L18 - Perception and Action

Question 1

What is the relationship between Perception and Action?

Answer 1

• The image on the back of the retina is constantly changing but we do not see it as such - the motion/instability
• Even when we sit down, the eyes move = small subtle changes
• Motion creates its own cues e.g motion parallex (train example where objects further away seem to move slower)
• Another cue is flow patterns = what cues tell us which way we are heading
• Vision is not the only thing that is not static: can be in sound too = timing diff between ears and the binaural cues
• We also move around to interact = claim that we have a brain because we move

Question 2

What is the perception versus action?

Answer 2

• What/Where pathways: what = ventral = used for identification, where = dorsal pathway = used for spatial perception = distinct pathways
• Seen through lesions in animals

Question 3

What was a study looking at separate perception and action pathway?

Answer 3

• Find people who have ablation to part of brains
• DF had carbon monoxide intoxication = damaged her ventral pathway completely but dorsal pathway preserved (lost what, kept where)
• Had visual form agnosia
• Got some slots in different angles and performed a perceptual task: match the shape to the letter box
• Second condition was DF had to post the object into the letter box in different angles
• For the posting = DF is slightly more variable than controls but she can do it = would think this would require her to do the first task
• But she fails to match the orientation matching task BUT controls do not
• One pathway is dedicated to perception, and the other action

Question 4

What is another study looking at the dissociation between perception and action

Answer 4

• Compared interaction with stimulus and perceptual judgement of stimulus
• Put perceived illusory things against reality e.g the circle size illusion = both circles are same size but do not look it
• Take both stimuli and over course of trials = fix size of centre circles in one config and then vary central circles of the other to find out what ppts think match
• When physical circles seem to match, they are actually different sizes
• In another condition, they wanted these circles to be objects so ppts could pick them up
• Measure grip aperture: as you pick up object = distance between thumb and forefinger increases
• When appeared different = might be physically same, compared to perceptual same
• Perception does not seem to correspond to where hand responds = same grip aperture regardless

Question 5

What was a follow up study about the dissociation of perception and action based on the previous research?

Answer 5

• Did same thing as circle study but with numbers
• When judging perceived size, you have to look back/forth = attending to both, but when you pick something out, you can ignore one of the comparison arrays
• Repeated exp but had one config of circles so action and perception condition were more similar
• Perceptual estimation are identical in both = unlike previous circle study
• No diff in perceptual estimates and grip apertures

Question 6

What is evidence that both pathways interact with each other? (what in the where)

Answer 6

• Compared visual agnostics (ventral damage) with controls through fMRI: possible vs impossible object contrast in neural activity, and behavioural: depth discrimination: which dot is in front (easier with a possible object)
• fMRI measures level of possibleness through contrasting blocks = had to say the one previous block was a possible/impossible one to create attention to task to increase brain activity
• In controls, more activity for impossible shapes in both ventral AND dorsal stream BUT the shape is to do with object identification so shouldn’t be activation in dorsal
• Those with ventral stream damage, but results show whatness is in dorsal areas, but not in ventral
• Controls: impossible objects makes your ability for depth perception less
• Those with visual agnosia have the same pattern for the depth perception = shows degree of whatness in the pathway = shows interaction where dorsal pathway does some ‘what’ processing, not just ventral passing info to dorsal