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Slide 1Slide 2Slide 3Slide 4Slide 5Spring EquationSlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15GraspingReaching vs. GraspingSlide 18Slide 19Development of reachingDevelopment of reachingSlide 22Early reach movementsDevelopment of reachingDevelopment of reachingDevelopment of reachingDevelopment of graspingDevelopment of graspingDevelopment of graspingReach and grasp developmentSlide 31Slide 32Adaptation to different relation between vision and movement.Adaptation to different relation between vision and movement.Slide 35Slide 36Neural control of GraspingNeural control of GraspingSlide 39Neural control of GraspingReaching and graspingRosenbaum Ch 7Factors in control of reach:Learnt motor program for ballistic phase (feedforward)Feedback during reach from vision or proprioception.Ballistic component might rely on a simple property of muscles,that is, muscles are like springs.Planned component depends on current sensory evidence plus pastexperience.Grasp height varies depending on height of platform where object is moved toPre-programmed component also depends of the goal of the movementRole of Visual FeedbackQuestion: why does error increase with speed?Note: 50 cm/sec = 5cm/100msecMass-Spring ModelMuscles are like springs: a spring has a resting length and stiffnesslength and stiffness of muscles can be neurally programmedSpring EquationMuscles can be modeled as springsF = -k(x1 - x0)Difference between current position and eq. pointk = spring constantEvidence for Mass-Spring ModelAccurate (??) reaching following deflection even when vision and proprioception were absent (dorsal roots severed).But is this consistent with the evidence from patients with large-fibre sensoryNeuropathy?Velocity profiles for small and large movements: note difference throughout movementEven at beginning. Implications?Fitt’s Law. Movement time increases with accuracy requirements.Planning reaching movementsReaching movements are initially planned and represented in the brain in a simplified abstract form as vectors in which extent (amplitude) and direction is specified (perhaps planned independently). Locate handLocate targetPlan movement vectorPlanning reaching movementsThe variability in direction errors (off-axis) are smaller than that of extent errors.Mean endpointOn-axis errorOff-axis errorThe patterns of errors reflect limitation of CNS, provide clues to control strategy.Are movements planned in joint space or hand space?Straight hand pathsPeople move their hand in a straight path even when they can’t see their hand motion, and so can only rely on proprioception.Straight hand pathsPeople move their arm so that the paths “look” straight even if it involves a curved path.GraspingReaching and grasping actions require close coordination, but would seem to depend on different kinds of visual information...Reaching: egocentric (where is the object relative to me)Grasping: object-centredReaching vs. Graspinghand positionhand velocitygrip sizeaperture velocityPeak deceleration time correlated with time to peak aperture.Also, when arm moves faster, hand opens wider (finger separation increases).Visuo-Motor Relationships:Plasticity and DevelopmentProblem of sensory-motor coordination: How do we relate the visual and motor worlds? For reaching, a visual signal about location must be transformed into a command to the arm and hand muscles.This is not innate, but must be learnt during development, and maintained through adulthood.Development of reachingWithin first 2 weeks, babies already directing arm towards objects. Some crude control of reach direction.Improves by the 5th month; consistently touch targets.Won’t reach for targets beyond arm’s length.Catching and anticipating target motion at 6 months.Distance accuracy develops more slowly, improving by 7 months.Development of reachingWithin first 2 weeks, already directing arm towards objects.Improves by the 5th month; consistently touch targets.Catching and anticipating target motion at 6 months.Distance accuracy develops more slowly, improving by 7 months. Visual information used early on to aid in sensory-motor integration.Increased use of visual feedback between 5 and 11 monthsEarly reach movementsInitially use the trunk & shoulder (proximal joints) to reach for objects; use elbow less frequently.When babies do make large movements, can’t control inter-segmental dynamics. So hand oscillates.Development of reachingBetween 5 and 9 months see many changes to kinematics: 1) Straightening of the hand pathDevelopment of reachingBetween 5 and 9 months see many changes to kinematics:2) Reduced number of “submovements”3) Reduced movement timeDevelopment of reachingJoint kinematics changes as well: coordination among jointsDevelopment of graspingNewborns have grasp reflex (clasp object brought against the palm) – disappears by 6 months.Use palmar grasp until about 12 months – then use fingers to grab.Corresponds to rapid increase in the rate of myelination of corticospinal tracts at 12 months – responsible for distal musculature.Development of graspingAt 5 months, babies orient hand, but only AFTER making contact with the object. Predictive orienting starts at 9 months.Development of graspingTailoring of grasp to object size only after 9 months (grip aperture wider for larger objects).Still adjusting grip force by 7-8 years (grip force larger for larger objects).Reach and grasp developmentBirthIncreased myelination of corticospinal tractsContinued refinementDirect hand to objectreach onsetfine tune reachCoordinated torque patterns/ joint patternsIntegrate sensory-motor signalsPincer graspmonthsyearsCalibrating visual information to form gripMore evidence that visuo-motor coordination must be learnt during development. Evidence: Kittens given visual experience without opportunity for movement, and motor experience without vision, don’t learn how to control their movements using vision. Correlating the two is necessary (Held & Hein study).Held & HeinRole of Experience in Development of Visuo-motor coordinationBoth kittens get visual experience and motor experienceK1. Visual experience correlated with motor commands/proprioceptive feedback/vision of limbsK2. Gets both, but uncorrelated. Kitten 2 -abnormal visuo-motor coordination.12If he saw an object on the right he would reach with his right hand and discover he should have reached with his left. He could not feed himself very well, could not tie his shoelaces,


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UT PSY 394U - Reaching and grasping

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