Motor Skills: Types of Body Movements and Control

1. ECE 796/896Chapter 9 Motor Skills

2. Types of body Movements • Movements occur around moveable joints. • Synovial Joints - fingers,knees,hips,shoulder • Cartilaginous joints - back

3. Movements cont. • Basic types: • Flexion: Movement of body causing a decrease in the angle at the joint. • Extension: Movement that causes an increase in the angle of the joint. Hyperextension is extension of a body segment to a position beyond its extended normal position.

4. Movement Cont. • Abduction: Movement of a body segment away in a lateral plane away from the midline of the body. • Adduction: Movement of a body segment toward the midline of the body. • Rotation: Movement of a segment around its own longitudinal axis. • Circumduction: Cone like movement.

5. Range of Movement • Amount of movement through a particular plane that can occur in a joint. • Mean, 5th-95th percentile • Muscular mass can change the amount.

7. Control and Acquisition of Motor Responses • Concept of SKILL … • The ability to use the correct muscles with the exact force necessary to perform the desired response. • Mechanisms involved in acquiring skill and coordination

8. Types of Responses • Classes of Motor Movements • Discrete movements • Repetitive movements • Sequential movements • Continuous movements • Static positioning movements

9. Sensory Feedback • Sensory information - feedback & feedforward • Sources of motor feedback • Kinesthesis - limb position • Muscle spindles - play a large role in controlling motor responses • Receptors in tendons are sensitive to muscle tension and inhibit it.

10. Higher-Level Control of Motor Responses • Two types fast and slow. • Fast movements >200 ms, such movements are planned and the executed with little or no conscious control. • Slow responses are consciously controlled and take more than 200 ms. • Open and closed loop explanations

11. Closed/Open loop theories • Closed loop employ sensory feedback, and all behavior is controlled (fast or slow). • It appears that fast behavior can not be feedback controlled, since 200 ms is not enough time.

12. Open Loop - Motor Programs • Higher level programs - motor programs • Movement patterning • Complex motor programs take longer to process (supporting open loop theory) • Motor programs can be innate (baby)

13. Errors Assoc. with Motor Programs • Two types of errors can occur: • Errors of selection: The person calls up the wrong motor program even though it is executed correctly. • Error of Execution: correct program is called but something goes wrong in the execution.

14. Some Problems for Motor Programs • Use of generalized motor programs • How you do something new • Hierarchical view of programming • Higher levels contain abstracted motion programs

15. Generalized Motor Programs • Parameters that can be supplied to such a program include, response speed, muscles that are used, force and size of the response. • Sequencing and timing connections could be invariant.

16. Schema • Formulate abstract rules (Schema) based on past experience to determine what parameter values might work for the present situation. • Briefly store: Parameters, Movement outcome, sensory consequences, and initial conditions.

17. Cont. • 2 primary types of schema developed • Recall schema: Relate initial conditions to specific values of parameters used. • Recognition schema: sensory consequences with the outcome of the movement in the environment.

18. Speed of Movements • Total response time = reaction time + movement time - reaction time: start of the signal calling for a response to the start of the response. - Movement time: from the beginning of the response to the completion.

20. Cont. • Reaction time: two types • Simple: time to initiate a response when a stimulus occurs. • Stimulus modality, stimulus detectability, spatial frequency, preparedness or expectancy of a signal, age, and Stimulus location

21. Cont. • Choice Reaction time: One of several possible stimuli are presented , each one gets a different response. • Factors that influence choice reaction time: Compatibility between stimuli and response, practice,warning,type of movement, more than one stimulus.

22. Movement time • Movement time is the time it takes to physically make the response called for. • Time increases as more body parts need to move as part of the response. • Accuracy of the movement also effects the time for the response.

25. Distance and Accuracy • Fitt’s law • MT = a + b log2 (2*D/W) • MT = movement time • Where: • A and b = empirically derived constants • D = distance of movement from start to target center • W = width of the target • Holds for a variety for work situations

27. Movements not Controlled by Visual Feedback • Movements under 200 ms are not controlled by visual feedback. • Movements that a person can not see. • Three factors: Target location, Distance of Movement and speed of Movement.

28. Target Location • Blind Positioning: Moving a hand or foot for a control when the eyes are otherwise busy. • We plot the results of test showing the accuracy of reaching in various positions.

30. Distance of Movement • Range effect: underestimate short distances and overestimate long distances.

31. Speed of Movement • Fitt’s formula does not apply to FAST movements. • Schmidt’s Law: • W = a + b (D/MT) W= effective target width, a &b empirical constants, D= distance, MT = movement time. Works for 140-200ms, dist < 12 inches.

33. Continuous Control and Tremor • High accuracy tasks and continuous freehand control (sign painting) • Such movements are done with the minimum of errors when the movement is on the horizontal plane , left-right, forearm pivoted at the elbow.

34. Static Muscular Control • Absence of movement • Muscles operate in opposition to hold the body member in position. • Usually takes considerable effort. • Deviations are tremor and drift.

35. Tremor in static position • 1. Use a visual reference. • 2. Support the body in general and the body member involved in static reaction. • 3. Hand position. There is less tremor if the hand is within 8 inches of level with the heart. • Friction. Mechanical friction in devices can damp out tremor.