Performance and Motor Control Characteristics of Functional Skills

Manual Aiming Skills

• involve hand movement to a target

• requires that the hand arrive at the target but at a speed that the performer determines

Speed/Accuracy Trade Off definition

a characteristic of motor skill performance when the speed of a movement at which a skill is performed, is affected by how much accuracy the task requires

What is the ‘trade-off’?

1. emphasis on increasing speed will decreasing accuracy

2. while emphasis on accuracy will reduce speed.

Fitt’s Law 

predict movement time (MT) for speed-accuracy skills if we know the spatial dimensions of two variables. 

What are the two variables that are required for Fitt’s Law?

• movement distance

• target size

Fitt’s Law equation

MT = a + b log2 (2D/W)

MT =

movement time

a and b = 

constants 

D -

distance moved

W -

the target width or size

What are the characteristics that we need to know to ensure accuracy?

• how accurate do we need to be

• what’s the size of the target

• how far away is the target

As the distance to move increases, the movement will take ______. 

longer

The more accurate we have to be in our movements, the _______ we have to go.

slower

As the target size becomes smaller, the movement speed will ________ to ensure accuracy.

decrease

Index of Difficulty definition

a measure of the difficulty of performing a skill involving the speed and accuracy requirements 

A higher ID means that the task is more _____ and will require _____ movement time. 

difficult, more

Index of Difficulty equation

log2 (2D/W)

Prehension defintion

general term for actions involving reaching for and grasping objects. 

What are the three components of Prehension?

1. Transport - movement of the hand to the object

2. Grasp - the hand taking hold of an object 

3. Object Manipulation - the hand carrying out the intended use for the object (e.g. drinking from a cup or moving it to a new location)

Components of Prehension are 

All interdependent on each other. Each component will be affected depending on the goal of the action. 

Object’s size influences 

• timing of maximum grip aperture (opening diameter)

• velocity profile of hand transport movement

Regardless of object size and distance to reach for the object, maximum grip aperture and hand closure occurs at _____ of the total movement time duration of the action.

~2/3

Prehension and Fitt’s Law

actions are speed-accuracy skills.

Accuracy is prioritized and speed is determined based on accuracy demands. 

If priority is speed then going to be less _______.

accurate

If priority is accuracy then it will be _____.

slower

Role of Vision in Prehension phases

1. preparation phase

2. in flight phase

3. termination phase

Preparation Phase

Assess conditions to determine size, location spatial orientation, distance 

ex. grasp key in hand 

In Flight Phase

Monitors limb displacement and velocity while gaze shifts to keyhole at around 50% completion of time to contact keyhole. 

ex. moving key to keyhole 

Termination Phase

Temporal and spatial corrections required for successful completion of task.

Supplements tactile and proprioceptive feedback to ensure intended use achieved.

ex. key inserted into keyhole

Motor Equivalence Definition

The capability of the motor control system to enable a person to achieve an action goal in a variety of situations and conditions.

Key Idea of Motor Equivalence

Brain store motor pattern and spatial plan for the task. 

CNS, PNS, MSK systems function as one coordinated unit.

• integration of motor and sensorimotor planning 

• cognitive processes and nervous system communication

• muscular execution 

• all to produce movements that adjust to the task demands

Motor Equivalence in Handwriting 

Execute the task in many different ways - either hand, foot, mouth. 

Person can make adaptations to various demands of the writing. (pen/crayon, light/heavy, writing fast/slow, big or small letters) — the brain figures out how to move whatever is needed to achieve the same goal. 

Bimanual Coordination Skills definition

Motor performance requiring simultaneous performance of both arms. 

Skill may require two arms to move with the same or different spatial and/or temporal characteristics.

• symmetric bimanual coordination 

• asymmetric bimanual coordination 

Symmetric Bimanual Coordination

both limbs are doing the same thing.

the MC system prefers this

Ex. rowing a boat, wheelchair (W/C) propulsion

Asymmetric Bimanual Coordination

Each limb is doing something different.

Ex. guitar playing, unscrewing the cap of a jar, serving a tennis ball

Catching a Moving Object definition

Object manipulation is the functional goal for the prehension action.

What are the three phases of Catching a Moving Object?

1. initial positioning of the arm and hand

2. shaping of hand and fingers

3. grasping of an object

______ is important or the spatial and temporal set of the arms, hands, and fingers before the ball arrives 

vision

T or F. Central and peripheral vision are both critical to catching the object.  

TRUE

_______ and ______ feedback are important after contact to make adjustments to grasp. 

proprioceptive, tactile 

What are the two critical time periods in Visual Contact for Catching a Moving Object?

1. initial flight

2. final flight

Initial Flight phase 

Vision is required to predict trajectory. 

To obtain info about direction and distance of flight.

• may be as little as 300 milliseconds to predict direction and distance of catching a ball.

Final Flight phase 

Obtain time-to-contact info, preparing final spatial positioning of hands and fingers and time grasp. 

Vision is required for only the last 200-300 milliseconds.

T or F. Between the two critical periods of visual contact for catching a moving object there is only a brief intermittent visual snapshot track/locate object is sufficient.

TRUE

What is the key factor of answering the question - Is vision of the hands necessary to catch a moving object?

how much experience does the athlete/person have in catching a moving object.

Striking a Moving Object (Baseball Batting)

• tracking the ball longer 

• skilled strikers demonstrate similar bat movement time for all ball speeds 

• initiation of the swing is adjusted based on the speed of the pitch 

• experience and skill determine how important it is to see ones own hands 

Striking a Moving Object (Table Tennis)

• vision triggers initiation of the swing and provides info that the player uses to make compensatory adjustments

• depending on the initiation time and the time to contact, players will adjust speed of swings to compensate 

• if time to contact is shorter at initiation of swing, the swing will be faster to compensate

The first two phases of Catching and Striking are usually complete by ___% of object flight.

75

T or F. Symmetric tasks are easier due to intrinsic coordination.

TRUE

T or F. Asymmetric taks are harder than symmetric takss.

TRUE

If you are doing a motion slowly you are prioritizing _______.

accuracy

Fitt’s Law predicts the speed-accuracy tradeoff based on - 

movement, distance, and target size

T or F. Both transport and grasp vary depending on the task goal.

TRUE

What are the 3 phases of catching

1. move hand

2. shape hand

3. grasp

Vision guides _______ and ________ for striking moving objects.

initiaion, adjustments