action as context

Question 1

how does perception interpretation change?

Answer 1

depending on the stimuli

Question 2

what are some examples of action as context?

Answer 2

• size constancy = retinal size is scaled by distance
• despite fact size of image is changing, perception is not changing (e.g., person in background walking to foreground)
• action causes dynamic changes at receptor surface which could be misinterpreted e.g., as object motion

Question 3

how do we perceive a stable world?

Answer 3

• fixation = eyes stationary
• pursuit = track with your eyes the moving object so object is stationary but everything around is moving and blurry
• possible interpretations of what is happening out in the world

Question 4

what is extra-retinal compensation?

Answer 4

• all background will be moving one way (e.g., left) but opposite speed/direction to wear the eye is going (it is following the moving object)
• estimate pursuit velocity from motor system
• eye pursuit (P)
• retinal motion (R)
• perceived motion = P + R
• movement of object is informed by measuring how eyes are moving

Question 5

are extra-retinal signals in or out?

Answer 5

• 6 muscles attached to eyes
• inflow theory
• muscles give motor feedback = proprioception
• afferent signals used by brain could be using this to work out how eyes are moving
• proprioception tells you what actually happens as you don’t always move your eyes accurately
• outflow theory
• or have to send motor commands to the eyes to move them (which is an efferent signal)
• these commands have info about movement of eyes
• motor commands tell you what is just about to happen

Question 6

what is the finger-in-the-eye demo?

Answer 6

• cover one eye and poke the eye that is seeing
• eye that is seeing = world moves/wobbles
• making eye move but not sending any motor commands to eye muscles to make eye move
• this is explained by proprioception
• this tells you that this must be motor commands that are important as they are lacking in this demo

Question 7

how does Brindley & Merton (1960) support outflow theory?

Answer 7

• pp’s could not tell which way their eyes were moving when they were being moved by forceps when being in the dark
• creating proprioceptive signals as they were making the muscles stretch and move around
• with light on and holding eyes with forceps and asking pp to move their eyes = world moves
• sending motor commands to eye muscles and eyes are not going anywhere

Question 8

how does Skavenski (1972) support inflow theory?

Answer 8

• trying to show that in some situations you can be in contact with proprioceptive info
• eye ball moved by hydraulic sucker and pulley system
• moving eyes backwards and forwards passively
• hard to isolate proprioceptive eye info
• sophisticated finger-in-eye-demo
• done in the dark
• pp’s could tell which way eye moved
• evidence for proprioceptive feedback/inflow

Question 9

how does partial paralysis support outflow theory?

Answer 9

• paralysed 4 rectus muscles with novocaine
• partial because paralysed 4/6 muscles
• objects tended to move on attempted eye movement even if no moving objects

Question 10

do complete paralysis studies support outflow theory?

Answer 10

• inconclusive
• one study reports movement whereas another does not
• problems with Troxler fading (the world disappears)
• if eyes are not moving, we can’t see as the world start to fade so impossible to make the aim of study for eyes to not move
• motor commands tell you what is just about to happen
• proprioception tells you what actually happens as you don’t always move your eyes accurately

Question 11

how do we perceive roughness from touch?

Answer 11

• rough surface = has more physical changes on it
• smooth surface = more plainer
• roughness perception from hands are to do with mechanisms from skins surface encoding these ups and downs on the surface
• more roughness = more activity in touch receptors
• can increase speed of firing by increases speed in which you rub the surface
• ambiguity = how rough is surface or how fast are your fingers moving

Question 12

how do we perceive roughness from touch: experiment?

Answer 12

• various flat surfaces and had to move hands across them
• other conditions: held something and ran that across the surface (e..g, pen)
• touch perception also works by using equipment to run along the surface
• used different surfaces/texture
• used different speeds or rubbing finger or item (scanning velocity)
• perceived roughness measured on scale from 1 to 1000
• active scan = move hand
• passive scan = move surface
• pseudo-passive = experimenter moves your hand (pp does not send motor commands to brain)

Question 13

how do we perceive roughness from touch: experiment - results and implications?

Answer 13

• trying to see if there is a roughness constancy so roughness does not depend on how fast your hand is moving
• whether you used finger or probe there is no change of perceived roughness
• relative motion between finger and surface only compensated for when finger actually moves
• and compensation seems to rely on proprioception (inflow), unlike vision and eye movements (inflow and outflow)

Question 14

what is perceived stability in hearing?

Answer 14

• when head moves, create dynamic change at the ears which could be misinterpreted
• stationary sound in front of you and rotate head = dynamic change across the ears and binaural cues
• cues and changes are identical to when head is stationary and sound is moving
• hearing system in contact with head moving system = how brain sorts out this issue

Question 15

what was the study looking at perceived stability in hearing?

Answer 15

• sound moved in opposition to head movement
• sound stationary
• sound moved with head
• people could adjust deghee of motion until sound is stationary
• if brain has solved this problem = sound should appear stationary and should be stationary
• complete compensation for head movement by hearing system