ch 6- speed accuracy trade off Flashcards
When does speed accuracy trade off occur?
when the goal is to move a limb/body part as fast as possible to reach a target with minimal error
3 different paradigms
- logarithmic (fitt’s paradigm)
- linear
- temporal
Experimental paradigm
-person moves a stylus back and forth to two targets as fast and accurately as possible
-experimenter manipulates target width and amplitude (distance between targets)
-emphasis on accuracy
-experimenter changes the index of difficulty (ID)
Index of difficulty formula
ID=Log2(2A/W)
A= amplitude
W= target width
When speed and accuracy are graphed logarithmically it produces a
straight line
logarithmic straight line (Movement time line)
MT= a+b[log2(2A/W)]
therefore MT= a+b(ID)
a and b are constants
MT= avg movement time/tap (from number of taps in a given time period)
what is 50 taps in 20 sec?
0.4 s/tap
Fitt’s law shows a(n) — relationship between difficulty of movement and speed
inverse
movement time must be traded off to maintain
accuracy under different values of ID (index of difficulty)
ID=0
accuracy required=?
none
When is ID=0
(give an example)
when two targets overlap in width
Different effectors have different
slopes
(because each effector has its own sensitivity to changes in ID)
slope — for larger effectors
increases
(larger and heavier limbs are more sensitive to changes in ID)
slope increase for larger muscles, what does this tell us?
-large/heavy limbs= more sensitive to changes in ID
-Fingers can be controlled more precisely
-older adults usually have higher slopes
Fitt’s law holds true for..
different age groups, lower/upper limb movements, underwater movements and imagined movements
Linear speed accuracy trade-off:
WHEN is this relationship observed?
during rapid single-aiming movements
Linear speed accuracy trade-off:
describe action and what the task required
the person reaches with a stylus from a starting position to a target that is 10-60cm away. MT (movement time) is constrained by experimenter. Target width is maintained. Task requires timing and distance accuracy
Errors are measured as
standard deviation (SD) of movement amplitude
= also called the variation in movement end point (We)
=variability/error
What is the linear-speed accuracy trade-off relationship equation?
We= a+b(A/MT)
a and b= constants
A= movement amplitude
MT= movement time
Linear speed-accuracy trade-off:
What happens to variability (We) as movement amplitude (A) increases
We (error) increases as amplitude increases
velocity=?
relation to A and MT
velocity= A/MT
What happens to We as velocity increases?
We increases
(error increases/accuracy decreases as velocity increases)
Logarithmic trade-off occurs for movements that are controlled by…
feedback-based corrections
Linear trade-offs occur for tasks that are…
entirely preprogrammed (NO FEEDBACK USED)
Feedback hypothesis
logarithmic trade off= feedback based
linear trade-offs= no feedback
What is an example of a linear trade off task?
rapid reaching task (no feedback used)
Movement time goal hypothesis
to increase accuracy, move slower
Temporal Speed-accuracy trade off:
give an example of a task and what is required
-tasks that require anticipation and timing
-example= hitting a baseball
–> you need to anticipate the flight of the ball, internal motor planning, and limb movement (effector anticipation) to decide when to swing
Temporal speed-accuracy trade off:
typical paradigm?
must move a slider to intercept/hit a target moving along a track
Temporal speed accuracy trade-off:
what is accuracy measured in terms of?
errors of time
(early of late arrival of the slider to the target)
Temporal speed accuracy trade-off:
the more “violently” the person performs the movement, the more — the timing
accurate
-violent movement= smaller MT or larger movement velocity
-timing is more accure
What principle is this violent movement, more accurate timing relationship opposite to?
temporal speed accuracy trade-off is opposite to the speed-accuracy principle for spatial accuracy movements
Does the temporal speed accuracy trade-off have anything to do with spatial accuracy?
NO
It is easier to estimate — time intervals
shorter
Variation of temporal speed accuracy trade-off
person performs discrete movement timing tasks
goal= to produce a specific MT
Smaller MTs produce — movement-timing consistency
(give an example)
improved
-example= have someone time you trying to count to 2 seconds and then to 20 seconds. it is easier to estimate shorter time intervals
Temporal speed accuracy trade-off
Application: baseball swing example about MT and errors
Temporal speed accuracy trade-off suggests that the person should swing the bat harder (smaller MT, larger movement distance) to decrease errors in timing
–> could be why batters practice with a weight on the end
–> when you take the weight off you will swing much harder
