Performance & Motor Control Characteris3cs of Func3onal Skills Chapter 7
Fi: s Law
Speed Accuracy Trade Off A characteris3c of motor skill performance in which the speed at which a skill is performed is influenced by movement accuracy demands e.g., the trade off is that increasing speed yields decreasing accuracy, and vice versa.
Fi: s Law Speed- Accuracy Trade Off Fi: s Law provide a mathema3cal model MT = a + blog 2 (2D/W) Variables that predict performance is distance to move and target size Fi: s law has an index that measures the difficulty of the task (ID s
Speed Accuracy Skills (Examples) Kicking a penalty kick in soccer Pitching a fastball for a strike in baseball/sozball Playing a song on a piano at a fast tempo Speed typing Moving a peg from one loca3on to insert them into a hole as fast as possible Pu[ng key into a key hole Threading a needle Prehension (reach, grasp, & manipulate) Handwri3ng
Fi: s Law Applies to any skill where the object of the task is speed and accuracy except bimanual skills. manual aiming task (e.g. placing pegs in board, throwing darts, grasping containers of different sizes, moving cursor across the screen to a word) Kicking a soccer ball to the different loca3on of the goal Greater the area where you want the ball to go, the greater the movement speed of the kick
Woodworth s Hypothesis When we begin to move our limb toward the target or object, the limb operates in a open loop fashion. Ini3al movement speed, direc3on, and accuracy is under the control of CNS opera3ng in absence of feedback (open loop) Visual feedback about the posi3on of target guides the hand during the homing in phase The homing in phase operates in a close loop. This assures us that we have a accurate landing on the target or object.
Controversy to Explain Fi: s Law Intermi:ent feedback hypothesis Impulse- 3ming hypothesis Mul3ple sub- movements hypothesis
Prehension
Why study prehension? These skills are the last skills to develop which if studied reveals secrets of how the brain controls complex movement. The study of these skills requires one to control the smallest muscles to produce movement that demands greatest precision and accuracy. Each skill is connected to many real world skills that relate to daily func3on motor skills and sport skills.
PREHENSION Act of reaching, grasping then manipula3ng the object. Reaching is considered to be the transport phase Grasping the object or target is the grasphing phase What we do with the object is the manipula3on phase Prehension is different from the ac3on of reaching and poin3ng to an object (aiming skill) Key into a key hole (aiming skill) Placing a pen in penholder (aiming skill) Threading a needle (aiming skill) Reaching for a cup and drinking from the cup (prehension) Catching and throwing a ball (prehension) Handwri3ng (prehension) continued
Motor Development Perspec3ve Very important skill that enables the human to interact with their environment because it involves manipula3on of objects Baby s ini3al a:empt to reach, grasp, and manipulate a object is an extremely important sign of motor development First sign of voluntary reach and grasp is around 4 months of age The reach and grasp seems to appears simultaneously
Manipula3on Once a object is grasped, one either manipulates the object or releases it. If the object is to be manipulated, stabiliza3on of the finger3p forces must be sustained for a period of 3me to prevent slippage. Manipula3on is the movement of the object in space that includes such things as tools, pencils, pens, and scissors; dressing, tying shoes, money handling, and cu[ng food.
Prehension The transport (reach) and grasp (manipula3on) seem to be temporally coupled and work coopera3vely. Vision & the Fi: s Law works together to control prehension. If the reach is ballis3c, the reach occurs from visual informa3on processed before the reach such as 3me to contact, velocity of limb, and how far one needs to move. If the reach is performed under closed loop control, vision feedback informa3on is used constantly during prehension by the performer.
Prehension & Fi: s Law Prehension skills always applies to the speed accuracy trade- off law, that is, the 3me of prehension (movement 3me) is affect by distance of the reach and size of object.
Role Vision Plays Prior to the reach the person uses vision to determine the regulatory condi3ons of the environment in which the ac3on will occur. We pre- program our transporta3on of the limb before we even move. During limb transporta3on stage, vision does not play much of a role. Than vision plays a very important role just prior to the grasp of the object.
Role Vision Plays Vision is very important in the grasp and manipula3on stage. Enables one to make slight correc9ons that occur just before the grasp Vision is necessary when to grasp Binocular vision aids the size of grip and force of grip Person needs to look directly at the object for the grasp (point of gaze).
