16 12

SUB 6 16 16

SUB 7 14 11

SUB 8 25 21

SUB 9 22 17

SUB 10 34 26

SUB 11 12 11

MEAN 19.09091 15.27273

SD 6.579583 4.818525

Scientific Method

Objectives

1. Compute, utilize, and interpret outcome and process

measures used to assess motor control, coordination, and learning

2. Design a research experiment to examine specific research questions in motor control and learning.

UNIT 1.2: Measurement and Evaluation of Performance

7/4/12

1

Introduction to Motor Learning

Unit 1.3

Prof. John Jeka

Unit 1 Outline

1.1 Introduction to Motor Control and Learning

1.2 Assessment of Motor Skill Performance

1.3 Motor Learning

•  Characteristics of the learning process

•  Assessment of motor learning

•  Learning stages

1.4 Effects of practice on motor learning

1.5 Assisting the Learning Process

Objectives

1.  Define and distinguish between motor performance and learning

2.  Identify key characteristics of the learning process

3.  Describe and compare / contrast different methods to assess motor learning

4.  Design research experiments to assess motor learning

5.  Describe and compare / contrast different stages of motor learning

UNIT 1.3: Introduction to Motor Learning

7/4/12

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Although we are born with the neural structures which facilitate the acquisition of knowledge and skill, with the exception of elementary reflexes, infants are born without repertoires of behaviour

Bandura (1977) !

Complex human behaviours acquired over time and development are the result of experience and observation. In essence, they are learned. "

Introduction to Motor Learning!

Understanding Learning

Learning is a relatively permanent change in the capability to perform a skill

Learning cannot be directly measured – it is inferred from performance!

Observable behavior Temporary

Not necessarily a result of practice

Influenced by performance variables

• refers to a change in the potential or capability to perform a behaviour ….why?

Learning

7/4/12

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Characteristics of the learning process

1. Performance of skills shows an improvement over a period of time


2. Performance becomes more consistent (less variable) over time

0 5 10 15 20 25 30 35 40 0

0.2

0.4

0.6

0.8

1

1.2

1.4

Varia

bilit

y

Blocks of Trials

3. There is greater persistence in the improvements made

Practice"Time delay"

Repeat"


Krakauer et al., 2005: Visuomotor adaptation

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4. Performance of the skill becomes more adaptable !


Performance Curves

…are a method of assessing learning by recording levels of performance across practice

time (or time period)"

Perfo

rman

ce

mea

sure"

Learning a new skill is typically characterized by one of four performance curves

Dependent variable for learning

e.g., absolute error, variable error, time-on-task, RT

Linear Negatively accelerated

Positively accelerated

S-shaped

(ceiling effect)

(ceiling effect)

Performance Curves

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Performance Curves in Kinematics

More complicated as they show not only changes in performance between trials, but within trials "

Improvement in performance can be assessed by how close the movement pattern matches the criterion.

Consistency can be assessed by the extent to which the movement patterns vary.

It is not wise to infer learning from practice because:

Practice data provides no evidence for permanent/semi-permanent changes in behavior

Performance during practice is susceptible to over-estimating and under-estimating learning

Performance in practice may temporarily plateau

150160170180190200210220230

1 2 3 4 5 6 7 8 9

Days of practice

Abs

olut

e er

ror

Assessment of Learning

Assessing Learning by Retention

The typical design is as follows:

Pre-test Practice/acquisition Post-test Retention test

Measures ability to

perform task before the treatment

+ 1 to 7 days

Measures ability to

perform task after period of

practice

Measures ability to perform task

after a no-practice retention interval

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Pre-test Practice/acquisition Post-test Retention test

Effect of practice on performance

Learning

Decay of performance

Assessing Learning by Retention

Experimenters may test several groups using the same design

Pre Post Retention

3 x 3 design

Control

Verbal Guidance

Video Model

Assessing Learning by Transfer

•  Transfer of learning describes how previous practice on a task influences the learning of a new skill

Transfer can be…

…negative, where previous practice of one skill hinders learning of a new skill

…or positive, where previous practice in one skill assists learning of a new skill

Positive Transfer

•  Sensorimotor adaptation experiment (Abeele & Bock, 2003)

•  Group A (left) performed tracking task in rotated environment before the pointing task (vice versa for Group B)

•  Group A smaller errors on pointing task compared to Group B (right) – Positive transfer across the tasks!!!!

