L7 NEUR3101 Sensorimotor control (1 slide per page).pdf

NEUR3101 Motor control Lecture 7 Sensorimotor control feedback and feedforward mechanisms A/Prof Ingvars Birznieks  Learning outcomes You should be able to... briefly describe how sensory inputs used by the motor system differ...

NEUR3101 Motor control Lecture 7 Sensorimotor control feedback and feedforward mechanisms A/Prof Ingvars Birznieks  Learning outcomes You should be able to... briefly describe how sensory inputs used by the motor system differ in their origins and purpose from those used for perception, briefly describe how sensory information is coded and processed in the brain to facilitate interactions between sensory modalities and with the motor system, list the different types of sensorimotor interaction, describe the role of feedback and feedforward control mechanisms, explain how efferent copy contributes to processing of sensory signal, explain what a corollary discharge is, how it is different from efferent copy and provide an example of how the motor system uses corollary discharge to correct for movement errors, provide example how corollary discharge is used for sensory processing and integration with motor system.  What does a receptor signal? Our receptors capture only a tiny fraction of the information in the environment, and Sensory inputs to motor we are consciously aware of only a small proportion of these sensory inputs. https://www.youtube.com/embed/IGQmdoK_ZfY Information provided by single receptors is unreliable and ambiguous. The nervous system processes sensory signals by: integrating within sensory modality - input from one single receptor often can not encode information due to ambiguity - across fibre pattern encoding (colour encoding in visual system) integrating across different receptor types and sensory modalities - limb position is estimated based on inputs from different types of proprioceptors (muscle spindles, Golgi tendon organs, joint receptors), tactile receptors and vision. integrating over time - receptors responses are variable, over longer observation time noise is averaged out associating partial and ambiguous sensory inputs with the context estimating the most probable stimulus - interpretation based on comparison with memories of previous sensory experience recalibrating the system - proprioceptive system is calibrated by vision  What does a receptor signal? Our receptors capture only a tiny fraction of the information in the environment, and Sensory inputs to motor we are consciously aware of only a small proportion of these sensory inputs. https://www.youtube.com/embed/IGQmdoK_ZfY Information provided by single receptors is unreliable and ambiguous. The nervous system processes sensory signals by: integrating within sensory modality - input from one single receptor often can not encode information due to ambiguity - across fibre pattern encoding (colour encoding in visual system) integrating across different receptor types and sensory modalities - limb position is estimated based on inputs from different types of proprioceptors (muscle spindles, Golgi tendon organs, joint receptors), tactile receptors and vision. integrating over time - receptors responses are variable, over longer observation time noise is averaged out associating partial and ambiguous sensory inputs with the context estimating the most probable stimulus - interpretation based on comparison with memories of previous sensory experience recalibrating the system - proprioceptive system is calibrated by vision Sensory inputs to motor Which senses are used in motor control? The motor control system can use all classical senses to initiate and guide the movement depending on biological context (starting from chemotaxis in more primitive animals). The motor control system has access to sensory information which we are not aware of and which doesn’t create conscious percept. Sensory systems may have dedicated information processing stream devoted specifically to motor control, as motor control may require different coordinate system as perception and it requires different kind of sensory information. Proprioception (position sense), kinaesthesia (movement sense) and the vestibular sense are predominantly motor-related, although they also contribute to perception. Vision, hearing, touch play significant role in motor control. Vision usually dominates perception if there is a mismatch between sensory inputs from different modalities. Sensory inputs to motor Ventral and dorsal streams of visual system About 25 areas have been identified to be predominantly or exclusively visual in function. V4 contains neurons responding selectively to the colour of visual stimulus without regard to its direction of movement. Part of the ventral stream. Middle temporal visual area (MT) contains neurons responding selectively to the direction of movement. Part of the dorsal stream. - Damage to this area causes Cerebral akinetopsia – inability to appreciate (see) movement of objects. Has difficulty to judge movement of approaching car or people, difficulty to pour tea because fluid seemed to be “frozen”. WHERE? Motion analyses (direction, speed) Egocentric or viewer- cantered frame of reference WHAT? Allocentric or object- cantered frame of reference High resolution form of vision (shape, colour, texture) Modified Figure 12.18 Sensory inputs to motor Ventral and dorsal streams of visual system About 25 areas have been identified to be predominantly or exclusively visual in function. V4 contains neurons responding selectively to the colour of visual stimulus without regard to its direction of movement. Part of the ventral stream. Middle temporal visual area (MT) contains neurons responding selectively to the direction of movement. Part of the dorsal stream. - Damage to this area causes Cerebral akinetopsia – inability to appreciate (see) movement of objects. Has difficulty to judge movement of approaching car or people, difficulty to pour tea because fluid seemed to be “frozen”. WHERE? Motion analyses (direction, speed) Egocentric or viewer- cantered frame of reference WHAT? Allocentric or object- cantered frame of reference High resolution form of vision (shape, colour, texture) Modified Figure 12.18  Use of visual information in motor control The “where” or dorsal stream pathway in vision is specialised to analyse Sensory inputs to motor movement: “where” is not sensitive to colour, “where” does not resolve a lot of detail in an image, “where” is much faster than the “what” pathway identifying objects, “where” may alert the “what” pathway to appropriate targets for analysis (for example, identifying moving camouflaged objects). Examples of controlled actions: visual monitoring of a moving limb during reach and grasp actions (prehension), interceptive actions such as catching a ball, maintaining balance by viewing the horizon, eye movements themselves are a specialised example of motor control. Regardless of specialisation, information at different stages at least partly converge. Function of higher visual areas involve the integration of information derived from distinct pathways. Sensory inputs to motor Processing of object properties and movement Two streams are served by two different size cells suited to analyse different types of information. Large neurons – magnocellular, small neurons – parvocellular (from Latin “parvus" - small). Parvocellular cells Magnocellular cells High spatial resolution High temporal resolution (encode shape, size, colour) (encode location, speed direction of moving objects) Figure 12.15  Somatotopic (topographic) organisation Somatosensory & motor maps are aligned Motor Sensory Sharing information  The multiple sensory representations are brought together in association areas Sharing information SOMATOSENSORY VISUAL AUDIO Single neurons in the single-coloured areas respond to signals of one sensory modality Single neurons in the multi-coloured areas respond to multiple senses STP - superior temporal polysensory area IP - intraparietal sulcus Association of different modalities requires time synchronisation their activity as it converges onto common neurons in the multi-sensory integration areas from Schroeder et al. (2003), Int. J. Psychophysiology 50: 5.  