Refining & Training Prehension In the beginning repeat the different types grasp and reach with the same familiar object (shape, size, and weight) this develops the ability to differen3ate between objects and improve the one s an3cipa3on of weight, force, and velocity of prehension. Then vary sizes, shapes, and weight of the objects and require different reaching and grasping techniques in light and dark environments. Realize that one s control of the rate of speed of their grasp and force of the grasp in the beginning of retraining is nega3vely associated but with prac3ce it becomes similar (Pare & Dugas, 1999). Provide a variety of func3onal (real life tasks) that involve reaching, grasping, and object manipula3on
Handwri3ng
Handwri3ng Difference control mechanism are involved in controlling: What people write(e.g., le:ers, words) How people write(e.g., wri3ng surface) Used to prove the existence of motor equivalence across the learning of motor skills. Wri3ng involves both cogni3ve (retrieve le:ers, words, gramma3cal construc3on, spelling) and motor skills (holding the pen, size of le:ers).
VISION AND HANDWRITING 1) Vision helps to control the overall spa3al (spaces between le:ers) arrangement of words on a horizontal line. 2) Vision helps one produce accurate handwri3ng pa:erns, that is, stroke pa:ern and le:ering.
Bimanual Skills Bimanual movements involve the limbs moving in same similar pa:ern (symmetric) or moving each limb differently (asymmetric). Examples: - Playing a guitar - Tying a shoe - Drummer - Serve in tennis
Bimanual Control Whether we perform symmetric or asymmetric bimanual skills, the two limbs prefer to do the same thing at the same 3me. - e.g., move your lez foot in the clockwise circle while tracing the number 6 with your lez hand.
Bimanual Control Bimanual skills do not apply to Fi: s law. - The more difficult task will always influence the performance of the less difficult task.* - Temporally moving both limbs eventually overcame the influence of the speed accuracy trade off rela3onship *Many bimanual skills occur when one limb performs a more difficult task while the other performs an easier task. The more difficult task will always influence the less difficult task.
Bimanual Control How do we become proficient (uncoupled) in performing bimanual skills? Answer is we learn to become uncoupled (dissociate) through prac3ce. Uncoupling is a difficult process for people but given proper instruc3on, feedback, and prac3ce one can become asymmetric indepenent.
Importance of Bimanual Control Bimanual skill development is a key sign of normal brain development.
Signs of Bimanual Control Bruner examined bimanual control in infants through early childhood. By 4 to 5 months children manipulates one toy at a 3me. By 6 th month the children reaches and grasps two toys. By the 9 th month, the child can manipulate & hold 3 toys at a 3me. By 18 months, the child is uses both their hands about 30% of the 3me.
Gait & Locomo3on
Development of Postural Control Stability Emerging Head Control At 2 mos Neck muscles can control the head Development of visual system contributes to head control Emerging Independent Si[ng Takes about 8 most to be able to control the neck & Trunk Development of visual and ves3bular system contributes to independent si[ng but mostly vision Transi3on to Independent Stance Need to be able to balance and strength in legs and thigh (contribu3on strength makes) Early on Vision should be contribu3ng greatly to one s independent stance but once it is a:ained we then switch to somatosensory informa3on Quiet Stance
Head Stability & Locomo3on Head stability is key factor of the Gait. The head contains the sensory and motor nervous system components that helps us navigate through an environment and in maintaining one posture. Maintaining a stable head during locomo3on op3mizes the use of vision so we can tracking a ball, catch an object, and avoiding objects. Adults with neurological impairment adopt an abnormal posture and gait as a means to maintain head stability (Holt, et al., 1995) such as Parkinson s disease
Upright Independent Gait When the child begins to walk: - the arms have a high carriage - very wide base of support - knees are in the flexed posi3on - toes pointed out - length of strides are highly inconsistent. - lateral stability is poor
Interes3ng Facts Walking solo typically begins between 9 and 17 months of age. As balance improves, the base of support narrows. Degree of toe- out deceases as we become more efficient Toe- in foot angle is considered to be always abnormal. Un3l one gains sufficient neuromuscular control, he or she will take more steps per unit of 3me to increase walking speed.
Motor Control of Upright Independent Gait (Walking & Running) Central pa@ern generators in the spinal cord controls human gait. Evidence is found: - Decerebrated cats (severing the spinal cord from the brain) can s3ll walk and perform locomo3on rhythmic muscular ac3vity (Sherrington, 1906). - Spinal cord plays a significant role in control of locomo3on
Rhythmic Structure of Locomo3on Between the arms and legs due to walking speed. - 2:1 ra3o (two arms swing to each leg stride) exists for slow walking and pelvis and thorax move as one. - 1:1 ra3o exists for fast walking but pelvis and thorax are independent in fast walking. Knowing that dis3nct rhythmic rela3onship exist is important in measuring locomo3on coordina3on: - problem in Parkinson s disease pa3ents - determine the effec3veness of reconstruc3ve knee surgery. - pa3ents with have ACL surgery walking phase is greatly altered due to segments of the leg have been changed. - post stroke pa3ents need for treadmill walking retraining to move both their arms and legs.