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Negative Transfer

•  Sensorimotor adaptation experiment (Caithness et al., 2004)

•  Task A = 30° CCW rotation; Task B = 30° CW rotation

•  Angular error on day 2 (task B) exceeded -30 degrees, suggesting that performance on Task A hindered performance on Task B

•  Negative transfer!!

The significance of transfer

1. It can define the appropriate sequencing of skills to be learned

•  Curricula tend to be organized in a simple-to-complex order

•  Early fundamentals need to be in place before moving on

•  Skill classifications can be a useful tool to guide transfer

•  PT’s need an appropriate order of functional treatment

2. It can assess the effectiveness of practice conditions!

Criterion performance"

Practice condition 1"



The significance of transfer

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Theoretical explanations for positive transfer of learning

Identical elements theory (Thorndike, 1914)

Task 1 Task 2 Task 3 Task 4

Little overlap of elements = little transfer

Greater overlap of elements = greater transfer

Transfer-appropriate processing theory

Suggests that movement components need not be similar.

Instead, positive transfer is more likely between two skills or practice conditions which share cognitive processing characteristics

(Morris et al, 1977)

Research designs to assess positive transfer

Experimental Practice skill A Perform skill B

Control No practice Perform skill B

Experimental Skill in context 1 Skill in context 2

Control No practice Skill in context 2

Group Practice conditions Transfer test

Experimental group – control group Percentage of transfer = x 100

Experimental group + control group

OR"

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Contextual variations in transfer tests

Changes to the physical environment

Changes in availability of feedback information

Changes to learner’s personal characteristics

Novel skill variations in transfer tests

Changes to the task itself (e.g., faster/slower)

i.e., Changes in constraints!

Transfer

Mobility Simulator

•  The devices can apply 6DOF forces and torques to the feet

•  Simulate varied support surface conditions. The platforms are integrated with two VE simulations, a street crossing and park path.

http://shrp.umdnj.edu/rivers/facilities/index.htm

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Nintendo Wii

•  Use of Wii in physical rehab settings (children with cerebral palsy)

Deutsch et al., 2008

Stages of Learning

Fitts & Posner (1967) 3-stage model

Practice time continuum

Cognitive stage Associative stage Autonomous stage Learner encounters cognitive problems, and must integrate information.

What should I do? How should I move? Large errors; variability

Learner makes associations b/w environmental cues and movements.

Learner detects errors. Performance is refined, variability and error decreases.

Learner performs skill in habitual or automatic manner. No conscious thought of action processes. Learner can divide attention.

Gentile’s two-stage model (1972, 2000)

Stage 1: Getting the idea of the movement

The learner organizes a movement pattern – by delimiting the potential muscular responses in tune with the demands of the environment.

Regulatory conditions Environmental features which specify how movement must be performed

Must discriminate

Non-regulatory conditions Environmental conditions which do not influence movement characteristics.

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Stage 1 also is highly cognitive – problem solving

Learner ‘leaves’ stage 1 with a framework for the organization of the movement, but performance is variable and inefficient

Stage 2: Fixation/diversification

Learner must acquire - adaptability for the skill consistency economy of effort


Closed Open

Skills require fixation

Learner must refine pattern for consistency.

Skills require diversification

Learner must diversify the basic movement pattern. Must be highly tuned to the regulatory conditions


…of coordination, control and skill (Newell, 1985)

Toward skill coordination

control

Early skill learning – emphasis within the synergy of coordination and control is upon assembling a new movement pattern (coordination)

Later in skill learning, when the movement pattern is assembled, the emphasis is upon scaling the movement pattern (control)

Embedded Hierarchy…

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Bernstein’s Degrees of Freedom

The degrees of freedom (DOF) in any system is the number of independent elements to be controlled

DOF problem: how can a complex system act to constrain so many degrees of freedom into a functional unit?

e.g., The human arm has 7 degrees of freedom"

3 at the shoulder"

1 at the elbow"

1 at radioulnar joint"

2 at the wrist"

Early learning – novice simplifies movement by “freezing” a portion of available DOF. Later learning – there is a release of the DOF. Dynamics of action become more apparent to the learner Expert - release and organization of DOF. Flexibility to freeze or release DOF at appropriate moments

Bernstein’s Degrees of Freedom

Objectives

1.  Define and distinguish between motor performance and learning

2.  Identify key characteristics of the learning process

3.  Describe and compare / contrast different methods to assess motor learning

4.  Design research experiments to assess motor learning

5.  Describe and compare / contrast different stages of motor learning

UNIT 1.3: Introduction to Motor Learning

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Role of Memory in Motor Control and Learning

Unit 4.1

Prof. John Jeka

Objectives

1.  Define / compare and contrast: verbal and motor memory, declarative and procedural memory, short- and long-term memory

2.  Describe methods used to assess memory

3.  Explain the neurophysiological processes underlying memory

4.  Describe different ‘causes’ of forgetting

UNIT 4.1: Role of Memory in Motor Control and Learning

Information processing does not simply refer to generating short-term responses.

