Lecture 10 - Vision and Optic Flow Flashcards
optic flow provides info regarding movement, specifically regarding ______
- > velocity
- > time to contact
- > balance
describe the time to contact portion of optic flow
- > the retinal image of an object expands as it approaches the eye
- > the rate of expansion on the retina indicates how fast the object is moving
TAU (t)
t = 1/retinal expansion
t is proportional to the time of contact
the moving room experiment
- > when the walls of the room are moved towards the subject, the subject unknowingly swayed backwards
- > when the walls of the rooms moved away from the subject, the subject unknowingly swayed forward
- > sway is visually induced using optic flow info to correct balance (automatic postural changes took aprox. 100ms)
visual dominance
refers to the dominance of visual information over other (especially conflicting types of sens info, i.e. vestibular info)
visual capture
refers to the tendency of visual information to “grab” attention
types of control systems
open loop
- > no feedback
closed loop
- > feedback is present
feedback takes ______ why is this important
TIME
- > the key to figuring out whether feeback is used in movement control is time constraint/ time availability
- > the time constraint for feedback use in motor control, generally speaking, is a reaction time
off-line feeback
feedback that is used after the movement
open loop in motor control
closed loop in motor control
relate closed loop system to error
the main objective of a closed loop is to minimize error
- > error serves as feedback for the system, the system then decides whether to turn the system on/off
*negative feedback system
Components of a closed loop
- Input
- Executive centre
- > the control centre that is responsible for initiating the action and making outgoing changes to correct for errors - Effector(s)
- > the components of the system that execute the decision made by the executive (i.e. muscles) - Output
the comparator uses a reference of correctness to ______
- > compare the the response produced feedback against the expected feedback
- > send the difference (error signal) to the executive
example of a closed loop
during movement, sensory info is produced during and after movement, which produces feedback, this feedback is used for ______
During
- > change the movement as necessary when it is being produces (on-line control)
- > time permitting
After
- > plan and initiate the next movement (off-line control)
initial movement commands of a closed loop
closed loop processes DO NOT REQUIRE detailed initial movement commands
- > instead, ongoing movement is regulated by an error detection process
*for target aiming tasks, the movement ends when the error is zero
Keele and Posner
- > subjects were trained to move a hand-held stylus to a small target at different movement speeds
- > after practice, the lights were turned off at the start of the movement
- in comparison to the lights on condition*
no effect on movement accuracy when time was less than 250ms
error increases (target missed) when the movement time was 350ms
further error increases when the movement time was 450ms
Smith, Roberts and Atkins
benefits of closed loop processes
- > good to produce new movements
- > provides for flexibility
- > used to produce accurate movement as evidenced in fine motor tasks
Costs of closed loop processes
- > requires attention
- > increased accuracy demands require increased error corrections
- > time constraints
what situations are suited/not suited for closed loop processes
Suited for
- > tasks of “long” duration
- > tracking tasks
Not suited for
- > tasks of “short” duration (rapid, discrete)
