Lecture 10 - Vision and Optic Flow

Question 1

optic flow provides info regarding movement, specifically regarding ______

Answer 1

• > velocity
• > time to contact
• > balance

Question 2

describe the time to contact portion of optic flow

Answer 2

• > 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

Question 3

TAU (t)

Answer 3

t = 1/retinal expansion

t is proportional to the time of contact

Question 4

the moving room experiment

Answer 4

• > 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)

Question 5

visual dominance

Answer 5

refers to the dominance of visual information over other (especially conflicting types of sens info, i.e. vestibular info)

Question 6

visual capture

Answer 6

refers to the tendency of visual information to “grab” attention

Question 7

types of control systems

Answer 7

open loop

• > no feedback

closed loop

• > feedback is present

Question 8

feedback takes ______ why is this important

Answer 8

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

Question 9

off-line feeback

Answer 9

feedback that is used after the movement

Question 9

open loop in motor control

Answer 9

Question 10

closed loop in motor control

Answer 10

Question 11

relate closed loop system to error

Answer 11

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

Question 12

Components of a closed loop

Answer 12

1. Input
2. Executive centre
   - > the control centre that is responsible for initiating the action and making outgoing changes to correct for errors
3. Effector(s)
   - > the components of the system that execute the decision made by the executive (i.e. muscles)
4. Output

Question 12

the comparator uses a reference of correctness to ______

Answer 12

• > compare the the response produced feedback against the expected feedback
• > send the difference (error signal) to the executive

Question 13

example of a closed loop

Answer 13

Question 14

during movement, sensory info is produced during and after movement, which produces feedback, this feedback is used for ______

Answer 14

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)

Question 15

initial movement commands of a closed loop

Answer 15

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

Question 16

Keele and Posner

Answer 16

• > 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

Question 17

Smith, Roberts and Atkins

Answer 17

Question 18

benefits of closed loop processes

Answer 18

• > good to produce new movements
• > provides for flexibility
• > used to produce accurate movement as evidenced in fine motor tasks

Question 19

Costs of closed loop processes

Answer 19

• > requires attention
• > increased accuracy demands require increased error corrections
• > time constraints

Question 20

what situations are suited/not suited for closed loop processes

Answer 20

Suited for

• > tasks of “long” duration
• > tracking tasks

Not suited for

• > tasks of “short” duration (rapid, discrete)