Perception & Action

17 important questions on Perception & Action

What is Optic Array? (ecological approach)

The pattern of light with respect to point of observation. This pattern contains all the information from the environment used for perception.

- this array changes as we move through the environment
- the information is unambiguous i.e. it provides 100% accurate information about the spatial layout of the environment (i.e. you don't need to go through Marr's complex processing)

What is the Ecological Approach?

Proposed by Gibson

- perception relies on optic array (i.e. you only need light information, you don’t need anymore than the optic array to perceive the world around you)
- requires little information processing
- perception is not brought about by neural/mental representations

How does the ecological approach compare with Marr?

In Gibson’s theory, you directly perceive the world i.e. light goes into your eye and you do no/very little cognitive processing to see what’s out there to guide your actions. We don’t need all of Marr’s stages (no need for mental representations)
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Gibson stressed the importance of optic flow when moving towards a goal, who refuted this?

Han, Anderson & Saidpour (2003) found that motion is not essential for accurate perception
- they found that absence of motion (and therefore optic flow)had no effect on accurate judgements

What is a limitation of optic flow?

What happens when we cannot move directly towards our goal e.g. we have to go around a bend? i.e  optic flow info and visual direction in conflict

How do you get meaning from optic array?

1. Affordances - we directly perceive all potential uses of an object
- this will satisfy particular goals i.e. how do we know to sit at a table or stand on it?

2. Resonance
- no need for memory (unlike Marr)
- the mind resonates in response to invariant information in the optic array, allowing us to know what objects are present

= today, this theory seems a bit simplistic

What are 3 limitations of Gibson's Ecological approach?

1. Gibson underestimates the difficulties of analysing optic array
2. Has problems with object meaning
3. Gibson's view that we have no internal representations (i.e. memories) of objects appears to be false

What did Ungerleider & Mishkin (1982) propose?

Proposed that we had more than 1 visual system. Investigated perception on monkeys.

They proposed 2 visual pathways:
1. Ventral pathway for object recognition ("What")
2. Dorsal pathway for spatial perception ("Where")

What did  Milner & Goodale propose?

- alternative to Ungerleider & Mishkin
- intimate relationship between perception and action
- they distinguish between vision for action (dorsal pathways) and vision for perception (ventral pathway)

According to Milner & Goodale, what are the differences between the ventral pathway and the dorsal pathway?

Dorsal Pathway: Vision for Action
- viewpoint dependant representation
- brief representations
- used to guide actions in "here" and "now"
- unconscious vision

Ventral Pathway: Vision for Perception
- viewpoint independant representations
- long lasting representation (e.g. memories of objects)
- used to gain knowledge about the world (semantic)
- conscious vision

Note: Gibson would have argued that vision for perception would have gone through the dorsal pathway as this pathway has a viewpoint dependant representation

What evidence supports Milner & Goodale's theory of the dorsal and the ventral pathways?

Neuropsychological evidence

Patient DF - had damage to ventral stream
= could not recognise objects
= she can interact with the world perfectly well i.e. she can guide action

Optic Ataxia - damage to dorsal stream
= can recognise objects
= cannot accurately reach objects i.e. cannot interact with the object properly

What are the limitations of the theory proposing completely separate dorsal & ventral pathways?

- oversimplified to say they are completely separate - there is actually lots of interaction between the streams
- the dorsal stream is more diverse than Milner & Goodale suggested 

What is Glover's Planning-control model?

- assessed how is visual information used to produce actions
- development of Milner & Goodale's ideas by demonstrating how the ventral and dorsal streams interact

Describe the planning part of Glover's model.

- planning occurs mostly before control
- planning can overlap with early phases of movement
- integrates information from many sources
- can be slow
- based in the Inferior Parietal Lobe

Describe the control part of Glover's model.

- operates during movement
- only uses spatial information about object i.e. doesn't care about identity
(treats a hosepipe and a snake in the same way!)
- not under conscious control
- very fast
- based in Superior Parietal Lobe

What evidence supports Glover's model?

Pisella (2002) - investigated if movements were corrected without conscious control
Task: participants must make fast reaches to targets. On some trials the target moves. In some blocks participants must cancel the movement, in others they must correct the movement.
Results:  If movements were fast (<250ms), P’s corrected, even when they should have cancelled   


Damage to SPL leads to optic ataxia

What is 1 benefit of Glover's model and what are 2 limitations?

Benefit
- lots of evidence for separate planning and control systems

Limitations
- model does not describe how actions are planned
- specific to arm and body movements - ignores eye movements

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