Introduction to Motor Control Flashcards
what is the movement scientists perspective
- the brain is specialised in movement
- if we understand movement, we understand the brain
why is movement so easy to us
- we do not recognise the difficulty of the movement control
- complicated high-level control strategies are used by our brain, even when we are thought-lessly doing simple motor tasks
what are empirical observations of fitts law
- if you need accuracy, you become slow
- a highly precise relationship can be found between movement duration and log (2A/W)
- this relationship is NOT limited to specific body parts or specific movement
what are empirical observations of two-third power law
- if you are making a curved movement you become slow - slower when more curved
- curvature (larger is flatter) and velocity may have a positive relationship
- this relationship is NOT limited to specific body parts or specific movement
- can be found in running, drawing, dancing etc
what is space
- set (of points) with some added structures
- e.g. plane: two dimensional space
- e.g. cube, sphere etc: three dimensional space
- e.g. world: three dimensional space + additional dimension of time
- e.g. space with a complex structure (non-Euclidean)
- end effector space / task space / operational space
- viewed from eye level
- configuration space / joint angle space / body space
- viewed from limb position
what is a coordinate system
- set of numbers (called coordinates) that uniquely determine a point in space
- a single space can have multiple coordinate systems
- also called coordinate frame / reference frame
what are the different coordinate systems
- cartesian
- all axes (x, y, z) cross through the origin
- cylindrical
- specifies point positions by the distance from a chosen reference axis, the direction from the axis relative to a chosen reference direction and the distance from a chosen reference plane perpendicular to the axis
- spherical
- determine the position of a point in three dimensional space based on the distance from the origin and two angles
what does egocentric mean
coordinate system attached to our body (first person view)
what does allocentric mean
coordinate system attached to external world (third person view)
what is linear vs angular kinematics
distances vs angles
what is linear vs angular kinetics
forces vs torques
what is the equation for force
F = Ma
force/dynamics = intertia x acceleration/kinematics
- newtons second law defines relationship between kinematics and dynamics
- this simple equation can be extended and applied to much more complex systems where F and a are vectors (of forces and torques) and M is a matrix (inertia matrix)
what is control in this context
- feedforward (open) loop: plan in advance (i.e. pre determined actions)
- feedback (closed) loop: policies (i.e. case by case actions)
what are the pros and cons of a feedforward controller
- pros
- movement can be controlled without gathering / processing any external information: good for fast movement
- cons
- error mode by controller accumulates over time
- no flexibility to environmental changes
- high cost of planning, no generalisation
what are the pros and cons of the feedback controller
- pros
- flexible: can deal with unexpected events
- robust: control error does not accumulate over time
- general: control is invariant to starting or goal position
- cons
- processing sensory feedback is time consuming - not so good for fast movement
- controller can become unstable when sensory feedbacks are noisy and the feedback gain (degree of how seriously I take the answer) is high
- can also become unstable when feedbacks are delayed
