movement constraints Flashcards
what are everyday examples of speed accuracy tradeoffs
high speed low accuracy = football tackle, parking in a large spot
low speed high accuracy = surgery, parallel parking
what are the 3 factors that affect the spatial and temporal accuracy of voluntary actions
motor variability scales with movement speed
fitts theorem
neurphysiological principles that contribute to variabliity
what is determined through fitts theorem
mvmt amplitude and accuracy demand both impact mvmt time
can predict average mvmt time
what is the difference in y intercept in older adults
higher average intercept
- slower mvmts on average
what is the difference in slope in older adults
higher average slope ofr older adults
- speed accuracy tradeoff is more severe
what is the difference in mvmts between old and young adults
young
- smooth, fast mvmts on average
- few corrections
old
- lower peak velocity
- more corrections in deceleration phase
why is the speed accuracy tradeoff more severe in older adults
muscle mass loss
white matter loss (slower conduction velocity)
loss in strength
precision of controlling forces (loss of fine MUs and larger ones take over)
what are everyday examples of fitts theorem in real life
keyboards
- frequently used keys = larger (reduces accuracy demand)
- rare keys = smaller (minimises error)
golf club
- driver = longer, increases ball speed but not as accurate
- wedge = shorter, decreases ball speed, increases accuracy
how to measure speed accuracy tradeoff
make alternating mvmts between targets as quickly and accurately as possible (251 lab)
MT increases with increased amplitude or accuracy demands
what is motor variability proportional to
the amount of force produced
- variability increases with force increase
what is the difference in variabilty at muscle contractions at 20% and 70-80% MVC
70-80% MVC = peak variability
20% MVC = low variability
why is variability greater at higher forces
larger MUs are recruited
- have higher twitch potentials (more force at a higher frequency)
- higher innveration # (more MUs turned on/off at the same time - larger jump in force)
why doesn’t variability peak at 100% MVC
change in force is happening so fast
derecruit-recruit is happening on top of each other (interference)
what types of muscles have a smaller innervation #
muscles that require more precise control (ex: hands)
- incremental change in force is slower than for a large MU
how is the force generating capacity different between slow and fast twitch fibres
slow twitch = force generating capacity plateaus at low frequencies
fast twitch = can produce high levels of force at high frequencies
what is the difference in force variability with age
larger variability in older adults as they produce more force
what is the difference in average force of MVCs with age
similar between young and older adults
how does the NS minimise the effects of noise / variance
moves slower when accurate mvmts are required
- NS selects motor commands to minimse the variance of the final hand position
- selects smaller mvmts to decrease variance
what is the benefit of minimising the effects of variance
leads to smooth, unimodal speed profiles that resemble human mvmt
other than fitts theorem, what plays into motor command selection
minimising energy costs
- leads to decreased variance as well
- correlated with the size of motor command and variability
what is involved in selecting motor commands that minimise energy costs
accounts for the cost of cycling calcium in muscles to activate them
- cost of muscle activation (effort) plays into the selection of motor commands
does the NS make decisions based on variance or energy cost
not known
- can be goal / task dependent
- both are closest to human mvmt
- NS spends more energy based on risk of losing reward
