Proprioception and vision Proprioception and Motor Control Proprioception

Proprioception and vision

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”

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

Neural Basis of Proprioception: Proprioceptors 1. Muscle spindles • In most skeletal muscles in a capsule of specialized muscle fibers and sensory neurons – Intrafusal fibers – 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

Neural Basis of Proprioception: Proprioceptors, cont’d 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

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

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

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

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”

The Moving Room Experiment 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 Ø When the walls moved, people adjusted their posture to not fall, even though they weren’t moving off balance Ø WHY?

Neurophysiology of Vision Basic Anatomy of the Eye • anatomical components – – – Cornea Iris Lens Sclera Aqueous humor Vitreous humor

Neurophysiology of Vision, cont’d Neural Components of the Eye and Vision • Retina – Fovea centralis – Optic disk – Rods – Cones • Optic nerve (cranial nerve II) – From the retina to the brain’s visual cortex

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

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

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

Role of Vision in Motor Control, 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

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

Role of Vision in Motor Control, cont’d. 3. Perception – Action Coupling refers to the “coupling” (i. e. linking together) of a perceptual event and an action

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)

Role of Vision in Motor Control, cont’d. 5. Time-to-Contact: The Optical Variable • 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 , which could be mathematically quantified Motor control benefit – Automatic movement initiation