Week 2.2: Characteristics of Movement Flashcards
Characteristics of Movement
Absolute Error
-Total variability accounts for bias and variability around a target position
-A related measure is absolute error
-absolute deviation between the performers movements and the target
-denoted as AE
-difference from TE is that you take absolute values instead
*Deviation magnitude (ignores direction)
Absolute Constant Error
Absolute constant error is a transformation of constant error
-just removing the sign of constant error
-calculate CE and then take absolute value from that
When would this be useful?
-when you’re using a Target where negative and positive are the same degree of error
-when you get almost equal sized positive and negative errors that cancel each other out
-Ex. half group in slightly right half group aim slightly left CE is approximately zero which is a false representation
Measuring Performance in a Continuous task
Can compute the difference between performed trajectory and Target trajectory
*RMSE - root means error
-measuring the deviation over sampling variable
Graph:
-Plot how error changes as a function of a sampling variable
-compare actual results to idealized Performance
Characterizing movement features (Muybridge, 1887, 1979)
Characteristics of movement by features have been done for centuries
-Muybridge (1887, 1979) Examined the different phases of movements in
humans and horses
-took photos of horses movement and defined different parts of gait by where the hoofs were located in the photo
Movement characteristics (biomechanics versus motor control)
Biomechanics and Rehabilitation is often concerned with the quality of movement
-examining loading muscle, activation patterns, joint reaction forces
-purpose preventing injury, making movements more efficient
-focused on quality/best movement
Motor control and learning is often concerned with errors and performance
-examining endpoint variables and strategies
-always compared to a Target
-not concerned with quality, efficiency, etc., only focus on completing the task/ able to complete it
Characterizing movement features (Kinematics and Kinematic Markers)
Movements can be characterized by looking at kinematics
-concerned with motion rather than the forces that created that motion
-kinematic markers can be used to describe movements:
1. position information ( where the limb is in space) *position to acceleration = take derivative of each other
2. velocity information ( rate of change of position)
3. Acceleration ( rate of change of velocity) *acceleration to velocity = take integral of each other
-Temporal and temporal kinematic variables are also used to describe movement
-reaction time, movement time, time to/after kinematic markers
Why are kinematics useful
Kinematics can give a researcher, teacher, coach detailed information about current performance and improvements in actions
can provide detailed and understandable feedback to participants
-Lindahl (1945) - used position data to examine the differences between
skilled and unskilled labor
-Neuronal firing patterns reflect direction and speed of upcoming actions
Kinematics in the brain
Neuronal recording studies have found that neuronal firing patterns in motor related areas in the brain predict the kinematics of movements
-posterior parietal cortex
-motor cortex
-Speed of upcoming movements correspond with speed of neuronal firing in the pre-frontal cortex (Maunsell and Van Essen)
-Kinematics (speed and direction) associated with neural responses and movement (Ashe and Georgeopolous)
Temporal characteristics - reaction time
-Reaction time (RT) was traditionally used as a proxy for cognitive function
-RT is a measure of the time from the arrival of a stimulus to the beginning
of the response
*stimulus is unanticipated
What are some ways we can control anticipation?
- Vary time between stimuli ( don’t know when signal will go off)
- Present a go and a no-go stimulus
- Make stimulus ambiguous
Process of Reaction Time
- Warning- Foreperiod (e.g. waiting for gun fire)
- Stimulus presented- RT starts, pre-motor and motor (e.g. gun fires)
- Response begins- movement time (e.g. start running)
- Response ends (e.g. stop running)
*total response time= reaction time + movement time
Temporal Characteristics - Movement Time
Movement time is the time interval from the initiation of the response to the completion of the movement
-Precision of units depends on the skill
Response time = RT + MT
-Different processes may be studied using RT and MT
-Processes to initiate a movement, studied during RT
-Processes to complete a movement, studied during MT
-Different processes may underlie correcting a movement as well
(corrections may affect movement time at specific segments of trajectory)
Measuring and evaluating relationships (How do we quantify strength of a relationship?)
Often we are concerned with the relationship between movement characteristics and performance
*simple statistical way to quantify the strength of a relationship= Correlation
Correlation vs. Regression
Correlations measure both the direction and strength of a relationship
-correlation coefficient (R)
-number indicates the strength of the relationship from negative one to one
-sign indicates direction of the relationship
-R2 measures the shared variance
Regression allows us to predict one variable from another
-simple regression fit a linear model to data that we have collected
Attention and Motor Performance: How to measure capabilities
An indirect way of measuring capability in a motor task is to measure performance on a dual cognitive task
-attention is a limited capacity resource it is harder to do a task when doing a dual cognitive task
-the less attention a task takes the more the performer has mastered it
*tells you how much attention they need to devote to the skill. the
better they are at dual tasks, the more proficient to perform the skill
Ex. juggle while performing tasks
