Week 9 - Motor control in complex environment & individual differences in motor behaviour

Microgravity

• refers to conditions wherein the force of gravity is very small

  • sum of the mechanical forces acting on the body is zero

  • can experience in space

• Motor control becomes harder because:

  • changes in physiological systems

  • changes in sensory consequences about learned actions

Parabolic flights

• offers an environment for which to sutdy the effects of microgravity

  • at the peak of the trajectory the gravitational force is close to 0

Experiments in Microgravity

• Eienstein’s equivalence principle: no measuring devices can distinguish between inertial and gravitational forces

  • postures and locomotion are possible becuase of mechanical contact forces

Experiments in orbit

• offers prolonged exposure to microgravity for studying motor and sensory adaptations

• can last days, months, years

• challenges:

  • long preparation times between launch and data collection

  • astronauts may experience physiological changes before the experiments are conducted

  • adaptation to space might already occur before data collection begins

  • results may be influenced by prolonged exposure or bodily adaptations

    • redistribution of bodily fluids becuase of no hydrostatic pressure

Experiments in parabolic flights

• can achieve microgravity within seconds

  • lasts for 20-30 sec

• can have variety of participants

• challenges:

  • aircraft can rotate and coniditions may not be as stable

Orbit micorgravity vs parabolic flights

• orbit:

  • pro: prolonges, exposure, comprehensive data collection

  • con: long delays in setup, physiological adaptations over time

• parabolic flights:

  • pro: quick access to microgravity, shorter durations for experiments

  • con: less stable conditions, limited exposure time

What is VOR?

• vestibulo-ocular reflex

• stabilizes vision during head movements by coordinating eye motion in the opposite direction of the head

VOR mechanism

• eye velocity is matched to the head velocity

• when the limit of eye motion is reached, the eyes make a rapid adjustment to bring gaze to the new location

• Nystagmus

  • alternating fast and slow eye movements adjust vision to maintain fixation

  • if head keeps moving, nystagmus stops

  • if the head stops, endolymph movement in the semicircular canals continues briefly

What do the otolith organs sense?

• linear accelerations

  • unloaded in microgravity

what do the semicircular canals sense?

• head rotations

  • unaffected by microgravity

Coriolis Cross Coupled stimulation

• unusal combination of linear and angular accelerations

  • elicited by tilting head whicle in rotating chair

• Skylab M-131 investigated if similar effects occur in space

  • no disorientation or nausea

  • do not know if this is an adaptation

  • could not determine if it was related to VOR

Velocity Decay

• after quick head movements, out vestibular ocular reflex works to move our eyes to stabilize our vision

• Velocity decay - the measure of the reduction in eye-movement velocity in the slow phase after the initial response

DiZio and Lackner set up

• investigated the VOR in microgravity conditions created during parabolic flight maneuvers

  • how VOR adapts and decays in alternating gravity (micro vs normal)

• data represented VOR responses (eye movements) as the had rotates during these conditions

DiZio and Lackner results

• slope of VOR decay is steeper in microgravity compared to normal

  • VOR adapts more rapidly under 0G conditions but is less stable over time

• microgravity conditions alter usual feedback systems that calibrate VOR

• velocity storage pheonomenon is affected by microgravity

Proprioception and microgravity?

• may be affected by microgravity

  • limb-matching experiments show decreased ability to compensate for vibration induced noise

  • perception of body position is less accurate in microgravity

  • could be from lack of vestibular inputs or less activation of muscle position sense

Proprioception and loading

• idea that the absence of gravity may affect proprioception

  • supports original assertions about kinesthesia (weber)

  • “our muscle always perceived space as affected by gravity”

    • proprioception relies on interplay of sensory input and gravitational loading

    • no loading in 0G

Bringoux et al 2012

• examined how joint-position sense and proprioception are affected in environments with varying gravity levels (0G, 1G, 1.8G)

  • particpants did reaching tasks in each

  • also 0G + external torque (replicate sensation of gravity)

• findings:

  • errors increased in 0G compared to 1G

  • error in torque conditions were reduced and more closely matched to 1G

    • addition of external torque improved joint-position sense in 0G

    • supports idea that proprioception during movement planning and control is tuned to the gravitational environement

How does microgravity affect online arm movement corrections?

• Limb-position sense is altered in microgravity

Double-step paradigm

• used method in motor control research to study adaptive and reactive movement processes

  • investigates online movement adjustments

• participants aim at a target location but on some percentage of the trials the target “jumps”

Bringoux et al 2020

• investigated motor control under different gravitational conditions (0G and normogravity)

• examined limb kinematics and endpoint error in participants performing a reaching task

• Findings:

  • very little differences in endpoint error or limb-kinematics between conditions

    • muscular torques required to generate corrections were significantly different in normo and microgravity

  • highlight that the CNS can flexibly adapt control processes to gravitational constraints

How does the nervous system adapt to microgravity?

