Chapter 6

1. Chapter 6 Touch, Proprioception and Vision Concept:Touch, proprioception and vision are important components of motor control

2. Introduction • Sensory information is essential for all theories of motor control and learning • Provides pre-movement information • Provides feedback about the movement in progress • Provides post-movement information about action goal achievement • Focus of current chapter is three types of sensory information • Touch, vision, and proprioception

3. Touch and Motor Control • Describe some ways we use touch to help us achieve action goals • Neural basis of touch [see Fig. 6.1] • Skin receptors • Mechanoreceptors located in the dermis layer of skin • Greatest concentration in finger tips • Provide CNS with temperature, pain, and movement info

4. Typical research technique Compare performance of task involving finger(s) before and after anesthetizing finger(s) Research shows tactile sensory info influences: Movement accuracy Movement consistency Movement force adjustments Touch and Motor Control, cont’d Roles of Tactile Info in Motor Control See an example of research for typing – A Closer Look, p. 109

5. Proprioception and Motor Control • Proprioception:The sensory system’s detection and reception of movement and spatial position of limbs, trunk, and head • We will use the term synonymously with the term “kinesthesis”

6. Neural Basis of Proprioception • CNS receives proprioception information from sensory neural pathways that begin in specialized sensory neurons known as proprioceptors • Located in muscles, tendons, ligaments, and joints • Three primary types of proprioceptors • Muscle spindles • Golgi tendon organs • Joint receptors

7. Neural Basis of Proprioception: Proprioceptors 1. Muscle spindles • In most skeletal muscles in a capsule of specialized muscle fibers and sensory neurons • Intrafusal fibers [see Fig. 6.2] • Lie in parallel with extrafusal muscle fibers • Mechanoreceptors that detect changes in muscle fiber length (i.e. stretch) and velocity (i.e. speed of stretch) • Enables detection of changes in joint angle • Function as a feedback mechanism to CNS to maintain intended limb movement position, direction, and velocity

8. 2. Golgi-Tendon Organs (GTO) In skeletal muscle near insertion of tendon Detect changes in muscle tension (i.e. force) Poor detectors of muscle length changes 3. Joint Receptors Several types located in joint capsule and ligaments Mechanoreceptors that detect changes in Force and rotation applied to the joint, Joint movement angle, especially at the extreme limits of angular movement or joint positions Neural Basis of Proprioception: Proprioceptors, cont’d

9. Techniques to Investigate the Role of Propioception in Motor Control Deafferentation techniques • Surgical deafferentation • Afferent neutral pathways associated with movements of interest have been surgically removed or altered • Deafferentation due to sensory neuropathy • Sometimes called “peripheral neuropathy” • Large myelinated fibers of the limb are lost, leading to a loss of all sensory information except pain and temperature • Temporary deafferentation • “Nerve block technique” – Inflate blood-pressure cuff to create temporary disuse of sensory nerves

10. Techniques to Investigate the Role of Propioception in Motor Control, cont’d • Tendon vibration technique • Involves high speed vibration of the tendon of the agonist muscle • Proprioceptive feedback is distorted rather than removed

11. Role of Proprioceptive Feedback in Motor Control Research using the deafferentation and tendon vibration techniques has demonstrated that proprioception influences: • Movement accuracy • Target accuracy • Spatial and temporal accuracy for movement in progress • Timing of onset of motor commands • Coordination of body and/or limb segments • Postural control • Spatial-temporal coupling between limbs and limb segments • Adapting to new situations requiring non-preferred movement coordination patterns

12. Vision and Motor Control Vision is our preferred source of sensory information • Evidence from everyday experiences • Beginning typists look at their fingers • Beginning dancers look at their feet • Evidence from research • The classic “moving room experiment”

13. Lee & Aronson (1974) Participants stood in a room in which the walls moved toward or away from them but floor did not move Situation created a conflict between which two sensory systems? Vision & proprioception Results When the walls moved, people adjusted their posture to not fall, even though they weren’t moving off balance WHY? The Moving Room Experiment

