Lecture 8b, Exteroceptive Contributions to Closed-Loop Motor Control

Question 1

What is our preferred source of sensory information?

Answer 1

vision
- vision seems to dominant in the beginning and as you become more skilled and practice more you can rely on other senses (proprioception kicks in)

Question 2

What are the two visual streams for information processing?

Answer 2

ventral & dorsal
- information coming in from the eye and is going to be processed at the back of the head where the visual cortex is and then it makes it way in one of the visual streams
- visual information in both streams travels first from the retina of the eye to the primary visual cortex and then visual information processing become specialized

Question 3

Dorsal Visual Stream

Answer 3

vision for action (where?) object interactions and guiding actions
- makes it way to the parietal cortex
- gives us an indication of where we are spatially
- important for navigation
- ventral stream is only sensitive to events in the central vision whereas, dorsal visions involves the entire vision field, central and peripheral

Question 4

Ventral Visual Stream

Answer 4

vision for perception (what?) object/stimulus identification and planning
- goes to temporal cortex
- perception stream
- identification - relates to stages of information processing where we engage in stimulus identification
- processed through the information-processing stages

Question 5

How do we know there are 2 visual streams?

Answer 5

1. “dissociations” in patients with brain injuries (who have damage to the various streams)
2. “dissociations” in seeing and doing in visual illusion research (identification shows the illusory effect but when you get people to act your action system is not subject to the same illusory effect)

Question 6

Dorsal stream function

Answer 6

online movement control, involving entire visual field and non-conscious
- important for online controlled movement
- as you are actually acting, as the movement is unfolding that during on concurrent with the action
- reflexive visual closed loop control
- keeps us on course
online = concurrent with/during movement (visually guided actions)

Question 7

What is one problem with the Dorsal Stream?

Answer 7

optic ataxia
- when a person has injury or lesion in some area to dorsal stream
if lights were off, could perform accurately
- problem in translating vision into action (to control the action)
- problem not at planning stage, rather ongoing movement stage

Question 8

What is this an Example of?
“thus, when asked to grasp a presented object, he would miss it regularly and would find it only when his hand knocked against it”

Answer 8

optic ataxia

Question 9

Ventral stream function

Answer 9

conscious identification of objects, primarily in centre of field-of-vision

Question 10

What is one problem with the Ventral Stream?

Answer 10

visual-form agnosia
- they have problem remembering the form of an object (perception, identification issue)
- patient could only identify this flashlight haptically (with touch)
- a patient with visual form agnosia could identify a pictured object only when he started moving his hands as though he was using it
- can only identify once they interact with it
- some information is getting through but ventral stream is causing issues in identifying what it is

Question 11

What is this an Example of?
“it’s made out of meta - is it aluminum? it has got something red on it; looks like plastic. is it some sort of kitchen utensil?”

Answer 11

visual form agnosia

Question 12

Ebbinghaus Illusion

Answer 12

perceptually different but physically identical
- the circle are the same size - just surrounded by different sized circles
◦ perceptual system
identifies them as being
different sizes
◦ is our action system also
tricked by this allusion?

Question 13

Illusions give evidence for 2 visual streams:

Answer 13

Perception is tricked, but action (grasp) is not
perceptual estimates x ≠ graph (kinematic) estimates ✓
- perceptual estimates were bias but kinematic did not show any bias or any effect of the illusion (dorsal knew what it was doing even though ventral was tricked)
- if you had to perform this with the lights off we would see bias
- since the dorsal stream is this in action visual motor interaction it does not appear to get tricked

Question 14

What stream is considered fast/non-conscious and reflexive loop?

Answer 14

dorsal

Question 15

What stream is considered slow/conscious?

Answer 15

ventral

Question 16

Evidence for fast vision-for-action (dorsal) regulation of motor control

Answer 16

optical flow for fast, non-conscious control of movements
1. avoidance/navigation
2. balance control
- as we move around light is hitting our retina and is giving us an indication of the direction that we are moving in which is allowing us to make adjustments
- automatically the size of the object on your retina gives you some information about approach time (time to duck)
- the size of the object on your retina and the rate of expansion of the object gives you some information about how you would navigate in the world and your relationship to other objects

Question 17

What does Dorsal vision provides information about?

Answer 17

time-to-contact (tau): rate of expansion of object on retina
α = retinal image
- mathematical law about the size of the object on your retina and the rate of expansion
◦ information about time
to contact
◦ as something is closer
the more space it takes
on your retina
◦ the rate of change of
that object on your
retina gives you an idea
about time to contact

Question 18

Optic flow

Answer 18

object on the retina that is giving information that feels like you are moving forward because the wall is coming towards you as a response kid falls forward
- vision in conflict with other proprioceptive sensory inputs

Question 19

Optic flow causes person to think they are falling/swaying forward…

Answer 19

despite conflict with other senses, the person (in this case, child) compensates by leaning back

Question 20

Optic flow causes person to think they are falling/swaying backwards…

Answer 20

• compensates by leaning forward
  “corrections” to moving room (optical flow) = very fast (less than 100 ms)
• pattern of flow is either sort of contracting or expanding
• very fast which makes it appear as a fast reflexive loop

Question 21

Mcgurk Effect

Answer 21

vision is our preferred source of sensory information, dominating other sources (eg audition)
- what you are seeing clashes with what you are hearing (vision dominates)

Question 22

2 types of visual closed-loop control:

Answer 22

conscious and non-conscious

Question 23

Non-conscious closed loop control (VISUAL)

Answer 23

• little or no conscious control
• does not require selective attention
• reflexive-like fast modulations when acting “intermediate-level” (adjustments to motor program)
• inflexible, rapid, mostly to correct balance/aid timing fine-level corrections

Question 24

Conscious closed loop control (VISUAL)

Answer 24

• consciously controlled adjustments based on sensory information
• require selective attention
• involves information processing stages