vestibular and visual mechanisms of motor control

vestibular receptors

• mechanoreceptors in inner ear that respond to head movement

  • semicircular canals and otoliths

semicircular canals

• detect angular acceleration of head

  • detect 3 directions of angular acceleration

otoliths

• detect linear acceleration of head

  • detect 3 directions of linear acceleration

vestibular tracts

• vestibular info transmitted to 4 key areas of CNS

  • parietal lobe, cerebellum, brainstem, spinal cord

parietal lobe

perception of body movement and motor planning

cerebellum

control posture, balance, and other motor skillsb

brainstem

control of eye movements (oculomotor nuclei)

spinal cord

control posture and balance

parietal projections

• mediate spatial awareness

  • multisensory integration with visual and proprioceptive info

brainstem projections

• control eye movements

• vestibulo-ocular reflex: rotates eyes in opposite direction of head movements

  • CNS mediates active control of visual acuity by stabilizing vision

cerebellum and spinal cord projections

• mediate control of posture and balance

• righting reflexes activate limb, neck, and trunk muscles to maintain balance

righting reflexes

stereotyped body, arm, and leg movements that maintain upright posture in response to head and neck motion during falls

retina

• contains photoreceptors that gather visual info from environment

  • 2 regions: fovea and periphery

fovea

• small central region of retina

  • high density of photoreceptors & high acuity (resolution) vision

periphery

• area of retina surrounding fovea

  • low density of photoreceptors and low acuity (resolution) vision

active control of visual processing

• CNS actively controls visual acuity of near and far objects

pupil reflex

controls amount of light that reaches retina

lens accommodation

focuses light on retina

vergence

eye movements position visual images on corresponding parts of each retina

visual tracts

• visual space divided into 2 visual hemifields

• eyes receive info from both hemifields

• each hemifield projects to opposite optic tract and opposite visual cortex

right hemifield

• projects to left optic tract and left visual cortex

• right eye projects to left optic tract

• left eye projects to left optic tract

left hemifield

• projects to right optic tract and right visual cortex

• Right eye projects to the right optic tract

• Left eye projects to the right optic tract

anatomical subdivisions of visual processing

• ventral stream: occipitotemporal

• dorsal stream: occipitoparietal

physiological subdivisions of visual processing

• focal and ambient visual system

focal visual system (ventral stream)

• processes what objects are in environment

• conscious identification of objects

  • uses primarily foveal info

ambient visual system (dorsal stream)

• processes where objects are in environment

• subconscious localization of objects

  • uses both foveal and peripheral info

visual contributions to motor ocntrol

• vision used for feedforward and feedback control (planning, monitoring, regulation)

motor planning (feedforward control)

• focal vision: object identification used for action selection and specification (grasping movements to pickup mug)

• ambient vision: object localization used for action selection and specification (reaching movements to pickup mug)

monitoring/regulation (feedback control)

• ambient vision: object and body location/motion used to correct errors (monitoring motion of hand and ball during catching)

visual search

• uses eye movements to actively gather focal visual info

• eye movements shift gaze (fovea) to fixate on relevant stimuli in environment

  • facilitates focal vision used for motor planning (reaching movements below)

optical flow (function of ambient vision)

• refers to changing patterns of light caused by body and object motion

• used to estimate loc and motion of objects

• used to est loc and motion of our body relative to objects

  • vital for planning and monitoring/regulation of many motor skills

anticipation timing (function of ambient vision)

• refers to predictive timing of motor skills from ambient vision (optical flow)

• requires estimation of object movement relative to our body

• may require est of body movement relative to objects

  • accurate anticipation timing required for interceptive actions (catching, hitting, kicking)

tau (function of ambient vision)

• est of object speed from ambient vision (optical flow)

• est from rate of change of object size on retina

  • accurate estimates of object speed required for interceptive actions (catching, hitting, kicking)

sensory integration

multimodal info, multisensory integration, sensory weighting

multimodal info

• info available from multiple sensory sources

• EX: redundant visual, vestibular, and proprioception info

multisensory integration

• combining info from multiple sensory sources

• occurs in many areas of brain (cortex, cerebellum, brainstem) and spinal cord

  • EX: visual, vestibular, and proprioception info combined to obtain more accurate est of body motion

sensory weighting

• feature of sensory integration that places greater weight (emphasis) on reliable (less variable) sensory sources

• continuous process used to est features of body and environment

  • occurs in response to changes to reliability of diff sensory sources

sensorimotor integration

• combining sensory and motor info to plan and regulate motor skills

• occurs in areas of brain (cortex, cerebellum, brainstem) and spinal cord

• walking involves sensorimotor integration in spinal cord

• anticipation timing involves sensorimotor integration in cortex and cerebellum

sensorimotor integration to enhance sensory perception

• vision: control of visual search, pupil size, lens shape, and vergence eye movements

• proprioception: alpha gamma coactivation