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Principles of Motor Control and Movement Accuracy- Oct. 22nd.docx

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Human Biology
Luc Tremblay

Principles of Motor Control and Movement Accuracy Preview - Planning a movement while controlling speed and accuracy. - Ballistic phase more important in tennis than in doing laundry  correcting trajectory is difficult. What do you do during practice to help this person serve better? Objectives: - To know Woodworth’s (1899) dual- component model - To understand how movement amplitude and target width determine movement time (Fitt’s Law)  Fitt’s Law is the closest we are getting to an exact science in motor learning! - To the know the factors influencing Fitt’s Law Woodworth (1899) - Dual- component model o Ballistic phase (Pre-planned) o Current Control phase (on-line control) - Displacement on the Y- axis; time on the X- axis o The task was to move pen up and down to a target. o We should see a perfect sinusoidal pattern. Why? Because we have a phase of acceleration and a perfectly matched phase of deceleration. But this not what we get! o We observe corrections that were taking place during the movement.  Ballistic Phase: Based on information prior to movement initiation. This is pre-planned.  The first component is similar to the expected pattern (it is somewhat ballistic).  Current Control Phase: Based on feedback from movement. - If the target is larger  trajectory amendments decrease. - If target is more precise  trajectory amendments increase! - Accuracy requirements have an influence on the current control phase. - This is where Fitt’s comes in. Which sensory information is least likely to contribute to the current control phase of a movement? - Visual - Vestibular - Golgi Tendon Organs - Muscle Spindles - Tactile  It depends on the task and the context.  The sensory information that is most likely to contribute to the CCP depends on the task. (Vestibular is more important to the CCP than tactile  Need to know where eyes are relative to head; head relative to body, and limb relative to body)  Retno centric (visual information); head centric (where the eyes are relative to the head); body centric (head relative to the body) needs vestibular information. Fitt’s Task - Task is to go back and forth between the two targets as quickly as possible with less than 5% error rate. Fitt’s Law - MT = a + b [logbase2 (2A/W)] o Hick’s Law + Fitt’s Law are the most robust, and ONLY laws in Motor Learning. This field is still in its infancy. o A = amplitude = distance between target o W = width of target. o When A decreases, MT increases. o Within an individual, you can predict how the average person will perform (how many saccades you can do between 2 targets based on previous results). We need some information about the individual, however. o Movement time is proportional to ID. - Index of Difficulty: ID = Log (base2) (2A/W) o Example  ID= Log(base2) (2x6/0.75)  Log(base 2) = 16  ID = 4  ID = Log(base2) (2x2/0.25)  Log(base 2) = 16  ID = 4 o Both impose the same demands on motor system!! They should both yield the same movement times! Same ID. o Practical example: When designing cockpit  small button will yield long movement time even if there is short amplitude. If there a bigger buttons with shorter amplitude is better. - Graph: Y axis: Time per movement; X axis: ID o Results for various target sizes. What is the ID range where the task is deemed difficult? - ID needs to be in a range of 3-6 to find a solid reproduction of Fitt’s Law. o If A is too small, you will be taping on the same place. o Some IDs are limited by biomechanics. - Having a control phase is a critical component to reproducing Fitt’s Law (Size of target width) - Cannot expect the linear ID slope to be reproduced perfectly in everyone o Slope and intercept will change within the self and across people, based on fatigue, energy, limb used, etc. o Fitt’s Law can only be reproduced only under specific conditions with the same individual. - Factors affecting slope (and intercept) o Different limbs: Expect steeper slope using legs o Expect steeper slope for fine skill. o U
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