Co-ordinating different senses is difficult For an end effector such as the hand, and a target such as a mug, Sharing information The proprioceptive signals from the hand are relative to the arm and body. The retinal location signals for the mug are relative to eye and head position. The two coordinate systems need to be brought into agreement. Fig. 7.38 Enoka RM. Neuromechanics of Human Movement. 2008 Human Kinetics, IL, USA. Sensorimotor integration Sensorimotor interaction Types of interactions between motor or sensory systems: reflexes: sensory input initiates reflex responses motor planning: sensory input is required to form the motor plan for action (demonstration touch your thumb with each finger from different starting positions and finger joint angles) corrective action: sensory input (feedback) is used during controlled movements to correct errors while you perform movement motor learning: sensory input (feedback) modifies the motor circuit to update motor commands to achieve a better task performance reafferent signals: sensory inputs created by a movement itself efferent or efference copy: motor system generates a copy of motor command - an efferent copy - and sends it to centres, which calculate expected sensory consequences or corollary discharge of intended action and thus can evaluate the deviation of its execution from the motor plan. Sensorimotor integration The role of efferent copy in sensory processing Building visual image Only the foveal region of the retina provides high resolution vision. To get a high resolution image of the whole visual scene we build up a montage by stitching fragmented snap-shots made after each saccade together. The motor command is used to suppress vision during the time of each saccade, as otherwise we would see a movement blur. Then information about the eye movement is used to allocate each seen visual scene fragment to the right location of the reconstructed visual image. from Gilling & Brightwell – the human brain 1982 Tactile perception Tactile exploration is another example: sensory input makes sense only when analysed in conjunction with knowledge of exploratory movement hands and fingers are performing Pattern of eye movements during this sensory task. tracked looking at a scene. Sensorimotor integration The role of efferent copy in sensory processing Building visual image Only the foveal region of the retina provides high resolution vision. To get a high resolution image of the whole visual scene we build up a montage by stitching fragmented snap-shots made after each saccade together. The motor command is used to suppress vision during the time of each saccade, as otherwise we would see a movement blur. Then information about the eye movement is used to allocate each seen visual scene fragment to the right location of the reconstructed visual image. from Gilling & Brightwell – the human brain 1982 Tactile perception Tactile exploration is another example: sensory input makes sense only when analysed in conjunction with knowledge of exploratory movement hands and fingers are performing Pattern of eye movements during this sensory task. tracked looking at a scene. Transforming efferent copy into corollary discharge The motor system generates a copy of motor command or efferent copy and sends it to centres, which calculate expected sensory consequences or corollary discharge. An efferent copy is a copy of a motor command, while corollary discharge mimics expected sensory signal. Note that in some literature sources these two terms might be used interchangeably. Sensorimotor integration Corollary discharge and motor error correction Corollary discharge can be used to correct for movement errors. Since corollary discharge mimics expected reafferent signal, if movement doesn’t go to the plan, there is a mismatch between the expected and received sensory input (between corollary discharge and reafferent sensory input). The nervous system can compare those two neural inputs and mismatch signal can be used to correct for movement errors. Sensorimotor integration Corollary discharge in sensory processing Electric fish have electroreceptors and electric organs to generate electric field. Corollary discharge is used by electric fish for navigation. If there are no objects in vicinity of the fish, the electric field is not disturbed. Corollary discharge predicts such undistorted ideal signal. When compared with the actual electroreceptor input, and they both match they cancel each other. Corollary discharge has to be recalculated every time there is a motor command which may bend body and thus change electric field as a consequence of own movement. Objects in environment distort electric field and do it differently depending on their electrical properties. Object size and properties can be estimated based on difference between corollary discharge and received electroreceptor signal. Corrective action Brainstem: vestibular feedback reflexes Vestibulo-ocular reflex is one of the fastest in the human body: eye movements lag the head movements by less than 10 ms. Vestibular apparatus detects postural instability and issues a rapid compensatory feedback command which reaches the spinal cord via direct projections from vestibular nuclei.  Brainstem: feedforward control by the reticular formation Corrective action Neurons within the reticular formation have a variety of functions: temporal and spatial coordination of limb and trunk movements – coordinate axial and proximal limb muscles control of sensory motor reflexes coordination of eye movements cardiovascular and respiratory control regulation of sleep and wakefulness  Brainstem: feedforward control by the reticular formation Figure 17.13 Corrective action Relevant neurons in the reticular formation initiate feedforward adjustments that stabilise posture during ongoing movements. Feedforward mechanism predicts the resulting disturbance in the body stability and generates an appropriate stabilizing response. Anticipatory maintenance of body posture At the onset of an audible tone, the subject pulls on a handle, contracting the biceps muscle. To ensure postural stability, contraction of the gastrocnemius muscle precedes that of the biceps.  Motor control centres in the brainstem feedback and feedforward control Corrective action Reticular formation Vestibular nuclei Figure 17.14  What happens with robots without or with bad feedforward control? They fall