Information must be retained, and accessed later.

In what form are memories stored?

??

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Memory

How is that I can remember the names of every teacher I had in school (Mrs. Bungay, Mrs. Abel, Mr. Jones, Miss Waugh, Miss. Wilson, Mr. Jones II, Mrs. Winterbottom, Mr. Robottom, Mr. Cormack, Mr. Dean, Mrs. Court… etc , etc)…

But I forget a name within 5 minutes of meeting someone new?

Why does repetition and association make it easier to remember something?

Why are phone numbers 7 digits?

Is memory for action the same as memory for numbers, language etc?

Memory

-  The internal record or representation of some prior event or experience

-  Retention of experience-dependent changes over time

- The capacity to remember

- Tulving (1985): ‘the capacity that permits the organism to benefit from past experiences’

Memory Some definitions…………….

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Schmidt & Lee (1999) “the persistence of the acquired capability for motor performance”

Motor Memory

Motor program: a memory structure, or representation that stores information necessary for action.

…theories of motor control & learning

Schema theory (Schmidt, 1975,88): we have a motor response schema which provides ‘rules’ governing an action.

Motor Memory

…as a reference of correctness in closed-loop motor control theory:

System goal

Reference mechanism

Executive level

Effector level

Environment

output

input

error

instructions

Decisions

Muscle response

Detection, recognition, matching

Motor Memory

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Carter, 2000

Caudate nucleus: instincts (genetically -coded memories)

Hippocampus: laying down/retrieving (spatial) memories

Putamen: procedural memories

Temporal lobe: LT memories

Amygdala: traumatic, uncon. mems

Human Memory System

• Memories are groups of neurons which fire together in the same pattern each time they become activated (Carter, 2000).

Neurophysiological Basis of Memory

A.

1

2

3

Initial stimulus

Linked connection strong enough to trigger firing

Weak connection



B.

1

2

3

Initial stimulus


Weak connection

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C.

1

2

3

Initial stimulus


Weak connection

The faster the neural activity, the more likely the charge will pass to neighboring cells

As memory fades, neural connections are lost. (Carter, 2000)

Every perceived sensation creates new neural connections…

But, if not laid down in memory the impression rapidly fades

Lingering patterns connect with and create activity in other neural networks … = an association

In principle, if same neural network is lit up – should give rise to same thought etc. In reality – similar, mutated patterns occur


Magill (2001): verbal and motor memory considered as part of same memory system.

•  But two conditions suggest they are not:

•  Apraxia – person cannot produce movement from verbal command

•  Agnosia – person can produce a movement but cannot name it

•  Also, depend on different neural structures

•  Verbal: consolidation into LTM depends on medial temporal lobe

Verbal vs. Motor Memory

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Retrieval: the process of calling up information from LT memory (ST memory?)

Retention: the information that we remember

Forgetting: the information we cannot remember Is memory not there?

Cannot retrieve it?

Serial search, activation

Key Definitions…

Measuring Memory

Recognition tests –ability to recognize something from list/group of stimuli.

Recall tests –ability to reproduce something from memory.

How do these relate to our examinations in this class???

Put down your pens…

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83

Tick…..tock

Recall: How many items do you remember from the previous slide?

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Recognition: Which of the following items were on the test slide?

List the 3 proposed stages of information processing ____________________________________________________________________________________________________________

With the condition apraxia, a person: A. Can’t remember the names of movements they do B. Can’t produce movement from a verbal command C. Can’t hear verbal commands D. Can’t remember anything

Stimulus identification Response selection Response programming

Recall vs. Recognition

Two-component Theory of Memory

Declarative Procedural

Episodic Semantic

‘explicit’ ‘implicit’

Short-term Memory

Long-term Memory

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- capacity to retain info for short time (Peterson & Peterson, 1959: <30 sec)

- involves short-term processes - sensation, attention, perception, etc...