14. Neurophysiology of Vision Basic Anatomy of the Eye • See Figure 6.6 for the following anatomical components • Cornea • Iris • Lens • Sclera • Aqueous humor • Vitreous humor

15. Neurophysiology of Vision, cont’d Neural Components of the Eye and Vision • Retina [see Fig. 6.6] • Fovea centralis • Optic disk • Rods • Cones • Optic nerve (cranial nerve II) [Fig. 6.7] • From the retina to the brain’s visual cortex

16. Techniques for Invesigating the Role of Vision in Motor Control • Eye movment recording • Tracks foveal vision’s “point of gaze” • i.e. “what” the person is looking at • Temporal occlusion techniques • Stop video or film at various times • Spectacles with liquid crystal lenses • Event occlusion technique • Mask view on video or film of specific events or characteristics

17. Role of Vision in Motor Control Evidence comes from research investigating specific issues and vision characteristics: 1. Monocular vs. Binocular Vision • Binocular vision important for depth-perception when 3-dimensional features involved in performance situation, e.g. • Reaching – grasping objects • Walking on a cluttered pathway • Intercepting a moving object

18. Role of Vision in Motor Control, cont’d. 2. Central and Peripheral Vision • Central vision • Sometimes called foveal vision • Middle 2-5 deg. of visual field • Provides specific information to allow us to achieve action goals, e.g. • For reaching and grasping an object – specific characteristic info, e.g. size, shape, required to prepare, move, and grasp object • For walking on a pathway – specific pathway info needed to stay on the pathway

19. Role of Vision in Motor Control, cont’d. 2. Central and Peripheral Vision, cont’d. • Peripheral vision • Detects info beyond the central vision limits • Upper limit typically ~ 200 deg. • Provides info about the environmental context and the moving limb(s) • When we move through an environment, peripheral vision detects info by assessing optical flow patterns • Optical flow = rays of light that strike the retina

20. Role of Vision in Motor Control, cont’d. 2. Central and Peripheral Vision, cont’d • Two visual systems • Vision for perception (central vision) • Anatomically referred to as the ventral stream – from visual cortex to temporal lobe • For fine analysis of a scene, e.g. form, features • Typically available to consciousness • Vision for action (peripheral vision) • Anatomically referred to as the dorsal stream – from visual cortex to posterior parietal lobe • For detecting spatial characteristics of a scene and guiding movement • Typically not available to consciousness

21. Role of Vision in Motor Control, cont’d. 3. Perception – Action Coupling • As discussed in ch. 5, refers to the “coupling” (i.e. linking together) of a perceptual event and an action • Example of research evidence: • See experiments by Helsen et al. (1998 & 2000) described in textbook (pp.127 – 128) • Results show that spatial and temporal characteristics of limb movements occurred together with specific spatial and temporal characteristics of eye movements

22. Role of Vision in Motor Control, cont’d. 4. Amount of Time Needed for Movement Corrections? • Concerns vision’s feedback role during movement • Researchers have tried to answer this question since original work by Woodworth in 1899 • Typical procedure: Compare accuracy of rapid manual aiming movements of various MTs with target visible and then not visible just after movement begins • Expect accurate movement with lights off when no visual feedback needed during movement • Currently, best estimate is a range of 100 – 160 msec. (The typical range for simple RT to a visual signal)

23. Role of Vision in Motor Control, cont’d. 5. Time-to-Contact: The Optical Variable tau • Concerns situations in which • Object moving to person must be intercept • Person moving toward object needs to contact or avoid contact with object • Vision provides info about time-to-contact object which motor control system uses to initiate movement • Automatic, non-conscious specification based on changing size of object on retina • At critical size, requisite movement initiated • David Lee (1974) showed the time-to-contact info specified by an optical variable (tau), which could be mathematically quantified • Motor control benefit – Automatic movement initiation