Motor Control Lecture 9_Student Version.pptx

# Motor Control Lecture 9_Student Version.pptx - Motor...

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Motor Control and Learning Lecture 9 : Speed and Accuracy Jessica Rodriguez, MS

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The Tradeof Speed-Accuracy tradeof An emphasis on speed of movement will reduce accuracy An emphasis on accuracy will reduce speed of movement Fitts’ Law Paul Fitts (1954) Predicts the movement time for a situation that requires speed and accuracy Primarily applied to pointing movenments
Fitts’ Law Based upon the following situation: Subject must move back and forth between targets Movement time depends on distance between targets, and the size of the targets MT = a + b(log 2 (2D/W)) MT: movement time D: distance to move W: width/size of target a and b are constants Multiple versions of this equation

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Fitts’ Law Index of difficulty log2(2D/W) Quantitative measure of difficulty of movement (based on speed/accuracy requirements, given in bits) Making the task more difficult increases the amount of information to be processed Human processing speed is limited
Fitts’ Law We can also perform the opposite and should see the same result: Ask a person to move in time with a metronome Measure spatial error of pointing performance Will see a tradeof in spatial error with increasing metronome speed.

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Fitts’ Law Fitts’ Law is l ogarithmic , similar to Hick’s Law Movement time increases a constant amount every time the Index of Difficulty increases by one bit 0 1 2 3 4 5 Index of Difficulty (bits) Movement Time
Fitts’ Law What does the equation mean? a: y-intercept MT when ID is zero What is a zero difficulty task? D and W overlap – no distance between targets Essentially tapping up and down b: slope of line Increase in MT per ID bit Slope can be reduced with practice Older people tend to have greater slopes

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Fitts’ Law Relationship holds for several other conditions: Movements at finger, wrist, arm, and foot Slope is diferent for each Movements underwater Microscopic movements s urgeons/dentists
Speed Accuracy Tradeof Alternate tapping is not a very useful function

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• Fall '17
• Gonzales
• Motor control, Paul Fitts

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