L20 - Action as Context

Question 1

What are some examples of actions in context?

Answer 1

• Size constancy: retinal size is scaled by distance: despite the fact that the image is changing, perception is not changing e.g person from background walking to foreground
• Action creates dynamic change across receptors surfaces but these are misinterpreted

Question 2

How do we perceive a stable world?

Answer 2

• Extra-retinal compensation: estimate pursuit velocity from motor system
• Perceived motion = eye pursuit + retinal motion
• All background will be moving in an equal but opposite speed/direction in pursuit
• Equation means it mostly cancels, making it mostly static
• Motor system makes eye moves, visual system measures things in image, when you add them up = perceived motion

Question 3

Are extra-retinal signals in or out?

Answer 3

• Eyes move due to 6 muscles
• Muscles give motor feedback = can be the extra-retinal signal (acts as a brain as a afferent signal)
• OR You have to send motor commands to eyes to move them (efferent signal) = outflow theory
• These commands have info about movement of eyes
• Known as corollary discharge/effort of will/efference copy

Question 4

What is a study that supports outflow theory?

Answer 4

1) Finger in-the-eye demo:
- Cover an eye, and poke the other = the eye moves and is reflected in the vision
- Mimicking moving the eye but not sending any commandments = no motor signals but there is proprioception = must be motor commands that must be important
2) the lateral or medial rectus muscle was seized through the
conjuctiva with fine-toothed forceps to move the eye
- Turned lights out and asked if the world moved = subjects could not tell which way the eye is moving
- One ppts both eyes were held with forceps while he moved his eyes actively (cant physically move them due to forceps but he tried to move) with the lights on and ppt thought objects moved = image not moving = lots of motor commands to eye muscles and eyes are not moving but you experience motion

Question 5

What is a study that supports inflow theory?

Answer 5

• Eye ball moved by hydraulic sucker and pulley system = moving eyes back/forth passively = making lots of proprioceptive activity
• Ppts could tell which way eye moved

Question 6

How does partial paralysis support outflow?

Answer 6

• Paralysed 4 rectus muscles with novocaine
• People tended to see movement even if there was not (objects moved on attempted eye movement)

Question 7

How does complete paralysis support outflow?

Answer 7

• completely paralysed, except for his little finger to indicate movement
• Measured eye movements
• Tried to make eye move = if it did = motor movements
• Inconclusive: Stevens reports movement but others do not
• No eye movements = no experiment as you cant see anything due to Troxler fading

Question 8

What is a study looking at perceived roughness?

Answer 8

• Roughness perception is do with mechanisms from skins surface = more roughness = more activity in touch receptors (more firing = rougher)
• BUT Can increase firing rate by changing speed of which you move = ambiguity
• Do surfaces feel rougher if we move our hand faster?
• Had various flat surfaces where hands would be moved across, other conditions would be holding a pen and running that across the surface
• Had to run the tool/hand across surface at constant speeds
• Asked ppts on a scale from 1-100 how rough the surface was = no change of perceived roughness if used tool/hand
• When passively scanned (when surface is moved instead of hand/tool), the same roughness feels rougher and rougher as the moving gets faster
• Third condition was someone moved hand for you = ppt does not send motor commands = propriorceptive feedback keeps it constant (inflow)

Question 9

What was a study looking at perceived stability in hearing?

Answer 9

• When head rotates, creates dynamic changes in ears that could be misinterpreted of motion
• Head moves, and sound moves = same binaural cues to motion
• Sound could move opposite direction to head movement, and other conditions
• Allowed people to adjust sound so it aligns = where sound appears stationary
• For sound to appear stationary, had to move with the head movement
• Complete compensation from hearing system