lecture 10 - principles of speed accuracy and coordination part 1

what are seed accuracy trade offs

If you perform the same action more quickly it

will be done with less accuracy - when youre rushing to do smth you make more mistakes

what is fitts law with speed accuracy trade offs

• Accuracy held constant (all dots in yellow lines) - had participants perform over and over again until they had 100% accuracy

• Independent variables (changes): Amplitude (A) and

• Width (W)

• Dependent variable (what they measured): Movement time (MT) - how long it took you to move between targets

• MT ~ A/W - Large amplitude movements to wide targets take the same time as small amplitude movements to narrow targets

• to get a linear relationship - MT = a + b [Log2 (2A/W)]

• [Log2 (2A/W)] = Index of difficulty (ID) *note this is the equation of a line = linear

...so MT is linearly related to ID

what are independent and dependent variables

Independent variables: The variables an

experimenter changes (manipulates, controls)

Dependent variable: The variables an

experimenter measurers

what happens to MT if you increase target width

it decreases bc velocity increases

what happens to mt if amplitude decreases

it will also decrease

when is MT the lowest

when width of target increases and when amplitude decreases

what does fitts law look like in everyday

• space button being so big 

• x’s on ads being so small or hard to see

what general law does fitts law represent

• General law of motor behaviour e.g. underwater, in space, in the lab, children, adults, fingers, hands, arms

• Extended to discrete movements (not just tapping task)

what are the two main effects for the linear speed-accuracy trade off

Two main effects:

1) For a given rapid MT, as A increases, We increases

2) As MT decreases, We (effective target width) increases

compare the linear speed accuracy trade off and fitts law

Variability ~ Velocity = We ~ A/MT

• Not identical to Fitt’s Law (logarithmic vs. linear) but both open (very rapid) and closed (slower) control show speed accuracy tradeoff

what are the sources of error in very rapid movements

• Every connection (synapse) is an analog process, susceptible to transient factors (e.g. amount of receptors / transmitter) Therefore, each connection can introduce error (noise)

• ...and, in general, when we produce more force (up to about 70% of max), we introduce more noise (variability)

what are some exceptions to the speed-accuracy trade off

• max force - movements at around 70% of max force become less variable, slide 34

• Movement timing :

  • Spatial accuracy: Accuracy of rapid movements for which the spatial position of the movement’s endpoint is important to task performance.

  • Timing accuracy: Accuracy of rapid movements for which the accuracy of the movement time is important to task performance.

use the batting example to put it all together

Assumptions: - slide 40 - 51

- Average pitch takes ~460 ms to get to home plate

- Average swing takes ~160 ms to contact ball

1) Extra 20 ms of visual information = 3ft of extra ball flight = better prediction

2) A shorter swing means better timing accuracy for initiation and production

3) Assuming that the fast swing is close to the fastest (i.e. max force) it would be more spatially accurate

4) More force = harder hit