Week 1/2 Flashcards
What is localisation and planning? in terms of reaching.
Localisation: Representation of where the object is
Planning: Strategy to reach object based off of the representation
Sensory Info required for localisation and planning?
Extrinsic information: spatial location of target gathered by visual and auditory info.
Intrinsic information: Bodies state (kinetic and kinematic info) provided by -
muscle spindles - length and velocity of each muscle
golgi tendon organs - force produced by each muscle mechanoreceptors - force exerted/received on skin
Coordinate systems during planning?
Extrinsic - Allo/Egocentric, relative to body or external space, eye centered or hand
Intrinsic: Internal representations such as joint angles and muscles lengths
Sources of Variability?
Input variability: Sensory noise affects the estimation of object location and movement goals.
Intrinsic variability: Neural noise = fluctuating membrane potentials, limits accuracy and precision.
Output variability: Increased motor neuron and muscle contraction/excitability, this is known as signal dependent noise
Types of models
Internal/Forward - Predicts the outcomes of motor commands by simulating how the body and environment will respond.
Inverse - Translates desired outcomes (behavioral goals) into specific motor commands
Extrinsic vs Intrinsic planning?
E = Focuses on the goal of the movement in external space
Uses allocentric/egocentric coordinates for localisation and trajectory definition
I = Converts extrinsic plans into internal representation like joint angles or muscle activation
Hierarchy of planning?
General plan - extrinsic coords, relies on sensory inputs (visual/auditory)
Tool specific plan - adapts general plan to specific motor tool such as hand, begins to incorporate body mechanisms and restraints
Muscle-specific commands - final level of planning, plan is translated to signals for muscles to execute
Space of planning?
End effector space planning: plans trajectories for end point of limb such as hand, results in straight trajectories but may appear curved, eg moving hand straight
Joint space planning:
Plans trajectories in terms of joint angles, produces straight joint trajectories which lead to curved hand paths, eg rotating shoulder and elbow to move hand
Sensorimotor Transformations in Planning?
Coordinate transformations: Localizing the target and movement trajectory in one coordinate system and moving to another, converting eye-centered to hand-centered or joint space
Inverse Models:
Plans “What commands are needed to achieve the desired movement?”
Forward Model: Predicts “What will happen when these commands are executed?”
Variability in Planning?
Planning is subject to variability due to noise in sensory inputs, neural processing, and motor output.
Analyses of variability patterns (e.g., bell-shaped velocity profiles or elliptical error patterns) provide insights into the spaces and coordinate systems used in planning.
Process of movement planning as a whole?
- Extrinsic Planning: Defines the goal in external space (e.g., “grab the apple”) using sensory input like vision or hearing.
- Coordinate Transformations: Converts the goal from external coordinates (eye/hand-centered) to internal body coordinates (joint angles/muscle lengths).
- Intrinsic Planning: Translates the transformed goal into specific motor commands for muscles and joints.
- Forward & Inverse Models:
Inverse Model: Determines the motor commands needed for the goal.
Forward Model: Predicts the outcome of those commands for error correction.
- Feedback Integration: Real-time sensory feedback adjusts movements, ensuring accuracy and adaptability.
Flow: High-level goals → Spatial transformations → Motor commands → Real-time adjustment.
Role of primary motor cortex in terms of movement planning?
Executes movements by encoding direction and location
Neurons tuned for final reach position
Control strategies of movement?
Feedforward Control:
Pre-planned, fast, but inflexible (e.g., saccades, Vestibulo-Ocular Reflex).
Feedback Control:
Relies on sensory input for flexibility but delayed by ~200 ms.
Observer model?
Combines predictions and actual sensory feedback.
Balances “expected” and “unexpected” feedback based on uncertainty, crediting improvement.
Why is there an integration of strategies with movement?
The brain uses a mix of feedforward and feedback strategies, optimizing flexibility and speed based on context.