• to understand body position it integrates multiple sensory inputs

  • visual, vestibular, proprioceptive, auditory

• when sensory information is compromised:

  • nervous system upweights other sensory modalities to maintain functional movement and spatial awareness

  • visial information = spatial localization

  • auditory information = timing and coordination in taks

electroencephalography (EEG)

• used to measure the brain response to sensory stimulation

  • evoked potential = meausring the brain response to stimulation

Sensory re-weighting in microgravity

• normagravity

  • proprioceptive feedback from ankles is needed for balance during stepping

  • increased somatosensory responses help maintain balance

• microgravity

  • proprioception becomes less critical for movement control

  • decrease in somatosensory responses

Saradjian

• participants exhibited increased late somatosensory evoked potential when preparing a step in normogravity

• in absence of postural constraints in microgravity, no facilitation of somatosensory information was found

• suggests that the nervous system can dynamically adjust the weighting of sensory information to gravitational constraints

Individual differences and abilities

• stable differences in between-individual performance

  • between-person variability

  • exacerbated in patient populations

• ablities: stable traits that underlie/support person’s skill

  • maybe has a genetic component

  • maybe is not completely trainable

History of study of individual differences and abilities

• Post-world war II there was an emergence of the study of individual differences for pilot selection

  • needed to select trainees rapidly for training in military aircraft

Fleishman

• argues that we could predict motor skill learning from differences in abilities

  • most important predictor for skill acquisition is the number of hours of practice

Fleishman study

• used battery tests to determine if transfer can be predicted performance on simple motor tasks

• found that bimanual coordination and RT predicted transfer performance

• organized motor abilities into a systematic taxonomy for evaluation

  • included RT, coordination, manual dexterity

  • used in application like designing training programs for NASA astronauts

Fleishman and Ellison

• conducted experiments using RT tasks and pathway tracing coordination tests

• found that higher test scores correlated with higher transfer rates

  • participants with strong perceptual motor abilities were better at applying learned skills to new contexts

• ability of these participants facilitated learning

• Issues:

  • experience using the

Early studies

• goal was to develop a motor aptitude test

  • design better environments and promote learning

  • tests lead to exclusion of individuals who do not possess the right aptitudes

• in practice these tests lead to exclusion of individual who do not possess the right aptitudes

Old debat nature vs nurture

• nature:

  • abilities are inherited traits

  • stable and enduring

  • about 50

  • underlies many different skills

• nurture:

  • skills are developed with practice

  • easily modified

  • essentially countless in number

  • depends on seval abilities

Individual difference research 3 areas of concern

1. differences in initial performance

2. differences in the rate of skill acquisition

3. differences in the maximum skill levels

Transfer in tasks

• when someone encounters a new task there is some degree of transfer

  • enters a skill learning paradigm with some degree of prior knowledge

• can be both positive and negative

  • positive: experience helps the learner perform the new skill

  • negative: experience may hamper the performance of the new skill

Pre-post design in skill learning

• learning paradigms often use a pre-post design to assess improvement

  • performance prior to acquisition is compared to performance in retention and transfer

• performance difference scores: the difference between initial acquisition performance and performance at retention or transfer stages

  • RMSE post - RMSE pre

  • performers with lowest initial performance will have greatest difference

Graphs plotting

• suggest that initial ability levels influence the rate and extent of skill acquisition over time

Maximum skill levels

• wechsler: difference between the best and worst performers was 3:1

  • best performer is 3x the amount of productivity as the next best performer

• difficult to determine if this is related to abilities

  • transfer effects and initial skill level change while progressing through practice

Early theories (Fleishman and Hempel)

• Intellectual and cognitive ability facilitated early performance and acquisition of motor skills

• suggested task-specific abilities are essential predictor of performance

• Limitations:

  • general ability is only important for initial learning of a skill

  • performance can only be predicted after practice

Ackerman three phase theory of individual differences

• supports the controversial idea that individual differences prior to practice could affect learning

Phase 1

• initial learning stage

  • strong attentional and cognitive demands

  • general intelligence (spatial, verbal, numerical)

Phase 2

• integration and consolidation

  • attentional demands are streamlined

    • transition from knowledge acquisition to skill execution

    • focusses on perceptual abilities and contrast abilities

    • thought to be associated with ability to chain responses

Phase 3

• skilled performance becomes more proceduralized (automatic)

  • more movement fluidity is acheived and attentional demans are reduced

    • dependent on psychomotor abilities

    • related to motor competence of the individual

Declining relationship between cognitive and motor capabilites

• numerous studies suggest that as cognitve demand decreases in motor learning, the relationship between cognitive ability and performance also diminishes

Ackerman and Cianciolo

• 1999:

  • combined simple RT, choice RT and psychomotor measures

  • found that adding perceptual-speed and psychomotor tests to intellectual measures improved predication of performance

  • only study looking at predictive validity of perceptual and psychomotor skills
    

Focus on practice, not abilities

• individual differences in the realm of skill learning is attributed to deliberate practice

  • idea that practice conditions can be optimized to facilitate the attainment of expertise

• idea that we can optimize practice conditions to help every learner achieve their goals

• significant individual variability in response to practice

  • some improve faster and some reach higher performance levels than others

• influence of factors like prior experience, cognitive ability, motor aptitude

Recommendations

• invent in everyone

• more grassroots focus, greater pool of players, more likley to generate an environment that fosters motor skill acquistion

• achieves larger goal of promoting physical acitvity