- is a workspace for association & integration of new info with retrieved old info.

Short-term Memory

George Miller (1956) - AT&T Laboratories. “The Magic #7” (7 +/- 2 items)

Functional Capacity of Short-term Memory

Immediate recall capacity = 5-9 digits (with or without practice) e.g., phone numbers = 7 digits.

• Chess Players - masters only better than novices with known board patterns

• Joystick movement errors increase after 8

movements (Wilberg & Samela, 1973)

•  Dancers - skilled only better than unskilled with

a known sequence (Starkes et al, 1987)


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C G Q T R L S W D H

E S P N L O L B M W

Remember the following lists:


Serial Position - movements that are first or last in a series are remembered best

Primary-Recency effect

Factors that Affect STM capacity

Limits to STM can be increased by organizing information - “chunking”


A chunk is the largest meaningful unit in the presented material that the person recognizes.

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Implications for instruction?

•  strategies are important

•  present “chunks” of information

•  first - last pieces of information remembered best.


Peterson & Peterson (1959)

00.10.20.30.40.50.60.70.80.91

1 2 3 4 5 6 7

Prob

abili

ty o

f re

call

0 3 6 9 12 15 18 Retention Interval

Duration of working memory: verbal

3 letter patterns, while counting backwards in threes.

Duration of working memory: position

Adams & Dijkstra (1966)

Varied retention interval

???

Criterion position

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Adams & Dijksta (1966)

Motor Memory

Increasing STM through meaningfulness

Semicircular positioning task with 5 or 60 sec retention interval. 3 types of info about criterion mm

Abs

olut

e er

ror (

deg)

9 7 5 0

5 60 Retention Interval (sec)

Clock-face

Verbal label

No label

Shea (1977)

Serial Position Movements that are 1st or last in a series are remembered best

Primary-Recency effect Design:

•  Subjects blindfolded •  linear positioning task •  criterion = total of 3, 6 or 9 movements •  recall criterion in same order

Magill & Dowell (1977)

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Abs

olut

e er

ror (

mm

)

!!!!!! 0

1 2 3 4 5 6 7 8 9 Serial Position

200 160 120 80 40

Results

Primacy-Recency effect seen w/longer MMs.

Two-component Theory of Memory

Declarative Procedural

Episodic Semantic

‘explicit’ ‘implicit’

Short-term Memory

Long-term Memory

Long-term memory

LTM is a relatively permanent storage repository for information (Magill, 2001).

Procedural memory:

Enables us to remember how to do something, so that we can perform learned procedures.

This is not verbally accessible.

Implicit

No known capacity

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Represents being able to verbalize what to do (or what we know). Explicit

- Episodic: knowledge of personally experienced events, and their temporal links.

- Semantic: general/conceptual knowledge developed from experience.

Declarative Memory

Early in skill learning: declarative knowledge predominates. As skill develops, you learn to proceduralize declarative knowledge to solve the action problem.

declarative procedural Anderson, 1987

Motor Learning

Forgetting…

Trace Decay: Refers to deterioration of a memory ‘trace’ as a function of time

Anterograde interference: When information presented before the test stimulus causes interference

Retrograde interference: When information presented after the test stimulus causes interference

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Time

Present “useless” info

Present “recall” info

(retention interval)

Recall info

Anterograde Interference

Time !

Present “useless” info

Present “recall” info

(retention interval)

Recall info

Retrograde Interference

Preventing Interference

Transcranial Magnetic Stimulation

(TMS)

Cohen & Robertson (2011) Nature Neuroscience, 14(8): 953-955

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Cohen & Robertson (2011) Nature Neuroscience, 14(8): 953-955

Preventing Interference

Transcranial Magnetic Stimulation

(TMS)

Motor Memory Consolidation

Kantak et al (2010) Nature Neuroscience, 13(8), 923-925

Practice: (arm movement task) Similar movement structure Same time – 800 ms 2 groups: Constant – A3 (120 trials) Variable – A3 (60 trials)

A1, A2, A4 (20 trials each)

Feedback: Target v Actual trajectories RMSE

Randomized!

target actual


Kantak et al (2010) Nature Neuroscience, 13(8), 923-925 Transcranial

Magnetic Stimulation (TMS)

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Kantak et al (2010) Nature Neuroscience, 13(8), 923-925

EoA = End of Acquisition R = RMSE

Interference effects temporally specific to immediate post-practice phase!

