Tradeoff of Speed and Accuracy

Question 1

what do we tradeoff to move fast

what do we tradeoff to move accurately

as speed goes up, what else goes up

furthest away target

Answer 1

accuracy

speed

error %

lowest accuracy, fastest average speed

Question 2

Fitts Theorem

changes in movement time

Answer 2

Fitts (1954) discovered the relation between movement
amplitude, accuracy, and MT could be described by a
log-linear equation
Fitts’ Theorem: MT = a[log2(2A/W)] + b
a = slope
A = movement amplitude
W = target width (i.e., accuracy demand)
b = y-intercept
Index of difficulty (ID) = [log2(2A/W)]

Movement time (MT) increases as movement
amplitude (A) increases
MT is constant for a fixed ratio of movement amplitude
(A) to target width (W)
MT increases as the target width (W) decreases (i.e., accuracy demand increases) or amplitude of movement increases

Question 3

speed-accuracy tradeoffs during lifespan

hand motion profiles

hand velocity profiles

Answer 3

Higher intercept for older adults means baseline movements (unconstrained) are slower than young adults.
Higher slope for older adults means speed-accuracy tradeoff is more severe than young adults

smooth motion for young adults, 50% accel 50%. decel

smooth and few corrections, faster overall movements

Question 4

which MU is the most variable

as force level increases, what happens to subjects maintaining a force level

Answer 4

As force increases, FG MU are recruited.

as force level increases, the subject shows more variability in maintaining a constant force level

more force, more error

Question 5

when does force variability peak
why

are faster movements are more variable, and require more force

what do larger motor units come with

Answer 5

force variability peaks at 75% of MVC, and decreases until 100%
because then it becomes a fused tetanus

Slight decrease in variability for very fast movements that approach an MVC

behaviour shows a decrease in variability near max exertion

large MU correlates with the variability of muscle force production

Question 6

how much larger can a single fast twitch fibre potential be than a slow
activating larger fibres can increase…

Answer 6

20x larger

activating larger fibres can increase. activating larger MU can increase the variablity of force production during Voluntary actions