Gait Transi3ons Walk to run or run to walk transi3ons occur at different speeds. These changes are spontaneous transi3ons but they vary between people. Why? It is not due to physical limita3ons. The spontaneous transi3on occurs at a speed where we minimize metabolic energy consump3on (VO2). This assump3on has not been totally supported but spontaneous transi3on remains a puzzle for researchers to solve.
Vision & Locomo3on Contac3ng an object Avoiding contact with an object
What type of informa3on is being used? Op9cal variable tau is Time to contact or distance based informa3on Tau is amount of 3me remaining un3l the object contacts the person(or vice versa) from a specific distance. Tau is predic3ve func3on which allows ac3on ini3a3on and object contact to occur automa9cally at a specific 3me to contact regardless of the speed of the object and person. E.g. breaking to avoid hifng a car process 9me needed by visual informa9on to brake rather than knowledge of how much distance there is between you and oncoming car.
Vision & Contac3ng Objects As you walk rapidly down a hallway a:empt to make contact with a target placed on the floor. 1) Visional informa3on is used to determine the amount of 3me it will take to contact the target (3me to contact) 2) Time to contact is used to make stride- length adjustments during the last few steps to correct any errors. 3) Time contract is a quality we possess that is not dependent on experience.
First phase of the run- up the stride length correc3on occurs while the jumper is accelera3ng followed by a zeroing- in phase where the jumper changes stride pa:ern to eliminate errors. Long Jump Study Accelera3on Phase Zero- in Phase Tau Lee, Leshman, Thomson, 1982)
Avoiding Objects As we walk If one is to maintain foot speed while avoiding an object three 3me periods are cri3cal Recognize the object that needs to be avoided* Adjust the foot Turn the foot to avoid the obstacle *The most cri3cal period is recognizing the object that needs to be avoided *Training implica3on is a person must recognize objects sufficiently early to allow appropriate movement adjustments.
Catching Ac3on of bringing an airborne object under control by using the hands and arms.
Three Phases of Catching an Object On ini3al ball flight, no arm ac3on is seen. About 25 to 80% of ball flight, elbow flexion and finger extension occurs slowly. At about 50% to 3me the ball is caught, the hand withdraw and become spa3ally posi3oned. Shortly before the catch, fingers become posi3oned. *Successful catchers had their hands and fingers ready to catch the ball earlier than unsuccessful catchers.
VISION AND CATCHING Visual contact is needed during the ini3al part of flight and period of 3me just prior to contact with the hand(s) Only the first 300 ms of flight is needed to determine direc3on & distance. Only the last 200-300 ms before hand contact is cri3cal. Viewing the object between these two 3me periods is not cri3cal to catching Performers visually sample the ball flight characteris3cs (snap shots every 80s of ball flight) to obtain up- to- date informa3on about when they need to catch the ball Op3cal variable tau (3me to contact) is involved in solving the 3me to contact problem in catching An approach object visual size increases (looming) which the visual system uses to determine when collision with the object will occur. An approaching object off the lez or right of the body, TAU controls the 3ming of the reach to catch the object
DOES ONE NEED TO SEE THEIR HANDS TO CATCH AN OBJECT? Smyth & Marrio: study of seeing or not seeing their hands.. Seeing their hands were more accurate All catchers were able to make correct spa3al posi3on of their hands to intercept the ball Experience in catching is an important factor Experienced catchers do not need to see their hand. Lowly skill catcher do need to see their hands throughout the flight
Interes3ng Fact about Catching Developmental characteris3cs of catching relates to the development of the visuoperceptual system ability to predict the the object s flight characteris3cs. The ability to predict the object s flight characteris3cs is usually not developed un3l around the age of 15 with extensive prac3ce. The first a:empt to catch occurred when as a infant we blocked a rolled object. Fear of the projec3le is a condi3oned response from earlier failures at the task. Catching with one s hands is the most advanced level of catching development.
Factors that Influence Catching Performance Ball size Ball color and background color Ball speed Trajectory angle Viewing 3me
VISION AND HITTING 1. One can see the ball only to the point at which the swing is made (Hubbard & Seng) not to the point of contact. 2. Success in hi[ng or striking is related to tau- base strategies: Ba:ers synchronize the start of their step to release of the ball. Successful hi:er s dura3on of the swing to swing was consistent from one swing to another. Ini3a3ons of the swing was adjusted according to the speed of the oncoming pitch. Successful hi:ers use the same visual tracking pa:ern and had a consistent stance to prepare for the pitch. Less Head movement (less than 1 degree) during the swing across all types of pitches is another factor to successful hi[ng. All adjustments and decision to swing is triggered by visual informa3on (TAU) that occurs in the first 500 msec of ball flight Last 2/3 of ball flight the striker can only make slight racquet or bat changes
The End