Retrograde - memory loss prior to trauma … you forget things you already knew

% o

f nor

mal

m

emor

y

100 50 0

Birth Time of Today Trauma

Time

Amnesia

Anterograde – impairment in the ability to form new memories

% o

f nor

mal

m

emor

y 100 50 0

Birth Time of Today Trauma

Time

Severe - inability to learn anything new Mild - learning is slow and requires more repetition

Amnesia

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Medial Temporal Lobe

Patient H.M Temporal lobe removed

to relieve epileptic seizures.

Profound anterograde amnesia

Medial Temporal Lobe

Anterograde amnesia limited to declarative memories – not procedural (i.e., motor)

Objectives

1.  Define / compare and contrast: verbal and motor memory, declarative and procedural memory, short- and long-term memory

2.  Describe methods used to assess memory

3.  Explain the neurophysiological processes underlying memory

4.  Describe different ‘causes’ of forgetting

UNIT 4.1: Role of Memory in Motor Control and Learning

1

Unit 4.2: Attention

Prof John Jeka

Outline:

1.  Introduction to attention

2.  Theories of Attention

a)  Fixed capacity vs. flexible capacity

b)  Filter theories

c)  Multiple Resource Theories

d)  Action Selection

3.  Measuring Attention

4.  Pre-attention

5.  Visual Search

UNIT 4.2: Attention

Objectives

1.  To describe / compare and contrast different theories of attention

2.  To describe techniques used to assess retention

3.  To define pre-attention and to compare and contrast exogenous and endogenous control

4.  To define and discuss the components of visual search

UNIT 4.2: Attention

2

What is attention?

In the context of human performance, attention is the conscious or unconscious engagement in perceptual, cognitive, and/or motor activities, before, during, and after performing motor skills

(Magill, 2001)

Is this definition helpful???

Concept 1: humans have a limited availability of resources for performing tasks and gaining information

Capacity to perform task Portion used

to perform task

Traditional resource model (Kroemer et al, 2000)

Concepts in Attention

Concept 2: environmental information must be reduced or filtered

Process Information stream in bits/s Registration in 1,000,000,000 sense organ At nerve junctions 3,000,000

Conscious awareness 16

Lasting impression 0.7

Concepts in Attention

3

Early Theories of Attention

Single, fixed capacity channel

Tasks

Fixed Capacity Models

Driving the car - steering, braking, signaling, etc…

Monitoring position on road

Talking to passengers

Monitoring other cars

The Beginner

Irrelevant info

Fixed Capacity

Driving the car

Monitoring position on road

Talking to passengers

Monitoring road position

Monitoring upcoming stoplight

Deciding to pass

Miscellaneous

The Expert

Fixed Capacity

4

Bottleneck or filter: filters out (ignores) information not selected for further processing.

All information

Selected information

Filter

Filter Theories of Attention

RESPONSE

Selection of Response

Preparation of response

Environmental information

Environmental information

Detection ID

Filter theories differ in terms of where the filtering takes place

Filter? Filter? Filter?


Look at this picture for a few seconds…

5

Was the woman using a cellphone?

Was she wearing a necklace?

Was she wearing glasses?

Name of the pub?

Where was your attention?

What was special about the red car?

Color of her jacket?

Filtering occurs at stimulus identification phase

Identified

Broadbent, 1958

Early Theories of Attention

Unidentified?

http://www.youtube.com/watch?v=Ahg6qcgoay4

Do the Test

6

What did you see?

What happened to all the other information … were you never aware that certain objects were

there, or did you filter them at the point that you selected items of

interest?

Broadbent (1958)

Sensory register

Selective filter

Short term memory

S2

S1


Triesman (1964) – also assumed filtering to occur early in processing.

However, she believed that the filter had more flexibility, considering it an attenuator, amplifying some stimuli and weakening others.

Filter as Attenuator

7

S1

S2

Sensory register

Short term memory

Attenuator

Triesman (1964)


Flexible Capacity Models

•  Attention capacity should not be considered fixed as task requirements change.

• Available attention that can be given to a task is a pool of effort. This can be distributed to several activities at once.

• Arousal becomes a factor.

Kahneman, 1973

Miscellaneous determinants

Responses

Arousal Miscellaneous manifestations

of arousal

Enduring disposition

s

Momentary intentions

Evaluations of demands on

capacity

Allocation policy

Possible activities

Available capacity

Flexible Capacity

8

Multiple Resource Theories

• Previous central resource theories consider attention to be taken from a central, single resource.

• Multiple resource theories suggest the presence of many attention mechanisms, each with limited resources, and differing functions.

e.g., Allport (1980), Wickens (1980, 84, 92)

Action-selection Accounts of Attention

• Disputed the very concept of capacity or resource limitations in attention.

• Rather, when we have the momentary goal of an action, the stimuli are all processed in parallel at first. The outcome of this is selection of an action.

• As a result of this selection, certain processes are prevented from happening.

Neuman (1987, 1996)

Change Blindness

http://www.youtube.com/watch?v=vBPG_OBgTWg

Daniel Simonds Experiment:

Derron Brown – Person Swap

http://www.youtube.com/watch?v=38XO7ac9eSs

9

The primary task is the one of interest, and the secondary task is the distractor.

Continuous secondary task:

Assesses if attention is required throughout performance of a motor skill. e.g., motor and verbal skills

Secondary-task probe: Assesses attention demand in preparation, of components of a skill, or at specific moments in performance.

The Dual Task Paradigm

MEASURING ATTENTION

Primary task - move a handle between 2 targets (RH) Secondary task (probe) - press a button in response to a buzzer (LH)

0 45 90 Movement Position of Primary Task (degrees)

Seco

ndar

y Ta

sk R

T

no primary task

Attentional demands change over time

primary + probe

Posner & Keele, 1969

Dual-Task Paradigm

• The process of detecting stimuli in the visual field (usually in the periphery) to guide future attention.

Pre-Attention

10

• The process of detecting stimuli in the visual field (usually in the periphery) to guide future attention.

Can be bottom-up (stimulus driven): if target is sufficiently different from distractors (targets ‘pop-out’). This is exogenous control.

Pre-Attention

Can be top-down (user-driven): uses a limited ‘vocabulary’. Evidence from detection of target colors among heterogenous colors.

This is endogenous control.

Pre-Attention

Pre- Attention to color

Parallel visual search: all items in the display are processed simultaneously-- the search time is independent of the number of distractors

Target = Red Circle

11

Pre- Attention to Form

Parallel visual search: all items in the display are processed simultaneously-- the search time is independent of the number of distractors

Target = Red Circle

Serial visual search: the attention system examines each item, one by one, to determine whether it does or does not have the required conjunction of features

Color and Form

Target = Red Circle

Attention….

•  Enhances Detection

•  Influences Reaction Time

Behavioral Consequences of Attention

12

Detection

Fixate on central point… fixation

point

attended location

Small circle flashed for 15 msec...

Left

cue ( , or +)

Attention shifts to the right...

Right

Cue / Target +/Right Right/Right Right/Left

% c

orre

ct d

etec

tion

100 80 60 40 20 0

(Posner et al., 1980)

Detection

Cue

Invalid Neutral Valid

300 250 200

Rea

ctio

n Ti

me

(mse

c)

(Posner et al., 1980)

Detection

13

Spotlight Metaphor

Selective attention is… •  a "beam" that is moved spatially •  may not be divided •  enhances detection of events falling within it.

Williams et al, (1999)

How does the anatomy of the retina explain pre-

attention?

Acuity drops to 50% in 2.5 deg of arc.

Spotlight Metaphor

Visual Search - Selective Visual Attention

• Visual search is the process of actively directing visual attention to locate relevant information in the environment.

• Evidence that eye movements directed to a location are preceded by a shift in attention to that area, & the coupling on attention and eye movements is mandatory.

Hoffman, 1998

14

The two visual system:

1. initial detection in the peripheral retina (pre-attention),

2. identification, recognition etc through foveal vision.

Components of visual search

Saccades:

Are conjugate eye movements, responsible for rapid jumping shifts in attention. We have dramatic loss of sensitivity during saccades. Saccades can be anticipatory.

Pursuit tracking eye movements: smooth eye movements which allow us to track slow moving objects of up to 100 deg/sec (decline at 30 deg/sec).

The vestibular-ocular reflex (VOR): stabilizes gaze during head movements.

Fixations: Pauses in visual search, between saccades. They stabilize vision for greater uptake of information. Typically a minimum of 100-120 ms.

Components of visual search

Eye Movements

15

EYE MOVEMENT SUMMARY

http://www.tutis.ca/Senses/L11EyeMovements/L11EyeMovements.swf

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